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  • 1
    Publication Date: 2019-05-07
    Description: The Sea surface KInematics Multiscale monitoring (SKIM) satellite mission is designed to explore ocean surface current and waves. This includes tropical currents, notably the unknown patterns of divergence and their impact on the ocean heat budget near the Equator, monitoring of the emerging Arctic up to 82.5$(\circ)$N. SKIM will also make unprecedented direct measurements of strong currents, from boundary currents to the Antarctic circumpolar current, and their interaction with ocean waves with expected impacts on air-sea fluxes and extreme waves. For the first time, SKIM will directly measure the ocean surface current vector from space. The main instrument on SKIM is a Ka-band conically scanning, multi-beam Doppler radar altimeter/wave scatterometer that includes a state-of-the-art nadir beam comparable to the Poseidon-4 instrument on Sentinel 6. The well proven Doppler pulse-pair technique will give a surface drift velocity representative of the top two meters of the ocean, after subtracting a large wave-induced contribution. Horizontal velocity components will be obtained with an accuracy better than 7 cm/s for horizontal wavelengths larger than 80~km and time resolutions larger than 15 days, with a mean revisit time of 4 days for of 99\% of the global oceans. This will provide unique and innovative measurements that will further our understanding of the transports in the upper ocean layer, permanently distributing heat, carbon, plankton, and plastics. SKIM will also benefit from co-located measurements of water vapor, rain rate, sea ice concentration, and wind vectors provided by the European operational satellite MetOp-SG(B), allowing many joint analyses. SKIM is one of the two candidate satellite missions under development for ESA Earth Explorer 9. The other candidate is the Far infrared Radiation Understanding and Monitoring (FORUM). The final selection will be announced by September 2019, for a launch in the coming decade.
    Type: Article , PeerReviewed
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  • 2
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    American Meteorological Society
    In:  Journal of Atmospheric and Oceanic Technology, 11 (4). pp. 982-993.
    Publication Date: 2019-03-14
    Description: Cicosal sea surface height (SSH) data in the tropical and midlatitude North Atlantic are analyzed with and without water vapor (WV) correction to study the WV influence on along-track SSH anomaly profits, mesoscale SSH variability, wavenumber spectra, and objectively mapped fields of SSH anomaly. Three different WV datasets were used, one from the Fleet Numerical Oceanographic Center (FNOC) model and two from the Special Sensor Microwave/Imager (SSM/I) based on different WV retrieval algorithms. These WV dataset show significant differences, in particular in the tropics. However, the method for deriving SSH anomalies from altimeter height data Alters out much of the WV corrections. The residual WV effect on SSH anomaly is shown to be most significant in the seasonally migrating intertropical convergence zone of the tropical Atlantic: there the SSM/I corrections reduce the along-track mesoscale SSH variability by typically 1–1.5 cm. On seasonal timescales the maximum WV effect in this region is characterized by a 2–3-cm rms difference between SSH anomaly with and without SSM/I WV corrections, whereas FNOC corrections have almost no effect. Inferred seasonal velocity variations in the North Equatorial Countercurrent core (4° – 6°N) in the region of maximum WY influence (30° – 40°W) are reduced by about 20% and 30%, depending on whether SSM/I corrections by Emery or Wentz are used
    Type: Article , PeerReviewed
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  • 3
    Publication Date: 2019-04-30
    Description: The adjoint method is used to calibrate the medium complexity climate model "Planet Simulator" through parameter estimation. Identical twin experiments demonstrate that this method can retrieve default values of the control parameters when using a long assimilation window of the order of 2 months. Chaos synchronization through nudging, required to overcome limits in the temporal assimilation window in the adjoint method, is employed successfully to reach this assimilation window length. When assimilating ERA-Interim reanalysis data, the observations of air temperature and the radiative fluxes are the most important data for adjusting the control parameters. The global mean net longwave fluxes at the surface and at the top of the atmosphere are significantly improved by tuning two model parameters controlling the absorption of clouds and water vapor. The global mean net shortwave radiation at the surface is improved by optimizing three model parameters controlling cloud optical properties. The optimized parameters improve the free model (without nudging terms) simulation in a way similar to that in the assimilation experiments. Results suggest a promising way for tuning uncertain parameters in non-linear coupled climate models.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 391 (1998), S. 476-479 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Motion of the Earth's pole of rotation relative to its crust, commonly referred to as polar motion, can be excited by a variety of geophysical mechanisms. In particular, changes in atmospheric wind and mass fields have been linked to polar motion over a wide range of timescales, but substantial ...
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2018-04-05
    Type: Article , PeerReviewed
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  • 6
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    American Meteorological Society
    In:  Journal of Physical Oceanography, 22 . pp. 732-752.
    Publication Date: 2018-04-05
    Description: Characteristic of the mesoscale variability in the Atlantic Ocean are investigated by analyzing the Geosat altimeter signal between 60°S and 60°N. The rms sea-surface variability for various frequency bands is studied, including the high-frequency eddy-containing band with periods 〈150 days. Wavenumber spectra and spatial eddy characteristics are analyzed over 10° by 10° boxes covering both hemispheres of the Atlantic Ocean. A comparison, with solutions of a high-resolution numerical experiment, developed as the Community Modeling Effort of the World Ocean Circulation Experiment, aids interpretation of the Geosat results in the tropical and subtropical Atlantic and provides a test of the model fluctuating eddy field. Results from Geosat altimetry show a wavenumber dependence close to k1−5 (k1 being the alongtrack wave-number) over almost the entire Atlantic Ocean except for areas in the tropical and subtropical Atlantic where the rms variability in the eddy-containing band is less than 5 cm, that is, not significantly different from the altimeter noise level. Characteristic eddy length scales inferred from Geosat data are linearly related with the deformation radius of the first baroclinic mode over the whole Atlantic Ocean, except for the equatorial regime (10°S to 10°N). The data-model comparison indicates that the high-resolution model with horizontal grid size of ⅓° and ° in latitude and longitude is quite capable of simulating observed eddy characteristics in the tropics and subtropics. In mid- and high latitudes, however, the model fails to simulate the pronounced poleward decrease in eddy scales. This leads to systematic discrepancies between the model and Geosat observation, with model scales being up to 50% larger than deduced from altimetry.
    Type: Article , PeerReviewed
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 408 (2000), S. 153-153 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Space-borne instruments have revolutionized research on the circulation patterns and strengths of the oceans. For instance, a satellite can observe all of the world's oceans in less than ten days. With radar technology, it can measure the shape of the sea surface and provide observations on the ...
    Type of Medium: Electronic Resource
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  • 8
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    In:  (Doctoral thesis/PhD), Christian-Albrechts-Universität Kiel, Kiel, Germany, 197 pp . Berichte aus dem Institut für Meereskunde an der Christian-Albrechts-Universität Kiel, 224 . DOI 10.3289/ifm_ber_224 〈http://dx.doi.org/10.3289/ifm_ber_224〉.
    Publication Date: 2014-10-14
    Type: Thesis , NonPeerReviewed
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  • 9
    Publication Date: 2015-09-28
    Description: Spaceborne sea surface salinity (SSS) measurements provided by the European Space Agency's (ESA) “Soil Moisture and Ocean Salinity” (SMOS) and the National Aeronautical Space Agency's (NASA) “Aquarius/SAC-D” missions, covering the period from May 2012 to April 2013, are compared against in situ salinity measurements obtained in the northern North Atlantic between 20°N and 80°N. In cold water, SMOS SSS fields show a temperature-dependent negative SSS bias of up to −2 g/kg for temperatures 〈5°C. Removing this bias significantly reduces the differences to independent ship-based thermosalinograph data but potentially corrects simultaneously also other effects not related to temperature, such as land contamination or radio frequency interference (RFI). The resulting time-mean bias, averaged over the study area, amounts to 0.1 g/kg. A respective correction applied previously by the Jet Propulsion Laboratory to the Aquarius data is shown here to have successfully removed an SST-related bias in our study area. For both missions, resulting spatial structures of SSS variability agree very well with those available from an eddy-resolving numerical simulation and from Argo data and, additionally they also show substantial salinity changes on monthly and seasonal time scales. Some fraction of the root-mean-square difference between in situ, and SMOS and Aquarius data (approximately 0.9 g/kg) can be attributed to short time scale ocean processes, notably at the Greenland shelf, and could represent associated sampling errors there.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2019-02-01
    Description: A German national project coordinates research on improving a global decadal climate prediction system for future operational use. MiKlip, an eight-year German national research project on decadal climate prediction, is organized around a global prediction system comprising the climate model MPI-ESM together with an initialization procedure and a model evaluation system. This paper summarizes the lessons learned from MiKlip so far; some are purely scientific, others concern strategies and structures of research that targets future operational use. Three prediction-system generations have been constructed, characterized by alternative initialization strategies; the later generations show a marked improvement in hindcast skill for surface temperature. Hindcast skill is also identified for multi-year-mean European summer surface temperatures, extra-tropical cyclone tracks, the Quasi-Biennial Oscillation, and ocean carbon uptake, among others. Regionalization maintains or slightly enhances the skill in European surface temperature inherited from the global model and also displays hindcast skill for wind-energy output. A new volcano code package permits rapid modification of the predictions in response to a future eruption. MiKlip has demonstrated the efficacy of subjecting a single global prediction system to a major research effort. The benefits of this strategy include the rapid cycling through the prediction-system generations, the development of a sophisticated evaluation package usable by all MiKlip researchers, and regional applications of the global predictions. Open research questions include the optimal balance between model resolution and ensemble size, the appropriate method for constructing a prediction ensemble, and the decision between full-field and anomaly initialization. Operational use of the MiKlip system is targeted for the end of the current decade, with a recommended generational cycle of two to three years.
    Type: Article , PeerReviewed
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