Open AccessTrains of African Easterly Waves and Their Relationship to Tropical Cyclone Genesis in the Eastern Atlantic
Author(s) -
Abdou Lahat Dieng,
Saïdou Moustapha Sall,
Laurence Eymard,
Marion Leduc-Leballeur,
Alban Lazar
Publication year - 2017
Publication title -
monthly weather review
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.862
H-Index - 179
eISSN - 1520-0493
pISSN - 0027-0644
DOI - 10.1175/mwr-d-15-0277.1
Subject(s) - african easterly jet , tropical wave , geology , trough (economics) , tropical cyclone , climatology , tropical cyclogenesis , intertropical convergence zone , tropical atlantic , cyclogenesis , orographic lift , oceanography , cyclone (programming language) , geography , meteorology , sea surface temperature , precipitation , field programmable gate array , computer science , computer hardware , economics , macroeconomics
In this study, the relationship between trains of African easterly waves (AEWs) and downstream tropical cyclogenesis is studied. Based on 19 summer seasons (July–September from 1990 to 2008) of ERA-Interim reanalysis fields and brightness temperature from the Cloud User Archive, the signature of AEW troughs and embedded convection are tracked from the West African coast to the central Atlantic. The tracked systems are separated into four groups: (i) systems originating from the north zone of the midtropospheric African easterly jet (AEJ), (ii) those coming from the south part of AEJ, (iii) systems that are associated with a downstream trough located around 2000 km westward (termed DUO systems), and (iv) those that are not associated with such a close downstream trough (termed SOLO systems). By monitoring the embedded 700-hPa-filtered relative vorticity and 850-hPa wind convergence anomaly associated with these families along their trajectories, it is shown that the DUO generally have stronger dynamical structure and statistically have a longer lifetime than the SOLO ones. It is suggested that the differences between them may be due to the presence of the previous intense downstream trough in DUO cases, enhancing the low-level convergence behind them. Moreover, a study of the relationship between system trajectories and tropical depressions occurring between the West African coast and 40°W showed that 90% of tropical depressions are identifiable from the West African coast in tracked systems, mostly in the DUO cases originating from the south zone of the AEJ.