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  • 1
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 44 (9). pp. 2524-2546.
    Publication Date: 2015-05-28
    Description: In this study, the authors discuss two different parameterizations for the effect of mixed layer eddies, one based on ageostrophic linear stability analysis (ALS) and the other one based on a scaling of the potential energy release by eddies (PER). Both parameterizations contradict each other in two aspects. First, they predict different functional relationships between the magnitude of the eddy fluxes and the Richardson number (Ri) related to the background state. Second, they also predict different vertical structure functions for the horizontal eddy fluxes. Numerical simulations for two different configurations and for a large range of different background conditions are used to evaluate the parameterizations. It turns out that PER is better suited to capture the Ri dependency of the magnitude of the eddy fluxes. On the other hand, the vertical structure of the meridional eddy fluxes predicted by ALS is more accurate than that of PER, while the vertical structure of the vertical eddy fluxes is well predicted by both parameterizations. Therefore, this study suggests the use of the magnitude of PER and the vertical structure functions of ALS for an improved parameterization of mixed layer eddy fluxes.
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  • 2
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    AMS (American Meteorological Society)
    In:  Journal of the Atmospheric Sciences, 71 (4). pp. 1494-1507.
    Publication Date: 2017-10-24
    Description: Northern Hemisphere stratospheric variability is investigated with respect to chaotic behavior using time series from three different variables extracted from four different reanalysis products and two numerical model runs with different forcing. The time series show red spectra at all frequencies and the probability distribution functions show persistent deviations from a Gaussian distribution. An exception is given by the numerical model forced with perpetual winter conditions—a case that shows more variability and follows a Gaussian distribution, suggesting that the deviation from Gaussianity found in the observations is due to the transition between summer and winter variability. To search for the presence of a chaotic attractor the correlation dimension and entropy, the Lyapunov spectrum, and the associated Kaplan–Yorke dimension are estimated. A finite value of the dimensions can be computed for each variable and data product, with the correlation dimension ranging between 3.0 and 4.0 and the Kaplan–Yorke dimension between 3.3 and 5.5. The correlation entropy varies between 0.6 and 1.1. The model runs show similar values for the correlation and Lyapunov dimensions for both the seasonally forced run and the perpetual-winter run, suggesting that the structure of a possible chaotic attractor is not determined by the seasonality in the forcing, but must be given by other mechanisms.
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  • 3
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    AMS (American Meteorological Society)
    In:  Journal of the Atmospheric Sciences, 71 (12). pp. 4611-4620.
    Publication Date: 2017-10-24
    Description: Southern Hemisphere (SH) stratospheric variability is investigated with respect to chaotic behavior using time series from three different variables extracted from four different reanalysis products. The results are compared with the same analysis applied to the Northern Hemisphere (NH). The probability density functions (PDFs) for the SH show persistent deviations from a Gaussian distribution. The variability is given by white spectra for low frequencies, a slope of −1 for intermediate frequencies, and −3 slopes for high frequencies. Considering the time series for winter and summer separately, PDFs show a Gaussian distribution and the variability spectra change their slopes, indicating the role of the transition between winter and summer variability in shaping the time series. The correlation (D2) and the Kaplan–Yorke (DKY) dimensions are estimated. A finite value of the dimensions can be computed for each variable and data product, except for the NCEP zonal-mean zonal wind and temperature data, which violate the requirement D2 ≤ DKY, possibly owing to the presence of spurious trends and inconsistencies in the data. The value of D2 ranges between 2.6 and 3.9, while DKY ranges between 3.0 and 4.5. The results show that both D2 and DKY display large variability in their values both for different datasets and for different variables within the same dataset. The variability of the values of D2 and DKY thus leaves open the question about the existence of a low-dimensional attractor or if the finite dimensions of the system are the result of the projection of a larger attractor in a low-dimensional embedding space.
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  • 4
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    AMS (American Meteorological Society)
    In:  Journal of the Atmospheric Sciences, 71 (7). pp. 2674-2694.
    Publication Date: 2017-10-24
    Description: The sensitivities of the Brewer–Dobson circulation (BDC) to different distributions of tropical SST heating are investigated in an idealized aquaplanet model. It is found that an increase in tropical SSTs generally leads to an acceleration of tropical upwelling and an associated reduction in the age of air (AOA) in the polar stratosphere and that the AOA near the subtropical tropopause is correlated with local isentropic mixing of tropospheric air with stratospheric air. The zonal distribution of SST perturbations has a major impact on the vertical and meridional structure of the BDC as compared with other SST characteristics. Zonally localized SST heatings tend to generate a shallow acceleration of the stratospheric residual circulation, enhanced isentropic mixing associated with a weakened stratospheric jet, and a reduction in AOA mostly within the polar vortex. In contrast, SST heatings with a zonally symmetric structure tend to produce a deep strengthening of the stratospheric residual circulation, suppressed isentropic mixing associated with a stronger stratospheric jet, and a decrease of AOA in the entire stratosphere. The shallow versus deep strengthening of the stratospheric residual circulation change has been linked to wave propagation and dissipation in the subtropical lower stratosphere rather than wave generation in the troposphere, and the former can be strongly affected by the vertical position of the subtropical jet. These results suggest that, while the longitudinally localized SST trends under climate change may contribute to the change in the shallow branch of the BDC, the upward shift of the subtropical jet associated with the zonal SST heating can impact the deep branch of the BDC.
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  • 5
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    AMS (American Meteorological Society)
    In:  Journal of the Atmospheric Sciences, 71 (2). pp. 566-573.
    Publication Date: 2017-10-24
    Description: The authors test the hypothesis that recent observed trends in surface westerlies in the Southern Hemisphere are directly consequent on observed trends in the timing of stratospheric final warming events. The analysis begins by verifying that final warming events have an impact on tropospheric circulation in a simplified GCM driven by specified equilibrium temperature distributions. Seasonal variations are imposed in the stratosphere only. The model produces qualitatively realistic final warming events whose influence extends down to the surface, much like what has been reported in observational analyses. The authors then go on to study observed trends in surface westerlies composited with respect to the date of final warming events. If the considered hypothesis were correct, these trends would appear to be much weaker when composited with respect to the date of the final warming events. The authors find that this is not the case, and accordingly they conclude that the observed surface changes cannot be attributed simply to this shift toward later final warming events.
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  • 6
    Publication Date: 2020-08-04
    Description: Precipitation is highly variable in space and time; hence, rain gauge time series generally exhibit additional random small-scale variability compared to area averages. Therefore, differences between daily precipitation statistics simulated by climate models and gauge observations are generally not only caused by model biases, but also by the corresponding scale gap. Classical bias correction methods, in general, cannot bridge this gap; they do not account for small-scale random variability and may produce artifacts. Here, stochastic model output statistics is proposed as a bias correction framework to explicitly account for random small-scale variability. Daily precipitation simulated by a regional climate model (RCM) is employed to predict the probability distribution of local precipitation. The pairwise correspondence between predictor and predictand required for calibration is ensured by driving the RCM with perfect boundary conditions. Wet day probabilities are described by a logistic regression, and precipitation intensities are described by a mixture model consisting of a gamma distribution for moderate precipitation and a generalized Pareto distribution for extremes. The dependence of the model parameters on simulated precipitation is modeled by a vector generalized linear model. The proposed model effectively corrects systematic biases and correctly represents local-scale random variability for most gauges. Additionally, a simplified model is considered that disregards the separate tail model. This computationally efficient model proves to be a feasible alternative for precipitation up to moderately extreme intensities. The approach sets a new framework for bias correction that combines the advantages of weather generators and RCMs.
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  • 7
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    AMS (American Meteorological Society)
    In:  Bulletin of the American Meteorological Society, 95 (2). pp. 293-296.
    Publication Date: 2019-09-23
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  • 8
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 44 (1). pp. 3-23.
    Publication Date: 2018-04-12
    Description: There is an ongoing discussion in the community concerning the wave-averaged momentum equations in the hybrid vertically Lagrangian and horizontally Eulerian (VL) framework and, in particular, the form stress term (representing the residual effect of pressure perturbations) which is thought to restrict the handling of higher order waves in terms of a perturbation expansion. The present study shows that the traditional pressure-based form stress term can be transformed into a set of terms that do not contain any pressure quantities but do contain the time derivative of a wave-induced velocity. This wave-induced velocity is referred to as the pseudomomentum in the VL framework, as it is analogous to the generalized pseudomomentum in Andrews and McIntyre. This enables the second expression for the wave-averaged momentum equations in the VL framework (this time for the development of the total transport velocity minus the VL pseudomomentum) to be derived together with the vortex force. The velocity-based expression of the form stress term also contains the residual effect of the turbulent viscosity, which is useful for understanding the dissipation of wave energy leading to transfer of momentum from waves to circulation. It is found that the concept of the virtual wave stress of Longuet-Higgins is applicable to quite general situations: it does not matter whether there is wind forcing or not, the waves can have slow variations, and the viscosity coefficient can vary in the vertical. These results provide a basis for revisiting the surface boundary condition used in numerical circulation models.
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  • 9
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 44 (2). pp. 445-463.
    Publication Date: 2020-08-04
    Description: Mooring observations and model simulations point to an instability of the Labrador Current (LC) during winter, with enhanced eddy kinetic energy (EKE) at periods between 2 to 5 days, and much less EKE during other seasons. Linear stability analysis using vertical shear and stratification from the model reveals three dominant modes of instability in the LC: - a balanced interior mode with along-flow wavelengths of about 30–45 km, phase velocities of 0.3 m/s, maximal growth rates of 1 d−1 and surface intensified, but deep reaching amplitudes, - a balanced shallow mode with along-flow wavelengths of about 0.3–1.5 km, about three times larger phase speeds and growth rates, but amplitudes confined to the mixed layer (ML), - and an unbalanced symmetric mode with largest growth rates, vanishing phase speeds and along-flow structure, and very small cross-flow wavelengths, also confined to the ML. Both balanced modes are akin to baroclinic instability, but operate at moderate to small Richardson numbers Ri with much larger growth rates as for the quasi-geostrophic limit of Ri ≫ 1. The interior mode is found to be responsible for the instability of the LC during winter. Weak stratification and enhanced vertical shear due to local buoyancy loss and the advection of convective water masses from the interior result in small Ri within the LC, and to three times larger growth rates of the interior mode in March compared to summer and fall conditions. Both the shallow and the symmetric mode are not resolved by the model, but it is suggested that they might also play an important role for the instability in the LC and for lateral mixing.
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  • 10
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 44 (2). pp. 482-491.
    Publication Date: 2020-08-04
    Description: Sensible and latent heat fluxes were estimated from turbulence measurements gathered during several Atlantic transects of the R/V Polarstern. The inertial dissipation method was used to analyze the data. Resulting bulk transfer coefficients were then applied to the data from the ship’s meteorological system to get continuous time series of the heat fluxes. Combined to the measured downward solar and longwave radiation fluxes allows for an estimate of the total energy budget at the air-sea interface. Comparing these parameterized energy fluxes to ones based on the COARE 3.0 bulk flux algorithm show very strong agreement.
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  • 11
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    AMS (American Meteorological Society)
    In:  Journal of the Atmospheric Sciences, 71 (6). pp. 2264-2279.
    Publication Date: 2020-08-04
    Description: The dynamical origin of the spectral and autocorrelation structure of annular variability in the troposphere is investigated by a deductive approach. Specifically, the structure of the power spectrum and autocorrelation function of the zonal-mean geopotential is analyzed for the case of a quasigeostrophic spherical atmosphere subject to a white noise mechanical forcing applied in a single Hough mode and concentrated at a particular level in the vertical, with vertically uniform Newtonian cooling and Rayleigh drag concentrated at a rigid lower boundary. Analytic expressions for the power spectrum are presented together with expressions for an approximate red noise (i.e., a Lorentzian-shaped) power spectrum. It is found that for an infinitely deep atmosphere the power spectrum can be well approximated by a red noise process for the first few Hough modes (associated with large Rossby heights), provided the distance from the forcing is not larger than about one Rossby height. When a frictional rigid lower boundary is included, however, the approximation is generally bad. The high-frequency part of the power spectrum exhibits near-exponential behavior and the autocorrelation function shows a transition from a rapid decay at short lags to a much slower decay at longer lags, if the thermal and mechanical damping time scales are sufficiently well separated. Since observed annular variability exhibits the same characteristics, the above results lead to the hypothesis that these characteristics may, to some extent, be intrinsic to the linear zonal-mean response problem—although the need for an additional contribution from eddy feedbacks is also implied by the results.
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  • 12
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 44 . pp. 2485-2497.
    Publication Date: 2020-08-04
    Description: A representation of an equatorial basin mode excited in a shallow water model for a single high order baroclinic vertical normal mode is used as a simple model for the equatorial deep jets. The model is linearized about both a state of rest and a barotropic mean flow corresponding to the observed Atlantic Equatorial Intermediate Current System. We found that the eastward mean flow associated with the North and South Intermediate Counter Currents (NICC and SICC, respectively) effectively shields the Equator from off-equatorial Rossby waves. The westward propagation of these waves is blocked and focusing on the Equator due to beta dispersion is prevented. This leads to less energetic jets along the Equator. On the other hand, the westward barotropic mean flow along the Equator reduces the gradient of absolute vorticity and hence widens the cross-equatorial structure of the basin mode. Increasing lateral viscosity predominantly affects the width of the basin modes’ Kelvin wave component in the presence of the mean flow while the Rossby wave is confined by the flanking NICC and SICC. Independent of the presence of the mean flow, the application of sufficient lateral mixing also hinders the focusing of off-equatorial Rossby waves, which is hence an unlikely feature of a low-frequency basin mode in the real ocean.
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  • 13
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 27 (7). pp. 2577-2587.
    Publication Date: 2014-10-22
    Description: A decadal change in the character of ENSO was observed around year 2000 toward weaker-amplitude, higher-frequency events with an increased occurrence of central Pacific El Niños. Here these changes are assessed in terms of the Bjerknes stability index (BJ index), which is a measure of the growth rate of ENSO-related SST anomalies. The individual terms of the index are calculated from ocean reanalysis products separately for the time periods 1980–99 and 2000–10. The spread between the products is large, but they show a robust weakening of the thermocline feedback due to a reduced thermocline slope response to anomalous zonal wind stress as well as a weakened wind stress response to eastern equatorial Pacific SST anomalies. These changes are consistent with changes in the background state of the tropical Pacific: cooler mean SST in the eastern and central equatorial Pacific results in reduced convection there together with a westward shift in the ascending branch of the Walker circulation. This shift leads to a weakening in the relationship between eastern Pacific SST and longitudinally averaged equatorial zonal wind stress. Also, despite a steeper mean thermocline slope in the more recent period, the thermocline slope response to wind stress anomalies weakened due to a smaller zonal wind fetch that results from ENSO-related wind anomalies being more confined to the western basin. As a result, the total BJ index is more negative, corresponding to a more strongly damped system in the past decade compared to the 1980s and 1990s.
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  • 14
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 27 (4). pp. 1821-1825.
    Publication Date: 2017-08-25
    Description: In his comment, G. Bürger criticizes the conclusion that inflation of trends by quantile mapping is an adverse effect.He assumes that the argument would be ‘‘based on the belief that long-term trends and along with them future climate signals are to be large scale.’’ His line of argument reverts to the so-called inflated regression. Here it is shown, by referring to previous critiques of inflation and standard literature in statistical modeling as well as weather forecasting, that inflation is built upon a wrong understanding of explained versus unexplained variability and prediction versus simulation. It is argued that a sound regressionbased downscaling can in principle introduce systematic local variability in long-term trends, but inflation systematically deteriorates the representation of trends. Furthermore, it is demonstrated that inflation by construction deteriorates weather forecasts and is not able to correctly simulate small-scale spatiotemporal structure.
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  • 15
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 44 (7). pp. 1776-1797.
    Publication Date: 2018-04-12
    Description: The relationship between the Agulhas Current and the Agulhas leakage is not well understood. Here, this is investigated using two basin-scale and two global ocean models, of incrementally increasing resolution. The response of the Agulhas Current is evaluated under a series of sensitivity experiments, in which idealised anomalies, designed to geometrically modulate zonal trade wind stress, are applied across the Indian Ocean basin. The imposed wind stress changes exceed ±2 standard deviations from the annual mean trade winds and, in the case of intensification, are partially representative of recently observed trends. The Agulhas leakage is quantified using complimentary techniques based on Lagrangian virtual floats and Eulerian passive tracer flux. As resolution increases, model behavior converges and the sensitivity of the leakage to Agulhas Current transport anomalies is reduced. In the two eddy-resolving configurations tested, the leakage is insensitive to changes in Agulhas Current transport at 32°S, though substantial eddy kinetic energy anomalies are evident. Consistent with observations, the position of the retroflection remains stable. The decoupling of Agulhas Current variability from the Agulhas leakage suggests that, while correlations between the two may exist, they may not have a clear dynamical basis. It is suggested that present and future Agulhas leakage proxies be considered in the context of potentially transient forcing regimes.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 16
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 27 . pp. 9101-9122.
    Publication Date: 2015-11-24
    Description: A surface diurnal warm layer is diagnosed from Seaglider observations, and develops on half the days in the CINDY/DYNAMO Indian Ocean experiment. The diurnal warm layer occurs on days of high solar radiation flux (〉 80 W m−2) and low wind speed (〈 6 m s−1), and preferentially in the inactive stage of the Madden–Julian Oscillation. Its diurnal harmonic has an exponential vertical structure with a depth scale of 4–5 m (dependent on chlorophyll concentration), consistent with forcing by absorption of solar radiation. The effective sea surface temperature (SST) anomaly due to the diurnal warm layer often reaches 0.8°C in the afternoon, with a daily mean of 0.2°C, rectifying the diurnal cycle onto longer time scales. This SST anomaly drives an anomalous flux of 4 W m−2 that cools the ocean. Alternatively, in a climate model where this process is unresolved, this represents an erroneous flux that warms the ocean. A simple model predicts a diurnal warm layer to occur on 30–50% of days across the tropical warm pool. On the remaining days, with low solar radiation and high wind speeds, a residual diurnal cycle is observed by the Seaglider, with a diurnal harmonic of temperature that decreases linearly with depth. As wind speed increases, this already weak temperature gradient decreases further, tending towards isothermal conditions.
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  • 17
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 27 (21). pp. 8135-8150.
    Publication Date: 2020-08-04
    Description: Sea surface temperature (SST) anomalies in the eastern equatorial Atlantic are connected to modulations in the strength of the South Atlantic subtropical high-pressure system, referred to as the South Atlantic Anticyclone (SAA). Using ocean and atmosphere reanalysis products we show here that the strength of the SAA from February to May impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorial Atlantic (EEA) via anomalous tropical wind power. This modulation of the timing and amplitude of the seasonal cold tongue development manifests as anomalous SST events peaking between June and August. The timing and impact of this connection is not completely symmetric for warm and cold events. For cold events, an anomalously strong SAA in February and March leads to positive wind power anomalies from February to June resulting in an early cold tongue onset and subsequent cold SST anomalies in June and July. For warm events the anomalously weak SAA persists until May, generating negative wind power anomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm SST anomalies. Mechanisms by which SAA induced wind power variations south of the equator influence EEA SST are discussed, including ocean adjustment via Rossby and Kelvin wave propagation, meridional advection, and local intraseasonal wind variations
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  • 18
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    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 31 (1). pp. 181-196.
    Publication Date: 2020-08-04
    Description: We present a detailed quality assessment of a novel underwater sensor for the measurement of CO2 partial pressure (pCO2) based on surface water field deployments carried out between 2008 and 2011. The commercially available sensor, which is based on membrane equilibration and NDIR spectrometry is small and can be integrated into mobile platforms. It is calibrated in water against a proven flow-through pCO2 instrument within a custom-built calibration setup. The aspect of highest concern with respect to achievable data quality of the sensor is the compensation for signal drift inevitably connected to absorption measurements. We use three means to correct for drift effects: (i) a filter correlation or dual-beam setup, (ii) regular zero gas measurements realized automatically within the sensor and (iii) a zero-based transformation of two sensor calibrations flanking the time of sensor deployment. Three sensors were tested against an underway pCO2 system during two major research cruises providing an in situ temperature range from 7.4 to 30.1°C and pCO2 values between 289 and 445 μatm. The average difference between sensor and reference pCO2 was found to be -0.6 ± 3 μatm with a RMSE of 3.7 μatm.
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  • 19
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 27 (3). pp. 977-993.
    Publication Date: 2019-01-08
    Description: Ammassalik in southeast Greenland is known for strong wind events that can reach hurricane intensity and cause severe destruction in the local town. Yet, these winds and their impact on the nearby fjord and shelf region have not been studied in detail. Here, data from two meteorological stations and the European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim) are used to identify and characterize these strong downslope wind events, which are especially pronounced at a major east Greenland fjord, Sermilik Fjord, within Ammassalik. Their local and regional characteristics, their dynamics and their impacts on the regional sea ice cover, and air–sea fluxes are described. Based on a composite of the events it is concluded that wind events last for approximately a day, and seven to eight events occur each winter. Downslope wind events are associated with a deep synoptic-scale cyclone between Iceland and Greenland. During the events, cold dry air is advected down the ice sheet. The downslope flow is accelerated by gravitational acceleration, flow convergence inside the Ammassalik valley, and near the coast by an additional thermal and synoptic-scale pressure gradient acceleration. Wind events are associated with a large buoyancy loss over the Irminger Sea, and it is estimated that they drive one-fifth of the net wintertime loss. Also, the extreme winds drive sea ice out of the fjord and away from the shelf.
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  • 20
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    AMS (American Meteorological Society)
    In:  Bulletin of the American Meteorological Society, 95 (7). S1-S279.
    Publication Date: 2019-07-10
    Description: In 2013, the vast majority of the monitored climate variables reported here maintained trends established in recent decades. ENSO was in a neutral state during the entire year, remaining mostly on the cool side of neutral with modest impacts on regional weather patterns' around the world. This follows several years dominated by the effects of either La Nina. or El Nino events. According to several independent analyses, 2013 was again among the 10 warmest years on record at the global scale, both at the Earth's surface and through the troposphere. Some regions in the Southern Hemispherehad record or near-record high temperatures for the year. Australia observed its hottest year on record, while Argentina and New Zealand reported their second and third hottest years, respectively. In Antarctica, Amundsen-Scott South Pole Station reported its highest annual temperature since records began in 1957 At the opposite pole, the Arctic observed its seventh warmest year since record's began in the early 20th century. At 20-m depth, record high temperatures were measured at some permafrost stations on the North Slope Of Alaska and in the Brooks Range. In the Northern Hemisphere extratropics, anomalous meridional atmospheric circulation occurred throughout much of the year leading to marked regional extremes of both temperature and precipitation. Cold temperature anomalies during Winter across Eurasia were followed by warm Spring temperature anomalies, which, were linked to a new record Eurasian snow cover extent in the May. Minimum sea ice extent in the :Arctic was the sixth lowest since satellite Observations began in 1979. Including 2013, all seven lowest extents on record have occurred in the past seven years Antarctica, on the other hand, had above average sea ice extent throughout 2013, with 116 days Of new daily high extent records, inclding a new daily maximum sea ice area of 19.57 million km(2) reached on 1 October. ENSO-neutral conditions in the eastern central Pacific Ocean and a negative Pacific decadal oscillation pattern in the North Pacific had the largest impacts on the global sea surface temperature in 2013: The North Pacific reached a historic high temperature in 2013 and on balance the globally-averaged sea surface temperature was among the 10 highest on record. Overall, the salt Content in near-surface ocean waters increased while in intermediate waters it decreased. Global mean sea level continued to rise during 2013, on pace with a trend of 3,2 mm yr(-1) over the past two decades. A portion of this trend (0.5 mm yr(-1)) has been attributed to natural variability associated with the Pacific decadal oscillation as Well as to ongoing contribution from the melting of glaciers and ice sheets and ocean warming. Global tropical cyclone frequency during 2013 was slightly above average with a total of 94 storms, although the North Atlantic Basin had its quietest hurricane season since 1994. In the Western North Pacific Basin, Super Typhoon Haiyan, the deadliest tropical Cyclone of 2013, had 1-minute sustained winds estimated to be 170 kt (OS m s(-1)) on 7 November, the highest Wind speed ever assigned to a tropical cyclone. High storm surge was also associated with Haiyan at it Made landfall over the central Philippines, an area where sea level is currently at historic highs increasing by 200 mm since 1970. In the atmosphere, carbon dioxide, methane, and nitrous oxide all Continued to increase in 2013. As in previous our years, each of these Major greenhouse gases once again reached historic high Concentrations. In the Arctic carbon dioxide and methane:, Increased at the same rate as:the global increase. These increases are likely due to export from lower latitudes rather than a consequence Of increases in Arctic sources such as thawing permafrost., At Mauna Loa, Hawaii, for the first time since measurement began in 1958, the daily average Mixing ratio Of carbon dioxide exceeded 400 ppm on 9 May. The state of these variables, along with dozens of others, and the 2013 climate conditions of regions around the world are discussed in further detail in this 24th, edition of the State of the Climate series
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  • 21
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 43 (12). pp. 2611-2628.
    Publication Date: 2021-06-17
    Description: The Denmark Strait Overflow (DSO) supplies about one-third of the North Atlantic Deep Water and is critical to global thermohaline circulation. Knowledge of the pathways of DSO through the Irminger Basin and its transformation there is still incomplete, however. The authors deploy over 10 000 Lagrangian particles at the Denmark Strait in a high-resolution ocean model to study these issues. First, the particle trajectories show that the mean position and potential density of dense waters cascading over the Denmark Strait sill evolve consistently with hydrographic observations. These sill particles transit the Irminger Basin to the Spill Jet section (65.25°N) in 5–7 days and to the Angmagssalik section (63.5°N) in 2–3 weeks. Second, the dense water pathways on the continental shelf are consistent with observations and particles released on the shelf in the strait constitute a significant fraction of the dense water particles recorded at the Angmagssalik section within 60 days (~25%). Some particles circulate on the shelf for several weeks before they spill off the shelf break and join the overflow from the sill. Third, there are two places where the water density following particle trajectories decreases rapidly due to intense mixing: to the southwest of the sill and southwest of the Kangerdlugssuaq Trough on the continental slope. After transformation in these places, the overflow particles exhibit a wide range of densities.
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  • 22
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 26 (6). pp. 2137-2143.
    Publication Date: 2020-08-04
    Description: Quantile mapping is routinely applied to correct biases of regional climate model simulations compared to observational data. If the observations are of similar resolution as the regional climate model, quantile mapping is a feasible approach. However, if the observations are of much higher resolution, quantile mapping also attempts to bridge this scale mismatch. Here, it is shown for daily precipitation that such quantile mapping-based downscaling is not feasible but introduces similar problems as inflation of perfect prognosis ("prog") downscaling: the spatial and temporal structure of the corrected time series is misrepresented, the drizzle effect for area means is overcorrected, area-mean extremes are overestimated, and trends are affected. To overcome these problems, stochastic bias correction is required.
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  • 23
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 43 . pp. 149-164.
    Publication Date: 2018-04-12
    Description: Previous attempts to derive the depth-dependent expression of the radiation stress have lead to a debate concerning (i) the applicability of Mellor’s approach to a sloping bottom, (ii) the introduction of the delta function at the mean sea surface in the later papers by Mellor, and (iii) a wave-induced pressure term derived in several recent studies. The authors use an equation system in vertically Lagrangian and horizontally Eulerian (VL) coordinates suitable for a concise treatment of the surface boundary, and obtain an expression for the depth-dependent radiation stress that is consistent with the vertically-integrated expression given by Longuet-Higgins and Stewart. Concerning (i)-(iii) in the above, the difficulty of handling a sloping bottom disappears when wave-averaged momentum equations in the VL coordinates are written for the development of (not the Lagrangian mean velocity but) the Eulerian mean velocity. There is also no delta function at the sea surface in the expression for the depth-dependent radiation stress. The connection between the wave-induced pressure term in the recent studies and the depth-dependent radiation stress term is easily shown by rewriting the pressure-based form stress term in the thickness-weighted-mean (TWM) momentum equations as a velocity-based term which contains the time derivative of the pseudomomentum in the TWM framework.
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  • 24
    Publication Date: 2018-07-04
    Description: The upper ocean, including the biologically productive euphotic zone and the mixed layer, has great relevance for studies of physical, biogeochemical, and ecosystem processes and their interaction. Observing this layer with a continuous presence, sampling many of the relevant variables, and with sufficient vertical resolution, has remained a challenge. Here a system is presented which can be deployed on the top of deep-ocean moorings, with a drive mechanism at depths of 150-200m, which mechanically winches a large sensor float and smaller communications float tethered above it to the surface and back down again, typically twice per day for periods up to 1 year. The sensor float can carry several sizeable sensors, and it has enough buoyancy to reach the near surface and for the communications float to pierce the surface even in the presence of strong currents. The system can survive mooring blow-over to 1000m depth. The battery-powered design is made possible by using a balanced energy-conserving principle. Reliability is enhanced with a drive assembly that employs a single rotating part that has no slip rings or rotating seals. The profiling bodies can break the surface to sample the near-surface layer and to establish satellite communication for data relay or reception of new commands. An inductive pass-through mode allows communication with other mooring components throughout the water column beneath the system. A number of successful demonstration deployments have been completed.
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  • 25
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    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 30 . pp. 112-126.
    Publication Date: 2020-08-04
    Description: In recent years, profiling floats, which form the basis of the successful international Argo observatory, are also being considered as platforms for marine biogeochemical research. This study showcases the utility of floats as a novel tool for combined gas measurements of CO2 partial pressure (pCO2) and O2. These float prototypes were equipped with a small-sized and submersible pCO2 sensor and an optode O2 sensor for high resolution measurements in the surface ocean layer. Four consecutive deployments were carried out during Nov. 2010 and June 2011 near the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic. The profiling float performed upcasts every 31 h while measuring pCO2, O2, salinity, temperature and hydrostatic pressure in the upper 200 m of the water column. In order to maintain accuracy, regular pCO2 sensor zeroings at depth and surface, as well as optode measurements in air, were performed for each profile. Through the application of data processing procedures (e.g., time-lag correction) accuracies of float-borne pCO2 measurements were greatly improved (10 – 15 μatm for water column and 5 μatm for surface measurements). O2 measurements yielded an accuracy of 2 μmol kg−1. First results of this pilot study show the possibility of using profiling floats as a platform for detailed and unattended observations of the marine carbon and oxygen cycle dynamics.
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  • 26
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 26 . pp. 7650-7661.
    Publication Date: 2020-08-04
    Description: The use of a coupled ocean/atmosphere/sea-ice model to hindcast (i.e. historical forecast) recent climate variability is described and illustrated for the cases of the 1976/77 and 1998/99 climate shift events in the Pacific. The initialization is achieved by running the coupled model in partially coupled mode whereby global observed wind stress anomalies are used to drive the ocean/sea-ice component of the coupled model while maintaining the thermodynamic coupling between the ocean/sea-ice and atmosphere components. Here we show that hindcast experiments can successfully capture many features associated with the 1976/77 and 1998/99 climate shifts. For instance, hindcast experiments started from the beginning of 1976 can capture sea surface temperature (SST) warming in the central-eastern equatorial Pacific and the positive phase of the Pacific Decadal Oscillation (PDO) throughout the 9 years following the 1976/77 climate shift, including the deepening of the Aleutian low pressure system. Hindcast experiments started from the beginning of 1998 can also capture part of the anomalous conditions during the 4 years after the 1998/99 climate. We argue that the dynamical adjustment of heat content anomalies that are present in the initial conditions in the tropics is important for the successful hindcast of the two climate shifts.
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  • 27
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    AMS (American Meteorological Society)
    In:  Invertebrate Biology, 132 (4). pp. 386-393.
    Publication Date: 2016-11-01
    Description: One of the most remarkable features of the reproductive systems of eubrachyuran crabs is the presence of specialized organs for sperm storage, the seminal receptacles. Descriptions of seminal receptacle morphology, sperm storage time, sperm retention across molts, and the capacity to store multiple ejaculates from different males can help in understanding crab mating strategies as well as in preventing negative effects of male-biased fisheries of heavily harvested species. Metacarcinus edwardsii is the most harvested crab in Chile, but its reproductive biology is largely unstudied. In this study, the morphology of the seminal receptacles of M. edwardsii is characterized from the macroscopic to the microscopic level, during key points in the reproductive cycle. The receptacles of experimentally mated and wild-caught females were included in this analysis. Metacarcinus edwardsii has ventral-type seminal receptacles that are able to retain sperm after molting, and even after extrusion of the eggs. Stratification of multiple ejaculates is clearly observed. In general, the pattern of sperm storage indicates that populations of this species, like those of other cancrid crabs, could have high resilience to the negative effects of the selective harvest of males, principally because females have a great sperm storage capacity.
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  • 28
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 44 (1). pp. 202-219.
    Publication Date: 2015-07-24
    Description: The Arctic continental shelf seas hold a globally significant source of freshwater that impacts Arctic Ocean stratification, circulation, and climate. This freshwater can be injected below the surface mixed layer by intense turbulent kinetic energy dissipation events, as resolved by Laptev Sea microstructure observations. The tides provide a major source of energy that can be dissipated and hence drive diapycnal mixing in the Laptev Sea. Multiyear ADCP mooring records from locations across the shelf reveal that semidiurnal tides are dominated by theM2 and S2 constituents, with the largest amplitudes on the outer shelf. Throughoutmost of the shelf, tides are clockwise polarized and sheared by stratification, as characteristic near the M2 critical latitude. Interannual variations of the tidal and shear structures on the inner shelf aremainly determined by the stratification-setting Lena River freshwater plume. In all locations,M2 tides are enhanced under sea ice, and therefore changes in the seasonal ice cover may lead to changes in tides and water column structure. The main conclusions of this study are that (i) tides play a comparatively greater role year-round on the outer shelf relative to the inner shelf; (ii) a sea ice reduction will overall decrease the predictability of the currents, especially on the inner shelf; and (iii) the freshwater distribution directly impacts diapycnal mixing by setting the vertical tidal structure. These combined effects imply that future sea ice loss will increase the variability and vertical mixing of freshwater, particularly on the inner shelf, where the Lena River first enters the Laptev Sea.
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  • 29
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    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 30 . pp. 2820-2837.
    Publication Date: 2014-07-30
    Description: A large number of quantities have to be measured and processed to determine the atmospheric-state variables, which are the actual measurands, from aircraft-based measurements. A great part of the dependencies between these quantities depends on the aerodynamic state of the aircraft. Aircraft-based meteorological measurements, hence, require in-flight calibration. Most operators of research aircraft perform some kind of calibration, but the schemes used and the degree they are documented greatly vary. The flight maneuvers and calculation methods required, however, are published in a number of partly overlapping and partly contradictory publications. Some methods are only presented as a minor issue in publications mainly focused on atmospheric processes and are therefore hard to find. For an aircraft user, it is hence challenging to either perform or verify a calibration because of missing comprehensive guidance. This lack was stated on occasion of the in-flight calibration of the German research aircraft Polar5 carried out for the field experiment Investigation of Katabatic Winds and Polynyas during Summer (IKAPOS). In the present paper, a comprehensive review of the existing literature on this field and a practical guide to the wind calibration of a research aircraft to be used for turbulent flux measurements are given.
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  • 30
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    AMS (American Meteorological Society)
    In:  Journal of the Atmospheric Sciences, 70 (12). pp. 3959-3976.
    Publication Date: 2018-04-16
    Description: Accurate projections of stratospheric ozone are required because ozone changes affect exposure to ultraviolet radiation and tropospheric climate. Unweighted multimodel ensemble-mean (uMMM) projections from chemistry–climate models (CCMs) are commonly used to project ozone in the twenty-first century, when ozone-depleting substances are expected to decline and greenhouse gases are expected to rise. Here, the authors address the question of whether Antarctic total column ozone projections in October given by the uMMM of CCM simulations can be improved by using a process-oriented multiple diagnostic ensemble regression (MDER) method. This method is based on the correlation between simulated future ozone and selected key processes relevant for stratospheric ozone under present-day conditions. The regression model is built using an algorithm that selects those process-oriented diagnostics that explain a significant fraction of the spread in the projected ozone among the CCMs. The regression model with observed diagnostics is then used to predict future ozone and associated uncertainty. The precision of the authors’ method is tested in a pseudoreality; that is, the prediction is validated against an independent CCM projection used to replace unavailable future observations. The tests show that MDER has higher precision than uMMM, suggesting an improvement in the estimate of future Antarctic ozone. The authors’ method projects that Antarctic total ozone will return to 1980 values at around 2055 with the 95% prediction interval ranging from 2035 to 2080. This reduces the range of return dates across the ensemble of CCMs by about a decade and suggests that the earliest simulated return dates are unlikely.
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  • 31
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 26 . pp. 7767-7782.
    Publication Date: 2020-08-04
    Description: Evidence is presented for the notion that some contribution to the recent decadal trends observed in the Southern Hemisphere, including the lack of a strong Southern Ocean surface warming, may have originated from longer-term internal centennial variability originating in the Southern Ocean. The existence of such centennial variability is supported by the instrumental sea surface temperatures (SSTs), a multimillennial reconstruction of Tasmanian summer temperatures from tree rings, and a millennial control integration of the Kiel Climate Model (KCM). The model variability was previously shown to be linked to changes in Weddell Sea deep convection. During phases of deep convection the surface Southern Ocean warms, the abyssal Southern Ocean cools, Antarctic sea ice extent retreats, and the low-level atmospheric circulation over the Southern Ocean weakens. After the halt of deep convection the surface Southern Ocean cools, the abyssal Southern Ocean warms, Antarctic sea ice expands, and the low-level atmospheric circulation over the Southern Ocean intensifies, consistent with what has been observed during the recent decades. A strong sensitivity of the time scale to model formulation is noted. In the KCM, the centennial variability is associated with global-average surface air temperature (SAT) changes of the order of a few tenths of a degree per century. The model results thus suggest that internal centennial variability originating in the Southern Ocean should be considered in addition to other internal variability and external forcing when discussing the climate of the twentieth century and projecting that of the twenty-first century.
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  • 32
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    In:  Journal of the Atmospheric Sciences, 70 (7). pp. 2103-2118.
    Publication Date: 2020-08-04
    Description: The wintertime northern annular mode (NAM) at the surface is known to undergo slow intraseasonal variations in association with stratospheric variability, which leads the surface signal by up to several weeks. The relative contributions, however, of potentially relevant stratosphere–troposphere coupling mechanisms are not yet fully understood. In this study the relative roles of (i) the downward effect of the zonal-mean secondary circulation induced by quasigeostrophic (QG) adjustment to stratospheric wave drag and radiative damping and (ii) wave drag local to the troposphere are estimated. For this purpose, a spectral tendency equation of the QG zonal-mean zonal wind is derived and used, in a first step, to obtain the external mechanical forcing that, in the QG framework, drives exactly the observed stratospheric and tropospheric daily NAM. In a second step, the equation is then integrated in time to reconstruct the daily NAM, but with the forcing restricted to either stratospheric or tropospheric levels, each case leaving a characteristic NAM surface signal. The relative roles of the above-mentioned mechanisms are found to be of similar quantitative importance, but to differ in a qualitative sense. The downward effect of stratospheric QG adjustment is responsible for the initiation of the NAM surface signal, whereas subsequently local tropospheric wave drag actively maintains and persists the signal over several weeks. Furthermore, the downward effect of QG adjustment to stratospheric radiative damping is shown to have only a minor impact, compared to that from stratospheric wave drag. The robustness of these conclusions is demonstrated by a sensitivity study with respect to various model parameters.
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  • 33
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 43 (10). pp. 2113-2131.
    Publication Date: 2020-08-04
    Description: The Agulhas Current plays a crucial role in the thermohaline circulation through its leakage into the South Atlantic. Under both past and present climates, the trade winds and westerlies could have the ability to modulate the amount of Indian-Atlantic inflow. Compelling arguments have been put forward suggesting that trade winds alone have little impact on the magnitude of Agulhas leakage. Here, employing three ocean models for robust analysis – a global coarse resolution, a regional eddy-permitting and a nested high-resolution eddy-resolving configuration – and systematically altering the position and intensity of the westerly wind belt in a series of sensitivity experiments, it is shown that the westerlies, in particular their intensity, control the leakage. Leakage responds proportionally to the westerlies intensity up to a certain point. Beyond this, through the adjustment of the large-scale circulation, energetic interactions occur between the Agulhas Return Current and the Antarctic Circumpolar Current that result in a state where leakage no longer increases. This adjustment takes place within 1 to 2 decades. Contrary to previous assertions, our results further show that an equatorward (poleward) shift in westerlies increases (decreases) leakage. This occurs due to the redistribution of momentum input by the winds. It is concluded that the reported present-day leakage increase could therefore reflect an unadjusted oceanic response mainly to the strengthening westerlies over the last few decades.
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  • 34
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    In:  Bulletin of the American Meteorological Society, 94 (8). S1-S258.
    Publication Date: 2019-07-09
    Description: For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.
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  • 35
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 43 (4). pp. 805-823.
    Publication Date: 2018-04-12
    Description: Mesoscale anticyclonic eddies in the Irminger Sea are observed using a mooring and a glider. Between 2002 and 2009, the mooring observed 53 anticyclones. Using a kinematic model, objective estimates of eddy length scales and velocity structure are made for 16 eddies. Anticyclones had a mean core diameter of 12 km, and their mean peak observed azimuthal speed was 0.1 m s(-1). They had core salinities and potential temperatures of 34.91-34.98 and 4.488-5.34 degrees C, respectively, making them warm and salty features. These properties represent a typical salinity anomaly of 0.03 and a temperature anomaly of 0.28 degrees C from noneddy values. All eddies had small (〈〈 1) Rossby numbers. In 2006, the glider observed two anticyclones having diameters of about 20 km and peak azimuthal speeds of about 0.3 m s(-1). Similar salinity anomalies were detected throughout the Irminger Sea by floats profiling in anticyclones. Two formation regions for the eddies are identified: one to the west of the Reykjanes Ridge and the other off the East Greenland Irminger Current near Cape Farewell close to the mooring. Observations indicate that eddies formed in the former region are larger than eddies observed at the mooring. A clear increase in eddy salinity is observed between 2002 and 2009. The observed breakup of these eddies in winter implies that they are a source of salt for the central gyre. The anticyclones are similar to those found in both the Labrador Sea and Norwegian Sea, making them a ubiquitous feature of the subpolar North Atlantic basins.
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  • 36
    Publication Date: 2022-03-10
    Description: In this article we address the causes of the large-scale tropical sea level pressure (SLP) changes during climate change. The analysis we present is based on model simulations, observed trends and the seasonal cycle. In all three cases the regional changes of tropospheric temperature (Ttropos) and SLP are strongly related to each other (considerably stronger than (sea) surface temperature and SLP). This relationship basically follows the Bjerknes Circulation Theorem, with relatively low regional SLP where we have relatively high Ttropos and vice versa. A simple physical model suggests a tropical SLP response to horizontally inhomogeneous warming in the tropical Ttropos, with a sensitivity coefficient of about -1.7 hPa/K. This relationship explains a large fraction of observed and predicted changes in the tropical SLP. It is shown that in climate change model simulations the tropospheric land-sea warming contrast is the most significant structure in the regional Ttropos changes relative to the tropical mean changes. Since the land-sea warming contrast exists in the absent of any atmospheric circulation changes it can be argued that the large-scale response of tropical SLP changes is to first order a response to the tropical land-sea warming contrast. Further, as land-sea warming contrast is mostly available moisture dependent, the models predict a stronger warming and decreasing SLP in the drier regions from South America to Africa and a weaker warming and increasing SLP over the wetter Indo-Pacific warm pool region. This suggests an increase in the potential for deep convection conditions over the Atlantic Sector and a decrease over the Indo-Pacific warm pool region in the future.
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  • 37
    Publication Date: 2022-03-10
    Description: Variations in eastern Indian Ocean upper-ocean thermal properties are assessed for the period 1970–2004, with a particular focus on asymmetric features related to opposite phases of Indian Ocean Dipole events, using high-resolution ocean model hindcasts. Sensitivity experiments, where atmospheric forcing variability is restricted to the Indian or Pacific Ocean only, support the interpretation of forcing mechanisms for large-scale asymmetric behavior in eastern Indian Ocean variability. Years are classified according to eastern Indian Ocean subsurface heat content (HC) as proxy of thermocline variations. Years characterized by anomalous low HC feature a zonal gradient in upper-ocean properties near the equator, while high events have a meridional gradient from the tropics into the subtropics. The spatial and temporal characteristics of the seasonal evolution of HC anomalies for the two cases is distinct, as is the relative contribution from Indian Ocean atmospheric forcing versus remote influences from Pacific wind forcing: low events develop rapidly during austral winter/spring in response to Indian Ocean wind forcing associated with an enhanced southeasterly monsoon driving coastal upwelling and a shoaling thermocline in the east; in contrast, formation of anomalous high eastern Indian Ocean HC is more gradual, with anomalies earlier in the year expanding from the Indonesian Throughflow (ITF) region, initiated by remote Pacific wind forcing and transmitted through the ITF via coastal wave dynamics. Implications for seasonal predictions arise with high HC events offering extended lead times for predicting thermocline variations and upper-ocean properties across the eastern Indian Ocean.
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  • 38
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    Publication Date: 2022-03-10
    Description: European Polar Low Working Group This workshop summarized the current state of PL research in the Arctic and Antarctic. A couple of related projects are in the planning phase or already funded. The creation of a PL database for the Norwegian Sea in the frame of the Sea Surface Temperature and Altimeter Synergy (STARS) project (http://projects.met.no stars) will provide a valuable resource for future research and, potentially, predictability improvements. The maintenance of this database and the creation of similar databases for other polar areas including satellite and NWP data are highly recommended. There is also a need for free and timely access to satellite data, in particular to SAR data to fill the gap caused by the mission end of Envisat. With the increasing resolution of climate models, mesoscale processes such as polar MCs will have to be considered in international research programs such as the World Climate Research Programme (WCRP) Polar Climate Predictability Initiative and the World Weather Research Programme (WWRP) Polar Predictability Project.
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  • 39
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 42 (5). pp. 824-839.
    Publication Date: 2018-04-12
    Description: The mechanisms involved in setting the annual cycle of the Florida Current transport are revisited using an adjoint model approach. Adjoint sensitivities of the Florida Current transport to wind stress reproduce a realistic seasonal cycle with an amplitude of ~1.2 Sv (1 Sv ≡ 106 m3 s−1). The annual cycle is predominantly determined by wind stress forcing and related coastal upwelling (downwelling) north of the Florida Strait along the shelf off the North American coast. Fast barotropic waves propagate these anomalies southward and reach the Florida Strait within a month, causing an amplitude of ~1 Sv. Long baroclinic planetary Rossby waves originating from the interior are responsible for an amplitude of ~0.8 Sv but have a different phase. The sensitivities corresponding to the first baroclinic mode propagate westward and are highly influenced by topography. Considerable sensitivities are only found west of the Mid-Atlantic Ridge, with maximum values at the western shelf edge. The second baroclinic mode also has an impact on the Florida Current variability, but only when a mean flow is present. A second-mode wave train propagates southwestward from the ocean bottom on the western side of the Mid-Atlantic Ridge between ~36° and 46°N and at Flemish Cap, where the mean flow interacts with topography, to the surface. Other processes such as baroclinic waves along the shelf and local forcing within the Florida Strait are of minor importance.
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  • 40
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 42 . pp. 725-747.
    Publication Date: 2018-04-12
    Description: The residual effect of surface gravity waves on mean flows in the upper ocean is investigated using thickness weighted mean (TWM) theory applied in a vertically Lagrangian and horizontally Eulerian coordinate system. Depth-dependent equations for the conservation of volume, momentum, and energy are derived. These equations allow for (i) finite amplitude fluid motions, (ii) the horizontal divergence of currents and (iii) a concise treatment of both the kinematic and viscous boundary conditions at the sea surface. Under the assumptions of steady and monochromatic waves and a uniform turbulent viscosity, the TWM momentum equations are used to illustrate the pressure- and viscosity-induced momentum fluxes through the surface that are implicit in previous studies of the wave-induced modification of the classical Ekman spiral problem. The TWM approach clarifies, in particular, the surface momentum flux associated with the so-called virtual wave stress of Longuet-Higgins. Overall the TWM framework can be regarded as an alternative to the three-dimensional Lagrangian mean framework of Pierson. Moreover the TWM framework can be used to include the residual effect of surface waves in large-scale circulation models. In specific models that carry the TWM velocity appropriate for advecting tracers as their velocity variable, the turbulent viscosity term should be modified so that the viscosity acts only on the Eulerian mean velocity.
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  • 41
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    In:  Invertebrate Biology, 131 (2). pp. 96-109.
    Publication Date: 2016-02-24
    Description: Many aspects of barnacle body form are known to be developmentally plastic. Perhaps the most striking examples of such plasticity occur in their feeding legs and unusually long penises, the sizes and shapes of which can change dramatically and adaptively with changes in conspecific density and local water flow conditions. However, whether variation in overall appendage form is mirrored by structural responses in cuticle and muscle is not known. In order to determine how structural variation underlies phenotypic plasticity in barnacle appendages, we examined barnacles occurring at low and high population densities from one wave-protected and one wave-exposed site. We used histological sectioning and fluorescence microscopy of feeding legs and penises to compare cuticle thickness, muscle thickness, and muscle organization, and artificial penis inflation to compare penis extensibility. We observed striking differences in cuticle thickness, muscle thickness, and muscle organization between sites that differed in water velocity, but we found no clear differences associated with variation in conspecific density. Penis extensibility also did not differ consistently between sites. These results are consistent with an adaptive explanation for much of the remarkable and complex variation in barnacle feeding leg and penis morphology among sites that differ in water velocity.
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  • 42
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 25 (12). pp. 4294-4303.
    Publication Date: 2015-01-12
    Description: The tropical Atlantic wind response to El Niño forcing is robust, with weakened northeast trade winds north of the equator and strengthened southeast trade winds along and south of the equator. However, the relationship between sea surface temperature (SST) anomalies in the eastern equatorial Pacific and Atlantic is inconsistent, with El Niño events followed sometimes by warm and other times by cold boreal summer anomalies in the Atlantic cold tongue region. Using observational data and a hindcast simulation of the Nucleus for European Modeling of the Ocean (NEMO) global model at 0.5° resolution (NEMO-ORCA05), this inconsistent SST relationship is shown to be at least partly attributable to a delayed negative feedback in the tropical Atlantic that is active in years with a warm or neutral response in the eastern equatorial Atlantic. In these years, the boreal spring warming in the northern tropical Atlantic that is a typical response to El Niño is pronounced, setting up a strong meridional SST gradient. This leads to a negative wind stress curl anomaly to the north of the equator that generates downwelling Rossby waves. When these waves reach the western boundary, they are reflected into downwelling equatorial Kelvin waves that reach the cold tongue region in late boreal summer to counteract the initial cooling that is due to the boreal winter wind stress response to El Niño. In contrast, this initial cooling persists or is amplified in years in which the boreal spring northern tropical Atlantic warming is weak or absent either because of a positive North Atlantic Oscillation (NAO) phase or an early termination of the Pacific El Niño event.
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  • 43
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    In:  Journal of Climate, 25 (6). pp. 1827-1846.
    Publication Date: 2017-08-25
    Description: Initial-value predictability measures the degree to which the initial state can influence predictions. In this paper, the initial-value predictability of six atmosphere–ocean general circulation models in the North Pacific and North Atlantic is quantified and contrasted by analyzing long control integrations with time invariant external conditions. Through the application of analog and multivariate linear regression methodologies, average predictability properties are estimated for forecasts initiated from every state on the control trajectories. For basinwide measures of predictability, the influence of the initial state tends to last for roughly a decade in both basins, but this limit varies widely among the models, especially in the North Atlantic. Within each basin, predictability varies regionally by as much as a factor of 10 for a given model, and the locations of highest predictability are different for each model. Model-to-model variations in predictability are also seen in the behavior of prominent intrinsic basin modes. Predictability is primarily determined by the mean of forecast distributions rather than the spread about the mean. Horizontal propagation plays a large role in the evolution of these signals and is therefore a key factor in differentiating the predictability of the various models.
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  • 44
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    In:  Journal of the Atmospheric Sciences, 69 . pp. 1824-1840.
    Publication Date: 2018-04-16
    Description: Sudden stratospheric warmings are prominent examples of dynamical wave–mean flow interactions in the Arctic stratosphere during Northern Hemisphere winter. They are characterized by a strong temperature increase on time scales of a few days and a strongly disturbed stratospheric vortex. This work investigates a wide class of supervised learning methods with respect to their ability to classify stratospheric warmings, using temperature anomalies from the Arctic stratosphere and atmospheric forcings such as ENSO, the quasi-biennial oscillation (QBO), and the solar cycle. It is demonstrated that one representative of the supervised learning methods family, namely nonlinear neural networks, is able to reliably classify stratospheric warmings. Within this framework, one can estimate temporal onset, duration, and intensity of stratospheric warming events independently of a particular pressure level. In contrast to classification methods based on the zonal-mean zonal wind, the approach herein distinguishes major, minor, and final warmings. Instead of a binary measure, it provides continuous conditional probabilities for each warming event representing the amount of deviation from an undisturbed polar vortex. Additionally, the statistical importance of the atmospheric factors is estimated. It is shown how marginalized probability distributions can give insights into the interrelationships between external factors. This approach is applied to 40-yr and interim ECMWF (ERA-40/ERA-Interim) and NCEP–NCAR reanalysis data for the period from 1958 through 2010.
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  • 45
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    In:  Journal of Climate, 25 (1). pp. 184-206.
    Publication Date: 2017-08-24
    Description: To analyze the probability density distributions of surface turbulent heat fluxes, the authors apply the twoparametric modified Fisher–Tippett (MFT) distribution to the sensible and latent turbulent heat fluxes recomputed from 6-hourly NCEP–NCAR reanalysis state variables for the period from 1948 to 2008. They derived the mean climatology and seasonal cycle of the location and scale parameters of the MFT distribution. Analysis of the parameters of probability distributions identified the areas where similar surface turbulent fluxes are determined by the very different shape of probability density functions. Estimated extreme turbulent heat fluxes amount to 1500–2000 W m22 (for the 99th percentile) and can exceed 2000 W m22 for higher percentiles in the subpolar latitudes and western boundary current regions. Analysis of linear trends and interannual variability in the mean and extreme fluxes shows that the strongest trends in extreme fluxes (more than 15 W m22 decade21) in the western boundary current regions are associated with the changes in the shape of distribution. In many regions changes in extreme fluxes may be different from those for the mean fluxes at interannual and decadal time scales. The correlation between interannual variability of themean and extreme fluxes is relatively low in the tropics, the SouthernOcean, and the Kuroshio Extension region.Analysis of probability distributions in turbulent fluxes has also been used in assessing the impact of sampling errors in theVoluntaryObserving Ship (VOS)-based surface flux climatologies, allowed for the estimation of the impact of sampling in extreme fluxes. Although sampling does not have a visible systematic effect onmean fluxes, sampling uncertainties result in the underestimation of extreme flux values exceeding 100 W m22 in poorly sampled regions.
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  • 46
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    AMS (American Meteorological Society)
    In:  Journal of Climate, 25 (1). pp. 207-221.
    Publication Date: 2014-10-21
    Description: Antarctic Intermediate Water (AAIW) is a dominant Southern Hemisphere water mass that spreads from its formation regions just north of the Antarctic Circumpolar Current (ACC) to at least 20°S in all oceans. This study uses an isopycnal climatology constructed from Argo conductivity–temperature–depth (CTD) profile data to define the current state of the AAIW salinity minimum (its core) and thence compute anomalies of AAIW core pressure, potential temperature, salinity, and potential density since the mid-1970s from ship-based CTD profiles. The results are used to calculate maps of temporal property trends at the AAIW core, where statistically significant strong circumpolar shoaling (30–50 dbar decade−1), warming (0.05°–0.15°C decade−1), and density reductions [up to −0.03 (kg m−3) decade−1] are found. These trends are strongest just north of the ACC in the southeast Pacific and Atlantic Oceans and decrease equatorward. Salinity trends are generally small, with their sign varying regionally. Bottle data are used to extend the AAIW core potential temperature anomaly analysis back to 1925 in the Atlantic and to ~1960 elsewhere. The modern warm AAIW core conditions appear largely unprecedented in the historical record: biennially and zonally binned median AAIW core potential temperatures within each ocean basin are, with the notable exception of the subtropical South Atlantic in the 1950s–70s, 0.2–1°C colder than modern values. Zonally averaged sea surface temperature anomalies around the AAIW formation latitudes in each ocean and sectoral southern annular mode indices are used to put the AAIW core property trends and variations into context.
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  • 47
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    AMS (American Meteorological Society)
    In:  Bulletin of the American Meteorological Society, 93 (7). S1-S282.
    Publication Date: 2019-07-09
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  • 48
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    In:  Weather, Climate, and Society, 4 (3). pp. 212-229.
    Publication Date: 2021-03-30
    Description: Anthropogenic emissions of greenhouse gases could lead to undesirable effects on oceans in coming centuries. Drawing on recommendations published by the German Advisory Council on Global Change, levels of unacceptable global marine change (so-called guardrails) are defined in terms of global mean temperature, sea level rise, and ocean acidification. A global-mean climate model [the Aggregated Carbon Cycle, Atmospheric Chemistry and Climate Model (ACC2)] is coupled with an economic module [taken from the Dynamic Integrated Climate–Economy Model (DICE)] to conduct a cost-effectiveness analysis to derive CO2 emission pathways that both minimize abatement costs and are compatible with these guardrails. Additionally, the “tolerable windows approach” is used to calculate a range of CO2 emissions paths that obey the guardrails as well as a restriction on mitigation rate. Prospects of meeting the global mean temperature change guardrail (2° and 0.2°C decade−1 relative to preindustrial) depend strongly on assumed values for climate sensitivity: at climate sensitivities 〉3°C the guardrail cannot be attained under any CO2 emissions reduction strategy without mitigation of non-CO2 greenhouse gases. The ocean acidification guardrail (0.2 unit pH decline relative to preindustrial) is less restrictive than the absolute temperature guardrail at climate sensitivities 〉2.5°C but becomes more constraining at lower climate sensitivities. The sea level rise and rate of rise guardrails (1 m and 5 cm decade−1) are substantially less stringent for ice sheet sensitivities derived in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, but they may already be committed to violation if ice sheet sensitivities consistent with semiempirical sea level rise projections are assumed.
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  • 49
    Publication Date: 2022-03-10
    Description: Historical hydrographic data (1940s–2010) show a distinct cross-slope difference of the lower halocline water (LHW) over the Laptev Sea continental margins. Over the slope, the LHW is on average warmer and saltier by 0.2°C and 0.5 psu, respectively, relative to the off-slope LHW. The LHW temperature time series constructed from the on-slope historical records are related to the temperature of the Atlantic Water (AW) boundary current transporting warm water from the North Atlantic Ocean. In contrast, the on-slope LHW salinity is linked to the sea ice and wind forcing over the potential upstream source region in the Barents and northern Kara Seas, as also indicated by hydrodynamic model results. Over the Laptev Sea continental margin, saltier LHW favors weaker salinity stratification that, in turn, contributes to enhanced vertical mixing with underlying AW.
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  • 50
  • 51
    Publication Date: 2023-11-08
    Description: The equatorial deep jets (EDJ) are a striking feature of the equatorial ocean circulation. In the Atlantic Ocean, the EDJ are associated with a vertical scale of between 300 and 700 m, a time scale of roughly 4.5 years and upward energy propagation to the surface. It has been found that the meridional width of the EDJ is roughly 1.5 times larger than expected based on their vertical scale. Here we use a shallow water model for a high order baroclinic vertical normal mode to argue that mixing of momentum along isopycnals can explain the enhanced width. A lateral eddy viscosity of 300 m2 s−1 10 is found to be sufficient to account for the width implied by observations.
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  • 52
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    In:  Journal of Climate, 24 (14). pp. 3345-3557.
    Publication Date: 2019-09-23
    Description: The suggestion is advanced that the remarkably low static stability of Antarctic surface waters may arise from a feedback loop involving global deep-water temperatures. If deep-water temperatures are too warm, this promotes Antarctic convection, thereby strengthening the inflow of Antarctic Bottom Water into the ocean interior and cooling the deep ocean. If deep waters are too cold, this promotes Antarctic stratification allowing the deep ocean to warm because of the input of North Atlantic Deep Water. A steady-state deep-water temperature is achieved such that the Antarctic surface can barely undergo convection. A two-box model is used to illustrate this feedback loop in its simplest expression and to develop basic concepts, such as the bounds on the operation of this loop. The model illustrates the possible dominating influence of Antarctic upwelling rate and Antarctic freshwater balance on global deep-water temperatures.
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  • 53
    Publication Date: 2020-08-14
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  • 54
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    In:  Bulletin of the American Meteorological Society, 92 (5). pp. 637-640.
    Publication Date: 2019-09-23
    Description: The importance of decadal climate variability (DCV) research is being increasingly recognized, including by the World Climate Research Program (WCRP) and the Intergovernmental Panel on Climate Change (IPCC). An improved understanding of DCV is very important because stakeholders and policymakers want to know the likely climate trajectory for the coming decades for applications to water resources, agriculture, energy, and infrastructure development. Responding to this demand, many climate modeling groups in the United States, Europe, Japan, and elsewhere are gearing up to assess the potential for decadal climate predictions. The magnitudes of regional DCV often exceed those associated with the trends resulting from anthropogenic changes. Therefore, differentiating between the two is also very important for planning, implementation, and national and international treaties.
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  • 55
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 41 (11). pp. 2242-2258.
    Publication Date: 2018-04-12
    Description: Simple idealized layered models and primitive equation models show that the meridional gradient of the zonally averaged pressure has no direct relation with the meridional flow. This demonstrates a contradiction in an often-used parameterization in zonally averaged models. The failure of this parameterization reflects the inconsistency between the model of Stommel and Arons and the box model of Stommel, as previously pointed out by Straub. A new closure is proposed. The ocean is divided in two dynamically different regimes: a narrow western boundary layer and an interior ocean; zonally averaged quantities over these regions are considered. In the averaged equations three unknowns appear: the interior zonal pressure difference Delta p(i), the zonal pressure difference Delta p(b) of the boundary layer, and the zonal velocity us at the interface between the two regions. Here Delta p(i) is parameterized using a frictionless vorticity balance, Delta p(b), by the difference of the mean pressure in the interior and western boundary, and u(delta) by the mean zonal velocity of the western boundary layer. Zonally resolved models, a layer model, and a primitive equation model validate the new parameterization by comparing with the respective zonally averaged counterparts. It turns out that the zonally averaged models reproduce well the buoyancy distribution and the meridional flow in the zonally resolved model versions with respect to the mean and time changes.
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  • 56
    Publication Date: 2017-08-24
    Description: Continuous estimates of the oceanic meridional heat transport in the Atlantic are derived from the Rapid Climate Change–Meridional Overturning Circulation (MOC) and Heatflux Array (RAPID–MOCHA) observing system deployed along 26.5°N, for the period from April 2004 to October 2007. The basinwide meridional heat transport (MHT) is derived by combining temperature transports (relative to a common reference) from 1) the Gulf Stream in the Straits of Florida; 2) the western boundary region offshore of Abaco, Bahamas; 3) the Ekman layer [derived from Quick Scatterometer (QuikSCAT) wind stresses]; and 4) the interior ocean monitored by “endpoint” dynamic height moorings. The interior eddy heat transport arising from spatial covariance of the velocity and temperature fields is estimated independently from repeat hydrographic and expendable bathythermograph (XBT) sections and can also be approximated by the array. The results for the 3.5 yr of data thus far available show a mean MHT of 1.33 ± 0.40 PW for 10-day-averaged estimates, on which time scale a basinwide mass balance can be reasonably assumed. The associated MOC strength and variability is 18.5 ± 4.9 Sv (1 Sv ≡ 106 m3 s−1). The continuous heat transport estimates range from a minimum of 0.2 to a maximum of 2.5 PW, with approximately half of the variance caused by Ekman transport changes and half caused by changes in the geostrophic circulation. The data suggest a seasonal cycle of the MHT with a maximum in summer (July–September) and minimum in late winter (March–April), with an annual range of 0.6 PW. A breakdown of the MHT into “overturning” and “gyre” components shows that the overturning component carries 88% of the total heat transport. The overall uncertainty of the annual mean MHT for the 3.5-yr record is 0.14 PW or about 10% of the mean value.
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  • 57
    Publication Date: 2019-09-23
    Description: The water mass structure of the Arctic Ocean is remarkable, for its intermediate (depth range ~150–900 m) layer is filled with warm (temperature 〉0°C) and salty water of Atlantic origin (usually called the Atlantic Water, AW). This water is carried into and through the Arctic Ocean by the pan-Arctic boundary current, which moves cyclonically along the basins’ margins (Fig. 1). This system provides the largest input of water, heat, and salt into the Arctic Ocean; the total quantity of heat is substantial, enough to melt the Arctic sea ice cover several times over. By utilizing an extensive archive of recently collected observational data, this study provides a cohesive picture of recent large-scale changes in the AW layer of the Arctic Ocean. These recent observations show the warm pulse of AW that entered the Arctic Ocean in the early 1990s finally reached the Canada Basin during the 2000s. The second warm pulse that entered the Arctic Ocean in the mid-2000s has moved through the Eurasian Basin and is en route downstream. One of the most intriguing results of these observations is the realization of the possibility of uptake of anomalous AW heat by overlying layers, with possible implications for an already-reduced Arctic ice cover.
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  • 58
    Publication Date: 2022-03-10
    Description: Vertical mixing in the bottom boundary layer and pycnocline of the Laptev Sea is evaluated from a rapidly sampled 12-h time series of microstructure temperature, conductivity, and shear observations collected under 100% sea ice during October 2008. The bottom boundary turbulent kinetic energy dissipation was observed to be enhanced (ϵ ∼ 10−4 W m−3) beyond background levels (ϵ ∼ 10−6 W m−3), extending up to 10 m above the seabed when simulated tidal currents were directed on slope. Upward heat fluxes into the halocline-class waters along the Laptev Sea seabed peaked at ∼4–8 W m−2, averaging out to ∼2 W m−2 over the 12-h sampling period. In the Laptev Sea pycnocline, an isolated 2-h episode of intense dissipation (ϵ ∼ 10−3 W m−3) and vertical diffusivities was observed that was not due to a localized wind event. Observations from an acoustic Doppler current meter moored in the central Laptev Sea near the M2 critical latitude are consistent with a previous model in which mixing episodes are driven by an enhancement of the pycnocline shear resulting from the alignment of the rotating pycnocline shear vector with the under-ice stress vector. Upward cross-pycnocline heat fluxes from the Arctic halocline peaked at ∼54 W m−2, resulting in a 12-h average of ∼12 W m−2. These results highlight the intermittent nature of Arctic shelf sea mixing processes and how these processes can impact the transformation of Arctic Ocean water masses. The observations also clearly demonstrate that absence or presence of sea ice profoundly affects the availability of near-inertial kinetic energy to drive vertical mixing on the Arctic shelves.
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  • 59
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    In:  Journal of Atmospheric and Oceanic Technology, 27 (9). pp. 1533-1546.
    Publication Date: 2018-07-04
    Description: The eddy correlation technique is rapidly becoming an established method for resolving dissolved oxygen fluxes in natural aquatic systems. This direct and noninvasive determination of oxygen fluxes close to the sediment by simultaneously measuring the velocity and the dissolved oxygen fluctuations has considerable advantages compared to traditional methods. This paper describes the measurement principle and analyzes the spatial and temporal scales of those fluctuations as a function of turbulence levels. The magnitudes and spectral structure of the expected fluctuations provide the required sensor specifications and define practical boundary conditions for the eddy correlation instrumentation and its deployment. In addition, data analysis and spectral corrections are proposed for the usual nonideal conditions, such as the time shift between the sensor pair and the limited frequency response of the oxygen sensor. The consistency of the eddy correlation measurements in a riverine reservoir has been confirmed—observing a night–day transition from oxygen respiration to net oxygen production, ranging from −20 to +5 mmol m−2 day−1—by comparing two physically independent, eddy correlation instruments deployed side by side. The natural variability of the fluctuations calls for at least ∼1 h of flux data record to achieve a relative accuracy of better than ∼20%. Although various aspects still need improvement, eddy correlation is seen as a promising and soon-to-be widely applied method in natural waters.
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  • 60
    Publication Date: 2020-08-04
    Description: Some studies of ocean climate model experiments suggest that regional changes in dynamic sea level could provide a valuable indicator of trends in the strength of the Atlantic meridional overturning circulation (MOC). This paper describes the use of a sequence of global ocean–ice model experiments to show that the diagnosed patterns of sea surface height (SSH) anomalies associated with changes in the MOC in the North Atlantic (NA) depend critically on the time scales of interest. Model hindcast simulations for 1958–2004 reproduce the observed pattern of SSH variability with extrema occurring along the Gulf Stream (GS) and in the subpolar gyre (SPG), but they also show that the pattern is primarily related to the wind-driven variability of MOC and gyre circulation on interannual time scales; it is reflected also in the leading EOF of SSH variability over the NA Ocean, as described in previous studies. The pattern, however, is not useful as a “fingerprint” of longer-term changes in the MOC: as shown with a companion experiment, a multidecadal, gradual decline in the MOC [of 5 Sv (1 Sv ≡ 106 m3 s−1) over 5 decades] induces a much broader, basin-scale SSH rise over the mid-to-high-latitude NA, with amplitudes of 20 cm. The detectability of such a trend is low along the GS since low-frequency SSH changes are effectively masked here by strong variability on shorter time scales. More favorable signal-to-noise ratios are found in the SPG and the eastern NA, where a MOC trend of 0.1 Sv yr−1 would leave a significant imprint in SSH already after about 20 years.
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  • 61
    Publication Date: 2020-08-04
    Description: Changes in the ventilation of the oxygen minimum zone (OMZ) of the tropical North Atlantic are studied using oceanographic data from 18 research cruises carried out between 28.5° and 23°W during 1999–2008 as well as historical data referring to the period 1972–85. In the core of the OMZ at about 400-m depth, a highly significant oxygen decrease of about 15 μmol kg−1 is found between the two periods. During the same time interval, the salinity at the oxygen minimum increased by about 0.1. Above the core of the OMZ, within the central water layer, oxygen decreased too, but salinity changed only slightly or even decreased. The scatter in the local oxygen–salinity relations decreased from the earlier to the later period suggesting a reduced filamentation due to mesoscale eddies and/or zonal jets acting on the background gradients. Here it is suggested that latitudinally alternating zonal jets with observed amplitudes of a few centimeters per second in the depth range of the OMZ contribute to the ventilation of the OMZ. A conceptual model of the ventilation of the OMZ is used to corroborate the hypothesis that changes in the strength of zonal jets affect mean oxygen levels in the OMZ. According to the model, a weakening of zonal jets, which is in general agreement with observed hydrographic evidences, is associated with a reduction of the mean oxygen levels that could significantly contribute to the observed deoxygenation of the North Atlantic OMZ.
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  • 62
    Publication Date: 2020-08-04
    Description: The Atlantic meridional overturning circulation (AMOC) makes the strongest oceanic contribution to the meridional redistribution of heat. Here, an observation-based, forty-eight-month-long time series of the vertical structure and strength of the AMOC at 26.5°N is presented. From April 2004 to April 2008 the AMOC had a mean strength of 18.7 ±2.1 Sv with fluctuations of 4.8 Sv rms. The best guess of the peak-to-peak amplitude of the AMOC seasonal cycle is 6.7 Sv, with a maximum strength in autumn and a minimum in spring. While seasonality in the AMOC was commonly thought to be dominated by the northward Ekman transport, this study reveals that fluctuations of the geostrophic mid-ocean and Gulf Stream transports of 2.2 Sv and 1.7 Sv rms, respectively, are substantially larger than those of the Ekman component (1.2 Sv rms). A simple model based on linear dynamics suggests that the seasonal cycle is dominated by wind stress curl forcing at the eastern boundary of the Atlantic. Seasonal geostrophic AMOC anomalies might represent an important and previously underestimated component of meridional transport and storage of heat in the subtropical North Atlantic. There is evidence that the seasonal cycle observed here is representative of much longer intervals. Previously, hydrographic snapshot estimates between 1957 and 2004 had suggested a long-term decline of the AMOC by 8 Sv. This study suggests that aliasing of seasonal AMOC anomalies might have accounted for a large part of the inferred slowdown.
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  • 63
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    In:  Bulletin of the American Meteorological Society, 91 (7, S). pp. 66-69.
    Publication Date: 2020-08-13
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  • 64
    Publication Date: 2018-04-12
    Description: Analysis of modern and historical observations demonstrates that the temperature of the intermediate-depth (150–900 m) Atlantic water (AW) of the Arctic Ocean has increased in recent decades. The AW warming has been uneven in time; a local 1°C maximum was observed in the mid-1990s, followed by an intervening minimum and an additional warming that culminated in 2007 with temperatures higher than in the 1990s by 0.24°C. Relative to climatology from all data prior to 1999, the most extreme 2007 temperature anomalies of up to 1°C and higher were observed in the Eurasian and Makarov Basins. The AW warming was associated with a substantial (up to 75–90 m) shoaling of the upper AW boundary in the central Arctic Ocean and weakening of the Eurasian Basin upper-ocean stratification. Taken together, these observations suggest that the changes in the Eurasian Basin facilitated greater upward transfer of AW heat to the ocean surface layer. Available limited observations and results from a 1D ocean column model support this surmised upward spread of AW heat through the Eurasian Basin halocline. Experiments with a 3D coupled ice–ocean model in turn suggest a loss of 28–35 cm of ice thickness after 50 yr in response to the 0.5 W m−2 increase in AW ocean heat flux suggested by the 1D model. This amount of thinning is comparable to the 29 cm of ice thickness loss due to local atmospheric thermodynamic forcing estimated from observations of fast-ice thickness decline. The implication is that AW warming helped precondition the polar ice cap for the extreme ice loss observed in recent years.
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  • 65
    Publication Date: 2020-08-04
    Description: The 20th century Northern Hemisphere surface climate exhibits a long-term warming trend, largely caused by anthropogenic forcing, and natural decadal climate variability superimposed on it. This study addresses the possible origin and strength of internal decadal climate variability in the Northern Hemisphere during the recent decades. We present results from a set of climate model simulations that suggest natural internal multidecadal climate variability in the North Atlantic-Arctic Sector could have considerably contributed to the Northern Hemisphere surface warming since 1980. Although covering only a few percent of the earth’s surface, the Arctic may have provided the largest share in this. It is hypothesized that a stronger Meridional Overturning Circulation in the Atlantic and the associated increase in northward heat transport enhanced the heat loss from the ocean to the atmosphere in the North Atlantic region, and especially in the North Atlantic portion of the Arctic due to anomalously strong sea ice melt. The model results stress the potential importance of natural internal multidecadal variability originating in the North Atlantic-Arctic Sector in generating inter-decadal climate changes not only on a regional, but possibly also on a hemispheric and even global scale.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 66
    facet.materialart.
    Unknown
    Univ. Bochum
    Publication Date: 2020-10-07
    Description: Die Dissertation behandelt die Konzepte sowie die Implementierung der operativen Aspekte der Kontrollsoftware des LUCIFER Instruments. Diese ist in vier Schichten aufgeteilt. Die Schnittstelle zwischen Software und Hardware bildet die Control-Schicht. In der Instrument-Schicht sind alle Komponenten des Instruments als Software-Dienste abgebildet und erfüllen die jeweils für diese Komponente notwendigen Aufgaben. In der obersten Schicht sind die wesentlichen Manager-Dienste beheimatet. Durch Beobachtungsskripte ist eine automatische Steuerung von Instrument und Teleskop möglich. Weiterhin wurden die stellaren Populationen im Zentrum von vier Galaxien untersucht. Ein Vergleich mit publizierten Werten für ähnliche Galaxien zeigt keinen signifikanten Trend zu jüngeren Populationen in den Galaxien, die einen Pseudo-Bulge zeigen. Eine Galaxie zeigt deutliche Hinweise auf eine sehr alte stellare Population im Buge, deutlich älter als die Populationen von elliptischen Galaxien.
    Description: thesis
    Keywords: 520 ; TCM 000 ; TIE 400 ; Mathematische und EDV-Verfahren {Astronomie} ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 142 S.
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  • 67
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    Univ. Bochum
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; TEG 000 ; THT 800 ; Kosmogonie {Astronomie} ; Massenreiche Sterne {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 131 S.
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  • 68
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; TCE 320 ; Photometer, Polarimeter, spektroskopische Instrumente {Astronomische Instrumente}
    Language: German
    Type: monograph , publishedVersion
    Format: 79 S.
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  • 69
    Publication Date: 2021-03-29
    Description: We investigate the double-peak profile of the emission of powerful cosmic non-thermal radiation sources with dominant magnetic field self-generation like TeV blazars. Therefore, we assume a flare to occur in the emission knot due to the uniform instantaneous injection of monoenergetic ultra-relativistic electrons via a relativistic pick-up process. The electrons are subjected to a linear or nonlinear synchrotron radiation cooling and the synchrotron photons are multiple Thomson scattered off their generating electrons (SSC process). We work out the differences between single and multiple instantaneous injections of monoenergetic relativistic electrons. This is of great interest, because it is very likely that injections into the plasmoids occur repeatedly, so that this would explain the short-time energy variability of blazars. We also compute for the first time the nonlinear SSC radiation quantities using a Thomson limit approximation and the full Klein-Nishina cross section.
    Description: thesis
    Keywords: 523 ; TIE 900 ; Sonstige Sternensysteme {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 84 S.
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  • 70
    facet.materialart.
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    Univ. Bochum
    Publication Date: 2021-03-29
    Description: This work deals with the search for substructures in four nearby galaxies (NGC 300, NGC 7793, M 33, M 83) in which it is possible to resolve single stars in their outer parts.The search is based on the photometry of wide field imaging data. This photometry is further analysed by the use of classical methods (colour-magnitude-diagrams, star counts) and by the use of data-mining tools (fuzzy c-means clustering). Finally, it could be shown that three out of four galaxies show signs of substructure. In NGC 300 the analysis of the red-giant-branch stars revealed a truncation in the outer parts, while in NGC 7793 hints for a tidal stream or spiral arm were found. In case of M 83 it was possible to recover an already known surface brightness arc first seen on old photographic plates.
    Description: thesis
    Keywords: 523 ; TIE 400 ; TIE 500 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie} ; Aufbau und Struktur von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 151 S.
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  • 71
    Publication Date: 2021-03-29
    Description: Die vorliegende Dissertation untersucht, ob heiße und expandierende Gasstrukturen gravitativ an ihre Galaxie gebunden sind (Ausfluss) oder ob sie das Gravitationspotential der Galaxie verlassen können (galaktischer Wind). Galaktische Winde, d.h. Massenverlust für die Galaxie und Anreicherung des intergalaktischen Mediums haben direkte Auswirkungen auf die Entwicklung von Galaxien und Galaxienhaufen. Spektroskopische Untersuchungen des neutralen und ionisierten Wasserstoffs wurden in einer Auswahl von vier nahen irregulären Zwerggalaxien durchgeführt. In allen vier Galaxien wurden expandierende Gasstrukturen gefunden und ihre Expansionsgeschwindigkeiten vermessen. Aus Dunkle Materie Halo Modellen wurde das Gravitationspotential der Galaxien abgeschätzt. Dadurch konnte gezeigt werden, dass das Gas in allen Fällen gravitativ gebunden bleibt. Dieses Ergebnis ist in Übereinstimmung mit hydrodynamischen Simulationen und legt nahe, dass galaktische Winde in masseärmeren Galaxien zu finden sind.
    Description: thesis
    Keywords: 523 ; TII 500 ; Emissionsnebel {Astronomie: Interstellare Materie}
    Language: English
    Type: monograph , publishedVersion
    Format: 136 S.
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  • 72
    Publication Date: 2021-03-29
    Description: Beim Ras-RasGAP-Komplex ist die Hydrolyse des Guanosintriphosphats stark beschleunigt im Vergleich zu Ras allein. Dies wird hauptsächlich durch den Argininfinger R789 verursacht, der direkt zur Triphosphatgruppe zeigt. QM/MM-Simulationen wurden durchgeführt, bei denen das Triphosphat quantenmechanisch mithilfe der DFT behandelt wurde, während der Proteinkomplex und die Wasserumgebung klassisch beschrieben wurden. Im Vergleich zu Ras sind beim Ras-RasGAP-Komplex die entscheidende Elektronenverschiebung, die Bindungsverlängerung und die Verdrillung hin zu einer ekliptischen gamma-beta-Orientierung wesentlich stärker ausgeprägt. Der Argininfinger interagiert durch Verdrängung von Wassermolekülen aus der Bindenische. Das resultierende verstärkte elektrische Feld katalysiert den Bindungsbruch. Eine hypothetische Protonierung des beta-Phosphats führt zum Bindungsbruch. Nach Abschluss der Hydrolyse sind die Schwingungen des Mono- und Diphosphats über Dipol-Dipol-Wechselwirkung gekoppelt.
    Description: thesis
    Keywords: 523 ; TIE 400 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 149 S.
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  • 73
    facet.materialart.
    Unknown
    Univ. Bochum
    Publication Date: 2021-03-29
    Description: Diese Dissertation untersucht, ob die Dynamik von Galaxien in Einklang mit den Ergebnissen aus CDM (cold dark matter) Simulationen ist. Im Wesentlichen wurden 19 Galaxien hinsichtlich Abweichungen von kreisförmigen Bewegungen analysiert. Diese nicht-kreisförmigen Bewegungen werden von den Simulationen vorhergesagt, um das lang bestehende cusp/core Problem zu erklären. Es konnte jedoch gezeigt werden, dass die Abweichungen von den kreisförmigen Bewegungen zu klein sind, um die Ergebnisse von CDM Simulationen mit den Beobachtungen in Einklang zu bringen. Große nicht-kreisförmige Bewegungen finden sich vor allem in den Zentren von massereichen Galaxien und Balkengalaxien. Dies lässt jedoch vermuten, dass diese Bewegungen durch baryonische Materie hervorgerufen werden und nicht durch den DM Halo. Die vorliegende Dissertation unterstreicht die Notwendigkeit, die CDM Simulationen zu verändern, bzw. alternative Lösungen zu CDM Modellen zu suchen.
    Description: thesis
    Keywords: 523 ; TII 100 ; Dunkle Materie {Astronomie: Interstellare Materie}
    Language: English
    Type: monograph , publishedVersion
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  • 74
    Publication Date: 2021-03-29
    Description: In der vorliegenden Arbeit wird zunächst eine verallgemeinerte Theorie der relativistischen Weibelinstabilität aufgestellt, indem auf eine Festlegung einer bestimmten Verteilungsfunktion verzichtet wird. Für große Parameterbereiche in anisotropen Plasmen kann die Wachstumsrate in allgemeiner Form bestimmt werden, deren Koeffizienten deutlich einfacher als bisher berechnet werden können. Diese Erleichterung wird anhand von vier Verteilungsfunktionen illustriert; es zeigt sich, dass ein Großteil der Verteilungen zu ähnlichen Ergebnissen führt.Weiterhin kann eine Solitongleichung für ein unmagnetisches Plasma aufgestellt und unter bestimmten Voraussetzungen an die Verteilung der Teilchen gelöst werden; es ergeben sich Verlauf und Stärke der elektromagnetischen Felder. Eine Anwendung findet sich in relativistischen Jets z.B. von Gamma Ray Bursts: Es wird die Strahlung von Elektronen berechnet, welche mit dem Soliton in einem solchen Jet wechselwirken.
    Description: thesis
    Keywords: 520 ; TFG 000 ; Magnetohydrodynamik und Plasma-Astrophysik
    Language: German
    Type: monograph , publishedVersion
    Format: 166 S.
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  • 75
    Publication Date: 2021-03-29
    Description: We have investigated the implications of isotropically distributed interstellar magnetohydrodynamic plasma waves on the scattering mean free path and the spatial anisotropy of high-energy cosmic rays. We demonstrate a drastic modification of the energy dependence of both cosmic ray transport parameters compared to previous calculations that have assumed that the plasma waves propagate only parallel or antiparallel to the ordered magnetic field (slab turbulence).
    Description: thesis
    Keywords: 539.7223 ; 523 ; 550 ; TFE 000 ; TFG 000 ; Kosmische Elektrodynamik {Astrophysik} ; Magnetohydrodynamik und Plasma-Astrophysik
    Language: English
    Type: monograph , publishedVersion
    Format: 91 S.
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  • 76
    Publication Date: 2021-03-29
    Description: Das Hexapod-Teleskop vereinigt zahlreiche innovative Ideen im Teleskopbau, die von industrieller Seite allerdings nie in einem astronomischen Betrieb getestet wurden. Obwohl die einzelnen Komponenten der Mechanik und Optik alle von höchster Präzision sind, wurde ihr Zusammenspiel weder im Labor noch am Himmel getestet. Die vorliegende Dissertation hat diese Arbeit geleistet und das Teleskop in die unmittelbare Nähe des astronomischen Betriebs gebracht. Erstmalig konnten mit dem Hexapod-Teleskop Sternaufnahmen gemacht und ausgewertet werden.
    Description: thesis
    Keywords: 522 ; TCE 200 ; Teleskope {Astronomische Instrumente}
    Language: German
    Type: monograph , publishedVersion
    Format: 116 S.
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  • 77
    facet.materialart.
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    Univ. Bochum
    Publication Date: 2021-03-29
    Description: In this work we introduced basic turbulence theory into the framework of the interstellar medium. In many cases turbulence simulations are applied to the interstellar medium (ISM) merely because it is a medium, where extremely high Reynolds numbers are actually realised, and the parameters of the ISM are only taken into account as far as they are needed for the turbulence research. Here, however, we investigated the basic turbulence properties, while at the same time we modelled the properties of the ISM as thoroughly as possible. The important point is that there are many physical processes going on in the ISM, which should be incorporated in the corresponding simulations. These processes reachfrom external influences of the radiation field originating from hot stars to the internal interaction of the particles culminating in the intricate chemistry of the molecular cloud medium. Each of the different phases of the ISM has its own dominant processes to be taken into account for a realistic modelling...
    Description: thesis
    Keywords: 523 ; TII 000 ; Interstellare Materie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 141 S.
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  • 78
    Publication Date: 2021-03-29
    Description: In der vorliegenden Arbeit wird zunächst der Transport von kosmischer Strahlung in der Turbulenz der Heliosphäre untersucht. Dabei werden für verschiedene Turbulenzmodelle aktuelle lineare und nichtlineare Theorien mit Simulationen verglichen. Insbesondere wird das Plasmawellen-Modell der quasilinearen Theorie und die nichtlineare Führungszentrums (NLGC)-Theorie für den Fall isotroper Turbulenz verallgemeinert, wobei sich für die NLC-Theorie eine akzeptable Übereinstimmung mit Simulationen ergibt. Weiterhin werden Mechanismen zur Erzeugung der Turbulenz aus Instabilitäten in anisotropen Teilchenverteilungen diskutiert, darunter insbesondere die Weibel-Instabilität in gegenströmenden Maxwellschen Plasmen und die relativistisch und dreidimensional verallgemeinerte Harris-Instabilität in den Jets von Gamma-ray Bursts (GRB). Für GRB erfolgt darüber hinaus eine Vorhersage über die Zusammensetzung der Jets.
    Description: thesis
    Keywords: 523 ; TFG 000 ; Magnetohydrodynamik und Plasma-Astrophysik
    Language: German
    Type: monograph , publishedVersion
    Format: 211 S.
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  • 79
    facet.materialart.
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    Univ. Bochum
    Publication Date: 2021-03-29
    Description: This thesis presents an imaging and spectroscopic study of the narrow-line region (NLR) in active galactic nuclei (AGNs). We find a correlation between size and luminosity of the NLR with different slopes for type-1 and type-2 AGNs which can be explained by the observers viewing angle and a receding torus. The radial properties of the NLR gas, such as reddening, electron density, ionization parameter, and velocity field are analyzed. We derive pure emission-line spectra and use the resulting absorption-line free ratios for spatially resolved spectral diagnostics. We find a transition between the AGN-excited NLR and the surrounding star-forming regions, allowing us to determine the NLR size independent of stellar contamination. The electron density and ionization parameter decrease with radius indicating that the NLR is photoionized by the central source only.The velocity fields suggest a disky NLR gas distribution with the torus axis lying in the galaxy disk.
    Description: thesis
    Keywords: 523 ; TIE 400 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 222 S.
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  • 80
    Publication Date: 2021-03-29
    Description: In der vorliegenden Dissertation wird die vertikale Struktur von edge-on Scheibengalaxien mit einer 'box or peanut shaped' (B/PS) Struktur in der Bulgeregion unter Verwendung von nahinfrarot Beobachtungen untersucht. Durch Nutzung von Konturhervorhebungsverfahren und Flaechenhelligkeitsprofilen entlang der Hauptachse der Galaxie kann gezeigt werden, dass Material aus der Scheibe in vertikaler Richtung umverteilt wird, und zur Entstehung der B/PS Struktur fuehrt. Dies ist in Einklang mit dem auf der vertikalen Ausdehnung eines in der Galaxie vorhandenen stellaren Balkens sich stuetzenden sekulaeren Evolutionsmodell. Die Analyse der vertikalen Flaechenhelligkeitsverteilung zeigt eine Variation der Skalenhoehe entlang der radialen Ausdehnung der stellaren Scheibe. Diese Variation wird hier zum ersten Mal deutlich beobachtet, wobei an der Position der B/PS Struktur ein lokales Maximum der Skalenhoehe festzustellen ist, im Einklang mit dem sekulaeren Evolutionsmodell.
    Description: thesis
    Keywords: 523 ; TBG 000 ; TIE 400 ; TIE 500 ; Infrarot-Astronomie ; Spektren und Leuchtkraft von Sternsystemen {Astronomie} ; Aufbau und Struktur von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 178 S.
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  • 81
    Publication Date: 2021-03-29
    Description: In the present work analytical solutions of the transport equation for hadronic cosmic rays are calculated. With these, it is possible for the first time to fit the energy spectra of the cosmic protons measured at the position of the earth. A focus lies on the investigation of the spatial diffusion of the galactic cosmic ray nuclei and their stochastic reacceleration by plasma waves superimposed on the interstellar medium. A realistic spatial distribution of supernova remnants as primary sources of the galactic cosmic rays and, as an additional process, the solar modulation are taken into account. Different fit parameters are obtained. Additionally, analytical approximations of the momentum solution for a power law injection spectrum for small and large momenta are calculated for the case without and for the case with spallation losses.
    Description: thesis
    Keywords: 523 ; TFE 000 ; Kosmische Elektrodynamik {Astrophysik}
    Language: English
    Type: monograph , publishedVersion
    Format: 192 S.
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  • 82
    facet.materialart.
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    Univ. Bochum
    Publication Date: 2021-03-29
    Description: In der vorliegenden Arbeit wird die Heizung des interstellaren Mediums durch die Dämpfung von Plasmawellenturbulenz untersucht. Es wird gezeigt, daß die Heizung ausreicht, das thermische Gleichgewicht im interstellaren Medium aufrecht zu erhalten. Außerdem lassen sich Rückschlüsse auf die Art der Turbulenz ziehen. Insbesondere kann gezeigt werden, daß die Turbulenz des interstellaren Mediums vermutlich anisotrop ist.
    Description: thesis
    Keywords: 523 ; TFG 000 ; TII 800 ; Magnetohydrodynamik und Plasma-Astrophysik ; Interstellares Gas {Astronomie: Interstellare Materie}
    Language: German
    Type: monograph , publishedVersion
    Format: 138 S.
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  • 83
    Publication Date: 2021-03-29
    Description: Die Cassini/Huygens-Mission ist ein gemeinsames Unternehmen von NASA und ESA, mit dem Ziel, das Saturnsystem zu erkunden. Die vorliegende Arbeit ist im Rahmen des Doppler-Wind-Experiments durchgeführt worden. Das Ziel der Arbeit war eine Methode zur Ermittlung der Ruhelage und Amplitude der angesetzten Pendelbewegung der Huygens-Sonde während des Abstiegs auf dem Saturnmond Titan zu entwickeln. Die verfügbaren Daten sind die Dopplerfrequenzverschiebung sowie die Empfangsleistung des Telemetriesignals. Dazu kommt das Rückstreusignal des Radar-Höhenmessers. Mit den Informationen des Telemetriesignals wurden ein deterministischer Ansatz und ein stochastischer Ansatz entwickelt, um die Parameter der Pendelbewegung zu ermitteln, je nach dem, ob die Messdaten genügend Information über die Bewegung abliefern, oder, ob eine Periodizität der Bewegung vorhanden ist. Mit dem Rückstreusignal des Radar-Höhenmessers wurde ein interaktives Verfahren zusätzlich zu diesem Zweck entwickelt.
    Description: thesis
    Keywords: 520 ; TJF 215 ; Satellitendynamik {Weltraumforschung: Künstliche Satelliten}
    Language: German
    Type: monograph , publishedVersion
    Format: 119 S.
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  • 84
    Publication Date: 2021-03-29
    Description: Die vorliegende Arbeit untersucht den Einfluß von thermisch verteiltem Plasma auf die Strahlungsemission in den Jets von aktiven galaktischen Kernen. Zur Bestimmung der Heiz- und Strahlungsproduktionsraten wird die Strahlungstransportgleichung für einige einfache Geometrien exakt gelöst und anschließend der maximale Fehler abgeschätzt, der aus der Unkenntnis der exakten Geometrien folgt. Es wird eine analytische Abschätzung hergeleitet, welcher Prozeß die Heizrate dominiert. Schließlich wird untersucht, welche Bedingungen an experimentelle Daten gestellt werden müssen, um die Parameter des Modells eindeutig fitten zu können.
    Description: thesis
    Keywords: 523 ; TFG 000 ; TFE 000 ; Magnetohydrodynamik und Plasma-Astrophysik ; Kosmische Elektrodynamik {Astrophysik}
    Language: German
    Type: monograph , publishedVersion
    Format: 129 S.
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  • 85
    Publication Date: 2021-03-29
    Description: I presented the first study of the SFH of LSB galaxies by using integrated spectra. The analyzed sample was derived during a search for LSBs in the HDFS. The selection was done using a new method based on the locations of the galaxies in the colorcolor diagrams. As shown by Haberzettl (1999), the LSB galaxies in the colorcolor diagrams do not follow the redshift tracks built by the HSB galaxies. In the colorcolor diagrams, these tracks represent the five standard Hubble types. The different locations of the selected LSB galaxies are a first hint for their different stellar population mix ...
    Description: thesis
    Keywords: 523 ; TEG 000 ; TIE 400 ; Kosmogonie {Astronomie} ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 155 S.
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  • 86
    Publication Date: 2021-03-29
    Description: In der vorliegenden Arbeit werden die Auswirkungen elektromagnetischer, sowie elektrostatischer Turbulenz speziell im Hinblick auf die Anwendung auf Jets aktiver galaktische Kerne untersucht. Dazu werden analytische Lösungen für ein Modell erstellt, dass bisher ausschließlich in numerischer Form vorlag. Mit Hilfe der analytischen Lösungen ist es nunmehr möglich, das Wechselspiel der unterschiedlichen, im Modell beschriebenen Prozesse zu analysieren. Ferner wird die Anwendbarkeit des Modelles durch Vergleich mit Datenmaterial bestätigt.
    Description: thesis
    Keywords: 523 ; TFG 000 ; TBK 000 ; Magnetohydrodynamik und Plasma-Astrophysik ; Hochenergieastronomie
    Language: German
    Type: monograph , publishedVersion
    Format: 110 S.
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  • 87
    Publication Date: 2021-03-29
    Description: This Ph.D. thesis is dealing with the modeling of the Diffuse Ionized Gas (DIG) in our Milky Way and external edge-on galaxies. The ionizing sources of this gas are up to now not known, energy estimations favor photoionization. The present work investigates the significance of this process. The observed emission line ratios are thereby modeled with the photoionization code CLOUDY. The present thesis is taking into account the correct geometry of the observations in contrast to previous models. The results show unambiguously that the trends of the line ratios are reproducible with the models. The strength of an additional heating source, as is discussed in the literature, is strongly diminished. Therefore photoionization is indeed the main ionizing source of the DIG.
    Description: thesis
    Keywords: 523 ; TII 800 ; Interstellares Gas {Astronomie: Interstellare Materie}
    Language: German
    Type: monograph , publishedVersion
    Format: 104 S.
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  • 88
    Publication Date: 2021-03-29
    Description: Triaxial compression experiments were performed on the synthesized samples and Fe-bearing clinopyroxenite in a solid medium apparatus at a confining pressure of 0.75 to 2.5 GPa, temperatures 900 to 1175oC, and strain rates between 1.1x10-6 s-1 to 8.5x 10-5 s-1. Samples of calcic compositions deformed at high differential stresses reveal abundant mechanical (100)[001] twins, whereas jadeite aggregates deformed at low differential stress show well developed subgrain boundaries. Combining the mechanical data and observed microstructures for deformed synthetic samples reveal that the deformation of diopside aggregates is controlled by dislocation glide, while the kinetics of dislocation climb controls the deformation of jadeite aggregates. The variation in strength with composition obeys scaling by the dependence of melting temperature and shear modulus on composition. In contrast to climb-controlled deformation, glide-controlled deformation should be insensitive to impurity concentrations.
    Description: thesis
    Keywords: 549 ; TQL 000 ; VAE 140 ; VGF 300 ; Sonstige Verfahren {Geophysik} ; Gesteinsdeformation {Strukturgeologie} ; Experimentelle Mineralogie
    Language: English
    Type: monograph , publishedVersion
    Format: 99 S.
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  • 89
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    Univ. Bochum
    Publication Date: 2021-03-29
    Description: Löslichkeitsdaten gesteinsbildender Minerale unter hohen Drücken sind für unser Verständnis von Fluideigenschaften und Massentransport von Mineralen in der Erdkruste und oberen Mantel von großer Wichtigkeit. In dieser Arbeit wurden neue in situ Masseverlust Methoden entwickelt um Löslichkeiten zu bestimmen, die dann in einer hydrothermalen Diamant Stempel Zelle getestet wurden. In der ersten Methode wird die Tendenz von Kristallen ausgenutzt während eines Experiments eine idiomorphe Form anzunehmen. Die zweite Methode basiert auf Messung und Analyse der Doppelbrechung eines Kristalls um dessen Dicke zu bestimmen. Masseverluste von wenigen æg können so bestimmt werden. Beide Methoden sind bis in den ppm Bereich anwendbar. Die Ergebnisse dieser Arbeit tragen sowohl zu unserem technischen Verständnis von Hockdruck/Hochtemperatur Equipment bei als auch zu unserem allgemeinen Verständnis der chemischen Eigenschaften von Fluiden in Hochdruck Umgebungen wie z.B. in Subduktionszonen.
    Description: thesis
    Keywords: 549 ; TQL 000 ; VGF 300 ; VAE 140 ; Sonstige Verfahren {Geophysik} ; Experimentelle Mineralogie ; Gesteinsdeformation {Strukturgeologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 232 S.
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  • 90
    Publication Date: 2021-03-29
    Description: Die physikalischen und mechanischen Eigenschaften von tonartigen Materialien, die für die Skalierung von Analogexperimenten relevant sind, werden mit Hilfe von Konzepten der modernen Bodenmechanik analysiert. Ein Verfahren zur Bestimmung dieser Eigenschaften wird vorgestellt. Skalierte Tonexperimente mit Riedelschem Mechanismus wurden durchgeführt. Sie erzeugen typische Pull-apart Strukturen entlang Riedel Frakturen sowie Push-up Strukturen in dazwischen liegenden Flachen. Die Scherfestigkeit und die Dicke des Tonkuchens beeinflussen sowohl die Geometrie der Scherzonen als die benötigte Hauptverschiebungsgröße für die Entstehung der Riedel Scherfrakturen an der Oberflache des Tonkuchens. Pull-apart Becken, die durch Riedelschen Mechanismus erzeugt wurden, lassen sich auf der Insel Gozo (Strait of Sicily rift zone) beobachten. Die gleichzeitige Entwicklung der Push-up Horste ist im komplexen Blattverschiebungsbecken des Meers von Marmara zu finden.
    Description: thesis
    Keywords: 551.8 ; VAE 130 ; VAE 400 ; Geomechanik ; Tektogenese {Geologie}
    Language: English
    Type: monograph , publishedVersion
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  • 91
    Publication Date: 2021-03-29
    Description: Diese Arbeit beschäftigt sich mit der Verknüpfung von manuellen und automatischen Inversionmethoden für die Interpretation gravimetrischer Anomalien. Eine neue Software mit dem Namen 3GRAINS wird vorgestellt. Sie wurde für das manuelle Modellieren entwickelt und benutzt rechteckförmige Prismen zur Berechnung des gravimetrischen Effekts eines Modells. Die Software bietet eine graphische Benutzeroberfläche, um eine komfortable Arbeit mit einer modellierten Struktur zu ermöglichen. Ein automatischer Inversionsalgorithmus basiert auf der Idee der evolutionären Berechnung. Die dargestellten Methoden werden auf die Interpretation der gravimetrischen Anomalien der Hellenischen Subduktionszone angewendet. Die tektonische Situation dieser Region und seismische Beobachtungen werden vorgestellt. Der Prozess der Datengewinnung und der Datenbearbeitung wird beschrieben. Schließlich werden die Ergebnisse der Interpretation der gravimetrischen Anomalien präsentiert.
    Description: thesis
    Keywords: 551 ; 622.15 ; 550 ; TOF 000 ; TQA 000 ; TSF 300 ; VAE 880 ; VEF 300 ; Schwerkraft {Geophysik} ; Gravimetrische Verfahren {Geophysik} ; Griechenland und griechische Inseln {Geophysik} ; Passive und aktive Kontinentalränder {Geologie} ; Griechenland und griechische Inseln {Geologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 139 S.
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  • 92
    Publication Date: 2021-03-29
    Description: In dieser Studie wird das Potential von Indentationsexperimenten bei erhöhten Temperaturen in der Gesteinsmechanik erkundet. Mikrohärtemessungen mit einem pyramidenförmigen Indenter werden an Olivin- und Klinopyroxen-Körnern innerhalb eines Gesteinsaggregates durchgeführt. Die Abhängigkeit der Härte der Olivin-Kristalle von der Kristallorientierung wird untersucht und die Orientierung von Gleitstufen auf der Probenoberfläche verwendet, um die während der Indentationsexperimente aktivierten Gleitsysteme zu ermitteln. Mikrohärtemessungen an Jadeit und Diopsid dienen dazu, die relative Festigkeit dieser Mitglieder einer Mischkristallreihe zu analysieren. Indentationskriechexperimente mit einem zylindrischen Indenter werden verwendet, um das rheologische Verhalten einer Legierung zu untersuchen, die als Modelmaterial für ein silikatisches Gesteinsaggregat dient. Die Ergebnisse dieser Tests an der TiAl-Legierung werden mit denen einachsiger Kriechversuche am gleichen Material verglichen.
    Description: thesis
    Keywords: 551.1 ; 550 ; VAE 140 ; VAE 120 ; VBB 000 ; VAE 140 ; VAE 120 ; VBB 000 ; Gesteinsdeformation {Strukturgeologie} ; Methodik {Strukturgeologie} ; Experimentelle Geologie
    Language: English
    Type: monograph , publishedVersion
    Format: 78 S.
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  • 93
    Publication Date: 2021-03-29
    Description: Die Arbeit untersucht, inwieweit die rechnergestützte Analyse digitaler Luft- und Satellitenbilddaten bestehende Verfahren im Umweltmonitoring optimieren kann. Zunächst wird der Stand der Forschung im Bereich "Fernerkundung im Umweltmonitoring" dokumentiert, bevor die verschiedenen Vorprozessierungen (Mosaikierung, Atmosphärenkorrektur etc.) der Daten erläutert werden. Anschließend wird der Stand der Forschung für Klassifikationsverfahren und Methoden der Veränderungsanalysen erarbeitet, bevor die eigenen zum Teil neu entwickelten Verfahren/Methoden angewandt werden; die Nachvollziehbarkeit bildet hier einen Schwerpunkt. Die Ergebnisse münden in einen Praxisleitfaden. Die kritische Auseinandersetzung mit möglichen Fehlerquellen soll dem Leser helfen, die Leistungsfähigkeit der Verfahren abzuschätzen. Ein Ausblick auf zukünftige Einsatzmöglichkeiten von Fernerkundungsdaten im Umweltmonitoring bildet den Schluß; im Vordergrund stehen ethische Fragen sowie die Rolle des Internets.
    Description: thesis
    Keywords: 550.28 ; 550 ; VBH 000 ; Fernerkundung
    Language: German
    Type: monograph , publishedVersion
    Format: 338 S.
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  • 94
    Publication Date: 2021-03-29
    Description: Die Gesetzmäßigkeiten zwischen dem Stickstoffhaushalt und dem Feuchteregime von Pseudogleyen werden analysiert. Neben der standortbezogenen Quantifizierung und Bilanzierung des Stickstoff- und Bodenwasserhaushaltes ist der Stellenwert der Denitrifikation im Stauwasserbereich abgeschätzt worden. Die Untersuchungen haben gezeigt, daß die grundsätzlichen Vorstellungen über die Prozesse des Stickstoffumsatzes in ackerbaulich genutzten Böden auch auf landwirtschaftlich genutzten Pseudogleyen zutreffen. Es konnte jedoch darüber hinaus in kombinierten Freilanduntersuchungen und Bodensäulenexperimenten nachgewiesen werden, daß die Dynamik des Bodenwassers (Wechselfeuchtephasen) auf die Denitrifikationsraten einen größeren Einfluß hat als der absolute Wassergehalt. Abschließend wird der Praxisbezug zur Denitrifikation landwirtschaftlich genutzter Pseudogleye aufgezeigt.
    Description: thesis
    Keywords: 531.43 ; 550
    Language: German
    Type: monograph , publishedVersion
    Format: 252 S.
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  • 95
    Publication Date: 2021-03-29
    Description: Die zentrale Fragestellung der Arbeit ist, inwieweit Telearbeit neue Impulse für die regionalwirtschaftliche Entwicklung generieren kann. Hierzu wird zunächst das zu Grunde liegende Leitbild der zukunftsfähigen Regionalentwicklung vorgestellt und der Zusammenhang zwischen Telearbeit und Regionalentwicklung in ausgewählten US-amerikanischen Referenzregionen untersucht. Die Ergebnisse der theoretischen und empirischen Untersuchungen dienen als Grundlage für Empfehlungen und Leitlinien, wie Telearbeit einen Beitrag zu einer zukunftsfähigen Regionalentwicklung leisten kann, und welche Bedingungen dafür im regionalen Umfeld herrschen müssen.
    Description: thesis
    Keywords: 910
    Language: German
    Type: monograph , publishedVersion
    Format: 339 S.
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  • 96
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 549 ; 552.4 ; VGF 300 ; TQL 000 ; VKB 291 ; Experimentelle Mineralogie ; Sonstige Verfahren {Geophysik} ; Metamorphe Komplexe, Alpen {Petrologie}
    Language: German
    Type: monograph , publishedVersion
    Format: 441 S.
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  • 97
    Publication Date: 2021-03-29
    Description: Kalorimetrische Untersuchungen sind ein unverzichtbares Instrument bei der Bestimmung der thermodynamischen Eigenschaften von Mineralen, um deren Gleichgewichts- und Reaktionsbeziehungen vorhersagbar zu machen.Im Rahmen dieser Arbeit wurden zwei verschiedene kalorimetrische Verfahren installiert und optimiert: zum einen die Leistungsdifferenzkalorimetrie zur Messung von Wärmekapazitäten, zum anderen die Hochtemperatur-Lösungskalorimetrie zur Bestimmung von Bildungsenthalpien. Für eine zuverlässige Bestimmung der Bildungsenthalpien wasserhaltiger Phasen wurden die seit Mitte der neunziger Jahre angewandten, speziellen Betriebsbedingungen bei der Lösungskalorimetrie eingesetzt: die Nutzung des Calvet-Kalorimeters als Einwurfkalorimeter für pelletierte Proben und die Technik einer gasgespülten Probenkammer. Auf der Grundlage dieser apparativen Voraussetzungen konnte das Verhalten der in diesem Zusammenhang kritischen Komponente H2O erstmals schlüssig auch im Rückblick auf frühere lösungskalorimetrische Arbeiten beschrieben werden. Auf dieser Basis wurden durch Verwendung mehrerer unabhängiger Berechnungszyklen, bei denen die volatile Komponente jeweils durch gänzlich unterschiedliches Verhalten berücksichtigt wird, mehrfach-konsistente Bestimmungen der Bildungsenthalpien von wasserhaltigen Phasen mit unterschiedlichen Wassergehalten verwirklicht...
    Description: thesis
    Keywords: 549 ; TQF 000 ; VGF 500 ; Geothermische Verfahren {Geophysik} ; Themodynamik {Mineralogie}
    Language: German
    Type: monograph , publishedVersion
    Format: 125 S.
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  • 98
    Publication Date: 2021-03-29
    Description: Die Arbeit leistet einen wesentlichen Beitrag zum geodynamischen Verständnis der kretazischen Inselbogen-Kontinent-Kollision und von subsequenten Exhumierungprozessen in Zentralkuba bei. Grundlage hierfür sind die zeitliche Fixierung von Metamorphose- und Exhumierungsereignissen, insbesondere von HP-Metamorphiten des Escambray Massivs, die petrogenetische Diskussion und die Datierung von Inselbogenmagmatiten. Aufgrund dieser neuen Datenbasis vom N-Rand der Karibischen Platte können entscheidende Impulse für die plattentektonische Rekonstruktion des karibischen Raumes vom oberen Jura bis in das mittlere Tertiär gegeben werden. Außerdem versteht sich die Arbeit als Evaluation der Anwendbarkeit geochronologischer Methoden bei der Datierung von subduktionsgebundenen HP-Metamorphiten. Insgesamt stellt die Arbeit durch die Synthese von geochemisch-geochronologischen, petrologischen und strukturgeologischen Daten ein Novum in der Geologie Kubas dar.
    Description: thesis
    Keywords: 551.701 ; 552.4 ; 550 ; VBN 500 ; VKB 296 ; VEW 200 ; VDH 300 ; VAE 400 ; Geochronologie einzelner Regionen im allgemeinen ; Metamorphe Komplexe; Südamerika {Petrologie} ; Karibischer Raum {Geologie} ; Kreide ; Tektogenese {Geologie}
    Language: German
    Type: monograph , publishedVersion
    Format: 227 S.
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  • 99
    Publication Date: 2021-03-29
    Description: Die Isla Margarita (Venezuela) am Südrand der Karibischen Platte besteht aus einem heterogenen Krustenkomplex aus Peridotiten, Metamorphiten, diversen Magmatiten und sedimentärem Deckgebirge. Die jüngsten Magmatite sind Lamprophyrgänge und Gabbros basaltisch-andesitischer Zusammensetzung, deren hoher Anteil an kompatiblen Elementen und intermediärer Zusammensetzung auf starke Fraktionierung bei relativ hohen partiellen Aufschmelzgraden deutet. Variable Anreicherung an leichten Seltenen Erden und LILE sowie erhöhte Strontium- und Blei-Isotopenverhältnisse lassen auf eine zusätzliche Subduktionskomponente schließen. Die Entstehung der Magmen und die zeitliche Einordnung der Platznahme sind wichtige Anhaltspunkte für die Aufschlüsselung der tektonischen Entwicklung des Südrandes der Karibischen Platte und erlauben eine Korrelation mit plattentektonischen Modellen.
    Description: thesis
    Keywords: 552.1 ; 551.701 ; 550 ; VBN 500 ; VKB 130 ; VEW 200 ; Geochronologie einzelner Regionen im allgemeinen ; Petrologie der Ganggesteine ; Karibischer Raum {Geologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 233 S.
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  • 100
    Publication Date: 2021-03-29
    Description: Im Rahmen dieser Arbeit wurden hochdruckmetamorphe Gesteinseinheiten der Sancti Spiritus Kuppel, Escambray Massiv, Zentralkuba, petrologisch und geochemisch untersucht. Die Analysen bestätigen eine Unterteilung der Gesteine in vier Deckeneinheiten, die durch eine unterschiedliche Druck-Temperatur-Entwicklung charakterisiert sind.
    Description: thesis
    Keywords: 552.4 ; 557 ; VKB 296 ; VKA 140 ; VEW 200 ; Metamorphe Komplexe; Südamerika {Petrologie} ; Thermodynamische Grundlagen und Verfahren der Petrologie ; Karibischer Raum {Geologie}
    Language: German
    Type: monograph , publishedVersion
    Format: 178 S.
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