A diagnostic study of tropospheric diabatic heating and the generation of available potential energy

Abstract

Calculations of the horizontal distribution of mid-tropospheric diabatic heating have been made through use of the first law of thermodynamics in conjunction with a simplified form of the vorticity equation. Objective analyses of the geopotential heights of the 850 and 500 mb surfaces over a region extending from the pole southward to approximately 15° N were utilized. Calculations of the daily distributions of the heat sources and sinks were obtained for the following months: January 1959, 1962, 1963; April 1961, 1962; July 1961, 1962; and October 1961, 1962. The daily distributions were then averaged within each month, and one of the resulting monthly distributions for each season is presented. Furthermore, the 9 monthly averaged zonal heating profiles are presented together with the latitudinal variation of the heat flux required to maintain these profiles. The zonal and eddy components of the generation of available potential energy were computed from the daily 500–850 mb thickness and heating patterns. The averaged zonal profiles of each component for each of the 9 months is presented. Furthermore, through a linear Fourier analysis method the eddy generation of available potential energy was obtained in the wave-number regime. The average monthly contribution and the standard deviation of the daily values were obtained for each of the 9 months for each harmonic from n = 1 to n = 20. The results of the monthly averaged heating patterns indicate that relatively intense heat sources and sinks exist during the winter months while the least intense ones exist in the summer months. An annual zonal heating maximum of 4 times 10 −3 kj t −1 sec −1 was found near 40° N and intense cooling existed in the high latitudes. All monthly averaged values of the zonal generation of available potential energy were positive with maximum values obtained for the winter months and minimum values obtained for the summer months. Results indicate that for the troposphere the available potential energy is generally destroyed by the eddies in all seasons except summer with the greatest destructions occurring in winter. Also, during winter the long waves, n = 1 to 5, are responsible for the majority of this destruction. The annual average of the zonal generation of available potential energy for the troposphere obtained from the 9 months considered here was + 19 times 10 −4 kj m −2 sec −1 and the corresponding value for the eddy generation was −9 times 10 −4 kj m −2 sec −1 . DOI: 10.1111/j.2153-3490.1964.tb00174.x