Equatorial Tropospheric Waves Induced by Diabatic Heat Sources

Takio Murakami Dept. of Meteorology, University of Hawaii, Honolulu 96822

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Abstract

The problem of finding the equatorial tropospheric response to a prescribed heat source is treated by using a linearized primitive system on a Mercator map projection. The diabatic heat source is assumed to be westward propagating in a sinusoidal form with zonal wavelength 7000 km and phase speed 4 m sec−1, the corresponding period being approximately 20 days. The structural features of the induced waves are quite sensitive to the vertical shear of the basic zonal current. The case with westerly vertical shear reveals that the axis of geopotential perturbation tilts eastward with increasing height in the lower troposphere, and the wave activity in the upper troposphere is far more pronounced than that in the lower troposphere. The amplitudes of perturbation geopotential and horizontal wind attain their maxima near 13 km and about 1–2° north of the maximum heating prescribed at 8.3° latitude. In the case with easterly vertical shear, a westward tilt of the axis of geopotential perturbation occurs in the lower troposphere, and at 13 km where the atmospheric response is most active the wind field is characterized by the predominance of its zonal component equatorward of the latitude of the maximum heating. Along that level, the geopotential perturbation becomes maximum right at the equator and is almost in phase with the perturbation zonal wind.

Abstract

The problem of finding the equatorial tropospheric response to a prescribed heat source is treated by using a linearized primitive system on a Mercator map projection. The diabatic heat source is assumed to be westward propagating in a sinusoidal form with zonal wavelength 7000 km and phase speed 4 m sec−1, the corresponding period being approximately 20 days. The structural features of the induced waves are quite sensitive to the vertical shear of the basic zonal current. The case with westerly vertical shear reveals that the axis of geopotential perturbation tilts eastward with increasing height in the lower troposphere, and the wave activity in the upper troposphere is far more pronounced than that in the lower troposphere. The amplitudes of perturbation geopotential and horizontal wind attain their maxima near 13 km and about 1–2° north of the maximum heating prescribed at 8.3° latitude. In the case with easterly vertical shear, a westward tilt of the axis of geopotential perturbation occurs in the lower troposphere, and at 13 km where the atmospheric response is most active the wind field is characterized by the predominance of its zonal component equatorward of the latitude of the maximum heating. Along that level, the geopotential perturbation becomes maximum right at the equator and is almost in phase with the perturbation zonal wind.

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