A numerical-physical planetary boundary layer model

A numerical-physical model for the planetary boundary layer has been formulated for the purpose of predicting the winds, temperatures and humidities in the lowest 1600 m of the atmosphere. An application of the model to the synoptic situation of 30 August, 1972, demonstrates its ability to produce useful forecasts for a period of 24 h. Results are illustrated in terms of horizontal maps and time-height sections of winds and temperatures. The model is divided in the vertical direction into three layers that are governed, respectively, by different physical formulations. At the lowest level, which is the surface of the earth, forecasts of temperature and humidity are computed from empirical relations. In the first layer, the surface layer, application is made of the similarity theories of Monin-Obukhov, Monin-Kazanski and Businger’s form of the universal functions. The second layer, the Ekman layer, is 1550 m deep and is governed by diagnostic momentum and time-dependent thermodynamic and humidity equations. External input to the model are large-scale pressure gradients and middle-level cloudiness. Cressman’s objective analysis procedure is applied to conventional surface and upper air data over a horizontal region of about 2500 km by 2500 km, centered about Lake Ontario. With a grid distance of 127 km and a time interval of 30 min, the computer time required on Control Data Cyber 76 for a 24 h forecast for the case study is less than two minutes.