An Analysis of Daily Humidity Patterns at a Mountainous and Urban Site in a Tropical High-Altitude Region

Abstract

Mixing ratio data of water vapor at different hours of the day in a high-altitude tropical plateau in Mexico are shown. The objective is to measure water vapor quantity in a mountainous zone, where no previous studies of this kind exist, and in an urban site. The selected mountain site is at 2700 m MSL about 70 km west southwest of Mexico City. The urban site is in Mexico City at 50 m above the city. Data for the 1989 rainy season (May?October) show that statistical differences in mixing ratio values from 0800 to 1200 LST and a regular increase were observed in the former place. A significant difference from 1400 to 1600 LST and a definite decrease during morning hours were observed in the latter. Explanations for these phenomena are given. The results indicate that in the absence of synoptic perturbations an analysis of the time elapsed between the beginning of mixing ratio increase and the beginning of rain can help to show the diurnal air circulation that controls rain cloud formation. Data also show that anabatic winds and convective updrafts induced by urban sites, heat sources are the predominant diurnal circulations in the mountainous and urban sites, respectively. The data were further subdivided into cloudy and clear hours and discussed. Since humility data during the dry season (November?April) are not well distributed throughout the day, only three days are presented as individual cases for the mountainous area.