Publication Date:
2019
Description:
Abstract
A remarkable, large‐amplitude, mountain wave (MW) breaking event was observed on the night of 21 June 2014 by ground‐based optical instruments operated on the New Zealand South Island during the Deep Propagating Gravity Wave Experiment (DEEPWAVE). Concurrent measurements of the MW structures, amplitudes and background environment were made using an Advanced Mesospheric Temperature Mapper, a Rayleigh Lidar, an All‐Sky Imager, and a Fabry‐Perot Interferometer. The MW event was observed primarily in the OH airglow emission layer at an altitude of ~82 km, over an ~2‐hour interval (~10:30‐12:30 UT), during strong eastward winds at the OH altitude and above, that weakened with time. The MWs displayed dominant horizontal wavelengths ranging from ~40‐70 km and temperature perturbation amplitudes as large as ~35 K. The waves were characterized by an unusual, “saw‐tooth” pattern in the larger‐scale temperature field exhibiting narrow cold phases separating much broader warm phases with increasing temperatures towards the east, indicative of strong overturning and instability development. Estimates of the momentum fluxes (MFs) during this event revealed a distinct periodicity (~25 min) with three well‐defined peaks ranging from ~600‐800 m2.s‐2, among the largest ever inferred at these altitudes. These results suggest that MW forcing at small horizontal scales (〈 100 km) can play large roles in the momentum budget of the mesopause region when forcing and propagation conditions allow them to reach mesospheric altitudes with large amplitudes. A detailed analysis of the instability dynamics accompanying this breaking MW event is presented in a companion paper, Fritts et al. [2019].
Print ISSN:
2169-897X
Electronic ISSN:
2169-8996
Topics:
Geosciences
,
Physics
Permalink