1. Links between African easterly waves, midlatitude circulation and intraseasonal pulsations of the West African heat low
- Author
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Lavaysse, C., Flamant, C., Janicot, Serge, Knippertz, P., SPACE - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), School of Earth and Environment [Leeds] (SEE), University of Leeds, Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris)
- Subjects
ECMWF ERA-40 reanalyses ,[PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph] ,[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere ,ECMWF ERA-40 ,West African monsoon ,tropical convection ,reanalyses ,[SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology ,[SDE.MCG]Environmental Sciences/Global Changes ,Tropical convection ,Satellite-derived brightness temperature ,AMMA ,satellite-derived brightness temperature - Abstract
During summer 2006. the intensity of the thermal depression over the Sahara. derived from European Centre for Medium-range Weather Forecast analyses. exhibited a strong decrease during the first couple of weeks of September Simultaneously. widespread convective activity over the Sahel was detected. The aims of this study are to identify the reasons for this decrease of the West African Heat Low (WAHL) activity, to discuss the possible relationship with convection and to assess the representativity of such an event at the climatological tune-scale. From spectral analysis of the daily WAHL thickness during summer 2006. two period bands of significant intraseasonal pulsations were identified. and confirmed using the ERA-40 reanalysis. namely 3-10d and 10-30d In both the 2006 case-study and the climatological composite study. we find that detrimental conditions in the 3-10d period band are associated with moist and cool advections in the lower troposphere linked to the southerly sector of African easterly waves (AEWs) which increase convective activity over the Sahel These humid and cold advections from the south are more pronounced when the AEW interacts with a midlatitude depression In the 10-30d period band. the impact of midlatitude circulation is demonstrated During the collapsing period of the 10-30d pulsations of the WAHL thickness, an upper-level trough is seen over northern West Africa This situation generates a surge of 700 hPa cold air from Libya into the Sahara. an increase of the 925 hPa anticyclonic circulation and a significant increase of convective activity over the Sahel Copyright (C) 2010 Royal Meteorological Society
- Published
- 2010
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