Quasi-zero wind layer measured by rayleigh wind lidar at night

In order to measure wind field of troposphere and stratosphere, a mobile Rayleigh Doppler wind lidar based on Double-edge technology was developed in Hefei, China. The detection range of the lidar is designed to cover altitudes from 10 km to 40 km with height resolution of 100m (below 20 km) and 500m (above 20 km). In the summer of 2011, wind field measurements were carried out in Urumqi (42.1N, 87.1E), the stratospheric quasi-zero wind layer, where wind velocity is almost 0 m/s, was successfully observed. Some typical results of the wind field at night were given. The quasi-zero wind layer's bottom was found stabled at about 17-18 km height. However, the thickness of the quasi-zero wind layer would increase with time until about 0-3 a.m. Beijing time, gaining its maximum, and then decrease. The maximum thickness could be more than 15 km and minimum thickness just 2-3 km according to the author's measurements. This phenomenon could be a result of change of the ultraviolet radiation's intensity emitted to the stratosphere at night. The decrease and increase of the ultraviolet radiation's intensity were different at different latitude at the same time, and that would lead to a change of temperature gradient in the stratosphere, which was pointed from lower latitudes to higher latitudes. Then the temperature gradient passes the affection to the stratosphere circulation, which was part of the quasi-zero wind layer, and eventually leads to this regular increase-decrease change.