The Effects of Released Latent Heat in Growing Baroclinic Waves

Abstract

The effects of released latent heat on the development of baroclinic waves are explored using two numerical experiments in which these waves are allowed to grow from small perturbations on a flow that initially was zonally constant. In one experiment the effects of released latent heat were excluded; in the other, these effects were included and the initial zonally constant flow was considered saturated everywhere. In the moist experiment the growth rates of all wavelengths were found to be significantly increased over the corresponding growth rates in the dry experiment. However, the wavelength of maximum growth rate (wavenumber 15) was the same in both the dry and moist experiments. At the time of maximum development of wavenumber 15, the kinetic energy structure in the moist experiment was quite different from that in the dry experiment. In the moist experiment there was a distinct double maximum in the vertical; while in the dry experiment most of the kinetic energy of wavenumber 15 was near the earth's surface. In this respect wavenumber 15 in the moist experiment more nearly resembles the corresponding wave observed in a full general circulation model than does the wave in the dry experiment. These differences in wavenumber 15 in the moist and dry experiments result from the convective adjustment process in the model, which tends to increase the warm-temperature perturbation of the baroclinic wave at mid-tropospheric levels, while reducing it at the earth's surface. A comparison of the structure of the longer waves in the moist and dry experiments showed that they did not differ significantly.