THE SURFACE-ENERGY BALANCE IN MEXICO-CITY

Results of a field observation programme to investigate the surface energy balance of Mexico City, D.F., are presented. Direct measurements of net all-wave radiation and the turbulent sensible heat flux were conducted from a 28 m tower located about 4 km from the city centre. Heat storage in the urban fabric was parameterized and the turbulent latent heat flux was found by the residual in the energy balance equation. Most of the data were gathered in the dry season from February to the end of March 1985. The results from this tropical highland city resemble those from temperate cities in respect of the magnitude of the Bowen ratio and the diurnal trend in the amount of the net radiation partitioned into turbulent sensible heat. On the other hand, the role of heat storage is much larger than in the temperate case so that the partitioning of the sensible heat between turbulent and conductive transfer seems to be more nearly equal. Nevertheless evaporation appears to be an important term in both the surface water and energy balances. The nature of the energy balance may help explain some of the previously observed features of the heat island and humidity regimes of Mexico City.