Case study of an intense african easterly wave

Gareth Berry, Chris Thorncroft

Research output: Contribution to journalArticleResearchpeer-review

144 Citations (Scopus)

Abstract

The life cycle of an intense African easterly wave (AEW) over the African continent is examined using European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses, Meteosat satellite images, and synoptic observations. This system, the strongest AEW of 2000, can be tracked from central North Africa into the eastern Atlantic Ocean, where it is associated with the genesis of Hurricane Alberto. Synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity (PV), allowing exploration at the role of multiple scales in the evolution of this AEW. The authors analysis promotes the division of the AEW life cycle into three distinctive phases. (i) Initiation: The AEW development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in Sudan. This convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical North Africa. (ii) Baroclinic growth: A low-level warm anomaly, generated close to the initial convection, interacts with a midtropospheric strip of high PV that exists on the cyclonic shear side of the African easterly jet, which is consistent with baroclinic growth. This interaction is reinforced by the generation of subsynoptic scale PV anomalies by deep convection that is embedded within the baroclinic AEW structure. (iii) West coast development: Near the West African coast, the baroclinic structure weakens, but convection is maintained. The midtropospheric PV anomalies embedded within the AEW merge with one another and with PV anomalies that are generated by convection over topography ahead of the system. These mergers result in the production of a significant PV feature that leaves the West African coast and rapidly undergoes tropical cyclogenesis
Original languageEnglish
Pages (from-to)752 - 766
Number of pages15
JournalMonthly Weather Review
Volume133
Issue number4
DOIs
Publication statusPublished - 2005
Externally publishedYes

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