Convection-generated gravity waves in the tropical lower stratosphere from Aeolus wind profiling, GNSS-RO, and ERA5 reanalysis

Abstract

The European Space Agency's Aeolus satellite, equipped with the Atmospheric LAser Doppler INstrument (ALADIN), provides near-global wind profiles from the surface to about 30 km altitude. These wind measurements enable the investigation of atmospheric dynamics, including gravity waves (GWs) in the upper troposphere and lower stratosphere (UTLS). This study analyzes ALADIN wind observations and ERA5 reanalysis by deriving GW kinetic energy (Ek) distributions and examining their temporal and spatial variability throughout the tropical UTLS. A prominent hotspot of enhanced GW activity is identified by Aeolus, migrating from the Indian Ocean in boreal summer to the Maritime Continent in boreal winter, closely matching outgoing longwave radiation minima and, thus, highlighting convective origins. Results show that ERA5 consistently underestimates Ek in convective regions, especially over the Indian Ocean, where conventional wind measurements are sparse. Additional comparisons with Global Navigation Satellite System Radio Occultation (GNSS-RO) measurements of GW potential energy (Ep) corroborate these findings and suggest a significant underrepresentation of convection-driven wave activity in reanalyses. A multi-instrumental exploratory analysis also allows one to verify the empirical grounding of the established Ek/Ep ratio. By providing direct wind measurements in otherwise data-sparse regions, Aeolus offers a valuable dataset for evaluating and potentially improving the representation of GWs in reanalyses, particularly in remote tropical areas. The combination of Aeolus and GNSS-RO data allows for an observationally based examination of the partitioning between kinetic and potential energy, highlighting discrepancies with reanalysis products that could inform future model parameterization development.