DETERMINATION OF CLOUD AMOUNT AND LEVEL FROM RADIOSONDE SOUNDINGS

A method developed in the former Soviet Union for predicting cloud amo unts is supplemented with a new method of determining the base and top s of clouds. Criteria for predicting a cloud layer are 0 less than or equal to T ''(z) and R ''(z) less than or equal to 0, where T '' is th e second derivative of the vertical profile of temperature and R '' is the second derivative of the relative humidity. This test was found f rom an analyses of United States radiosonde data. Cloud amount (sky co ver) is predicted from a relationship between cloud amount and dewpoin t depression within the predicted cloud layer and the temperature at t hat level. This relationship is based on data from the former Soviet U nion and data from the Indian Ocean and divides cloud amount into four categories: 0%-20%, 20%-60%, 60%-80%, and 80%-100% coverage. The new composite method is evaluated using data from several United States ra diosonde stations within different climates. Evaluation data was selec ted to include only situations in which the observer (providing the '' truth'') could see only one cloud layer. Consequently, the evaluation is biased toward stratified cloud conditions. The method will provide cloud information that can be used in models of radiosonde sensors to adjusted temperature data.