Long-Lived High-Frequency Gravity Waves over the Southern Ocean and the East Antarctic coastline and Their Influence on Cloud Properties

Abstract. The Southern Ocean near the East Antarctic coast is a dynamic source of gravity waves, yet long-lived high-frequency gravity waves (HFGWs) remain poorly documented. Using four months of ship-based remote sensing and in-situ observations, this study analyses the characteristics of HFGWs and their influence on cloud properties near three Antarctic coastal stations (Davis, Casey, and Mawson) through statistical analyses and detailed case studies. Doppler vertical velocity oscillations are observed in clouds with tops around 8 km, with amplitudes mainly near 0.02 m s^-1. These clouds are primarily ice. Based on radiosonde ascent rates and Richardson number analysis, the oscillations are identified as gravity waves. The observed gravity waves typically exhibit periods close to the buoyancy period (about 10 minutes) and horizontal wavelengths of 3 km, and can be tracked for up to 48 hours (approximately 220–320 wave cycles). Approximately 46 % of valid Doppler velocity data within clouds exhibited high-frequency oscillations associated with HFGWs. These occurrences covered 91 % of cloudy days, indicating that such waves are ubiquitous. Periodic variations in reflectivity further suggest that these waves modulate cloud properties. Potential sources of the HFGWs are investigated using air-mass trajectories, ERA5 reanalysis, and MODIS observations. The waves are most likely generated by multiple sources including cyclonic activity, katabatic winds, and jet-related synoptic forcing. In some cases a thermal duct, together with a concurrent low-frequency gravity wave background, provides a multiscale environment that likely supports the HFGWs long-lived nature.