Generation of the African Easterly Jet and Its Role in Determining West African Precipitation

Cook, Kerry H.

doi:10.1175/1520-0442(1999)012<1165:gotaej>2.0.co;2

Cited by 343 publications

(347 citation statements)

References 31 publications

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“…The more southerly location of the AEJ in HadGEM3-RA and HadGEM3 is consistent with the more southerly location of the region of zonal temperature gradient (see Fig. 3c-f), as the AEJ is associated with the surface temperature gradient (Cook 1999;Thorncroft and Blackburn 1999). These results suggest that the models' southward shift of the zone of temperature gradient may be associated with a warm bias in the Sahel related to the dry bias, and thus the convection scheme may be implicated.…”

Section: Temperature Climatologysupporting

confidence: 75%

“…The models reproduce well the general features of the observed pattern including the meridional surface temperature gradient between Guinea Coast and the Saharan desert. This temperature gradient is instrumental to the formation and evolution of the African Easterly Jet (AEJ) (Cook 1999;Thorncroft and Blackburn 1999). HadGEM3 and HadGEM3-RA errors are characterized by cold biases over the Sahara, largely over and to the east of the observed 2 m temperature maximum, and warm biases between 10°N and 15°N.…”

Section: Temperature Climatologymentioning

confidence: 99%

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Simulation of the West African monsoon onset using the HadGEM3-RA regional climate model

et al. 2014

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Section: Temperature Climatologysupporting

confidence: 75%

Section: Temperature Climatologymentioning

confidence: 99%

Simulation of the West African monsoon onset using the HadGEM3-RA regional climate model

et al. 2014

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“…Figure 5(b) shows the potential temperature anomaly at 850 hPa, below the jet level, overlaid by the vorticity structure: we anticipate from previous studies (Reed et al, 1977;Parker et al, 2005a;Cook, 1999) that the AEW and AEJ structures resemble thermal wind balance, with the jet-level winds linked to the thermal patterns in the layer beneath. The temperature anomaly shows a cool region over the western branch of the system.…”

Section: Thermal Structurementioning

confidence: 83%

Anatomy of an observed African easterly wave in July 2006

Bain

Parker

Dixon

et al. 2011

Quart J Royal Meteoro Soc

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The detailed structure of an African easterly wave (AEW) observed during the AMMA field campaign is analysed. The wave was present from 25 to 29 July 2006. A complex circulation pattern was observed: the overall structure of convection and the positive vorticity of the trough region had an elongated inverted-V appearance, wrapped around an area of low winds and clear skies. Satellite imagery showed that the AEW was a significant influence on the modulation of convection on the large scale.The wave was identified initially through its strong signature on soil moisture and convection. The AEW structure observed was not anticipated and has not been discussed in previous literature. In addition, wave tracking using a Hovmöller diagram of meridional winds did not detect the wave, and a Hovmöller of vorticity showed the wave moved at a slower speed than other AEWs in July.New schematics explaining the structure are presented, describing the case as observed by satellites and analysed by a limited-area version of the Met Office Unified Model. It is proposed that the positive vorticity branches of the inverted-V can be regarded as analogous to atmospheric fronts, with characteristic gradients in winds and thermodynamic properties, acting as locations for enhanced convection. The implications of the new case are discussed in relation to previous theory and it is suggested that the accepted model of an idealised AEW is incomplete and should be extended to include more complex structures.

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“…7b. The African easterly jet, which forms over the strongest surface temperature gradients when Coriolis accelerations act on the northerly outflow from the Saharan High (Cook 1999), is located at about 15°N. Both the Saharan high and the African easterly jet are represented more strongly, but reasonably, in the RCM (Fig.…”

Section: Model Validationmentioning

confidence: 94%

Northern African climate at the end of the twenty-first century: an integrated application of regional and global climate models

2009

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A method for simulating future climate on regional space scales is developed and applied to northern Africa. Simulation with a regional model allows for the horizontal resolution needed to resolve the region's strong meridional gradients and the optimization of parameterizations and land-surface model. The control simulation is constrained by reanalysis data, and realistically represents the present day climate. Atmosphere-ocean general circulation model (AOGCM) output provides SST and lateral boundary condition anomalies for 2081-2100 under a business-as-usual emissions scenario, and the atmospheric CO 2 concentration is increased to 757 ppmv. A ninemember ensemble of future climate projections is generated by using output from nine AOGCMs. The consistency of precipitation projections for the end of the twenty-first century is much greater for the regional model ensemble than among the AOGCMs. More than 77% of ensemble members produce the same sign rainfall anomaly over much of northern Africa. For West Africa, the regional model projects wetter conditions in spring, but a midsummer drought develops during June and July, and the heat stoke risk increases across the Sahel. Wetter conditions resume in late summer, and the likelihood of flooding increases. The regional model generally projects wetter conditions over eastern Central Africa in June and drying during August through September. Severe drought impacts parts of East Africa in late summer. Conditions become wetter in October, but the enhanced rainfall does not compensate for the summertime deficit. The risk of heat stroke increases over this region, although the threat is not projected to be as great as in the Sahel.

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Generation of the African Easterly Jet and Its Role in Determining West African Precipitation

Cited by 343 publications

References 31 publications

Simulation of the West African monsoon onset using the HadGEM3-RA regional climate model

Simulation of the West African monsoon onset using the HadGEM3-RA regional climate model

Anatomy of an observed African easterly wave in July 2006

Northern African climate at the end of the twenty-first century: an integrated application of regional and global climate models

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