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

Abraham Zangvil The Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, 84990, Israel

Search for other papers by Abraham Zangvil in
Current site
Google Scholar
PubMed
Close
and
Michio Yanai Department of Atmospheric Sciences, University of California, Los Angeles 90024

Search for other papers by Michio Yanai in
Current site
Google Scholar
PubMed
Close
Full access

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.

Save