The Large-Scale Response of the Tropical Atmosphere to Cloud-Modulated Infrared Heating

Abstract

Infrared beating rates determined from the Line Islands Experiment radiometersonde measurements vary from −4 to −0.5°C day⁻¹ at 250 nib. Correspondingly, the beating rates at 500 mb vary from +0.5 to −3°C day⁻¹. These variations result from high-middle cloudiness occurring every 6–8 days. The structure of waves forced by the observed differences in radiative beating is determined through the use of a large-scale diagnostic model. In this model, the diabatic heating is specified and the response of the atmosphere to this forcing is computed. When the radiative beating is combined with convective heating, the vertical structure of the forced motions is shown to be very sensitive to the phase difference between the convective and the radiative beating. The amplitude of the weridional wind perturbations at 200 mb varies from 1 m s⁻¹ for the use when radiatively active upper tropospheric clouds am centered over the convective beating to 5.5 m s⁻¹ when the cloud is centered a half wavelength from the convective heating. For the same cloud configurations, the mass divergence at 200mb varies from 3×10⁻⁶ to 1×10⁻⁶s⁻¹ and the convergence at 900 mb varies from 3×10⁻⁶s⁻¹ at the region of the maximum convective heating.

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