Observation of Kelvin–Helmholtz instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

Abstract

Abstract. We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short-period wave-like features using polar mesospheric summer echoes (PMSEs) as a tracer for the neutral dynamics. We conducted a multibeam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two Kelvin–Helmholtz instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Ri < 0.25. In addition, we observed 15 wave-like events in our MAARSY multibeam observations applying a sophisticated decomposition of the radial velocity measurements using volume velocity processing. We retrieved the horizontal wavelength, intrinsic frequency, propagation direction, and phase speed from the horizontally resolved wind variability for 15 events. These events showed horizontal wavelengths between 20 and 40 km, vertical wavelengths between 5 and 10 km, and rather high intrinsic phase speeds between 45 and 85 m s−1 with intrinsic periods of 5–10 min.

VHF radar measurements of momentum flux using summer polar mesopause echoes

“…2. We note that clear signatures of KH instabilities were observed in wintertime using this radar by Reid et al (1987), and more recently in PMSE over Andøya by Stober et al (2018).…”

Can VHF radars at polar latitudes measure mean vertical winds in the presence of PMSE?

“…It results in ice spheres from 5 to ∼ 35 nm from the altitude range of 90 down to 82 km and a rapid decrease to a few nanometres at the lower altitudes. Observations sometimes show the NLC with the ice particles in 100 nm (von Cossart et al, 1999). Therefore the second scenario considers the extreme size distribution of ice grains from 10 to 100 nm at the above-mentioned altitudes.…”

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

“…Using phased arrays with electronic beam steering, modern atmospheric radars also provide horizontal information using a multibeam approach (e.g., Fukao et al, 1985;Latteck et al, 2012;Sato et al, 2014). Although the horizontal coverage is extended with this approach, the relatively long correlation time of atmospheric targets, the effects of a truncated antenna aperture, and the way electronic phasing is done (i.e., from pulse to pulse), the achieved angular and temporal resolutions have not been good enough to resolve atmospheric structures in the scales of kilometer-and minute-resolution, at least in the mesosphere (e.g., Stober et al, 2018). Besides the multibeam approach, in-beam radar imaging of ionospheric and atmospheric irregularities has been implemented.…”