{"corpus_id":129820176,"paper_sha":"a64443fb1038b6526c4a3950b3eb25ad6a7caa53","doi":"10.1175/1520-0442(1999)012<1165:GOTAEJ>2.0.CO;2","arxiv_id":null,"pmid":null,"pmcid":null,"mag_id":2027158583,"dblp_id":null,"acl_id":null,"title":"Generation of the African Easterly Jet and Its Role in Determining West African Precipitation","year":1999,"publication_date":"1999-05-01","venue":"","journal":{"name":"Journal of Climate","pages":"1165-1184","volume":"12"},"journal_issn":null,"journal_title":null,"publication_types":[],"pubmed_pub_types":null,"s2_fields_of_study":["Geology","Geography","Environmental Science"],"reference_count":35,"citation_count":432,"influential_citation_count":71,"is_open_access":false,"arxiv_categories":null,"arxiv_license":null,"arxiv_journal_ref":null,"mesh_headings":null,"chemicals":null,"comments_corrections":null,"source_flags":1,"s2_open_access_pdf_url":null,"s2_open_access_landing_url":null,"s2_open_access_license":null,"s2_open_access_status":null,"pmc_open_access_pdf_url":null,"pmc_open_access_landing_url":null,"pmc_open_access_license":null,"pmc_open_access_status":null,"unpaywall_open_access_pdf_url":null,"unpaywall_open_access_landing_url":null,"unpaywall_open_access_license":null,"unpaywall_open_access_status":null,"abstract":"An examination of analyses and model simulations is used to show that the African easterly jet forms over West Africa in summer as a result of strong meridional soil moisture gradients. In a series of GCM experiments, the imposition of realistic surface wetness contrasts between the Sahara and equatorial Africa leads to strong positive meridional temperature gradients at the surface and in the lower troposphere; the associated easterly shear in the atmosphere is strong enough to establish easterly flow—the African easterly jet—above the monsoon westerlies at the surface. Positive temperature gradients associated with the summertime distributions of solar radiation, SSTs, or clouds are not large enough to produce the easterly jet in the absence of soil moisture gradients. A thermally direct ageostrophic circulation is identified that can accelerate the largely geostrophic zonal flow and maintain the jet. While moisture converges throughout the lower troposphere over East Africa, moisture divergence between 600 and 800 mb overlies low-level convergence over West Africa to the south of the African easterly jet. This moisture divergence is important for determining the total column moisture convergence. Since the moisture divergence is closely tied to the jet dynamics, and the jet’s magnitude and position are sensitive to SST and land surface conditions, a mechanism by which the West African precipitation field is sensitive to surface conditions is suggested. 1.","claims":[{"public_id":"cl_0924331425ad4bc5bd99bc632007863c","status":"active","text":"A thermally direct ageostrophic circulation accelerates the largely geostrophic zonal flow and helps maintain the jet.","confidence":0.9,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_0924331425ad4bc5bd99bc632007863c"},{"public_id":"cl_4f7bc7e0d5b9f111c761df401700ce99","status":"active","text":"Moisture divergence between 600 and 800 mb over West Africa south of the African easterly jet is important for determining total column moisture convergence and links jet dynamics to the sensitivity of West African precipitation to surface conditions.","confidence":0.95,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_4f7bc7e0d5b9f111c761df401700ce99"},{"public_id":"cl_2384a7b3c702cc9647714e96e8e4a90a","status":"active","text":"Realistic surface wetness contrasts between the Sahara and equatorial Africa generate strong positive meridional temperature gradients that produce easterly shear sufficient to establish the African easterly jet above the monsoon westerlies.","confidence":0.97,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_2384a7b3c702cc9647714e96e8e4a90a"},{"public_id":"cl_e509988b91698d9496efcf595440df54","status":"active","text":"Summertime distributions of solar radiation, sea surface temperatures, or clouds do not produce the African easterly jet without soil moisture gradients.","confidence":0.93,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_e509988b91698d9496efcf595440df54"},{"public_id":"cl_198deb6853132997a94d1d443b245383","status":"active","text":"The African easterly jet forms over West Africa in summer as a result of strong meridional soil moisture gradients.","confidence":0.99,"contributors":[{"id":1,"public_id":"12632b8b5f","public_label":"Anonymous (12632b8b5f)","roles":["extraction"],"url":"https://sah.borca.ai/u/12632b8b5f"}],"url":"https://sah.borca.ai/claims/cl_198deb6853132997a94d1d443b245383"}],"concepts":[{"public_id":"co_317262ef0265359edb17a3c392d7ccd5","status":"active","name":"sea surface temperatures","description":"Ocean surface temperatures considered as a boundary forcing in the 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