Latent Heat Release as a Possible Forcing Mechanism for Atmospheric Tides

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  • 1 Geophysical Fluid Dynamics Program, Princeton University, Prinecton, NJ 08540
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Abstract

The consequences of the hypothesis of Lindzen (1978) that latent heat release may be a significant excitation mechanism for the semidiurnal atmospheric tide are examined in some detail. Harmonic analysis of hourly rainfall data from 79 tropical stations shows that the semidiurnal variation of rainfall in the tropics is ∼1 mm day−1 and has a phase near 0300 LST, just as Lindzen's theory requires. Analysis of data at 85 midlatitude stations shows that the sermidiurnal rainfall oscillation there has its phase rather later (about 0600). The results of simple classical tidal theory calculations which indicate that the geographical distribution of the surface pressure response to latent heat forcing largely follows that of the forcing itself are presented. This result is then used to suggest a plausible explanation for the observed seasonal cycle of the semidiurnal pressure oscillation in midlatitudes. Further calculations show that the magnitude of the non-migrating components of the semidiurnal barometric oscillation produced by latent heat excitation is not likely to be unrealistically large. These calculations also suggest that Lindzen's hypothesis might be verified by observing the phase of the semidiurnal pressure oscillation in particularly and regions.

The rainfall observations also show a strong diurnal (24 h) component in the rainfall both in the tropics and in midiatitudes. The effects of latent heat release on the 24 h tide are briefly discussed.

Abstract

The consequences of the hypothesis of Lindzen (1978) that latent heat release may be a significant excitation mechanism for the semidiurnal atmospheric tide are examined in some detail. Harmonic analysis of hourly rainfall data from 79 tropical stations shows that the semidiurnal variation of rainfall in the tropics is ∼1 mm day−1 and has a phase near 0300 LST, just as Lindzen's theory requires. Analysis of data at 85 midlatitude stations shows that the sermidiurnal rainfall oscillation there has its phase rather later (about 0600). The results of simple classical tidal theory calculations which indicate that the geographical distribution of the surface pressure response to latent heat forcing largely follows that of the forcing itself are presented. This result is then used to suggest a plausible explanation for the observed seasonal cycle of the semidiurnal pressure oscillation in midlatitudes. Further calculations show that the magnitude of the non-migrating components of the semidiurnal barometric oscillation produced by latent heat excitation is not likely to be unrealistically large. These calculations also suggest that Lindzen's hypothesis might be verified by observing the phase of the semidiurnal pressure oscillation in particularly and regions.

The rainfall observations also show a strong diurnal (24 h) component in the rainfall both in the tropics and in midiatitudes. The effects of latent heat release on the 24 h tide are briefly discussed.

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