Atlantic Tropical Cyclogenesis: A Three-Way Interaction between an African Easterly Wave, Diurnally Varying Convection, and a Convectively Coupled Atmospheric Kelvin Wave

Abstract

This paper explores a three-way interaction between an African easterly wave (AEW), the diurnal cycle of convection over the Guinea Highlands (GHs), and a convectively coupled atmospheric equatorial Kelvin wave (CCKW). These interactions resulted in the genesis of Tropical Storm Debby over the eastern tropical Atlantic during late August 2006. The diurnal cycle of convection downstream of the GHs during the month of August is explored. Convection associated with the coherent diurnal cycle is observed off the coast of West Africa during the morning. Later, convection initiates over and downstream of the GHs during the afternoon. These convective features were pronounced during the passage of the pre-Debby AEW. The superposition between the convectively active phase of a strong CCKW and the pre-Debby AEW occurred shortly after merging with the diurnally varying convection downstream of the GHs. The CCKW-AEW interaction preceded tropical cyclogenesis by 18 h. The CCKW provided a favorable environment for deep convection. An analysis of highamplitude CCKWs over the tropical Atlantic and West Africa during the Northern Hemisphere boreal summer highlights a robust relationship between CCKWs and the frequency of tropical cyclogenesis. Tropical cyclogenesis is found to be less frequent immediately prior to the passage of the convectively active phase of the CCKW, more frequent during the passage, and most frequent just after the passage.

The “Year” of Tropical Convection (May 2008–April 2010): Climate Variability and Weather Highlights

“…The YOTC dataset should be exploited to ascertain the relative roles of these factors. Finally, it is now well known that Kelvin waves can significantly modulate rainfall and can both trigger and intensify EWs (e.g., Mekonnen et al 2008;Ventrice et al 2011). Figure 4 highlights the presence of Kelvin waves in spring, when they are known to be important in the equatorial African region (Nguyen and Duvel 2008), but they are also known to influence the Guinea coastal region of West Africa (not shown).…”

The XWS open access catalogue of extreme European windstorms from 1979 to 2012

“…Tropical cyclone catalogues are an essential resource for the scientific community and are used to understand how climate variability modulates the development and activity of tropical cyclones (e.g. Ventrice et al, 2012) and for evaluating climate models (e.g. Strachan et al, 2013;Manganello et al, 2012).…”

Synoptic Kelvin type perturbation waves over Congo basin over the period 1979–2010

“…CCKW have been shown to modify the background state and to intensify westward moving features travelling through its convectively active phase. Ventrice et al (2012) explored the superposition between the convectively active phase of a strong CCKW and an African Easterly Wave that occurred downstream of the Guinea Highlands. The CCKW provided a favourable environment for deep convection.…”

“…An analysis of high amplitude CCKW over the tropical Atlantic and West Africa during the Northern Hemisphere boreal summer ) highlights a robust relationship between CCKW and the frequency of tropical cyclogenesis. Tropical cyclogenesis was found to be less frequent immediately prior to the passage of the convectively active phase of the CCKW (Ventrice et al, 2012). Wang and Fu (2007) have examined the role of convectively coupled Kelvin waves during the boreal spring in tropical Africa.…”