Mesoscale Time and Space Wind Variability

Abstract

The results of a program to study the time and space variability of the wind field below 5 km are presented. Wind data were collected using pilot balloons tracked with the METRAC positioning system. Balloons were launched at 10-30 min intervals from a single launch point and at 30 min intervals from pairs of launch points separated by 20 m, 4.415 km and 20.910 km. Winds were averaged over 100 m layers. Experiments were separated by cyclonic and anticyclonic weather patterns. It was found that the average time variability of the wind for anticyclonic weather patterns followed a 1/3 power law for time lags from 30 to 300 min. The result of frontal passages during the cyclonic experiments increased the power law relationship to about 1/2. The wind variability for a space separation of 4.415 km was found to correspond to a time lag of ? 17 min. The wind variability for a space separation of 20.910 km was found to correspond to a time lag of ?90 min though this estimate is based upon relatively few observations. It was found that variabilities as small as 1 m s?1 could be accurately measured with the balloon and ground system used in this study.