High-Frequency Gravity Waves and Kelvin-Helmholtz Billows in the Tropical UTLS, as Seen From Radar Observations of Vertical Wind

The present study analyzes novel observations of vertical wind (Formula presented.) in the tropical upper troposphere-lower stratosphere obtained from a radar wind profiler in Cochin, India. Between December 2022 and April 2023, 63 consecutive 4 hr curtains of (Formula presented.) were measured with a vertical spacing of 180 m and a sampling time step of 44 s, thus resolving almost the whole spectrum of vertical motions. Spectra of (Formula presented.) strongly vary with altitude. They are generally flat up to the local Brunt-Väisälä frequency (BVF), but sometimes exhibit a peak of (Formula presented.) variance closer to BVF, a feature which may be attributed to trapped gravity waves. At other times and locations, the (Formula presented.) profiles reveal Kelvin-Helmholtz billows. Finally, the variability of (Formula presented.) variance over the 4 month campaign period is investigated. Using brightness temperature from geostationary satellites as a convective proxy, it is found that (Formula presented.) variance is highly correlated with fluctuations in convective activity.