Midlatitude daytime wind measurements in the dynamo region with a sounding rocket chemical release technique

Abstract:

The sounding rocket chemical release technique can provide wind measurements in the mesosphere and lower thermosphere with excellent height resolution and extended altitude coverage, but such measurements are generally limited to nighttime conditions. Lithium trails, however, have a sufficiently bright resonant emission in sunlight to be detected with cameras or photometers using very narrow-band filters tuned to the emission wavelength. This type of measurement was attempted successfully a few times in the 1970's. We present the results of a recent experiment that represents the first use of the technique since those early attempts. Specifically, a rocket launched from Wallops Island, Virginia, on July 4, 2013, at 1031 LT, released a series of three lithium trails covering the altitude range from 95 to 125 km. The trails were observed with cameras equipped with 2-nm telecentric filter lenses on a NASA aircraft at an altitude of 28,000 feet, above the majority of the lower-level haze layer. The wind profile obtained from the observations showed maximum wind speeds of approximately 150 m/s in the altitude range where the strongest dynamo currents are expected. A large shear was evident below the altitude of the wind maximum, and the turbopause transition could be seen in the trail within the region of the large shear. In addition, there were large changes in the wind speed and wind direction during the 10 to 15 minute observing period. The results are of interest in terms of the technique development, which improves significantly on the measurements from the 1970's by using modern filter lens systems and sensitive digital cameras. In addition, the observed wind profiles show the characteristics of the winds and their time variations in daytime conditions across this critical altitude range.