2019, Laskar, F.I., Stober, G., Fiedler, J., Oppenheim, M.M., Chau, J.L., Pallamraju, D., Pedatella, N.M., Tsutsumi, M., Renkwitz, T.

The Andenes specular meteor radar shows meteor trail diffusion rates increasing on average by about 10% at times and locations where a lidar observes noctilucent clouds (NLCs). This high-latitude effect has been attributed to the presence of charged NLC after exploring possible contributions from thermal tides. To make this claim, the current study evaluates data from three stations at high, middle, and low latitudes for the years 2012 to 2016 to show that NLC influence on the meteor trail diffusion is independent of thermal tides. The observations also show that the meteor trail diffusion enhancement during NLC cover exists only at high latitudes and near the peaks of NLC layers. This paper discusses a number of possible explanations for changes in the regions with NLCs and leans towards the hypothesis that the relative abundance of background electron density plays the leading role. A more accurate model of the meteor trail diffusion around NLC particles would help researchers determine mesospheric temperature and neutral density profiles from meteor radars at high latitudes. © 2019 Author(s).

2020, Chau, J.L., Urco, J.M., Avsarkisov, V., Vierinen, J.P., Latteck, R., Hall, C.M., Tsutsumi, M.

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 4) numbers, the observed event is a KHI that occurs under weak stratification and generates strong turbulence. © 2019. The Authors.