Diurnal Variation in the Troposphere's Energy Balance

The tropospheric energy balance is examined in an effort to ascertain the diurnal variation of its components. The mean local diurnal temperature change in the 850–300 mb layer was observationally determined utilizing upper air data collected at 142 Northern Hemisphere radiosonde stations. Temperature data from the GATE, ATEX, BOMEX and LIE experiments, and Operations Redwing and Hardtack in the tropical west Pacific were also analyzed. Diurnal radiative cooling values are computed for specific geographical regions, and the magnitude of the required diurnal warming for each region is determined. Required warming is composed of a variety of atmospheric processes such as condensation energy release, surface to air sensible heat transfer, horizontal advection and vertical motion. A large morning maximum and late afternoon-early evening minimum of tropospheric required warming is found for all data sets, at all latitudes, in all seasons, and for both oceanic and land areas. These morning versus late afternoon required warming differences are of magnitudes of 2–3 to 1. It is hypothesized that the subsidence warming contribution to the diurnal variation of required warming dominates the other components. Increased morning subsidence and weaker afternoon–early evening subsidence is apparently a generally operating phenomenon in the troposphere.