Observations in the polar middle atmosphere by rocket-borne Rayleigh lidar: First results

We present a new rocket instrument which measures total atmospheric density with great precision and resolution by Rayleigh scattering of infrared lig ht. Comparison with a ground-based lidar shows: (a) both instruments measur e the same physical parameters, even though they have different integration times and volumes. (b) The observed density structures change little over the course of an hour and the horizontal distance of 14 km. The rocket inst rument has a basic vertical resolution of approximately 8 m and a number de nsity precision of 4.2.10(19) m(-3). Above 56 km we integrate over an incre asing vertical range, reaching 80 m at 70 km. The measured number density p rofile shows remarkable alternations between very stable layering and metas table layering (adiabatic lapse rate) in the atmosphere between 52 km and 7 1 km. Comparison with the hodograph of the horizontal wind profile measured by a falling sphere 29 minutes later shows that the metastable height regi ons coincide with height regions where the hodograph deviates from an ideal spiral. The observation is tentatively interpreted as a gravity wave that is saturating (or encountering a critical level) in these height regions. T he comparison of the fine-scale neutral number density observations with me asurements of ion density by; electrostatic skin probes on board the same v ehicle shows a number of ion density enhancements in the stably-layered hei ght regions. With one exception out of six cases, these enhancements occur where the vertical gradient of the meridional wind would collect positive i ons as in sporadic E layers. This may be the first observation of such ion density enhancements in the height region 55 to 70 km.