Sodium lidar-observed gravity wave breaking followed by an upward propagation of sporadic sodium layer over Hefei, China

Abstract

The University of Science and Technology of China sodium temperature/wind lidar observed a strong zonal wind shear (~60m/s/km) near 98km between 1315 and 1330 UT on 29 July 2013 and a cooling near 96-100km (above a warming near 90-95km) between 1330 and 1430 UT. This suggests a possible gravity wave (GW) breaking event. Comparison of the lidar results with observations from a nearby meteor radar and with satellite results indicated that the GW likely broke down over a large horizontal area. In addition, the sodium number density suddenly increased 10-12 times (∼13,000atm/cm3) near 95km at 1400 UT, immediately following the GW breaking. This sporadic sodium layer (SSL), which is different from most previously observed SSL events (which propagate downward), tended to propagate upward and also appeared ~2min earlier in the west channel than in the east channel. The horizontal propagation direction of the SSL was aligned with the horizontal wind direction, which was likely due to the propagation of a high-density sodium layer from the northwest of the lidar site, and was possibly related to the earlier GW breaking event. Key Points Large zonal wind shear and temperature increase indicated a possible gravity wave breaking Sodium density suddenly increased 10-12 times after the wave breaking Sporadic sodium layer propagation direction aligned with wind direction.