The effect of gravity waves on NLC

Height profile of temperature with wave-like modulation and the Lidar backscatter crosssection during the occurrence of NLC.

First studies with CARMA were conducted in order to interpret high resolution temperature measurements from in situ soundings of an NLC observed from the Andoya Rocket Range at 69°N. The above figure shows the results of such measurements: in the 80-100 km altitude range, the temperature profile (measured with a rocket borne instrument) is prominently modulated by wave-like modulations with amplitudes in the range 5 – 15 K. Simultaneous NLC measurements by a ground based lidar revealed that the NLC was located at the exact altitude of a local temperature minimum (at 83 km).

Motivated by these observations, CARMA was used to study the generation and development of an NLC in the presence of temperature variations imposed by an inertia gravity waves with amplitudes, wavelengths and period as derived from our own in situ observations. The results of two such simulations are presented in the second figure. These simulations show that the NLC should follow the wave induced local temperature minima in such cases where the wave period was larger than ~6 hours. In such cases, temperature variations and microphysical processes are synchronized leading to the coincidence of NLC-height and temperature minima as well as to a brightness amplification of the cloud.