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A Further Study of Comma Cloud Development in the Eastern Pacific

Richard J. ReedDepartment of Atmospheric Sciences, Seattle, WA 98195

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Warren BlierDepartment of Atmospheric Sciences, Seattle, WA 98195

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Abstract

In a companion paper the authors presented a case study of the development of a comma-shaped cloud pattern and associated small cyclone that formed in a cold air mass over the eastern Pacific. This paper confirms the reproducibility of the previous analysis by documenting a second, similar case. A schematic model of comma cloud development appearing in the companion paper is based in part on this second example.

An added feature of the present paper is a detailed examination of the physical processes responsible for the enhanced convective activity that occurred during the intensifying stage of the disturbance. It is found that the lifted index decreased markedly in the vicinity of the developing comma and that the decrease was associated with warming and moistening of the surface air and cooling of the air at 500 mb. Sensible and latent heat fluxes from the surface of approximately 100 and 300 W m−2, respectively were essential to the low-level warming and moistening. Amplification of an upper-level long-wave trough contributed to the cooling aloft.

As the system came ashore in southern California, convective activity was much more severe in this case than in the previous one. A likely important factor in this difference was the greater warmth of the coastal waters in this (November) case than in the earlier (March) case.

Abstract

In a companion paper the authors presented a case study of the development of a comma-shaped cloud pattern and associated small cyclone that formed in a cold air mass over the eastern Pacific. This paper confirms the reproducibility of the previous analysis by documenting a second, similar case. A schematic model of comma cloud development appearing in the companion paper is based in part on this second example.

An added feature of the present paper is a detailed examination of the physical processes responsible for the enhanced convective activity that occurred during the intensifying stage of the disturbance. It is found that the lifted index decreased markedly in the vicinity of the developing comma and that the decrease was associated with warming and moistening of the surface air and cooling of the air at 500 mb. Sensible and latent heat fluxes from the surface of approximately 100 and 300 W m−2, respectively were essential to the low-level warming and moistening. Amplification of an upper-level long-wave trough contributed to the cooling aloft.

As the system came ashore in southern California, convective activity was much more severe in this case than in the previous one. A likely important factor in this difference was the greater warmth of the coastal waters in this (November) case than in the earlier (March) case.

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