Quasi-decadal signals of Sahel rainfall and West African monsoon since the mid-twentieth century
Sahel rainfall shows pronounced decadal variability and a negative trend between wet conditions in the 1950s-1960s and dry ones in the 1970s-1980s. Using continuous wavelet transform, the quasi-decadal variability (QDV) of rainfall reveals zonal contrasts. The highest QDV is identified in the 1950s-...
Main Authors: | , , , , , , , |
---|---|
Format: | Article in Journal/Newspaper |
Language: | unknown |
Published: |
eScholarship, University of California
2013
|
Subjects: | |
Online Access: | https://escholarship.org/uc/item/1737z6tw |
id |
ftcdlib:oai:escholarship.org/ark:/13030/qt1737z6tw |
---|---|
record_format |
openpolar |
spelling |
ftcdlib:oai:escholarship.org/ark:/13030/qt1737z6tw 2023-05-15T17:35:13+02:00 Quasi-decadal signals of Sahel rainfall and West African monsoon since the mid-twentieth century Dieppois, B Diedhiou, A Durand, A Fournier, M Massei, N Sebag, D Xue, Y Fontaine, B 12 - 599 2013-11-27 application/pdf https://escholarship.org/uc/item/1737z6tw unknown eScholarship, University of California qt1737z6tw https://escholarship.org/uc/item/1737z6tw public Journal of Geophysical Research Atmospheres, vol 118, iss 22 West African Monsoon Sahel rainfall Sea-Surface Temperature Quasi-decadal scale zonal contrast Atmospheric Sciences Physical Geography and Environmental Geoscience article 2013 ftcdlib 2020-04-03T22:54:23Z Sahel rainfall shows pronounced decadal variability and a negative trend between wet conditions in the 1950s-1960s and dry ones in the 1970s-1980s. Using continuous wavelet transform, the quasi-decadal variability (QDV) of rainfall reveals zonal contrasts. The highest QDV is identified in the 1950s-1960s over western Sahel and in the 1970s-1980s over eastern Sahel. The quasi-decadal atmospheric anomalies have been reconstructed using Fourier transform for the 1950s-1960s and the 1970s-1980s, respectively, and assessed by the composite analysis of the QDV phases for the periods before and after 1968. Over western Sahel, the rainfall QDV in the 1950s-1960s is related to the North Atlantic sea surface temperature (SST) variability, as highlighted by the wavelet coherence. A southward shift trend of the Intertropical Convergence Zone (ITCZ) is identified through an enhancement of northeasterly fluxes and moisture convergence over the western part of West Africa. A decrease (increase) of southern (northern) subtropical sinking motions seems to be involved. In the 1970s-1980s, a strengthening of cross-equatorial Atlantic SST and pressure gradients is related to an increase of monsoon flow from lower troposphere up to the midtroposphere and to the northward shift of the ITCZ, mainly over eastern Sahel. The Pacific SST influence is also identified, which involves changes in the global zonal circulation. Key Points Zonal contrasts are detected in Sahel rainfall at quasi-decadal scale Quasi-decadal signals of the WAM are identified in both wet and dry periods Modifications of SST forcing are observed between wet and dry periods ©2013. American Geophysical Union. All Rights Reserved. Article in Journal/Newspaper North Atlantic University of California: eScholarship Pacific |
institution |
Open Polar |
collection |
University of California: eScholarship |
op_collection_id |
ftcdlib |
language |
unknown |
topic |
West African Monsoon Sahel rainfall Sea-Surface Temperature Quasi-decadal scale zonal contrast Atmospheric Sciences Physical Geography and Environmental Geoscience |
spellingShingle |
West African Monsoon Sahel rainfall Sea-Surface Temperature Quasi-decadal scale zonal contrast Atmospheric Sciences Physical Geography and Environmental Geoscience Dieppois, B Diedhiou, A Durand, A Fournier, M Massei, N Sebag, D Xue, Y Fontaine, B Quasi-decadal signals of Sahel rainfall and West African monsoon since the mid-twentieth century |
topic_facet |
West African Monsoon Sahel rainfall Sea-Surface Temperature Quasi-decadal scale zonal contrast Atmospheric Sciences Physical Geography and Environmental Geoscience |
description |
Sahel rainfall shows pronounced decadal variability and a negative trend between wet conditions in the 1950s-1960s and dry ones in the 1970s-1980s. Using continuous wavelet transform, the quasi-decadal variability (QDV) of rainfall reveals zonal contrasts. The highest QDV is identified in the 1950s-1960s over western Sahel and in the 1970s-1980s over eastern Sahel. The quasi-decadal atmospheric anomalies have been reconstructed using Fourier transform for the 1950s-1960s and the 1970s-1980s, respectively, and assessed by the composite analysis of the QDV phases for the periods before and after 1968. Over western Sahel, the rainfall QDV in the 1950s-1960s is related to the North Atlantic sea surface temperature (SST) variability, as highlighted by the wavelet coherence. A southward shift trend of the Intertropical Convergence Zone (ITCZ) is identified through an enhancement of northeasterly fluxes and moisture convergence over the western part of West Africa. A decrease (increase) of southern (northern) subtropical sinking motions seems to be involved. In the 1970s-1980s, a strengthening of cross-equatorial Atlantic SST and pressure gradients is related to an increase of monsoon flow from lower troposphere up to the midtroposphere and to the northward shift of the ITCZ, mainly over eastern Sahel. The Pacific SST influence is also identified, which involves changes in the global zonal circulation. Key Points Zonal contrasts are detected in Sahel rainfall at quasi-decadal scale Quasi-decadal signals of the WAM are identified in both wet and dry periods Modifications of SST forcing are observed between wet and dry periods ©2013. American Geophysical Union. All Rights Reserved. |
format |
Article in Journal/Newspaper |
author |
Dieppois, B Diedhiou, A Durand, A Fournier, M Massei, N Sebag, D Xue, Y Fontaine, B |
author_facet |
Dieppois, B Diedhiou, A Durand, A Fournier, M Massei, N Sebag, D Xue, Y Fontaine, B |
author_sort |
Dieppois, B |
title |
Quasi-decadal signals of Sahel rainfall and West African monsoon since the mid-twentieth century |
title_short |
Quasi-decadal signals of Sahel rainfall and West African monsoon since the mid-twentieth century |
title_full |
Quasi-decadal signals of Sahel rainfall and West African monsoon since the mid-twentieth century |
title_fullStr |
Quasi-decadal signals of Sahel rainfall and West African monsoon since the mid-twentieth century |
title_full_unstemmed |
Quasi-decadal signals of Sahel rainfall and West African monsoon since the mid-twentieth century |
title_sort |
quasi-decadal signals of sahel rainfall and west african monsoon since the mid-twentieth century |
publisher |
eScholarship, University of California |
publishDate |
2013 |
url |
https://escholarship.org/uc/item/1737z6tw |
op_coverage |
12 - 599 |
geographic |
Pacific |
geographic_facet |
Pacific |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
Journal of Geophysical Research Atmospheres, vol 118, iss 22 |
op_relation |
qt1737z6tw https://escholarship.org/uc/item/1737z6tw |
op_rights |
public |
_version_ |
1766134298818117632 |