ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    facet.materialart.
    AGU
    In:  Geophysical Research Letters, 44 (21). 11,166-11,173.
    Publication Date: 2019-02-01
    Description: The Summer East Atlantic (SEA) mode is the second dominant mode of summer low-frequency variability in the Euro-Atlantic region. Using reanalysis data, we show that SEA-related circulation anomalies significantly influence temperatures and precipitation over Europe. We present evidence that part of the interannual SEA variability is forced by diabatic heating anomalies of opposing signs in the tropical Pacific and Caribbean that induce an extratropical Rossby wave train. This precipitation dipole is related to SST anomalies characteristic of the developing ENSO phases. Seasonal hindcast experiments forced with observed sea surface temperatures (SST) exhibit skill at capturing the interannual SEA variability corroborating the proposed mechanism and highlighting the possibility for improved prediction of boreal summer variability. Our results indicate that tropical forcing of the SEA likely played a role in the dynamics of the 2015 European heat wave.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2018-11-09
    Description: The sea surface temperature (SST) in the eastern tropical Atlantic exhibits pronounced variability on interannual time scales being associated with wind and rainfall anomalies within the tropical Atlantic region. It has been proposed that the interannual variability of SST is partly driven by the variability of the deep equatorial zonal circulation, the so-called equatorial deep jets (EDJs). The EDJs may be described as a superposition of quasi-resonant equatorial basin modes and the direction of vertical phase propagation implies that their energy is propagating towards the surface. Furthermore, recent findings revealed that the EDJs in turn are maintained by intra-seasonal waves that are generated by the barotropic and baroclinic instability of the near-surface circulation. This talk will present the relevant mechanisms that are involved in the conversion of energy from one type of variability to another, i.e. from chaotic intra-seasonal surface variability via deep interannual zonal variability to interannual surface climate variability, with a special focus on the maintenance of the EDJs by intra-seasonal waves. Since EDJs, a key component of the mechanism discussed above, are not well represented in state-of-the-art Ocean General Circulation Models, preliminary findings on the sensitivity of the EDJs to model parameters and configuration are presented.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: slideshow
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    facet.materialart.
    facet.materialart.
    American Meteorological Society
    In:  Journal of Physical Oceanography, 48 (2). pp. 261-281.
    Publication Date: 2019-02-01
    Description: Multi-year moored velocity observations of the Angola Current near 11°S reveal a weak southward mean flow superimposed by substantial intraseasonal to seasonal variability, including annual and semiannual cycles with distinct baroclinic structures. In the equatorial Atlantic these oscillations are associated with basin-mode resonances of the fourth and second baroclinic modes, respectively. Here, the role of basin-mode resonance and local forcing for the Angola Current seasonality are investigated. A suite of linear shallow-water models for the tropical Atlantic is employed, each model representing a single baroclinic mode forced at a specific period. The annually and semiannually oscillating forcing is given by 1) an idealized zonally uniform zonal forcing restricted to the equatorial band corresponding to a remote equatorial forcing or 2) realistic, spatially-varying Fourier components of wind stress data that include local forcing off Angola, particularly alongshore winds. Model-computed modal amplitudes are scaled to match moored velocity observations from the equatorial Atlantic. The observed annual cycle of alongshore velocity at 11°S is well reproduced by the remote equatorial forcing. Including local forcing slightly improves the agreement between observed and simulated semiannual oscillations at 11°S compared to the purely equatorial forcing. However, the model-computed semiannual cycle lacks amplitude at mid-depth. This could be the result of either underestimating the strength of the second equatorial basin-mode of the fourth baroclinic mode or other processes not accounted for in the shallow-water models. Overall, our findings underline the importance of large-scale linear equatorial wave dynamics for the seasonal variability of the boundary circulation off Angola.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2019-03-28
    Description: Beside its global effects, climate change is manifested in many regionally pronounced features mainly resulting from changes in the oceanic and atmospheric circulation. Here we investigate the influence of the North Atlantic SST on shaping the winter-time response to global warming. Our results are based on a long-term climate projection with the Max Planck Institute Earth System Model (MPI-ESM) to investigate the influence of North Atlantic sea surface temperature pattern changes on shaping the atmospheric climate change signal. In sensitivity experiments with the model’s atmospheric component we decompose the response into components controlled by the local SST structure and components controlled by global/remote changes. MPI-ESM simulates a global warming response in SST similar to other climate models: there is a warming minimum—or ”warming hole”—in the subpolar North Atlantic, and the sharp SST gradients associated with the Gulf Stream and the North Atlantic Current shift northward by a few a degrees. Over the warming hole, global warming causes a relatively weak increase in rainfall. Beyond this, our experiments show more localized effects, likely resulting from future SST gradient changes in the North Atlantic. This includes a significant precipitation decrease to the south of the Gulf Stream despite increased underlying SSTs. Since this region is characterised by a strong band of precipitation in the current climate, this is contrary to the usual case that wet regions become wetter and dry regions become drier in a warmer climate. A moisture budget analysis identifies a complex interplay of various processes in the region of modified SST gradients: reduced surface winds cause a decrease in evaporation; and thermodynamic, modified atmospheric eddy transports, and coastal processes cause a change in the moisture convergence. The changes in the the North Atlantic storm track are mainly controlled by the non-regional changes in the forcing. The impact of the local SST pattern changes on regions outside the North Atlantic is small in our setup.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    facet.materialart.
    facet.materialart.
    In:  [Talk] In: EGU General Assembly 2018, 08.-13.04.2018, Vienna, Austria .
    Publication Date: 2018-06-28
    Description: A large fraction of interannual variability of the East Asian Summer Monsoon (EASM) can be described by the first two modes of a Multivariate Empirical Orthogonal Functions (MV-EOF) analysis of horizontal wind vectors in the lower and upper troposphere over the East Asian region. The first mode resembles the Pacific-Japan pattern and represents about 20% of the EASM interannual variance. The positive phase of the PJ-pattern is associated with anomalous anticyclonic flow over the tropical western North Pacific in the lower troposphere, leading to enhanced rainfall over the climatological East Asian rain band. Focusing on June/July/August and on the first MV-EOF mode (PJ-mode here) we investigate the relation between tropical intraseasonal variability, namely the Madden-Julian Oscillation (MJO) and the EASM. The second MV-EOF mode had previously been found to be influenced mainly by the Indian Summer Monsoon and is not discussed in this presentation. First, it is found that the MJO modulates the intraseasonal variability of the PJ-pattern, in that early MJO phases, related to enhanced convective precipitation over the Indian Ocean, favour the positive phase of the PJ-mode and late MJO phases, related to enhanced convective precipitation over the Maritime Continent and the western tropical Pacific, favour the negative phase of the PJ-mode. Second, using a decomposition method introduced by Yoo, Feldstein and Lee (2011), we show that interannual variability of the MJO contributes about 11% to the interannual variability of the EASM. Thereby, interannual changes in the frequency of occurrence of the eight standard MJO phases are more important to the variability of the EASM than changes in the circulation patterns associated with the different MJO phases. Some discussion on the involved mechanisms will be given.
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    facet.materialart.
    facet.materialart.
    In:  [Poster] In: MiKlip Status Seminar 2018, 28.- 30.05.2018, Berlin, Germany .
    Publication Date: 2018-10-02
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    facet.materialart.
    facet.materialart.
    In:  [Poster] In: MiKlip Status Seminar 2017, 28.-30.05.2018, Berlin, Germany .
    Publication Date: 2018-10-02
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2019-04-01
    Description: Benthic storms are important for both the energy budget of the ocean and for sediment resuspension and transport. Using 30 years of output from a high-resolution model of the North Atlantic, it is found that most of the benthic storms in the model occur near the western boundary in association with the Gulf Stream and the North Atlantic Current, in regions that are generally co-located with the peak near-bottom eddy kinetic energy. A common feature are meander troughs in the near-surface jets that are accompanied by deep low pressure anomalies spinning up deep cyclones with near-bottom velocities of up to more than 0.5 m/s. A case study of one of these events shows the importance of both baroclinic and barotropic instability of the jet, with energy being extracted from the jet in the upstream part of the meander trough and partly returned to the jet in the downstream part of the meander trough. This motivates examining the 30-year time mean of the energy transfer from the (annual mean) background flow into the eddy kinetic energy. This quantity is shown to be co-located well with the region in which benthic storms and large increases in deep cyclonic relative vorticity occur most frequently, suggesting an important role for mixed barotropic-baroclinic instability driven cyclogenesis in generating benthic storms throughout the model simulation. Regions of largest energy transfer and most frequent benthic storms are found to be the Gulf Stream west of the New England Seamounts and the North Atlantic Current near Flemish Cap.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2019-02-01
    Description: The parameterization of sub-grid scale processes is one of the key challenges towards improved numerical simulations of the atmospheric and oceanic circulation. Numerical weather prediction models as well as climate models would benefit from more sophisticated turbulence closures that allow for less spurious dissipation at the grid-scale and consequently higher and more realistic levels of eddy kinetic energy (EKE). Recent studies propose to use a hyperviscous closure in combination with an additional deterministic forcing term as a negative viscosity to represent backscatter of energy from unresolved scales. The sub-grid EKE is introduced as an additional prognostic variable that is fed by dissipation at the grid scale, and enables recycling of EKE via the backscatter term at larger scales. This parameterization was previously shown to work well in zonally re-entrant channel configurations. Here, a generalization in the form of a Rossby number-dependent scaling for the strength of the backscatter is introduced to represent the emergence of a forward energy-cascade in unbalanced flows near the boundaries. We apply the parameterization to a shallow water model of a double gyre basin and provide evidence for its general applicability. In terms of mean state and variability, a low resolution model is considerably improved towards a high resolution control run at low additional computational cost.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    facet.materialart.
    facet.materialart.
    In:  [Invited talk] In: ETH Zürich Switzerland, 05.11.2018, Zürich, Switzerland .
    Publication Date: 2018-11-16
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...