Easterly wave regimes and associated convection over West Africa and tropical Atlantic: results from the NCEP/NCAR and ECMWF reanalyses

Regional comparison of West African convective characteristics: a TRMM‐based climatology

“…As mentioned previously, MCSs often travel faster than AEWs, and therefore life-cycle characteristics could be aliased to wave regimes other than the formative and decay stages. Despite this limitation, occurrence frequency results were consistent with previous studies (most of which concentrated on genesis/lysis of MCS with respect to AEW phase) that have found that deep convection occurs east of AEW troughs near the continental sites and west of and in the trough near the coast and Atlantic (Carlson, 1969;Payne and McGarry, 1977;Reed et al, 1977;Diedhiou et al, 1999;Fink et al, 2006;Kiladis et al, 2006;Laing et al, 2008). Fink and Reiner (2003) and Laing et al (2008), primarily using microwave and infrared observations for squall line and deep convective tracking, respectively, found a large fraction of systems were not associated with any AEW phase.…”

“…The zonal distributions of northern (ConNE, ConNW, Cos, MarN) and southern (ConSE, ConSW, MarS) regions correspond to two commonly identified AEW latitude tracks (Reed et al, 1977;Nitta et al, 1985;Diedhiou et al, 1999;Pytharoulis and Thorncroft, 1999;Thorncroft and Hodges, 2001;Fink and Reiner, 2003). The ConNE, Cos and MarN regions were contrasted for zonal variations and were chosen to correspond to ground-based radar locations used in Guy et al (2011).…”

“…Modulation of precipitation (and deep convective events) with synoptic disturbances in the form of African easterly waves (AEWs) has been suggested by many previous studies (Carlson, 1969;Burpee, 1974;Duvel, 1990;Diedhiou et al, 1999;Fink and Reiner, 2003;Gu et al, 2004;Petersen and Boccippio, 2004;Mekonnen et al, 2006;Guy et al, 2011). The wave disturbances, which may be initiated east of 20 • E (Berry et al, 2005;Thorncroft et al, 2008), are maximized near the AEJ level and progress westward at ∼ 8 m s −1 , with a wavelength of 2000-4000 km.…”

“…The wave disturbances, which may be initiated east of 20 • E (Berry et al, 2005;Thorncroft et al, 2008), are maximized near the AEJ level and progress westward at ∼ 8 m s −1 , with a wavelength of 2000-4000 km. Deep convection has been observed behind AEW troughs inland and in the eastern Atlantic and ahead of and within AEW troughs near the coast (Payne and McGarry, 1977;Reed et al, 1977;Duvel, 1990;Machado et al, 1993;Diedhiou et al, 1999;Kiladis et al, 2006). Westward-propagating MCSs in West Africa often move faster than AEW troughs (Aspliden et al, 1976;Fortune, 1980;Fink et al, 2006), and interact with the larger-scale environment through the transport of momentum (Moncrieff, 1992) and moisture (Lafore et al, 1988) and can reinforce cyclonic rotation when embedded in an AEW trough (Barthe et al, 2010).…”

Evidence of two independent modes of convection at intraseasonal timescale in the West African summer monsoon

“…Finally the NCEP-DOE AMIP-II Reanalysis (R-2) dataset, an updated version of the NCEP/NCAR reanalysis has been used to document the low-level circulation associated with the different intraseasonal modes of convection in the African monsoon. Several studies [Diedhiou et al, 1999;Sultan et al, 2003] have demonstrated the accuracy of the first version [Kalnay et al, 1996] of these reanalyzes in the description of the atmospheric circulation over West Africa, as well as high consistency with the IRD-rainfall and NOAA-OLR fields from synoptic to interannual timescales. The updated version of the reanalyzes shows significant improvements upon the first one in land surface parameters and land-ocean fluxes [Kanamitsu et al, 2002].…”