Single-station integral measures of atmospheric stagnation, recirculation and ventilation

Abstract

Mathematical definitions of integral quantities used to characterize the stagnation, recirculation and ventilation potential of various airsheds are proposed. These integral quantities can be calculated from wind data collected at fixed time intervals and at fixed heights in the atmosphere, and could be calculated, for example, from data from ground-based remote wind profilers. These integral quantities, since they are calculated from data at single stations, provide useful characterizations of the flow at individual measurement points, but are true measures of the transport of a plume only under idealized homogenous wind conditions. The utility of these single-station measures for characterizing the air pollution transport potential of an airshed is illustrated using three months of hourly surface and radar profiler measurements of horizontal wind speed and direction collected at three locations in the Colorado Plateaus Basin region of Arizona during the winter of 1990. A surface station at Bullfrog Basin, located on a sheltered basin floor and exposed to diurnal wind systems, experienced stagnations 62% of the time, recirculations 34% of the time, and ventilations 8% of the time. A surface station at Desert View, located on the south rim of the Grand Canyon and exposed to synoptic-scale wind systems, experienced stagnations 8% of the time, recirculations 4% of the time, and ventilations 35% of the time. A radar profiler station at Page, Arizona, experienced stagnations about 20% of the time and recirculations about 25% of the time during the winter at heights below ∼ 400 m a.g.l.; above this height, to levels near 1100 m a.g.l. (the approximate height of surrounding plateaus), the frequency of stagnations and recirculations dropped rapidly, and the frequency of ventilations ranged from 40 to 70%.