Warm and cold water events in the tropical southeast Atlantic Ocean

  • The tropical oceans exhibit high interannual sea surface temperature (SST) variability that strongly impacts the regional climate of the adjacent continents. However, the influence of tropical SST variability is not limited to the regional scale but can be perceived in remote regions all over the globe. Earlier work has mainly focused on the Pacific El Niño Southern Oscillation (ENSO) and its regional and global impacts. Yet, recent studies show that a similar phenomenon exists in the tropical Atlantic Ocean. Warm and cold events in the tropical southeast Atlantic have been described to impact regional rainfall variability and are further assumed to play a role in the development of Pacific ENSO events. In contrast to the Pacific Ocean two Niño-like phenomena have been described for the eastern tropical Atlantic: one of them centered in the equatorial region, also known as Atlantic Niño, and another one close to the coast of northern Namibia and Angola, referred to as Benguela NiThe tropical oceans exhibit high interannual sea surface temperature (SST) variability that strongly impacts the regional climate of the adjacent continents. However, the influence of tropical SST variability is not limited to the regional scale but can be perceived in remote regions all over the globe. Earlier work has mainly focused on the Pacific El Niño Southern Oscillation (ENSO) and its regional and global impacts. Yet, recent studies show that a similar phenomenon exists in the tropical Atlantic Ocean. Warm and cold events in the tropical southeast Atlantic have been described to impact regional rainfall variability and are further assumed to play a role in the development of Pacific ENSO events. In contrast to the Pacific Ocean two Niño-like phenomena have been described for the eastern tropical Atlantic: one of them centered in the equatorial region, also known as Atlantic Niño, and another one close to the coast of northern Namibia and Angola, referred to as Benguela Niño. Although similar forcing mechanisms are proposed for their evolution, the two Niño types have mainly been analyzed in separate studies and regarded as independent phenomena. Yet, recent studies suggest a possible interdependence. This thesis thoroughly explores tropical Atlantic SST variability based on long-term observational data aiming at the extraction of robust indices, which are suitable for a further analysis of the link between Atlantic and Benguela Niños. The newly defined indices, which represent both the equatorial and coastal SST variability, are strongly correlated and thus indicate a close connection between anomalous warming and cooling in both regions. Therefore, instead of considering equatorial Atlantic and Benguela Niños as separate phenomena, they are both combined into a classification of one comprehensive Atlantic Niño. With regard to the different regional character of the events, this classification contains the three sub-types major event, minor event and episode. The newly defined indices and classification of Atlantic Niños are further used to study the influence of tropical southeast Atlantic SST variability on African west coast precipitation. The analyses show that during Atlantic Niños and Niñas anomalous rainfall is observed in different seasons nearly along the entire sub-Saharan west coast. Yet, results indicate a seasonally asymmetric response in some west coast regions. Moreover, a significant impact on precipitation is not limited to major warm or cold water events but is also observed for minor events. Furthermore, this work studies teleconnections of the tropical Atlantic to the tropical Pacific and Indian Oceans. Analyses are carried out with respect to the dominant influence of the Pacific El Niño Southern Oscillation (ENSO) system. Therefore, in addition to the investigation of the relationship between the Pacific and Atlantic Oceans, the aim of these analyses is to find links between the Atlantic and Indian Oceans that are not ENSO-dependent. For that, additional analyses are performed that exclude the ENSO signal. Results show a significant anticorrelation between the Atlantic and Pacific Oceans in recent decades and suggest a possible enhancement and delay of the peak of a Pacific La Niña when preceded by a boreal summer Atlantic Niño. By contrast, Indian Ocean SST variability is mainly dependent on the Pacific Ocean. The Atlantic Ocean does not seem to exert a significant influence on the Indian Ocean that is independent of ENSO.show moreshow less

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Metadaten
Author:Karin Romberg
URN:urn:nbn:de:bvb:384-opus4-30201
Frontdoor URLhttps://opus.bibliothek.uni-augsburg.de/opus4/frontdoor/index/index/docId/3020
Advisor:Jucundus Jacobeit
Type:Doctoral Thesis
Language:English
Publishing Institution:Universität Augsburg
Granting Institution:Universität Augsburg, Fakultät für Angewandte Informatik
Date of final exam:2014/12/03
Release Date:2015/03/24
Tag:African precipitation variability; Atlantic Niño; Atlantic SST variability; teleconnections; tropical Atlantic
GND-Keyword:Afrika; Atlantischer Ozean; El-Niño-Phänomen; Meeresoberfläche; Niederschlag; Oberflächentemperatur; Temperaturschwankung; Tropen; Wassertemperatur
Institutes:Fakultät für Angewandte Informatik / Geographie
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften
Licence (German):License LogoVeröffentlichungsvertrag für Publikationen ohne Print on Demand

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