Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification
Future projections of the atmospheric circulation over the Northern Hemisphere high latitudes, especially the North Atlantic, have high uncertainties and some of the projected changes are opposed to circulation changes that have been observed since the 2000s. In this thesis, we focus on three partic...
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Universite de Liege
2015
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Online Access: | http://bictel.ulg.ac.be/ETD-db/collection/available/ULgetd-03262015-160037/ |
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Université de Liege: BICTEL/e-ULg - Serveur institutionnel des thèses de doctorat |
op_collection_id |
ftbictel |
language |
unknown |
topic |
atmospheric circulation circulation type classification Arctic Greenland Europe reanalyses general circulation models |
spellingShingle |
atmospheric circulation circulation type classification Arctic Greenland Europe reanalyses general circulation models Belleflamme, Alexandre Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification |
topic_facet |
atmospheric circulation circulation type classification Arctic Greenland Europe reanalyses general circulation models |
description |
Future projections of the atmospheric circulation over the Northern Hemisphere high latitudes, especially the North Atlantic, have high uncertainties and some of the projected changes are opposed to circulation changes that have been observed since the 2000s. In this thesis, we focus on three particular aspects of the past and projected future summertime atmospheric circulation over the broader North Atlantic region. First, we analyse whether the 2007-2012 summertime anticyclonic anomaly over the Beaufort Sea, the Canadian Arctic Archipelago, and Greenland might rather be due to global warming or to the internal variability of the atmospheric circulation by putting it in perspective with the circulation variability over the last 150 years given by five reanalysis datasets. Then, this analysis is extended for the future circulation projected towards 2100 by CMIP3 and CMIP5 General Circulation Models (GCMs) over Greenland. Finally, we evaluate the impact of the uncertainties of the future atmospheric circulation projections on the mitigating or enhancing influence of the summertime circulation changes on temperature and precipitation over Europe. We use an automatic circulation type classification to analyse in detail the atmospheric circulation changes by grouping similar daily SLP (mean sea level pressure) or Z500 (500 hPa geopotential height) fields into homogeneous circulation types. It appears that the choice of the index, on the basis of which the days are grouped together, strongly influences the characteristics of the circulation types and the kinds of circulation changes that can be detected. In comparison with Euclidean distance and pressure gradient-based indices, correlation-based indices, especially the Spearman rank correlation, are the most suitable indices when focusing on the circulation pattern. Over the Arctic region, four periods with circulation anomalies similar to that of 2007-2012 (i.e. a summertime anticyclonic anomaly over the western Arctic region) have been detected over the last 150 years, despite a higher uncertainty of the circulation given by the reanalyses due to the scarcity of observational data before 1940. Nevertheless, the 2007-2012 anomaly appears to be exceptional and several connections with other variables, such as the North Atlantic Oscillation index and sea ice loss, suggest that it could be part of a major climatic anomaly extending beyond the Arctic region. However, the occurrence of similar periods in the past and the influence of several external and internal forcings do not allow us to attribute it to global warming. The future summertime atmospheric circulation projected by GCMs over Greenland confirms this conclusion. In fact, no significant circulation pattern changes are simulated towards 2100, besides a generalised Z500 increase caused by the projected warming. Since GCMs are able to simulate atmospheric circulation changes over other regions and since the atmospheric circulation itself is influenced by other variables, such as sea ice or snow extent, which are already impacted by long-term changes, we conclude that the 2007-2012 anomaly could rather be attributed to the internal variability of the climatic system. Finally, we evidence that projected future atmospheric circulation changes impact on the SLP and precipitation changes simulated over Europe towards 2100 for summer. Over north-western Europe, these circulation changes could mitigate the SLP decrease by around 50 % and cancel out the precipitation increase. Nevertheless, high uncertainties among the GCMs on the magnitude and even on the sign of these changes cast doubt on the reliability of these projections. On the other hand, future atmospheric circulation changes are not projected to affect significantly the warming and drying simulated for the next decades over the Mediterranean region and eastern Europe. |
author2 |
Cornet, Yves Hubert, Aurelia Erpicum, Michel Carrega, Pierre Fettweis, Xavier Schneider, Christoph |
format |
Text |
author |
Belleflamme, Alexandre |
author_facet |
Belleflamme, Alexandre |
author_sort |
Belleflamme, Alexandre |
title |
Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification |
title_short |
Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification |
title_full |
Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification |
title_fullStr |
Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification |
title_full_unstemmed |
Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification |
title_sort |
detection of past and future atmospheric circulation changes over the north atlantic region with the help of an automatic circulation type classification |
publisher |
Universite de Liege |
publishDate |
2015 |
url |
http://bictel.ulg.ac.be/ETD-db/collection/available/ULgetd-03262015-160037/ |
geographic |
Arctic Canadian Arctic Archipelago Greenland |
geographic_facet |
Arctic Canadian Arctic Archipelago Greenland |
genre |
Arctic Archipelago Arctic Beaufort Sea Canadian Arctic Archipelago Global warming Greenland North Atlantic North Atlantic oscillation Sea ice |
genre_facet |
Arctic Archipelago Arctic Beaufort Sea Canadian Arctic Archipelago Global warming Greenland North Atlantic North Atlantic oscillation Sea ice |
op_source |
http://bictel.ulg.ac.be/ETD-db/collection/available/ULgetd-03262015-160037/ |
op_rights |
mixed Je certifie avoir complété et signé le contrat BICTEL/e remis par le gestionnaire facultaire. |
_version_ |
1766303159650615296 |
spelling |
ftbictel:oai:ETDULg:ULgetd-03262015-160037 2023-05-15T14:29:04+02:00 Detection of past and future atmospheric circulation changes over the North Atlantic region with the help of an automatic circulation type classification Belleflamme, Alexandre Cornet, Yves Hubert, Aurelia Erpicum, Michel Carrega, Pierre Fettweis, Xavier Schneider, Christoph 2015-03-25 application/pdf http://bictel.ulg.ac.be/ETD-db/collection/available/ULgetd-03262015-160037/ unknown Universite de Liege mixed Je certifie avoir complété et signé le contrat BICTEL/e remis par le gestionnaire facultaire. http://bictel.ulg.ac.be/ETD-db/collection/available/ULgetd-03262015-160037/ atmospheric circulation circulation type classification Arctic Greenland Europe reanalyses general circulation models text 2015 ftbictel 2020-10-21T06:30:23Z Future projections of the atmospheric circulation over the Northern Hemisphere high latitudes, especially the North Atlantic, have high uncertainties and some of the projected changes are opposed to circulation changes that have been observed since the 2000s. In this thesis, we focus on three particular aspects of the past and projected future summertime atmospheric circulation over the broader North Atlantic region. First, we analyse whether the 2007-2012 summertime anticyclonic anomaly over the Beaufort Sea, the Canadian Arctic Archipelago, and Greenland might rather be due to global warming or to the internal variability of the atmospheric circulation by putting it in perspective with the circulation variability over the last 150 years given by five reanalysis datasets. Then, this analysis is extended for the future circulation projected towards 2100 by CMIP3 and CMIP5 General Circulation Models (GCMs) over Greenland. Finally, we evaluate the impact of the uncertainties of the future atmospheric circulation projections on the mitigating or enhancing influence of the summertime circulation changes on temperature and precipitation over Europe. We use an automatic circulation type classification to analyse in detail the atmospheric circulation changes by grouping similar daily SLP (mean sea level pressure) or Z500 (500 hPa geopotential height) fields into homogeneous circulation types. It appears that the choice of the index, on the basis of which the days are grouped together, strongly influences the characteristics of the circulation types and the kinds of circulation changes that can be detected. In comparison with Euclidean distance and pressure gradient-based indices, correlation-based indices, especially the Spearman rank correlation, are the most suitable indices when focusing on the circulation pattern. Over the Arctic region, four periods with circulation anomalies similar to that of 2007-2012 (i.e. a summertime anticyclonic anomaly over the western Arctic region) have been detected over the last 150 years, despite a higher uncertainty of the circulation given by the reanalyses due to the scarcity of observational data before 1940. Nevertheless, the 2007-2012 anomaly appears to be exceptional and several connections with other variables, such as the North Atlantic Oscillation index and sea ice loss, suggest that it could be part of a major climatic anomaly extending beyond the Arctic region. However, the occurrence of similar periods in the past and the influence of several external and internal forcings do not allow us to attribute it to global warming. The future summertime atmospheric circulation projected by GCMs over Greenland confirms this conclusion. In fact, no significant circulation pattern changes are simulated towards 2100, besides a generalised Z500 increase caused by the projected warming. Since GCMs are able to simulate atmospheric circulation changes over other regions and since the atmospheric circulation itself is influenced by other variables, such as sea ice or snow extent, which are already impacted by long-term changes, we conclude that the 2007-2012 anomaly could rather be attributed to the internal variability of the climatic system. Finally, we evidence that projected future atmospheric circulation changes impact on the SLP and precipitation changes simulated over Europe towards 2100 for summer. Over north-western Europe, these circulation changes could mitigate the SLP decrease by around 50 % and cancel out the precipitation increase. Nevertheless, high uncertainties among the GCMs on the magnitude and even on the sign of these changes cast doubt on the reliability of these projections. On the other hand, future atmospheric circulation changes are not projected to affect significantly the warming and drying simulated for the next decades over the Mediterranean region and eastern Europe. Text Arctic Archipelago Arctic Beaufort Sea Canadian Arctic Archipelago Global warming Greenland North Atlantic North Atlantic oscillation Sea ice Université de Liege: BICTEL/e-ULg - Serveur institutionnel des thèses de doctorat Arctic Canadian Arctic Archipelago Greenland |