Lidar observations of gravity waves in the middle atmosphere over Lauder, New Zealand

Abstract

The DEEP propagating gravity WAVE experiment was carried out over New Zealand in June/July 2014. As part of the DEEPWAVE campaign, we conducted extensive observations with a ground-based Rayleigh lidar at Lauder (45°S, 170°E). The Lauder site is in the proximity of the polar vortex, with sufficiently high horizontal wind speeds in austral winter that allow for deep propagating gravity waves. Moreover, Lauder is located just east of the Southern Alps. Prevailing westerlies facilitate excitation of large orographic gravity waves which can be observed by lidar. We report on gravity waves detected in high-resolution temperature measurements in the altitude range 20-90 km. Spectral filtering of the temperature data reveals large-scale waves with periods of several hours as well as small-scale waves with periods down to 10-20 minutes. Observed vertical wave lengths and periods are retrieved from the 2D Fourier transform of measured temperature. Using this information to calculate phase speeds, waves are then classified into categories which may be associated with different wave types, i.e. waves originating from different wave sources. We present first results from ~500 observation hours acquired between 19 June and 6 November 2014. We identify orographic wave events, deep propagating non-orographic waves, and small-scale waves which possibly result from breaking large-scale waves. Results are compared with ECMWF data. We find that large-scale waves are surprisingly well represented in ECMWF up to the stratosphere.