The impact of vertical resolution on regional model simulation of the west African summer monsoon

Authors

  • Leonard M. Druyan,

    Corresponding author
    1. Center for Climate Systems Research, Earth Institute at Columbia University, 2880 Broadway, New York NY 10025 USA
    2. The NASA/Goddard Institute for Space Studies, 2880 Broadway, New York NY 10025 USA
    • Center for Climate Systems Research, Earth Institute at Columbia University, 2880 Broadway, New York NY 10025 USA.
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  • Matthew Fulakeza,

    1. Center for Climate Systems Research, Earth Institute at Columbia University, 2880 Broadway, New York NY 10025 USA
    2. The NASA/Goddard Institute for Space Studies, 2880 Broadway, New York NY 10025 USA
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  • Patrick Lonergan

    1. Center for Climate Systems Research, Earth Institute at Columbia University, 2880 Broadway, New York NY 10025 USA
    2. The NASA/Goddard Institute for Space Studies, 2880 Broadway, New York NY 10025 USA
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Abstract

The RM3 regional climate model is used to simulate the west African summer monsoon for six June–September seasons using NCEP reanalysis data for lateral boundary forcing. The study compares the performance of the previously published 16-level version with a newly tested 28-level version, both running on a horizontal grid with 0.5° spacing, in order to determine what improvements in simulations are achieved by increased vertical resolution. Comparisons between the performances include diagnostics of seasonal mean precipitation rates and circulation, vertical profiles of cumulus heating rates, frequencies of shallow and deep convection and diagnostics related to transient African easterly waves (AEWs). The characteristics of a composite AEW simulated at both vertical resolutions are presented. Results show that the most significant impact of increasing the vertical resolution is stronger circulation, stronger vertical wind shear and higher amplitude AEWs. The simulations with higher vertical resolution also achieve higher peaks of cumulus latent heating rates. Spatial–temporal correlations between simulated daily 700 mb meridional winds versus corresponding NCEP reanalysis data and simulated daily precipitation versus estimates from the Tropical Rainfall Measurement Mission (TRMM) archive were equally high at both vertical resolutions. Copyright © 2007 Royal Meteorological Society

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