A SHORT-TERM RAINFALL PREDICTION TAKING INTO CONCIDERATION NONLINEAR EFFECT OF NON-OROGRAPHIC RAINFALL ON ORGRAPHIC RAINFALL

Abstract

A nonlinear effect ofnon-orographic rainfall on orographic rainfall is introduced into a short-term rainfall predictionmethod which uses Tatehira's orographic rainfall model. In the previous paper, orographic rainfall is assumed tobe simply proportional to non-orographic rainfall. In the seeder-feeder mechanism, which is themost importantpart in the generation of orographic rainfall, ratio of capturingcloud drops by raindrops (by non-orographic rainfall) c is taking a vital role. However, c is not proportional to the non-or0graphic rainfall intensity. In this paper, therefore, c is assumed to be anonlinear function in terms of the non-orographic rainfall and a method ofsolving simultaneous equationscomposed of the nonlinear function and theconservation equation of clouddrop is proposed. As a result, it is found that, when the nonlinear effect is taken into account, computedorographic rainfall becomesmuch smaller and that assumed depth of atmospheric layer ofhundred meters is not enough. Therefore, the computation method is further modified so thatorographic rainfall can be generated frommulti layers.