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

Abstract

A 13-year (1998-2010) climatology of mesoscale convective characteristics associated with the West African monsoon are investigated using precipitation radar and passive microwave data from the NASA Tropical Rainfall Measuring Mission satellite. Seven regions defined as continental northeast and northwest, southeast and southwest, coastal, and maritime north and south are compared to analyse zonal and meridional differences. Data are categorized according to identified African easterly wave (AEW) phase and when no wave is present. While some enhancements are observed in association with AEW regimes, regional differences were generally more apparent than wave vs. no-wave differences. Convective intensity metrics confirm that land-based systems exhibit stronger characteristics, such as higher storm top and maximum 30 dBZ heights and significant 85 GHz brightness temperature depressions. Continental systems also contain a lower fraction of points identified as stratiform. Results suggest that precipitation processes also varied depending upon region and AEW regime, with warm-rain processes more apparent over the ocean and the southwest continental region and ice-based microphysics more dominant over land, including mixed-phase processes. AEW regimes did show variability in stratiform fraction and ice and liquid water content, suggesting modulation of mesoscale characteristics possibly through feedback with the synoptic environment.

Convection over Tropical Africa and the East Atlantic during the West African Monsoon: Regional and Diurnal Variability

“…Schumacher and Houze (2006) found that conditional convective rain rates are greatest over the Sahel and related this to the high conditional instability and frequency of convective systems with deep intense updrafts in the region. In addition, Guy and Rutledge (2012) found that high echo-top convection is most frequent in the northerly phase of African easterly waves where there is a tongue of high low-level u e air (Berry andThorncroft 2005, 2012). In addition, Guy and Rutledge (2012) found that high echo-top convection is most frequent in the northerly phase of African easterly waves where there is a tongue of high low-level u e air (Berry andThorncroft 2005, 2012).…”

Comparing the Convective Structure and Microphysics in Two Sahelian Mesoscale Convective Systems: Radar Observations and CRM Simulations

“…Guy et al (2011) showed that precipitation and MCS size are both larger in this region when an AEW is present. Similar life cycle phase and system morphology allowed direct comparison of the two events, though the size difference (greater horizontal coverage of the 8 September case) and temporal extents within the radar domain (8 and 11 h for the 14 July and 8 September cases, respectively) should be noted.…”

“…Radar reflectivity Z volume scans were partitioned into convective and stratiform components using the Steiner et al (1995) algorithm, which uses a convective threshold value to identify convective cores, along with a convective peakedness criterion that evaluates the surrounding pixels for convective classification. Further details regarding MIT radar data and processing can be found in Guy et al (2011).…”

“…A few studies note the existence of MCSs with no association to AEWs (Fink et al 2006;Laing et al 2008, Guy et al 2011. Analysis of ground-based radar data at continental, coastal, and maritime locations revealed that regional differences in convective characteristics were more apparent than differences between AEWs and no-wave events (Guy et al 2011); however, the system structure and duration exhibited variations according to synoptic-dynamic and local thermodynamic forcing.…”

“…Analysis of ground-based radar data at continental, coastal, and maritime locations revealed that regional differences in convective characteristics were more apparent than differences between AEWs and no-wave events (Guy et al 2011); however, the system structure and duration exhibited variations according to synoptic-dynamic and local thermodynamic forcing. A climatological analysis using 13 yr of Tropical Rainfall Measuring Mission (TRMM) data (precipitation radar and microwave) showed differences in stratiform fractions, microphysics, and ice and liquid water mass when subdivided by AEW phase and when no wave was present (Guy and Rutledge 2012).…”