Characteristics of gravity waves and influences of source conditions on mountain wave penetration into the stratosphere and mesospahere above New Zealand

Abstract

We present atmospheric gravity wave (GW) measurements obtained by a Rayleigh/Raman lidar at Lauder, New Zealand, during and after the Deep Propagating Gravity Wave Experiment campaign. Gravity wave characteristics are derived from 557 h of lidar data acquired over a period of five months in winter 2014. Enhancements in gravity wave activity occurred in sporadic intervals lasting a few days. We employ spectral analysis of lidar temperature measurements to detect and sort wave packets into specific classes corresponding to propagating gravity waves and quasi-stationary gravity waves (mountain waves). Large-amplitude mountain waves are detected during periods with high tropospheric wind speeds perpendicular to the Southern Alps. During the strongest event (29 July to 1 August) amplitudes in excess of 15 K were observed at 40 km altitude. Surprisingly, the largest response at mesospheric altitudes is observed for conditions with low to moderate mountain wave forcing. Large-amplitude mountain waves excited by large cross-mountain wind speeds often do not penetrate into the mesosphere, either due to refraction away from New Zealand or wave breaking and dissipation in the stratosphere.