ESTIMATING THE ROLE OF LOCAL EVAPORATION IN PRECIPITATION FOR A 2-DIMENSIONAL REGION

Budyko's model for estimating the contributions of locally evaporated and advected moisture to regional precipitation is extended to two dim ensions. II is shown that a simple extension by analogy of the pre-dim ensional Budyko's formula to a two-dimensional region is inconsistent unless the flow in the region is parallel and uniform. The correct ext ension based on the two-dimensional equations of conservation of water vapor in the region leads to a generalization of Budyko's formula tha t includes a correction factor depending on the atmospheric flow struc ture. A general procedure for calculating the correction factor for a given atmospheric flow field is presented. Calculations of the correct ion factor for specific flow structures show that the deviations of th e flow from the rectilinear structure can significantly affect the deg ree to which the local evaporation contributes to precipitation.