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African Easterly Jet: Barotropic Instability, Waves, and CyclogenesisThis study investigates the structure of the African easterly jet, focusing on instability processes on a seasonal and subseasonal scale, with the goal of identifying features that could provide increased predictability of Atlantic tropical cyclogenesis. The Modern-Era Retrospective Analysis for Research and Applications (MERRA) is used as the main investigating tool. MERRA is compared with other reanalyses datasets from major operational centers around the world and was found to describe very effectively the circulation over the African monsoon region. In particular, a comparison with precipitation datasets from the Global Precipitation Climatology Project shows that MERRA realistically reproduces seasonal precipitation over that region. The verification of the generalized Kuo barotropic instability condition computed from seasonal means is found to have the interesting property of defining well the location where observed tropical storms are detected. This property does not appear to be an artifact of MERRA and is present also in the other adopted reanalysis datasets. Therefore, the fact that the areas where the mean flow is unstable seems to provide a more favorable environment for wave intensification, could be another factor to include-in addition to sea surface temperature, vertical shear, precipitation, the role of Saharan air, and others-among large-scale forcings affecting development and tropical cyclone frequency. In addition, two prominent modes of variability are found based on a spectral analysis that uses the Hilbert-Huang transform: a 2.5-6-day mode that corresponds well to the African easterly waves and also a 6-9-day mode that seems to be associated with tropical- extratropical interaction.
Document ID
20140001060
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1175/2011JCLI4241.1
Authors
Wu, Man-Li C (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Reale, Oreste (Universities Space Research Association Columbia, MD, United States)
Schubert, Siegfried D. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Suarez, Max J. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Thorncroft, Chris D. (State Univ. of New York Albany, NY, United States)
Date Acquired
March 6, 2014
Publication Date
March 1, 2012
Publication Information
Publication: Journal of Climate
Volume: 25
Issue: 5
Subject Category
Meteorology And Climatology
Report/Patent Number
GSFC-E-DAA-TN9041
Funding Number(s)
CONTRACT_GRANT: NNG11HP16A
Distribution Limits
Public
Copyright
Public Use Permitted.

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