Propagating Mesoscale Cloud Bands

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  • 1 Department of Physics, University of Toronto, Toronto, Ontario, Canada MSS 1A7
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Abstract

Banded cloud patterns are an often observed mesoscale phenomenon which may be produced under a variety of physical conditions and for a variety of reasons. This paper concerns a detailed analysis of a propagating pattern which was observed with the NOAA-2 satellite following a period of severe thunderstorm activity in the southwestern United States. We review the local atmospheric conditions existing at the time the disturbance was observed and address the question concerning its mechanism of initiation and propagation. We first test the hypothesis that the banded cloud formation could simply be a manifestation of a freely propagating packet of internal waves launched by earlier convective activity. This hypothesis is shown to be unsatisfactory. We next consider the modal structure of the atmosphere in the vicinity of the cloud bands and show that the slowest spatially decaying mode of the mean state has a horizontal wavelength and phase speed which match those of observed disturbance.

Abstract

Banded cloud patterns are an often observed mesoscale phenomenon which may be produced under a variety of physical conditions and for a variety of reasons. This paper concerns a detailed analysis of a propagating pattern which was observed with the NOAA-2 satellite following a period of severe thunderstorm activity in the southwestern United States. We review the local atmospheric conditions existing at the time the disturbance was observed and address the question concerning its mechanism of initiation and propagation. We first test the hypothesis that the banded cloud formation could simply be a manifestation of a freely propagating packet of internal waves launched by earlier convective activity. This hypothesis is shown to be unsatisfactory. We next consider the modal structure of the atmosphere in the vicinity of the cloud bands and show that the slowest spatially decaying mode of the mean state has a horizontal wavelength and phase speed which match those of observed disturbance.

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