Lidar observations of a horizontal variation in the atmospheric sodium layer

A steerable laser radar system has been used to measure the distributions of sodium between 80 and 105 km by observations of resonance scattering in three directions from Winkfield (51.4 deg N, 0.7 deg W). Simultaneous observations of Rayleigh scattering from heights of 20 to 35 km were used to normalize the sodium concentration. Sequences of measurement at zenith angles of 30 deg have permitted a comparison to be made of the sodium concentrations at three locations separated horizontally by distances of about 80 km. The results for two nights in August 1976 showed clear evidence of a horizontal variation near the peak of the layer, the concentration changing by about 50% between locations. The results for a third night did not show such a variation near the peak of the layer, the major differences being observed at greater heights.