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Four‐Dimensional Quantification of Kelvin‐Helmholtz Instabilities in the Polar Summer Mesosphere Using Volumetric Radar Imaging

2019; American Geophysical Union; Volume: 47; Issue: 1 Linguagem: Inglês

10.1029/2019gl086081

1944-8007

Jorge L. Chau, Juan Miguel Urco, Victor Avsarkisov, Juha Vierinen, Ralph Latteck, Chris Hall, Masaki Tsutsumi,

Oceanographic and Atmospheric Processes

Abstract We present and characterize in time and three spatial dimensions a Kelvin‐Helmholtz Instability (KHI) event from polar mesospheric summer echoes (PMSE) observed with the Middle Atmosphere Alomar Radar System. We use a newly developed radar imaging mode, which observed PMSE intensity and line of sight velocity with high temporal and angular resolution. The identified KHI event occurs in a narrow layer of 2.4 km thickness centered at 85 km altitude, is elongated along north‐south direction, presents separation between billows of 8 km in the east‐west direction, and its billow width is 3 km. The accompanying vertical gradients of the horizontal wind are between 35 and 45 m/s/km and vertical velocities inside the billows are 12 m/s. Based on the estimated Richardson ( 0.25), horizontal Froude ( 0.8), and buoyancy Reynolds ( 2.5 10 ) numbers, the observed event is a KHI that occurs under weak stratification and generates strong turbulence.