scholarly journals 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

2009 ◽  
Vol 22 (10) ◽  
pp. 2591-2604 ◽  
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.

scholarly journals Coupled Model Simulations of the West African Monsoon System: Twentieth- and Twenty-First-Century Simulations

2006 ◽  
Vol 19 (15) ◽  
pp. 3681-3703 ◽  
Author(s):  
Kerry H. Cook ◽  
Edward K. Vizy
Keyword(s):  
Twentieth Century ◽  
West African Monsoon ◽  
West African ◽  
First Century ◽  
Gulf Of Guinea ◽  
Physical Processes ◽  
The West ◽  
African Monsoon ◽  
The Third ◽  
Twenty First Century

Abstract The ability of coupled GCMs to correctly simulate the climatology and a prominent mode of variability of the West African monsoon is evaluated, and the results are used to make informed decisions about which models may be producing more reliable projections of future climate in this region. The integrations were made available by the Program for Climate Model Diagnosis and Intercomparison for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. The evaluation emphasizes the circulation characteristics that support the precipitation climatology, and the physical processes of a “rainfall dipole” variability mode that is often associated with dry conditions in the Sahel when SSTs in the Gulf of Guinea are anomalously warm. Based on the quality of their twentieth-century simulations over West Africa in summer, three GCMs are chosen for analysis of the twenty-first century integrations under various assumptions about future greenhouse gas increases. Each of these models behaves differently in the twenty-first-century simulations. One model simulates severe drying across the Sahel in the later part of the twenty-first century, while another projects quite wet conditions throughout the twenty-first century. In the third model, warming in the Gulf of Guinea leads to more modest drying in the Sahel due to a doubling of the number of anomalously dry years by the end of the century. An evaluation of the physical processes that cause these climate changes, in the context of the understanding about how the system works in the twentieth century, suggests that the third model provides the most reasonable projection of the twenty-first-century climate.

The diurnal cycle of the West African monsoon circulation

2005 ◽  
Vol 131 (611) ◽  
pp. 2839-2860 ◽  
Author(s):  
D. J. Parker ◽  
R. R. Burton ◽  
A. Diongue-Niang ◽  
R. J. Ellis ◽  
M. Felton ◽  
...  
Keyword(s):  
Diurnal Cycle ◽  
West African Monsoon ◽  
West African ◽  
Monsoon Circulation ◽  
The West ◽  
African Monsoon

scholarly journals Some aspects of the West African monsoon circulation As deduced from a geostationary satellite

MAUSAM ◽  
2022 ◽  
Vol 44 (4) ◽  
pp. 359-364
Author(s):  
OLUWAGBEMIGA O. JEGEDE
Keyword(s):  
West African Monsoon ◽  
West African ◽  
Geostationary Satellite ◽  
Monsoon Circulation ◽  
Land Area ◽  
The West ◽  
African Monsoon ◽  
Low Level ◽  
Tropospheric Circulation ◽  
Line Of Discontinuity

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.

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

2017 ◽  
Vol 9 (1) ◽  
pp. 149-167 ◽  
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

scholarly journals The influence of biomass burning and transport on tropospheric composition over the tropical Atlantic Ocean and Equatorial Africa during the West African monsoon in 2006

2010 ◽  
Vol 10 (20) ◽  
pp. 9797-9817 ◽  
Author(s):  
J. E. Williams ◽  
M. P. Scheele ◽  
P. F. J. van Velthoven ◽  
V. Thouret ◽  
M. Saunois ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Temporal Resolution ◽  
Biomass Burning ◽  
Southern Africa ◽  
West African Monsoon ◽  
West African ◽  
Tropical Atlantic ◽  
The West ◽  
African Monsoon ◽  
Equatorial Africa

Abstract. Biomass burning (BB) in southern Africa is the largest emission source of CO and O3 precursors within Africa during the West African Monsoon (WAM) between June and August. The long range transport and chemical processing of such emissions thus has the potential to exert a dominant influence on the composition of the tropical troposphere over Equatorial Africa (EA) and the Tropical Atlantic Ocean (TAO). We have performed simulations using a three-dimensional global chemistry-transport model (CTM) to quantify the effect that continental transport of such BB plumes has on the EA region. BB emissions from southern Africa were found to exert a significant influence over the TAO and EA between 10° S–20° N. The maximum concentrations in CO and O3 occur between 0–5° S near the position of the African Easterly Jet – South as placed by the European Centre for Medium range Weather Forecasts (ECMWF) meteorological analysis data. By comparing co-located model output with in-situ measurements we show that the CTM fails to capture the tropospheric profile of CO in southern Africa near the main source region of the BB emissions, as well as the "extreme" concentrations of both CO and O3 seen between 600–700 hPa over EA around 6° N. For more northerly locations the model exhibits high background concentrations in both CO and O3 related to BB emissions from southern Africa. By altering both the temporal resolution and the vertical distribution of BB emissions in the model we show that changes in temporal resolution have the largest influence on the transport of trace gases near the source regions, EA, and in the outflow towards the west of Central Africa. Using a set of trajectory calculations we show that the performance of the CTM is heavily constrained by the ECMWF meteorological fields used to drive the CTM, which transport biomass burning plumes from southern Africa into the lower troposphere of the TAO rather than up towards the middle troposphere at 650 hPa. Similar trajectory simulations repeated using an updated meteorological dataset, which assimilates additional measurement data taken around EA, show markedly different origins for pollution events and highlight the current limitations in modelling this tropical region.

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

2016 ◽  
Vol 144 (4) ◽  
pp. 1571-1589 ◽  
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.

scholarly journals A Lagrangian perspective on stable water isotopes during the West African Monsoon

2021 ◽  
Author(s):  
Christopher Johannes Diekmann ◽  
Matthias Schneider ◽  
Peter Knippertz ◽  
Andries Jan de Vries ◽  
Stephan Pfahl ◽  
...  
Keyword(s):  
West African Monsoon ◽  
West African ◽  
Water Isotopes ◽  
Stable Water Isotopes ◽  
The West ◽  
African Monsoon
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