Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought
Abstract Trends in the general circulation setting during 1948–1983 accompanying the progressive aggravation of drought in sub‐Saharan Africa are investigated from ship observations over the tropical Atlantic and surface station records in western Africa. Decadal‐scale circulation changes in the Atl...
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crwiley:10.1002/joc.3370100504 2024-06-23T07:54:59+00:00 Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought Hastenrath, Stefan 1990 http://dx.doi.org/10.1002/joc.3370100504 https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjoc.3370100504 https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/joc.3370100504 en eng Wiley http://onlinelibrary.wiley.com/termsAndConditions#vor International Journal of Climatology volume 10, issue 5, page 459-472 ISSN 0899-8418 1097-0088 journal-article 1990 crwiley https://doi.org/10.1002/joc.3370100504 2024-06-06T04:20:48Z Abstract Trends in the general circulation setting during 1948–1983 accompanying the progressive aggravation of drought in sub‐Saharan Africa are investigated from ship observations over the tropical Atlantic and surface station records in western Africa. Decadal‐scale circulation changes in the Atlantic sector include a pressure rise over the tropical North Atlantic; southward displacement of the near‐equatorial wind confluence and associated maximum cloud belt; acceleration of the north‐east trades and possibly a strengthening of the South Atlantic trades, along with increasing cloudiness in the equatorial zone; increasing cloudiness over the tropical North Atlantic and Central American seas; and cooling of surface waters in a band across the tropical North Atlantic contrasting with warming in the South Atlantic. These changes occurred in all seasons, but were most pronounced at the height of boreal summer. Records at land stations in western Africa show that near the coasts the temperature and pressure trends are consistent with the adjacent ocean areas. In the interior of sub‐Saharan Africa, warming trends prevail in boreal summer, presumably as a direct consequence of reduced inflow of cool maritime monsoon air; the concomitant downward pressure trends at continental stations in sub‐Saharan Africa may reflect the hydrostatic effect of increasing temperature. In contrast to boreal summer, slight cooling trends and pressure rises prevail in the interior during winter. In the course of the past four decades, the near‐equatorial wind confluence over the eastern Atlantic migrated southward by 200 km in July–August and 150 km for the rainy season as a whole. Given the steep meridional precipitation gradients across the Sahel, these circulation shifts are large enough to account for the observed downward trend in Sahel rainfall. Article in Journal/Newspaper North Atlantic Wiley Online Library International Journal of Climatology 10 5 459 472 |
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Wiley Online Library |
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crwiley |
language |
English |
description |
Abstract Trends in the general circulation setting during 1948–1983 accompanying the progressive aggravation of drought in sub‐Saharan Africa are investigated from ship observations over the tropical Atlantic and surface station records in western Africa. Decadal‐scale circulation changes in the Atlantic sector include a pressure rise over the tropical North Atlantic; southward displacement of the near‐equatorial wind confluence and associated maximum cloud belt; acceleration of the north‐east trades and possibly a strengthening of the South Atlantic trades, along with increasing cloudiness in the equatorial zone; increasing cloudiness over the tropical North Atlantic and Central American seas; and cooling of surface waters in a band across the tropical North Atlantic contrasting with warming in the South Atlantic. These changes occurred in all seasons, but were most pronounced at the height of boreal summer. Records at land stations in western Africa show that near the coasts the temperature and pressure trends are consistent with the adjacent ocean areas. In the interior of sub‐Saharan Africa, warming trends prevail in boreal summer, presumably as a direct consequence of reduced inflow of cool maritime monsoon air; the concomitant downward pressure trends at continental stations in sub‐Saharan Africa may reflect the hydrostatic effect of increasing temperature. In contrast to boreal summer, slight cooling trends and pressure rises prevail in the interior during winter. In the course of the past four decades, the near‐equatorial wind confluence over the eastern Atlantic migrated southward by 200 km in July–August and 150 km for the rainy season as a whole. Given the steep meridional precipitation gradients across the Sahel, these circulation shifts are large enough to account for the observed downward trend in Sahel rainfall. |
format |
Article in Journal/Newspaper |
author |
Hastenrath, Stefan |
spellingShingle |
Hastenrath, Stefan Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought |
author_facet |
Hastenrath, Stefan |
author_sort |
Hastenrath, Stefan |
title |
Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought |
title_short |
Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought |
title_full |
Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought |
title_fullStr |
Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought |
title_full_unstemmed |
Decadal‐scale changes of the circulation in the tropical atlantic sector associated with Sahel drought |
title_sort |
decadal‐scale changes of the circulation in the tropical atlantic sector associated with sahel drought |
publisher |
Wiley |
publishDate |
1990 |
url |
http://dx.doi.org/10.1002/joc.3370100504 https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjoc.3370100504 https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/joc.3370100504 |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
International Journal of Climatology volume 10, issue 5, page 459-472 ISSN 0899-8418 1097-0088 |
op_rights |
http://onlinelibrary.wiley.com/termsAndConditions#vor |
op_doi |
https://doi.org/10.1002/joc.3370100504 |
container_title |
International Journal of Climatology |
container_volume |
10 |
container_issue |
5 |
container_start_page |
459 |
op_container_end_page |
472 |
_version_ |
1802647348882440192 |