The Santa Ana Winds of California

Abstract

A 33-yr, numerical dataset of the occurrence of Santa Ana winds for the period 1968?2000 has been created and validated. Daily Weather Maps were examined to identify the days when a surface high pressure system existed over the Great Basin simultaneously with a surface low pressure system offshore of southern California, and the prevailing wind over southern California was from the northeast quadrant. The dates of these occurrences, as well as the wind speed, temperature, and dewpoint temperature among other variables, were extracted and tabulated. The frequency of Santa Ana events derived from the weather maps was compared to events defined by wind direction only and there is agreement between the two. Preliminary results show that the Santa Ana event is limited to the period September?April and that the month of peak occurrence is December. The average frequency of events is 20 yr?1 and the average duration of an event is 1.5 days. Humidity levels are not uniform across Santa Ana events; the driest months are the months with the highest frequency of events. The frequency of Santa Ana events is usually lower than average during El Niño events. These preliminary results indicate that the dataset is useful for in depth study of the local phenomenon and its effect on the region within the context of the large-scale circulation.