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  • 1
    Keywords: Hochschulschrift ; Tropen ; Allgemeine atmosphärische Zirkulation ; Erwärmung
    Type of Medium: Online Resource
    Pages: Online-Ressource
    DDC: 551.69162
    Language: English
    Note: Kiel, Univ., Diss., 2013
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  • 2
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: Online-Ressource (125 Blatt = 18 MB)
    Language: German
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 3
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (76 Seiten = 11 MB) , Illustrationen, Graphen, Karten
    Edition: Online-Ausgabe
    Language: English
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 4
    Publication Date: 2021-02-08
    Description: El Niño events are characterized by surface warming of the tropical Pacific Ocean and weakening of equatorial trade winds that occur every few years. Such conditions are accompanied by changes in atmospheric and oceanic circulation, affecting global climate, marine and terrestrial ecosystems, fisheries and human activities. The alternation of warm El Niño and cold La Niña conditions, referred to as the El Niño–Southern Oscillation (ENSO), represents the strongest year-to-year fluctuation of the global climate system. Here we provide a synopsis of our current understanding of the spatio-temporal complexity of this important climate mode and its influence on the Earth system.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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  • 5
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    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 45 (4). pp. 1989-1996.
    Publication Date: 2021-02-08
    Description: Climate models depict large diversity in the strength of the El Niño/Southern Oscillation (ENSO) (ENSO amplitude). Here we investigate ENSO-amplitude diversity in the Coupled Model Intercomparison Project Phase 5 (CMIP5) by means of the linear recharge oscillator model, which reduces ENSO dynamics to a two-dimensional problem in terms of eastern equatorial Pacific sea surface temperature anomalies (T) and equatorial Pacific upper ocean heat content anomalies (h). We find that a large contribution to ENSO-amplitude diversity originates from stochastic forcing. Further, significant interactions exist between the stochastic forcing and the growth rates of T and h with competing effects on ENSO amplitude. The joint consideration of stochastic forcing and growth rates explains more than 80% of the ENSO-amplitude variance within CMIP5. Our results can readily explain the lack of correlation between the Bjerknes Stability index, a measure of the growth rate of T, and ENSO amplitude in a multimodel ensemble.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: archive
    Format: text
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  • 6
    Publication Date: 2016-09-13
    Description: This study investigates the global warming response of the Walker Circulation and the other zonal circulation cells (represented by the zonal stream function), in CMIP3 and CMIP5 climate models. The changes in the mean state are presented as well as the changes in the modes of variability. The mean zonal circulation weakens in the multi model ensembles nearly everywhere along the equator under both the RCP4.5 and SRES A1B scenarios. Over the Pacific the Walker Circulation also shows a significant eastward shift. These changes in the mean circulation are very similar to the leading mode of interannual variability in the tropical zonal circulation cells, which is dominated by El Niño Southern Oscillation variability. During an El Niño event the circulation weakens and the rising branch over the Maritime Continent shifts to the east in comparison to neutral conditions (vice versa for a La Niña event). Two-thirds of the global warming forced trend of the Walker Circulation can be explained by a long-term trend in this interannual variability pattern, i.e. a shift towards more El Niño-like conditions in the multi-model mean under global warming. Further, interannual variability in the zonal circulation exhibits an asymmetry between El Niño and La Niña events. El Niño anomalies are located more to the east compared with La Niña anomalies. Consistent with this asymmetry we find a shift to the east of the dominant mode of variability of zonal stream function under global warming. All these results vary among the individual models, but the multi model ensembles of CMIP3 and CMIP5 show in nearly all aspects very similar results, which underline the robustness of these results. The observed data (ERA Interim reanalysis) from 1979 to 2012 shows a westward shift and strengthening of the Walker Circulation. This is opposite to what the results in the CMIP models reveal. However, 75 % of the trend of the Walker Circulation can again be explained by a shift of the dominant mode of variability, but here towards more La Niña-like conditions. Thus in both climate change projections and observations the long-term trends of the Walker Circulation seem to follow to a large part the pre-existing dominant mode of internal variability.
    Type: Article , PeerReviewed
    Format: text
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  • 7
    Publication Date: 2016-09-13
    Description: In analysis of climate variability or change it is often of interest how the spatial structure in modes of variability in two datasets differ from each other, e.g. between past and future climate or between models and observations. Often such analysis is based on Empirical Orthogonal Function (EOF) analysis or other simple indices of large-scale spatial structures. The present analysis lays out a concept on how two datasets of multivariate climate variability can be compared against each other on basis of EOF analysis and how the differences in the multivariate spatial structure between the two datasets can be quantified in terms of explained variance in the leading spatial patterns. It is also illustrated how the patterns of largest differences between the two datasets can be defined and interpreted. We illustrate this method on the basis of several well-defined artificial examples and by comparing our approach with examples of climate change studies from the literature. These literature examples include analysis of changes in the modes of variability under climate change for the sea level pressure (SLP) of the North Atlantic and Europe, the SLP of the Southern Hemisphere, the surface temperature of the Northern Hemisphere, the sea surface temperature of the North Pacific and for precipitation in the tropical Indo-Pacific.
    Type: Article , PeerReviewed
    Format: text
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  • 8
    Publication Date: 2016-09-13
    Description: In this study the observed non-linearity in the spatial pattern and time evolution of El Niño Southern Oscillation (ENSO) events is analyzed. It is shown that ENSO skewness is not only a characteristic of the amplitude of events (El Niños being stronger than La Niñas) but also of the spatial pattern and time evolution. It is demonstrated that these non-linearities can be related to the non-linear response of the zonal winds to sea surface temperature (SST) anomalies. It is shown in observations as well as in coupled model simulations that significant differences in the spatial pattern between positive (El Niño) versus negative (La Niña) and strong versus weak events exist, which is mostly describing the difference between central and east Pacific events. Central Pacific events tend to be weak El Niño or strong La Niña events. In turn east Pacific events tend to be strong El Niño or weak La Niña events. A rotation of the two leading empirical orthogonal function modes illustrates that for both El Niño and La Niña extreme events are more likely than expected from a normal distribution. The Bjerknes feedbacks and time evolution of strong ENSO events in observations as well as in coupled model simulations also show strong asymmetries, with strong El Niños being forced more strongly by zonal wind than by thermocline depth anomalies and are followed by La Niña events. In turn strong La Niña events are preceded by El Niño events and are more strongly forced by thermocline depth anomalies than by wind anomalies. Further, the zonal wind response to sea surface temperature anomalies during strong El Niño events is stronger and shifted to the east relative to strong La Niña events, supporting the eastward shifted El Niño pattern and the asymmetric time evolution. Based on the simplified hybrid coupled RECHOZ model of ENSO it can be shown that the non-linear zonal wind response to SST anomalies causes the asymmetric forcings of ENSO events. This also implies that strong El Niños are mostly wind driven and less predictable and strong La Niñas are mostly thermocline depth driven and better predictable, which is demonstrated by a set of 100 perfect model forecast ensembles.
    Type: Article , PeerReviewed
    Format: text
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  • 9
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    In:  [Poster] In: EGU General Assembly 2013, 07.-12.04.2013, Vienna, Austria .
    Publication Date: 2019-02-06
    Description: In analysis of climate variability or change it is often of interest how the spatial structure in modes of variability in two datasets differ from each other, e.g. between past and future climate or between models and observations. Often such analysis is based on Empirical Orthogonal Function (EOF) analysis or other simple indices of large-scale spatial structures. The present analysis lays out a concept on how two datasets of multi-variate climate variability can be compared against each other on basis of EOF analysis and how the differences in the multi-variate spatial structure between the two datasets can be quantified in terms of explained variance in the leading spatial patterns. It is also illustrated how the patterns of largest differences between the two datasets can be defined and interpreted. We illustrate this method on the basis of several well-defined artificial examples and by comparing our approach with examples of climate change studies from the literature. These literature examples include analysis of changes in the modes of variability under climate change for the Sea Level Pressure (SLP) of the North Atlantic and Europe, the SLP of the Southern Hemisphere, the Surface Temperature of the Northern Hemisphere, the Sea Surface Temperature of the North Pacific and for Precipitation in the tropical Indo-Pacific. The discussion of the literature examples illustrates that the method introduced here is at least partly more sensitive than the approaches used in the literature and it allows a better quantification of the changes in the modes of variability.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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  • 10
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    In:  [Poster] In: EGU General Assembly 2012, 22.-27.04.2012, Vienna, Austria .
    Publication Date: 2019-02-06
    Description: In this presentation we address the causes of the large-scale tropical sea level pressure (SLP) changes during climate change. The analysis we present is based on climate change 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. This relationship basically follows the Bjerknes Circulation Theorem, with relative low regional SLP where we have relative high Ttropos and vice versa. A simple physical model suggests a tropical SLP response to horizontally inhomogeneous warming in the tropical Ttropos, with a regression 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 tropical land-sea warm-ing contrast, is the most significant structure in the regional Ttropos changes relative to the tropical mean changes. Since the land-sea warming contrast exist 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 con-trast, with decreasing SLP over the sector of strongest warming (South America to Afri-ca) and increasing SLP elsewhere, which is roughly the Indo-Pacific warm pool region. A model intercomparison reveals that climate models with a strong land-sea contrast in surface temperature tend to have also a strong land-sea contrast in Ttropos and SLP. In an idealized land-sea contrast experiment a similar response of the SLP and Ttropos as in the climate change experiments can be found. As SLP changes and changes in atmospheric circulation go hand in hand, these results suggest 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.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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