Temporal and spatial characteristics of Arizona dust storms (1965–1980)

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Abstract
Hourly meteorological data for four first order stations (Phoenix, Tucson, Winslow and Yuma) were used to identify dust storms which occurred in Arizona from 1965 to 1980. Supporting data on diurnal dust storm frequencies for three Air Force bases in southern Arizona were also used in the analysis. In this study, dust storms have been defined as blowing dust events when visibility is reduced to si‐6 km. Data, however, were also collected for all events when visibility was sll‐3 km which is the dust storm definition used by Orgill and Sehmel (1976).In general, Yuma experiences the most dust storms per year followed closely by Phoenix, with Tucson and Winslow having very few events. Dust storms at Phoenix, on average, tend to be more severe than those experienced at the other sites. The most intense and frequent dust storms in Arizona occur during the summer months and are associated with strong downdrafts generated by intense thunderstorm activity. Several less intense dust storms of longer duration also occur at most sites during the late winter and early summer months with peak occurrence in April. These events are usually associated with cyclonic storm activity including cold frontal passages and upper level cut‐off lows which are common throughout the state at this time of year.Phoenix and Tucson are dominated by late, afternoon dust storms (1700–1800 h) especially during the summer months. Start times are much more irregular at Yuma and Winslow but modes are evident al 0900 h and 1200 h respectively.Phoenix and Tucson experience relatively short duration dust storms averaging 66 and 15 minutes, respectively. Although these dust storms are relatively short, they are rather intense, which is indicated by low visibilities associated with these dust storms. In contrast, storms at Yuma and Winslow are typically longer, lasting more than two hours (160 and 202 minutes, respectively).The dust storm frequency patterns based on visibility criteria pose an important question as to whether higher annual sediment fluxes result from many low‐to‐intermediate magnitude events or fewer, higher magnitude events. This question cannot be readily answered at the present time because of the lack of sediment load data during dust storms. Although meteorological conditions may play a major role in dust storm generation, detailed research is required to evaluate the relative importance of antecedent moisture conditions, surface soil and vegetation conditions, and anthropogenic factors.