West African Summer Monsoon Research Articles

Understanding the summertime diurnal cycle of precipitation over sub-Saharan West Africa: regions with daytime rainfall peaks in the absence of significant topographic features

Convection-permitting regional model output is analyzed to better understand the diurnal cycle of rainfall during the height of the West African summer monsoon. This investigation focuses on two regions, the western Bodele of Chad and eastern Burkina Faso, that have a propensity for daytime rainfall, but why this occurs does not conform to our conventional understanding of being directly associated with the presence of significant topographic feature(s). The August diurnal cycle of rainfall for the Bodele is characterized by an afternoon peak, with mesoscale convective systems (MCSs) originating within 500 km accounting for 80% of the afternoon precipitation. These MCSs are associated with a deepening of the monsoon trough over the western Sahara related to northern storm track African easterly wave (AEW) disturbance activity, combined with anomalous ridging over eastern Chad associated with cold pool outflow from convection that originates over the Marra Mountains the previous afternoon. These circulation features enhance the moist low-level southwesterly flow and increase instability over the Bodele. Over Burkina Faso rainfall has a primary afternoon peak, and a secondary morning peak. MCSs account for 95% of the total rainfall. Morning rainfall is primarily due to MCSs forming over the Damergou Gap of Niger, while the afternoon rainfall is associated with MCSs that originate over the Damergou Gap as well as locally. While both types of MCSs are associated with an approaching southern storm track AEW disturbance, it is differences in northern storm track activity that helps explain why some MCSs originate over the Damergou Gap.

Ensemble-based CMIP5 simulations of West African summer monsoon rainfall: current climate and future changes

The West African summer monsoon (WASM) rainfall is of significant socioeconomic importance. Therefore, its response to climate change is of great concern to climate scientists. Based on observations, reanalysis, and multi-model ensemble mean (EnsMean) simulations of Coupled Model Intercomparison Project phase 5 (CMIP5) models, the responses of WASM rainfall, as well as some relevant atmospheric features, to global warming are investigated. Results from the historical period (1980–2005) indicate that EnsMean reasonably reproduced the characteristics of WASM rainfall, and the strength and position of the upper-level Tropical Easterly Jet (TEJ) and mid-level African Easterly Jet (AEJ). Under global warming, EnsMean exhibits localized future changes in spatial rainfall pattern; specifically, a statistically significant increase (decrease) is evident over the central-eastern (western) Sahel subregion. Similarly, the annual cycle exhibits a decrease (increase) in pre-monsoon (post-monsoon) rainfall over the region, evident over the Sahel subregion. Increased surface evaporation and enhanced atmospheric moisture convergence are notable over the region of increasing WASM rainfall, while a weakened and possible alteration of large-scale atmospheric circulation features is evident over the study area.

Projections of West African summer monsoon rainfall extremes from two CORDEX models

Global warming has a profound impact on the vulnerable environment of West Africa; hence, robust climate projection, especially of rainfall extremes, is quite important. Based on two representative concentration pathway (RCP) scenarios, projected changes in extreme summer rainfall events over West Africa were investigated using data from the Coordinated Regional Climate Downscaling Experiment models. Eight (8) extreme rainfall indices (CDD, CWD, r10mm, r20mm, PRCPTOT, R95pTOT, rx5day, and sdii) defined by the Expert Team on Climate Change Detection and Indices were used in the study. The performance of the regional climate model (RCM) simulations was validated by comparing with GPCP and TRMM observation data sets. Results show that the RCMs reasonably reproduced the observed pattern of extreme rainfall over the region and further added significant value to the driven GCMs over some grids. Compared to the baseline period 1976–2005, future changes (2070–2099) in summer rainfall extremes under the RCP4.5 and RCP8.5 scenarios show statistically significant decreasing total rainfall (PRCPTOT), while consecutive dry days and extreme rainfall events (R95pTOT) are projected to increase significantly. There are obvious indications that simple rainfall intensity (sdii) will increase in the future. This does not amount to an increase in total rainfall but suggests a likelihood of greater intensity of rainfall events. Overall, our results project that West Africa may suffer more natural disasters such as droughts and floods in the future.

Assessment of moisture budget over West Africa using MERRA-2’s aerological model and satellite data

The study assessed the performance of NASA’s Modern-Era Retrospective Analysis for Research and Applications (MERRA) and MERRA-2 aerological (P–E*) model in reproducing the salient features of West Africa water balance including its components from 1980 to 2013. In this study we have shown that recent reanalysis efforts have generated imbalances between regional integrated precipitation (P) and surface evaporation (E), and the effect is more in the newly released MERRA-2. The atmospheric water balance of MERRA and MERRA-2 were inter-compared and thereafter compared with model forecast output of European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-I) and Japanese 55-year Reanalysis (JRA-55). Results indicated that a bias of 12–20 (5–13) mm/month in MERRA-2 (ERA-I) leads to the classification of the Sahel (14°N–20°N) as a moisture source during the West African Summer Monsoon. Comparisons between MERRA/MERRA-2 and prognostic fields from two ERA-I and JRA-55 indicated that the average P–E* in MERRA is 18.94 (52.24) mm/month which is less than ERA-I (JRA-55) over Guinea domain and 25.03 (4.53) mm/month greater than ERA-I (JRA-55) over the Sahel. In MERRA-2, average P–E* indicated 25.76 (59.06) mm/month which is less than ERA-I (JRA-55) over Guinea and 73.72 (94.22) mm/month less than ERA-I (JRA-55) over the Sahel respectively. These imbalances are due to adjustments in data assimilation methods, satellite calibration and observational data base. The change in convective P parameterization and increased re-evaporation of P in MERRA-2 is suggestive of the cause of positive biases in P and E. The little disagreements between MERRA/MERRA-2 and CRU precipitation highlights one of the major challenges associated with climate research in West Africa and major improvements in observation data and surface fluxes from reanalysis remain vital.

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

West African summer monsoon precipitation is characterized by distinct decadal variability. Due to its well-documented link to oceanic boundary conditions in various ocean basins it represents a paradigm for decadal predictability. In this study, we reappraise this hypothesis for several sub-regions of sub-Saharan West Africa using the new German contribution to the coupled model intercomparison project phase 5 (CMIP5) near-term prediction system. In addition, we assume that dynamical downscaling of the global decadal predictions leads to an enhanced predictive skill because enhanced resolution improves the atmospheric response to oceanic forcing and land-surface feedbacks. Based on three regional climate models, a heterogeneous picture is drawn: none of the regional climate models outperforms the global decadal predictions or all other regional climate models in every region nor decade. However, for every test case at least one regional climate model was identified which outperforms the global predictions. The highest predictive skill is found in the western and central Sahel Zone with correlation coefficients and mean-square skill scores exceeding 0.9 and 0.8, respectively.

Subseasonal Predictability of Boreal Summer Monsoon Rainfall from Ensemble Forecasts

Subseasonal forecast skill over the broadly defined North American (NAM), West African (WAM) and Asian (AM) summer monsoon regions is investigated using three Ensemble Prediction Systems (EPS) at sub-monthly lead times. Extended Logistic Regression (ELR) is used to produce probabilistic forecasts of weekly and week 3-4 averages of precipitation with starts in May-Aug, over the 1999-2010 period. The ELR tercile category probabilities for each model gridpoint are then averaged together with equal weight. The resulting Multi-Model Ensemble (MME) forecasts exhibit good reliability, but have generally low sharpness for forecasts beyond one week; Multi-model ensembling largely removes negative values of the Ranked Probability Skill Score (RPSS) seen in individual forecasts, and broadly improves the skill obtained in any of the three individual models except for the AM. The MME week 3-4 forecasts have generally higher RPSS and comparable reliability over all monsoon regions, compared to week 3 or week 4 forecast separately. Skill is higher during La Nina compared to El Nino and ENSO-neutral conditions over the 1999-2010 period, especially for the NAM. Regionally averaged RPSS is significantly correlated with the Maden-Julian Oscillation (MJO) for the AM and WAM. Our results indicate potential for skillful predictions at subseasonal time-scales over the three summer monsoon regions of the Northern Hemisphere.

Recent assessment of West African summer monsoon daily rainfall trends

This study analyses observed spatial trends in the summer monsoon rainfall over West Africa from 1998 to 2013 using two gridded observation datasets. The trends are calculated with the Kendall’s tau based slope estimator. Results show significant changes of the West African summer monsoon rainfall. Increases in the summer monsoon rainfall (measured as daily mean rainfall, frequency of wet days or extreme rainfall events) are observed over Sahel and decreases are observed along the Guinea Coast. Also, instead of the agreement between both observation datasets, they show some differences which can be attributed to the difference in their spatial resolution.

Dust induced changes on the West African summer monsoon features

ABSTRACTDust generation and transportation from North Africa are thought to modulate the West African Monsoon (WAM) features. In this study, we investigated the relationship between the Saharan Air Layer located above Atlantic Ocean (OSAL) and WAM features, including Monsoon flow, African Easterly Jet (AEJ) and Tropical Easterly Jet (TEJ) over West Africa using the RegCM4 regional model at 30 km grid resolution. Two sets of experiments with and without dust load were performed between 2007 and 2013 over the simulation domain, encompassing the whole of West Africa and a large part of the adjacent Atlantic Ocean. An intercomparison of the two simulations shows that dust load into the atmosphere greatly influences both the wind and temperature structure at different levels, resulting in the observed changes in the main features of the WAM system during summer. These changes lead to a westward shift with a slight strengthening of AEJ core over tropical Atlantic and weakening of both TEJ and monsoon flux penetration over land. In addition, despite running the RegCM4 with prescribed sea surface temperature, a correlation has been found between Aerosol Optical Depths in OSAL and WAM dynamics suggesting a mechanistic link between dust and WAM well reproduced by RegCM4.

Why Do Global Climate Models Struggle to Represent Low-Level Clouds in the West African Summer Monsoon?

Abstract Climate models struggle to realistically represent the West African monsoon (WAM), which hinders reliable future projections and the development of adequate adaption measures. Low-level clouds over southern West Africa (5°–10°N, 8°W–8°E) during July–September are an integral part of the WAM through their effect on the surface energy balance and precipitation, but their representation in climate models has received little attention. Here 30 (20) years of output from 18 (8) models participating in phase 5 of the Coupled Model Intercomparison Project (Year of Tropical Convection) are used to identify cloud biases and their causes. Compared to ERA-Interim reanalyses, many models show large biases in low-level cloudiness of both signs and a tendency to too high elevation and too weak diurnal cycles. At the same time, these models tend to have too strong low-level jets, the impact of which is unclear because of concomitant effects on temperature and moisture advection as well as turbulent mixing. Part of the differences between the models and ERA-Interim appear to be related to the different subgrid cloud schemes used. While nighttime tendencies in temperature and humidity are broadly realistic in most models, daytime tendencies show large problems with the vertical transport of heat and moisture. Many models simulate too low near-surface relative humidities, leading to insufficient low cloud cover and abundant solar radiation, and thus a too large diurnal cycle in temperature and relative humidity. In the future, targeted model sensitivity experiments will be needed to test possible feedback mechanisms between low clouds, radiation, boundary layer dynamics, precipitation, and the WAM circulation.

Impact of GCM boundary forcing on regional climate modeling of West African summer monsoon precipitation and circulation features

In this study, the latest version of the International Centre for Theoretical Physics Regional Climate Model (RegCM4) driven by three CMIP5 Global Climate Models (GCMs) is used at 25 km grid spacing over West Africa to investigate the impact of lateral boundary forcings on the simulation of monsoon precipitation and its relationship with regional circulation features. We find that the RegCM4 experiments along with their multimodel ensemble generally reproduce the location of the main precipitation characteristics over the region and improve upon the corresponding driving GCMs. However, the provision of different forcing boundary conditions leads to substantially different precipitation magnitudes and spatial patterns. For instance, while RegCM4 nested within GFDL-ESM-2M and HadGEM2-ES exhibits some underestimations of precipitation and an excessively narrow Intertropical Convergence Zone, the MPI-ESM-MR driven run produces precipitation spatial distribution and magnitudes more similar to observations. Such a superior performance originates from a much better simulation of the interactions between baroclinicity, temperature gradient and African Easterly Jet along with an improved connection between the Isentropic Potential Vorticity, its gradient and the African Easterly Waves dynamics. We conclude that a good performing GCM in terms of monsoon dynamical features (in this case MPI-ESM-MR) is needed to drive RCMs in order to achieve a better representation of the West Africa summer monsoon precipitation.

Cloud properties during active and break spells of the West African summer monsoon from CloudSat–CALIPSO measurements

High resolution of daily rainfall dataset from the Tropical Rainfall Measuring Mission (TRMM) was used to identify active and break cloud formation periods. The clouds were characterized based on CloudSat-CALIPSO satellite images over West Africa during the summer monsoon during the period 2006–2010. The active and break periods are defined as the periods during the peak monsoon months of June to August when the normalized anomaly of rainfall over the monsoon core zone is greater than 0.9 or less than −0.9 respectively, provided the criteria is satisfied for at least three consecutive days. It is found that about 90% of the break period and 66.7% of the active spells lasted 3–4 days. Active spells lasting duration of about a week were observed while no break spell had such a long span. Cloud macrophysical (cloud base height (CBH), cloud top height (CTH) and cloud geometric depth (∆H), microphysical (cloud liquid water content, (LWC), liquid number concentration (LNC), liquid effective radius, ice water content (IWC), ice number concentration (INC) and ice effective radius) and radiative (heating rate properties) over South Central West Africa (5–15°N; 15°W–10°E) during the active and break spells were also analyzed. High-level clouds are more predominant during the break periods compared to the active periods. Active spells have lower INC compared to the break spells. Liquid water clouds are observed to have more radiative forcing during the active than break periods while ice phase clouds bring more cooling effect during the break spells compared to the active spells.

Impact of land cover characterization on regional climate modeling over West Africa

The impact of high resolution modern vegetation cover on the West African climate is examined using the International Centre for Theoretical Physics Regional Climate Model implementing the NCAR Community Land Model. Two high resolution 25 km long-term simulations driven by the output from a coarser 50-km resolution simulation are performed for the period 1998–2010. One high resolution simulation uses an earlier and coarser-resolution version of plant functional type distribution and leaf area index, while the other uses a more recent, higher-quality, and finer-resolution version of the data. The results indicate that the new land cover distribution substantially alters the distribution of temperature with warming in Central Nigeria, northern Gulf of Guinea and part of the Sahel due to the replacement of C4 grass with corn; and cooling along the coastlines of the Gulf of Guinea and in Central Africa due to the replacement of C4 grass with tropical broadleaf evergreen trees. Changes in latent heat flux appear to be largely responsible for these temperature changes with a net decrease (increase) in regions of warming (cooling). The improved land cover distribution also results in a wetter monsoon season. The presence of corn tends to favor larger precipitation amounts via more intense events, while the presence of tropical broadleaf evergreen trees tends to favor the occurrence of both more intense and more frequent events. The wetter conditions appear to be sustained via (1) an enhanced soil moisture feedback; and (2) elevated moisture transport due to increased low-level convergence in regions south of 10N where the most substantial land cover differences are present. Overall the changes induced by the improved vegetation cover improve, to some extent, the performance of the high resolution regional climate model in simulating the main West African summer monsoon features.

Daily characteristics of West African summer monsoon precipitation in CORDEX simulations

We analyze and intercompare the performance of a set of ten regional climate models (RCMs) along with the ensemble mean of their statistics in simulating daily precipitation characteristics during the West African monsoon (WAM) period (June–July–August–September). The experiments are conducted within the framework of the COordinated Regional Downscaling Experiments for the African domain. We find that the RCMs exhibit substantial differences that are associated with a wide range of estimates of higher-order statistics, such as intensity, frequency, and daily extremes mostly driven by the convective scheme employed. For instance, a number of the RCMs simulate a similar number of wet days compared to observations but greater rainfall intensity, especially in oceanic regions adjacent to the Guinea Highlands because of a larger number of heavy precipitation events. Other models exhibit a higher wet-day frequency but much lower rainfall intensity over West Africa due to the occurrence of less frequent heavy rainfall events. This indicates the existence of large uncertainties related to the simulation of daily rainfall characteristics by the RCMs. The ensemble mean of the indices substantially improves the RCMs’ simulated frequency and intensity of precipitation events, moderately outperforms that of the 95th percentile, and provides mixed benefits for the dry and wet spells. Although the ensemble mean improved results cannot be generalized, such an approach produces encouraging results and can help, to some extent, to improve the robustness of the response of the WAM daily precipitation to the anthropogenic greenhouse gas warming.

Assessing the Capabilities of Three Regional Climate Models over CORDEX Africa in Simulating West African Summer Monsoon Precipitation

This study evaluates the ability of three Regional Climate Models (RCMs) used in Coordinated Regional Climate Downscaling Experiment (CORDEX) to simulate the characteristics of rainfall pattern during the West Africa Summer Monsoon from 1998 to 2008. The seasonal climatology, annual rainfall cycles, and wind fields of the RCMs output were assessed over three homogenous subregions and validated using precipitation data from eighty-one (81) ground observation stations and TRMM satellite data. Furthermore, the ability of the RCMs to simulate response to El Nino and La Nina events was assessed. Results show that two of the RCMs (RCA and REMO) simulated the main features of the rainfall climatology and associated dynamics over the three subregions (Guinea Coast, Savannah, and Sahel) of West Africa. The RCMs also capture the African Easterly Jet (AEJ) and Tropical Easterly Jet (TEJ) with little variations in position and intensity. Analysis shows significant biases in individual models depending on subregion and season under consideration which may be attributed to strong cyclonic circulation observed at 850 mb pressure level. In general, the study shows RCA and REMO fairly simulate West Africa rainfall adequately and can therefore be used for the assessment of West African Summer Monsoon and future climate projections.

Solar forcing of Nile discharge and sapropel S1 formation in the early to middle Holocene eastern Mediterranean

AbstractWe present high‐resolution records for oxygen isotopes of the planktic foraminifer Globigerinoides ruber (δ18Oruber) and bulk sediment inorganic geochemistry for Holocene‐age sediments from the southeast Mediterranean. Our δ18Oruber record appears to be dominated by Nile discharge rather than basin‐scale salinity/temperature changes. Nile discharge was enhanced in the early to middle Holocene relative to today. The timing of the long‐term maximum in Nile discharge during the early Holocene corresponds to the timing of maximum intensity of the Indian Ocean‐influenced Southwest Indian summer monsoon (SIM). This coincidence suggests a major influence of an Indian Ocean moisture source on Nile discharge in the early to middle Holocene, while, presently, the Atlantic Ocean is the main moisture source. Nile discharge was highly variable on multicentennial time scale during the early to middle Holocene, being strongly influenced by variable solar activity. This solar‐driven variability is also recorded in contemporaneous SIM records, however, not observed in an Atlantic Ocean‐derived West African summer monsoon record from the Holocene. This supports the hypothesis that the Indian Ocean moisture source predominantly controlled Nile discharge at that time. Solar‐driven variability in Nile discharge also influenced paleoenvironmental conditions in the eastern Mediterranean. Bulk sediment Ba/Al and V/Al, used as indicators for (export) productivity and redox conditions, respectively, varied both in response to solar forcing on multicentennial time scales. We suggest that changes in Nile discharge on these time scales have been concordant with nutrient inputs to, and shallow ventilation of, the eastern Mediterranean.

Interdecadal variation of the West African summer monsoon during 1979–2010 and associated variability

This paper addresses the interdecadal variation of the West African summer monsoon (WASM) along with its background of atmospheric circulation and possible physical mechanism over the past 32 years (1979–2010). It is indicated that the WASM starts to strengthen from 1998 as the rainfall begins to increase over western West Africa on the whole, which shows a new interdecadal variation. In this interdecadal variation, the strengthened ascending motion corresponding to enhanced divergence (convergence) movement on the upper (lower) troposphere is prone to develop the local circulation of the monsoon. Moreover, the strengthened southwestern (eastern) wind on the lower (upper) level leads to more moisture from the Atlantic and the Gulf of Guinea transported to the West African continent. In addition, the summer subtropical high over the north Atlantic and western West Africa is strong and northward, and the tropical east wind is also strong. Statistically, the weaker (stronger) the spring North Atlantic Oscillation (NAO) is, the stronger (weaker) the tropical easterly is, and then the WASM is also stronger. But the effect of the NAO on the decadal variation of the WASM is not so significant from the north Atlantic anomaly sensitivity simulation with a single model. This is also an indication that the relationship between the WASM and NAO is complicated in an interdecadal time scale and is needed further study. In terms of sea surface temperature (SST) variation, the tendency is toward warming in the subtropical north Pacific, the south Pacific and north Atlantic. Numerical simulation experiments and data analysis show that the SST variation in the north Pacific plays an important role in the latest interdecadal strengthening of the WASM during the past 32 years, while the influences of the south Pacific and the north Atlantic SST anomalies are not so significant to the associated atmospheric circulation changes.

Propagation of Convective Complexes Observed by TRMM in the Eastern Tropical Atlantic

Precipitation maxima during the West African summer monsoon propagate generally westward in tandem with African easterly waves. A heretofore unreported, repeating pattern of northward drift of precipitation maxima is detected on Tropical Rainfall Measurement Mission (TRMM satellite) time-latitude distributions of daily accumulations over the eastern tropical Atlantic. Corresponding 3-hourly TRMM accumulations show that the northward drifting envelopes of precipitation during August 2006 are often comprised of individual swaths propagating towards the southwest, presumably as mesoscale squall lines. The implied northward drift on the time-latitude distribution is a component of a resultant northwestward movement. The study examines the entire available record of TRMM precipitation observations, 1998-2010, to summarize TRMM maxima propagation over the eastern tropical Atlantic. Meridional displacements of precipitation maxima are most prevalent in June-September 2006, occurring less frequently during other summers. An investigation of geopotential and circulation fields, limited to two case studies, suggests mechanisms to explain some of the observed propagation of TRMM maxima. In one event, northward drift of the precipitation envelope is consistent with the corresponding displacement of the intertropical convergence zone trough, although the southwest propagation of individual mesoscale convection maxima does not correspond to any synoptic feature on reanalysis circulation or reanalysis downscaled by a regional model. One speculation is that southwestward propagation of precipitation maxima could be caused by regeneration of convection at outflow boundaries of mature thunderstorms.

Regional Climate Model Sensitivity to Domain Size for the Simulation of the West African Summer Monsoon Rainfall

We use the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM3) to study the impact of different domain sizes on the simulation of the West African summer monsoon rainfall and circulation features. RegCM3 simulates drier conditions over the default domain (RegCM-D1) and its westward extension (RegCM-D2), much less dryness over the eastward extended domain (RegCM-D3) and excessive wetness in the domain extended northward into the extratropical regions (RegCM-D4). This overestimation is related to the existence of larger source of humidity due to the inclusion of a more significant portion of the Atlantic Ocean and to a weakening of the African Easterly Jet (AEJ), which both favor stronger westerlies advecting moisture towards the land. The best performance is, however, captured in the RegCM-D3 experiment, and this originates from a simulation of moderate westerly moisture fluxes along with a stronger AEJ and occurrences of more frequent African Easterly Waves (AEWs). Therefore, the choice of the domain for regional climate model simulation of the West African summer monsoon rainfall is of critical importance, and caution needs to be taken to account for the main regional forcings including mostly the necessary humidity sources of the tropical Atlantic Ocean and the AEWs genesis region upstream of Sudanese Highlands.

The vertical cloud structure of the West African monsoon: A 4 year climatology using CloudSat and CALIPSO

The West African summer monsoon (WAM) is an important driver of the global climate and locally provides most of the annual rainfall. A solid climatological knowledge of the complex vertical cloud structure is invaluable to forecasters and modelers to improve the understanding of the WAM. In this paper, 4 years of data from the CloudSat profiling radar and CALIPSO are used to create a composite zonal mean vertical cloud and precipitation structure for the WAM. For the first time, the near-coincident vertical radar and lidar profiles allow for the identification of individual cloud types from optically thin cirrus and shallow cumulus to congestus and deep convection. A clear diurnal signal in zonal mean cloud structure is observed for the WAM, with deep convective activity enhanced at night producing extensive anvil and cirrus, while daytime observations show more shallow cloud and congestus. A layer of altocumulus is frequently observed over the Sahara at night and day, extending southward to the coastline, and the majority of this cloud is shown to contain supercooled liquid in the top. The occurrence of deep convective systems and congestus in relation to the position of the African easterly jet is studied, but only the daytime cumulonimbus distribution indicates some influence of the jet position.

The impact of deep convection on the West African summer monsoon climate: a regional climate model sensitivity study

AbstractThe role of the representation of deep convection on key elements of the West African summer monsoon climate is addressed using the Regional Climate Model RegCM3. Two simulations in which a scheme of deep convection is activated and then turned off are performed and intercompared. Results show that the presence of deep convective heating along the intertropical convergence zone sustains increased lower‐level baroclinicity favoring intensification of the jet core and leading to a more realistic African easterly jet. In addition, although the isentropic potential vorticity (IPV) is lower when the convection scheme is switched off, African easterly waves (AEWs) are still generated and propagate westwards but they dissipate around the west coast. Substantial differences between the two simulations occur mainly at the 6‐ to 9‐day time‐scale over land, when much weaker activity is simulated in the absence of convection. This indicates that orographic friction and low‐level large‐scale moisture convergence, generating high values of latent heat and IPV, may play the dominant role in the genesis and growth of AEWs and that deep convection acts to strengthen the overall wave activity and to favor their west coast development. Copyright © 2011 Royal Meteorological Society