Dynamically Unstable Strong Wind Shears Observed in the Polar Mesosphere Summer Echo Layer Associated With Geomagnetic Disturbances

• Published in: Journal of geophysical research. Space physics 2020-02, Vol.125 (2), p.n/a
• Main Authors: Lee, Young‐Sook, Kwak, Young‐Sil, Kim, Kyung‐Chan, Kim, Yong Ha
• Format: Article
• Language: English
• Subjects: Electron precipitation; Geomagnetic disturbances; Geomagnetism; high‐speed solar wind streams; Kelvin‐Helmholtz instability; Mesosphere; Polar mesosphere summer echoes; polar mesospheric summer echoes; Polar Mesospheric Summer Echoes (PMSE); Radar; Radar measurement; Richardson number; Shear rate; Shears; Solar wind; Solar wind velocity; strong wind shear; Strong winds; Very high frequencies; VHF radar; Wind profiles; Wind shear
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2019JA027013

We report observations of dynamically unstable strong wind shear (Richardson number < 0.25) capable of inducing Kelvin‐Helmholtz instability in the polar mesospheric summer echoes (PMSE) layer (80–90 km) using very high frequency radar measurements in Kiruna (67.8°N, 20.4°E), Sweden, in 2006. The unstable strong wind shear can play an important role in producing PMSE by inducing turbulence and adiabatic cooling. We find that the strong shears take up 64% of the observed wind profiles and are frequently composed of systematically single‐shear/multishear (layer) structures, which gradually or abruptly vary in wind directions, so‐called wind shifts, through heights at intervals of 4–8 km. The strong shear rate normalized by PMSE counts has a good correlation (R = 0.7) in day‐to‐day variation with energetic electron (>30 keV) precipitations that were related to high‐speed solar wind streams. The observations of strong wind shear can be supported by satellite‐measured temperature modulations matching with the peaks of the first three high‐speed solar wind stream events. This study suggests that PMSE production is closely associated with the strong shear that is in turn linked to the effects of energetic electron precipitation. Key Points Strong shears capable of producing KH instability are found in 64% of wind profiles in the PMSE layer measured by VHF radar in Esrange, Sweden Occurrences of the strong shear and PMSE have been distinctively enhanced since the arrival of high‐speed solar wind streams Normalized strong shear rates and PMSE are well correlated with energetic electron precipitation during recurrent HSS in day‐to‐day variation