Elements of the West African Monsoon Circulation Deduced from METEOSAT Cloud Winds and Simultaneous Aircraft Measurements

This paper focusses on some aspects or the West African monsoonal circulation observed during the period 15 July-l0 August 1979 of the PGGE, as derived from the satellite cloud windvectors. Temporal averages of the computed winsfields reveal that the flow at the low level is southerly (monsoonal), and Its line of discontinuity with the continental northeasterly was found at approximately 16°-18°N, lying about 300 km south of the accepted mean position. At both the middle and upper tropospheres the flow is easterly with axis about 12o-14,N and, latitude 8 No respectively, such that it is a circulation south of the axis and northwards, it is anticyclonic. The satellite-observed tropospheric circulation IS then discussed in relation to the, weather manifestations over the sub-region typical of the July / August period. The mass fields obtained from our gridded satellite-winds indicate that inflow into the land area occur mainly at the lowest layer (1000:850 hPa), whereas at the upper, levels (that is, above 850 hPa) it is predominantly an outflow, The tropospheric average gives a net mass for divergence from within the area, The significance of this result in relation to the observed weather phenomenology of a temporary cessation of the monsoon precipitations occurring about the peak of the season IS also discussed.

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Development of a Coupled Regional Model and Its Application to the Study of Interactions between the West African Monsoon and the Eastern Tropical Atlantic Ocean

Journal of Climate ◽

10.1175/2008jcli2466.1 ◽

2009 ◽

Vol 22 (10) ◽

pp. 2591-2604 ◽

Cited By ~ 20

Author(s):

Samson M. Hagos ◽

Kerry H. Cook

Keyword(s):

West African Monsoon ◽

Coupled Model ◽

West African ◽

Monsoon Circulation ◽

Tropical Atlantic ◽

Gulf Of Guinea ◽

The West ◽

African Monsoon ◽

Wind Speeds ◽

Westerly Flow

Abstract A regional ocean–atmosphere coupled model is developed for climate variability and change studies. The model allows dynamic and thermodynamic interactions between the atmospheric boundary layer and an ocean mixed layer with spatially and seasonally varying depth prescribed from observations. The model reproduces the West African monsoon circulation as well as aspects of observed seasonal SST variations in the tropical Atlantic. The model is used to identify various mechanisms that couple the West African monsoon circulation with eastern Atlantic SSTs. By reducing wind speeds and suppressing evaporation, the northward migration of the ITCZ off the west coast of Africa contributes to the modeled spring SST increases. During this period, the westerly monsoon flow is expanded farther westward and moisture transport on to the continent is enhanced. Near the end of the summer, upwelling associated with this enhanced westerly flow as well as the solar cycle lead to the seasonal cooling of the SSTs. Over the Gulf of Guinea, the acceleration of the southerly West African monsoon surface winds contributes to cooling of the Gulf of Guinea between April and July by increasing the entrainment of cool underlying water and enhancing evaporation.

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Examining the West African Monsoon circulation response to atmospheric heating in a GCM dynamical core

Journal of Advances in Modeling Earth Systems ◽

10.1002/2016ms000728 ◽

2017 ◽

Vol 9 (1) ◽

pp. 149-167 ◽

Cited By ~ 4

Author(s):

R. Chadwick ◽

G.M. Martin ◽

D. Copsey ◽

G. Bellon ◽

M. Caian ◽

...

Keyword(s):

West African Monsoon ◽

West African ◽

Monsoon Circulation ◽

The West ◽

Dynamical Core ◽

African Monsoon ◽

Atmospheric Heating

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On What Scale Can We Predict the Agronomic Onset of the West African Monsoon?

Monthly Weather Review ◽

10.1175/mwr-d-15-0274.1 ◽

2016 ◽

Vol 144 (4) ◽

pp. 1571-1589 ◽

Cited By ~ 6

Author(s):

Rory G. J. Fitzpatrick ◽

Caroline L. Bain ◽

Peter Knippertz ◽

John H. Marsham ◽

Douglas J. Parker

Keyword(s):

West Africa ◽

Noise Analysis ◽

West African Monsoon ◽

West African ◽

New Method ◽

The West ◽

African Monsoon ◽

Spatial Consistency ◽

Local Stakeholders ◽

Local Rainfall

Abstract Accurate prediction of the commencement of local rainfall over West Africa can provide vital information for local stakeholders and regional planners. However, in comparison with analysis of the regional onset of the West African monsoon, the spatial variability of the local monsoon onset has not been extensively explored. One of the main reasons behind the lack of local onset forecast analysis is the spatial noisiness of local rainfall. A new method that evaluates the spatial scale at which local onsets are coherent across West Africa is presented. This new method can be thought of as analogous to a regional signal against local noise analysis of onset. This method highlights regions where local onsets exhibit a quantifiable degree of spatial consistency (denoted local onset regions or LORs). It is found that local onsets exhibit a useful amount of spatial agreement, with LORs apparent across the entire studied domain; this is in contrast to previously found results. Identifying local onset regions and understanding their variability can provide important insight into the spatial limit of monsoon predictability. While local onset regions can be found over West Africa, their size is much smaller than the scale found for seasonal rainfall homogeneity. A potential use of local onset regions is presented that shows the link between the annual intertropical front progression and local agronomic onset.

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