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Climatology of Vertical Wind Shear over the Tropical Atlantic

Anantha R. AiyyerDepartment of Earth and Atmospheric Sciences, The University at Albany, State University of New York, Albany, New York

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Chris ThorncroftDepartment of Earth and Atmospheric Sciences, The University at Albany, State University of New York, Albany, New York

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Abstract

The spatiotemporal variability of the 200–850-hPa vertical wind shear over the tropical Atlantic is examined for a period of 46 yr. This work extends and updates past studies by considering a longer data record as well as a tropospheric-deep measure of vertical wind shear. Composite fields are constructed to illustrate the spatial pattern of the large-scale circulation associated with the mean and extreme cases of vertical shear within the tropical Atlantic. The contemporaneous relationship of vertical shear with El Niño–Southern Oscillation (ENSO) and Sahel precipitation are also examined. While the ENSO–shear correlation appears to have slightly strengthened during the past decade, the Sahel–shear correlation has become significantly degraded.

A combined empirical orthogonal function (EOF) analysis of the zonal and meridional components of the vertical shear reveals interannual and multidecadal modes. The leading EOF exhibits mainly interannual variability and is highly correlated with ENSO. The second EOF is associated with a multidecadal temporal evolution and is correlated with Sahel precipitation. Both EOFs correlate at the same level with tropical cyclones in the main development region of the tropical Atlantic.

Corresponding author address: Dr. Anantha R. Aiyyer, Dept. of Earth and Atmospheric Sciences, The University at Albany, State University of New York, Albany, ES 321, 1400 Washington Ave., Albany, NY 12222-0001. Email: aiyyer@atmos.albany.edu

Abstract

The spatiotemporal variability of the 200–850-hPa vertical wind shear over the tropical Atlantic is examined for a period of 46 yr. This work extends and updates past studies by considering a longer data record as well as a tropospheric-deep measure of vertical wind shear. Composite fields are constructed to illustrate the spatial pattern of the large-scale circulation associated with the mean and extreme cases of vertical shear within the tropical Atlantic. The contemporaneous relationship of vertical shear with El Niño–Southern Oscillation (ENSO) and Sahel precipitation are also examined. While the ENSO–shear correlation appears to have slightly strengthened during the past decade, the Sahel–shear correlation has become significantly degraded.

A combined empirical orthogonal function (EOF) analysis of the zonal and meridional components of the vertical shear reveals interannual and multidecadal modes. The leading EOF exhibits mainly interannual variability and is highly correlated with ENSO. The second EOF is associated with a multidecadal temporal evolution and is correlated with Sahel precipitation. Both EOFs correlate at the same level with tropical cyclones in the main development region of the tropical Atlantic.

Corresponding author address: Dr. Anantha R. Aiyyer, Dept. of Earth and Atmospheric Sciences, The University at Albany, State University of New York, Albany, ES 321, 1400 Washington Ave., Albany, NY 12222-0001. Email: aiyyer@atmos.albany.edu

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