Gravity wave characteristics from OH airglow imager over Maui

The gravity wave (GW) characteristics over Maui from 2002 to 2007 are deduced from OH airglow imager. The dominant horizontal wavelength falls between 15 and 30 km. Intrinsic phase speeds are mainly in the range of 50-100 m s ^-1. Observed phase speeds are mainly in the range of 20-70 m s ^-1. Intrinsic wave periods are mostly below 30 min with the majority clusters around 5-15 min. For intrinsic wave period larger than 5 min, as wave period increases, the number of wave events decreases. Observed wave periods fall in the range of 8-20 min. The vertical wavelength distribution peaks between 20 and 30 km and falls rapidly as wavelength decreases. GWs propagating against (along) background wind are Doppler shifted to a higher (lower) frequency, larger (smaller) vertical wavelength, and decreased (enhanced) chance of observation. During all seasons Doppler shifting is part of the explanation as to why the majority of observed GWs propagate against the background wind. The preferentially poleward or equatorward propagation of GWs during summer or winter observed by airglow imagers at Maui can be explained by the effects of critical layer filtering, ducting, and Doppler shifting. In March, when critical layer filtering effects are not important, Doppler shifting and ducting play dominant roles in determining preferred zonal propagation direction. In December, ducting and wave source location predominantly determine wave propagation direction. Momentum flux deduced from OH imager is also highly anticorrelated with background wind on both seasonal and diurnal time frames. Momentum flux is highly modulated by tidal wind. Waves with shorter vertical wavelengths have much smaller power in GW spectra. OH imager may capture the majority of momentum flux of high-frequency GW spectra through the airglow layer.