Fluctuations in annual cycles and inter-seasonal memory in West Africa: rainfall, soil moisture and heat fluxes,Reportar como inadecuado

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1 CRC - Centre de Recherches de Climatologie

Abstract : Annual cycle and inter-seasonal persistence of surfaceatmosphere water and heat fluxes are analyzed at a 5-day time step over the West African Monsoon WAM through observational precipitation estimates CMAP, model datasets NCEP=DOE level 2 reanalyses and a Soil Water Index SWI from the ERS scatterometer. Coherent fluctuations 30–90 days distinct from supra-synoptic variability 10–25 day periods are first detected in the WAM precipitation and heat fluxes over the period 1979–2001. During all the northward excursion of the WAM rain band, a succession of four active phases abrupt rainfall increases occurs. They are centered in the first days of March, mid- April, the second half of May and from the last week of June to mid-July the Sahelian onset. A simple statistical approach shows that the Spring to Summer installation of the monsoon tends to be sensitive to these short periods. Other analyses suggest the existence of lagged relationship between rainfall amounts registered in successive Fall, Spring active periods and Summer top of the rainy season implying land surface conditions. The spatial extension of the generated soil moisture anomalies reaches one maximum in March, mainly at the Guinean latitudes and over the Sahelian belt where the signal can persist until the next monsoon onset. Typically after abnormal wet conditions in September– October two signals are observed: 1 more marked fluctuations in Spring with less more Sahelian rainfall in May June and after at the Sahelian-Sudanian latitudes; 2 wetter rainy seasons along the Guinean coast in Spring and Summer with an advance in the mean date of the ‘little dry season-. The reverse arises after abnormal dry conditions in autumn.

Autor: Bernard Fontaine - Samuel Louvet - Pascal Roucou -

Fuente: https://hal.archives-ouvertes.fr/


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