A novel identification method for stratospheric gravity waves in nadir viewing satellite observations

Atmospheric gravity waves (GWs) are an important mechanism for vertical transport of energy and momentum through the atmosphere. Their impacts are apparent at all scales, including aviation, weather, and climate. Identifying stratospheric GWs from satellite observations is challenging due to instrument noise and effects of weather processes, but they can be observed from nadir sounders such as the AIRS instrument onboard Aqua. Here, a new method (hereafter "neighbourhood method") to detect GW information is presented and applied to AIRS data. This uses a variant of the 3D S-transform to calculate the horizontal wavenumbers of temperature perturbations, then find areas of spatially constant horizontal wavenumbers (assumed to be GWs), which allow for creating a binary wave-presence mask. We describe the concept of the neighbourhood method and use it to investigate GW amplitudes, zonal pseudomomentum fluxes, and vertical wavelengths over 5 years of AIRS data. We compare these results to those calculated from GWs detected using another widely used method based on an amplitude cutoff. 35 % of regions of wave activity detected using the neighbourhood method have amplitudes lower than is visible using the amplitude cutoff method. Three regions are studied in greater depth: the Rocky Mountains, North Africa, and New Zealand/Tasmania. GWs detected using the neighbourhood method have wave phase propagation angles consistent with linear theory. Using the neighbourhood method produces new statistics for regional and global GW studies, which compare favourably to the amplitude cutoff GW detection method.