Because of the topographic setting of the city, the moderately strong insolation associated with its tropical latitude and high elevation, and weak prevailing synoptic winds, Mexico City is strongly affected by thermally and topographically induced circulation patterns. Three daytime flow patterns were observed during February and much of (1) a regional plain-to-plateau flow of air from the lower lying areas to the north and east into the basin from the north in the late afternoon, driven by the heating of the elevated terrain in central Mexico; (2) local valley-to-basin flow in which southerly winds would develop and propagate through the gap in the mountains to.
