Non-frontal Crachin and the Cool Season Clouds of the China Seas

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  • 1 Royal Observatory, Hong Kong
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The crachin of the coastal regions of south China and northern Indochina develops during the cool season whenever relatively moist air is cooled sufficiently by contact with the cold coastal waters to lower its condensation level below the level of turbulent mixing. Inter-mensal and diurnal variation of crachin are discussed as well as its coincidence with low-level winds veering with height. Forecasting procedures are listed. Over the China Seas beyond the crachin zone, convective cloud predominates, but as sea-air temperature differences steadily decrease through the latter part of the cool season, cloud amounts also diminish.

* This work was completed at the University of Chicago during tenure of a Commonwealth Fund Fellowship.

The crachin of the coastal regions of south China and northern Indochina develops during the cool season whenever relatively moist air is cooled sufficiently by contact with the cold coastal waters to lower its condensation level below the level of turbulent mixing. Inter-mensal and diurnal variation of crachin are discussed as well as its coincidence with low-level winds veering with height. Forecasting procedures are listed. Over the China Seas beyond the crachin zone, convective cloud predominates, but as sea-air temperature differences steadily decrease through the latter part of the cool season, cloud amounts also diminish.

* This work was completed at the University of Chicago during tenure of a Commonwealth Fund Fellowship.

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