Na Doppler/temperature lidar: Initial mesopause region observations and comparison with the Urbana medium frequency radar

Abstract

Meteoric ablation in the upper atmosphere is the source of a dense layer of atomic Na between about 80 and 105 km altitude. Peak densities are typically several thousand atoms/cm3, and the total abundance varies seasonally at mid‐latitudes with the maximum in winter. The Na layer is a sensitive tracer of the thermal and density structure of this region of the atmosphere and can be probed with exceptional accuracy and resolution using resonance fluorescence lidar techniques. We report the first observations of vertically resolved Na density, temperature, and wind profiles in the mesopause region using a new four‐frequency Doppler/temperature lidar. The initial zonal wind and temperature observations were obtained with a resolution of 30 min and 1.5 km and rms accuracies of 12 m/s and 2 K. These measurements were conducted simultaneously with the medium frequency (MF) radar at the Urbana Atmospheric Observatory (40°N, 88°W) during the night of March 14–15, 1991. The mean temperature profile exhibits a well‐defined mesopause at 95.5 km with a temperature of 181 K. The mean zonal wind profile exhibits a strong 58 m/s westward jet at 97 km which appears to be related to the mesopause. During the 6‐hour and 45‐min observation period the Na Doppler winds, averaged between 88 and 98 km, exhibit the same general trends as the MF radar apparent and true winds in this same region. However, the lidar and radar velocity estimates differ by as much as 40 m/s at some times during the night.