The Low-Level Wind Field at Phoenix and Tucson

Abstract

Resultant surface winds presented as monthly averages for each hour of the day for two years have been computed for Tucson and Phoenix and are displayed as hodographs showing the diurnal variation of the surface wind. Resultant winds for these two years were computed from upper air observations for all times and all levels of observation up to and including 4000 meters above mean sea level for both Phoenix and Tucson, and are presented in the form of tabulated listings as monthly averages. In addition, mean speeds of the upper air winds are presented and a tabulation of the occurrence of calm winds at the surface vs. month and hour is given. Results of this study show that a distinct diurnal variation in the surface winds is present at both Tucson and Phoenix. The most persistent feature of the wind field at both of these stations is the drainage wind which occurs during the early morning hours. During the warmer portions of the day air motion tends to be toward higher elevations. Thus, in general, the air motion conforms to what is expected on the basis of theory. Mean air motion for each month is presented. Considerable difference between months and between the same months of the two years is noted. High frequencies of reported calms at Phoenix for certain months lead to rather small net air movement. The diurnal variation in the number of reported calms is seen to be related to the diurnal reversal in wind direction associated with the mountain-valley circulation. The relationship of these resultant winds to the air pollution problem at these two cities is discussed.