Precipitation Flux Climatology of the Free Atmosphere

Abstract

The diabatic heating of the atmosphere can be very closely represented by the convergence of a vertical energy flux. It consists of two components: the flux of net radiation and the flux of precipitation. The latter comprises the vertical flux of water in condensed form (rain, snow, ice). The concept of precipitation flux is investigated employing the zonal mean equation of potential heat. Input data are radiation flux from a model, adjusted at the top and bottom of the atmosphere with observed data; horizontal advective heat flux convergence and heat storage with the data of the MIT Library; and vertical sub-synoptic eddy flux of sensible heat (a small quantity) from a parameterization. Output is the precipitation flux in the free atmosphere. Time scale is 1 month, space domain is the zonal mean Northern Hemisphere. The precipitation flux is downward everywhere. It is maximum in the tropics. Comparison of the flux across the 1000 mb level with the observed surface precipitation shows satisfactory agreement. The balance in the potential heat equation is largely between radiation and precipitation; thus the atmosphere can be characterized by an approximate radiative-precipitative equilibrium. The accuracy of the method (±10 W m?2) depends critically on the validity of the radiation data.