Spatial properties of wind differences in the lowest three kilometers of the atmosphere

Spatial properties of wind differences are important to launch operations because wind hazards and vehicle wind loads are assessed based on measurements by instruments located some distance from the planned flight track of the vehicle. When the measurements are near operational go/no-go thresholds ("redlines"), the question arises as to the likelihood that the vehicle will experience winds above those thresholds. The answer requires knowledge of the temporal and spatial properties of the wind field.

Temporal differences have been extensively explored in studies reported in the literature, especially for the mid and upper troposphere in the region of maximum dynamic pressure on ascent. Spatial differences have not been as well examined because such research requires a network of wind sensors with the appropriate spacing and such networks are rare. Wind tower measurements are limited to the lowest hundred meters or less and balloons provide small sample sizes at uncontrollable locations as they slowly ascend following the wind. The Eastern Range (ER) network of five 915 MHz boundary layer wind profilers provided a unique opportunity to examine the spatial variability of winds in the Shuttle roll maneuver region below 3 km altitude as requested by the Shuttle program.

This paper will present an analysis of windspeed differences between pairs of wind profilers. Five profilers allow for ten distinct pair combinations spaced from 8.5 to 31 km apart. A research grade data set was prepared covering the period from November 1999 through August 2001. Extensive automated and manual quality control was applied. Complete profiles of wind speed and direction were available at 15 minute intervals covering the altitude range from about 100 to 3000 meters in "range gates" about 100m thick.

Separate results will be presented for the summer (June through September) and winter (December through March) seasons as defined for ER wind climatology by the Space Shuttle program. Depending on the significance of the results (analysis is underway as this abstract is being written), structure functions, correlations or coherence spectra will be presented. The results will be interpreted in the context of the launch team's desire to quantitatively access the risk of exceeding an operational redline at the vehicle given wind measurements at a known distance from the planned trajectory.