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Upper Tropospheric Waves in the Tropics. Part II. Association with Clouds in the Wavenumber-Frequency Domain

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  • 1 The Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, 84990, Israel
  • | 2 Department of Atmospheric Sciences, University of California, Los Angeles 90024
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Abstract

The relationship between the large-scale transient wave disturbances at the 200 mb level and the associated cloud field is studied in the latitude belt 20°S to 40°N based on wind and satellite-measured brightness data for the period June–August 1967. Space-time cross-spectral analysis is used to examine the degree of association of the wind and cloud fields in the wavenumber-frequency domain. The total time variance of the brightness field has a well-defined maximum near 10°N corresponding to a belt of sea surface temperature maximum. The divergence and relative vorticity as well as the brightness have a pronounced spatial scale of zonal wavenumber s ≈ 10 at this latitude. The major component contributing to this scale is westward moving disturbances with a period ∼ 5 days. There is high coherence between the brightness and divergence fields at these scales. In addition, high coherence is found for s = 3–6 and a period ∼ 5 days of westward moving disturbances corresponding to the wavenumber and period of the mixed Rossby-gravity waves. Some evidence suggesting the connection of long-period eastward moving waves with the large-scale cloud field is presented also.

Abstract

The relationship between the large-scale transient wave disturbances at the 200 mb level and the associated cloud field is studied in the latitude belt 20°S to 40°N based on wind and satellite-measured brightness data for the period June–August 1967. Space-time cross-spectral analysis is used to examine the degree of association of the wind and cloud fields in the wavenumber-frequency domain. The total time variance of the brightness field has a well-defined maximum near 10°N corresponding to a belt of sea surface temperature maximum. The divergence and relative vorticity as well as the brightness have a pronounced spatial scale of zonal wavenumber s ≈ 10 at this latitude. The major component contributing to this scale is westward moving disturbances with a period ∼ 5 days. There is high coherence between the brightness and divergence fields at these scales. In addition, high coherence is found for s = 3–6 and a period ∼ 5 days of westward moving disturbances corresponding to the wavenumber and period of the mixed Rossby-gravity waves. Some evidence suggesting the connection of long-period eastward moving waves with the large-scale cloud field is presented also.

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