Exploring long-term satellite observations of global 3-D gravity wave characteristics in the stratosphere

Atmospheric gravity waves are a fundamental component of the Earth’s dynamical system. These mesoscale waves play a key role in the coupling of different atmospheric layers, acting as crucial drivers of the middle atmospheric circulation through the transport and deposition of energy and momentum. As Global Circulation Models (GCMs) achieve ever higher resolution in the stratosphere, there is a need to ensure that the simulated gravity waves resolved in these models are well constrained by observations, which in turn ensures that modelled circulations are realistic and not over-dependent on tuning with parameterisations. However, obtaining 3-D gravity-wave measurements in the real atmosphere is notoriously difficult. Global 3-D observations of wave properties in the stratosphere are required in order to accurately estimate gravity wave fluxes that can be compared to models. Here we analyse a unique long-term satellite dataset of specialised high-resolution 3-D temperature measurements from NASA’s AIRS/Aqua instrument from 2002-2020. By analysing these data with a 3-D Stockwell transform (3DST) using high-performance computing, we can reveal global distributions of gravity-wave amplitudes, wavelengths, intermittency and directional momentum fluxes in the stratosphere across two decades - the largest such 3-D study of stratospheric gravity waves performed yet. This long-term dataset reveals solar-cycle variability of gravity-wave amplitudes in the tropics, significant reductions in gravity-wave fluxes during southern Sudden Stratospheric Warmings (SSWs) and the persistent oblique propagation of wintertime gravity waves into the southern polar vortex around 60S each year, a phenomenon that is not observed in the northern hemisphere. With these new observations we can begin to better constrain simulated gravity waves and their impacts in GCMs, ultimately leading to better forecasts of weather and climate.