Heat and moisture fluxes on the time scale of 20 to 60 days over the Indian monsoon area

Summary In this paper we have studied the low frequency variability of the sensible and latent heat flux over the Indian monsoon area. We have used an atmospheric energy budget (vertical integrated heat sources and moisture sinks), as well as the similarity theory in order to compute the surface fluxes on a darly basis. Mainly, the three following data sets were used: the First GARP Global Experiment analyzed data, the TIROS-N outgoing longwave radiation data and the Monsoon Experiment precipitation data.Our three main findings are the following. First, the variability of the temperature and the specific humidity at the surface is more important over the land than over the sea on the intraseasonal time scale (30% over land, but 20% over sea). For the wind an energy peak appears clearly around 30–40 days. The surface fluxes show an uneven variance percentage field (10% to 40%); the energy peaks stretch from 10 to 40 days. Second, the wind has a significant influence on the surface fluxes, except at some locations exclusively over the land areas. Of the temperature and the specific humidity, the temperature is the one which influences the fluxes the most. (This influence may be very strong over land.) The specific humidity may have a significant influence, over the land and sea, at the same time. Thus, one cannot neglect the influence of temperature and specific humidity over land on the intraseasonal time scale. Third, we have found a close relation between the propagation of low frequency waves and the propagation of surface flux patterns. This may suggest a feedback mechanism which relates surface processes to the northward propagation of these waves over India.With 17 FiguresOn leave from Etablissement d'études et de recherches méteorologiques Paris, France