Ray-tracing global gravity wave observations in 21 years of AIRS data

Abstract

Gravity waves have a variety of different sources including wind flow over mountains, convection and jet stream instabilities. Yet when working with observations of gravity waves we can only make informed guesses of their sources. In this work we use GROGRAT to backwards ray trace stratospheric observations of gravity waves globally to learn more about their origins.We use observations of temperatures at 40km altitude observed by the AIRS (Atmospheric InfraRed Sounder) instrument on NASA’s Aqua satellite. From these observations we extract temperature perturbations and use the 3D Stockwell transform to derive gravity wave properties such as momentum flux, horizontal wavelength, vertical wavelength. These gravity waves are then backwards ray traced through the ERA5 atmosphere. The significance in this work lies in the volume: we ray trace 21 years (2002-2022) of AIRS data globally, representing by far the largest such observational dataset ever reverse ray-traced.By investigating the lowest traceable altitude of these rays, we can attribute the gravity waves to their sources (orographic gravity waves will originate near the surface whilst convective waves will have a higher origin). We can also investigate the horizontal propagation of orographic gravity waves from specific mountain ranges and how this changes seasonally. This work aims to answer the question: “Where do gravity waves observed by AIRS come from?”