Secondary Gravity Wave Generation Over New Zealand During the DEEPWAVE Campaign

Multiple events during the Deep Propagating Gravity Wave Experiment measurement program revealed mountain wave (MW) breaking at multiple altitudes over the Southern Island of New Zealand. These events were measured during several research flights from the National Science Foundation/National Center for Atmospheric Research Gulfstream V aircraft, utilizing a Rayleigh lidar, an Na lidar, and an Advanced Mesospheric Temperature Mapper simultaneously. A flight on 29 June 2014 observed MWs with horizontal wavelengths of ~80–120 km breaking in the stratosphere from ~10 to 50 km altitude. A flight on 13 July 2014 observed a horizontal wavelength of ~200–240 km MW extending from 20 to 90 km in altitude before breaking. Data from these flights show evidence for secondary gravity wave (SGW) generation near the breaking regions. The horizontal wavelengths of these SGWs are smaller than those of the breaking MWs, indicating a nonlinear generation mechanism. These observations reveal some of the complexities associated with MW breaking and the implications this can have on momentum fluxes accompanying SGWs over MW breaking regions.