Abstract
We present a study of upper tropospheric westward transport of air masses coming from the Indian monsoon zone over the period 1998–2008. The objective is to characterize upper tropospheric transport of water vapor from the Indian to Sahelian regions, and to improve the understanding of the dynamical mechanisms that govern water vapor variations in West Africa and the interconnections between India and the Sahel, focusing on the direct role of the Indian monsoon region on Sahel tropospheric water vapor and precipitation. The calculations of forward trajectories with LACYTRAJ (LACY TRAJectory code) and humidity fluxes show that a substantial part (40 to 70% at 300 hPa) of trajectories coming from the upper troposphere of the monsoon region crossed the Sahelian region in a few days (3–14 days), and water vapor fluxes connecting these two regions are established when the Indian monsoon begins at latitudes higher than 15° N in its south–north migration. The intensity and orientation of water vapor fluxes are related to the tropical easterly jet, but they are from the east above the high convection zones. Between 1998 and 2008, these fluxes between the 500–300 hPa pressure levels are associated with precipitation in Sahel only if they are from the east and with an intensity exceeding 8 kg·(m·s)−1.
Highlights
The Sahel region is a transitional belt limited by the wet tropics of Africa to the south and by the Sahara desert to the north
Our work aims to contribute to the following scientific questions: Is the Indian monsoon directly influencing the African monsoon through transport of upper tropospheric air masses? Is the TEJ the only direct link between these two monsoons regions? Which atmospheric layers contribute the most to the water vapor fluxes?
In this article we have documented the transport of air masses coming from the Indian monsoon zone over the period 1998–2008, and characterized the influence of Indian monsoon fluxes on the Sahelian region
Summary
The Sahel region is a transitional belt limited by the wet tropics of Africa to the south and by the Sahara desert to the north. Analyzed upper tropospheric water vapor in the Indian Boreal monsoon region They found two intraseasonal modes of variability (30–60 and 10–20 days) and showed that the 10–20-day wave moves westward to the Arabian Sea from the western Pacific. Estimated that the Indian Ocean is not an important source, but Salih et al [22], using the same model, found that most of the air masses that reach Sahel during the monsoon period come from the Arabian. In a more recent study, Salih et al [2] suggest that 40% of the moisture comes from the monsoon flow and that the regions of the Mediterranean Sea, the Arabian Peninsula, and the South. These works suggest a link between the Indian and the West African monsoons, the Indian monsoon being a moisture source for rainfall in Sahel. We will detail the spatiotemporal variability and the annual cycle of the moisture fluxes before establishing the link between the fluxes and the monsoon dynamics
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