Dynamical Downscaling for Assessment of the Climate in Ghana

Dynamical downscaling (DDS), in which a regional atmospheric model (RAM) experiment nested into coarser-resolution data provides a spatio-temporal fine dataset for a particular region, was performed to assess the present climate in Ghana. The DDS successfully evaluated realistic seasonal march and inter-annual variability in rainfall, in comparison with gauge and satellite observation. The DDS also indicated that land-lake and land-sea circulation interacted with the West African monsoon likely characterized the local climate in Ghana.

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Coupled Land–Atmosphere Intraseasonal Variability of the West African Monsoon in a GCM

Journal of Climate ◽

10.1175/2010jcli3419.1 ◽

2010 ◽

Vol 23 (21) ◽

pp. 5557-5571 ◽

Cited By ~ 19

Author(s):

Sally L. Lavender ◽

Christopher M. Taylor ◽

Adrian J. Matthews

Keyword(s):

Soil Moisture ◽

Sensible Heat Flux ◽

Intraseasonal Variability ◽

West African Monsoon ◽

Atmospheric Model ◽

West African ◽

The West ◽

African Monsoon ◽

Surface Sensible Heat Flux ◽

Fully Coupled

Abstract Recent observational studies have suggested a role for soil moisture and land–atmosphere coupling in the 15-day westward-propagating mode of intraseasonal variability in the West African monsoon. This hypothesis is investigated with a set of three atmospheric general circulation model experiments. 1) When soil moisture is fully coupled with the atmospheric model, the 15-day mode of land–atmosphere variability is clearly identified. Precipitation anomalies lead soil moisture anomalies by 1–2 days, similar to the results from satellite observations. 2) To assess whether soil moisture is merely a passive response to the precipitation, or an active participant in this mode, the atmospheric model is forced with a 15-day westward-propagating cycle of regional soil moisture anomalies based on the fully coupled mode. Through a reduced surface sensible heat flux, the imposed wet soil anomalies induce negative low-level temperature anomalies and increased pressure (a cool high). An anticyclonic circulation then develops around the region of wet soil, enhancing northward moisture advection and precipitation to the west. Hence, in a coupled framework, this soil moisture–forced precipitation response would provide a self-consistent positive feedback on the westward-propagating soil moisture anomaly and implies an active role for soil moisture. 3) In a final sensitivity experiment, soil moisture is again externally prescribed but with all intraseasonal fluctuations suppressed. In the absence of soil moisture variability there are still pronounced surface sensible heat flux variations, likely due to cloud changes, and the 15-day westward-propagating precipitation signal is still present. However, it is not as coherent as in the previous experiments when interaction with soil moisture was permitted. Further examination of the soil moisture forcing experiment in GCM experiment 2 shows that this precipitation mode becomes phase locked to the imposed soil moisture anomalies. Hence, the 15-day westward-propagating mode in the West African monsoon can exist independently of soil moisture; however, soil moisture and land–atmosphere coupling act to feed back on the atmosphere and further enhance and organize it.

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Spatio-temporal evolution of the West African monsoon during the last deglaciation

Geophysical Research Letters ◽

10.1029/2011gl047805 ◽

2011 ◽

Vol 38 (13) ◽

pp. n/a-n/a ◽

Cited By ~ 14

Author(s):

Syee Weldeab ◽

Martin Frank ◽

Torben Stichel ◽

Brian Haley ◽

Mark Sangen

Keyword(s):

Temporal Evolution ◽

West African Monsoon ◽

West African ◽

Last Deglaciation ◽

The West ◽

African Monsoon ◽

The Last Deglaciation ◽

Spatio Temporal

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Decadal and multi-year predictability of the West African monsoon and the role of dynamical downscaling

Meteorologische Zeitschrift ◽

10.1127/metz/2017/0811 ◽

2017 ◽

Vol 26 (4) ◽

pp. 363-377 ◽

Cited By ~ 5

Author(s):

Heiko Paeth ◽

Andreas Paxian ◽

Dmitry V. Sein ◽

Daniela Jacob ◽

Hans-Jürgen Panitz ◽

...

Keyword(s):

Dynamical Downscaling ◽

West African Monsoon ◽

West African ◽

The West ◽

African Monsoon

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Atmospheric response to SST tendancy in the Eastern topical Atlantic in July-August

10.5194/egusphere-egu21-16204 ◽

2021 ◽

Author(s):

Dahirou Wane ◽

Gaëlle de Coëtlogon ◽

Lazar Alban ◽

Malick Wade ◽

Amadou T. Gaye

Keyword(s):

Atmospheric Model ◽

West African ◽

Strong Reduction ◽

The West ◽

Sharp Drop ◽

Sst Cooling ◽

Western Sahel ◽

Regional Atmospheric Model ◽

Sensitivity Tests ◽

Rainfall Anomalies

The objective of this work is to understand how the seasonal tendances of the tropical Atlantic SST influence the migration of the Intertropical Convergence Zone (ITCZ) and the West African precipitation associated with it. For this we carried out different sensitivity tests to the SST, climatological, with the regional atmospheric model WRF-ARW. Our results, based on the July-August period, show a strong influence of SST anomalies in the Dakar Nino (DN) and Atlantic cold tongue (ACT) regions on the marine ITCZ and West African precipitation. Above the ocean, the cooling of the tropical northeast Atlantic induces a strong reduction in precipitation north of 10&#176;N, associated with the southward displacement of the ITCZ which is located between 5&#176;-10&#176;N with a slight increase in rains. On the other hand, the warming of the SST of the tropical south-eastern Atlantic induces an increase in marine precipitations, with a maximum centered on 5&#176;N, explained by the location of the ITCZ further south than that associated with the cooling in the region of DN. On the continent, the influence of these SST tendances is characterized by the presence of a zonal dipole of rainfall anomalies over the Sahelian regions. The SST cooling effect in the DN region is more marked in the western Sahel, particularly in Senegal, with a sharp drop in rainfall in this region. While that of warming in the LEF region is more marked in the Sahel, which also induces a strong reduction in the intensity of the rains in this region. However, the combined experience of these two type anomalies shows a dipole of rainfall anomalies over the ocean and over the continent. This dipole is characterized by a decrease (increase) in Sahelian (Guinean) rainfall. Our results also show that, for all simulations, the increase (reduction) in precipitation is more explained by the convective (non-convective) part of the rain. The influence of the SST of DN contributes 40% to 100% on the decrease in rainfall in the West Sahel, while the SST of the ACT reduces rainfall in the eastern Sahel by 40% to 100%. Thus, this work underlines the importance of taking into account the effect of the seasonal anomaly of the SST of DN on Sahelian precipitations in forecasting models.

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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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