HR: 15:00h
AN: A43E-05    [Abstracts]
TI: Shallow Meridional Circulation of the West African Monsoon: A New Conceptual Model
AU: * Zhang, C
EM: czhang@rsmas.miami.edu
AF: RSMAS, University of Miami, 4600 Richenbacker Causeway MPO, Miami, FL 33149, United States
AB: The large-scale meridional circulation of the West African monsoon consists of, according to conventional wisdom, a classic, Hadley-type deep overturning cell. The ascending branch of this overturning cell is collocated with the monsoon rainband, its low-level southerly branch is in the boundary layer, commonly referred to as the monsoon flow, its northerly return flow is in the upper troposphere, and its descending branch spreads over a broad region over the eastern Atlantic Ocean. Recent diagnoses of in situ sounding data and global reanalysis products have revealed a different picture: In addition to this deep overturning cell, there exists a shallow meridional circulation (SMC). This SMC shares the same boundary-layer southerly monsoon flow with the deep overturning cell. But its ascending branch is further inland, north of the monsoon rainband, and is collocated with the Saharan heat low. Its northerly return flow, in the lower troposphere, penetrates through the monsoon rainband in the mean. This dual meridional circulations associated with the West African monsoon forms a contrast not only to the traditional concept of its large-scale circulation patterns, but also to the dual meridional circulations associated with the marine ITCZ. There are substantial discrepancies among existing global reanalyses and climate models in their capability of capturing the SMC of the West African monsoon. It is postulated that the springtime northward "jump" of the West African monsoon rainband is partially related to this shallow meridional circulation.
DE: 3319 General circulation (1223)
DE: 3337 Global climate models (1626, 4928)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3354 Precipitation (1854)
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly