Multi-static spatial and angular studies of polar mesospheric summer echoes combining MAARSY and KAIRA

Abstract

Abstract. Polar mesospheric summer echoes (PMSEs) have been long associated with noctilucent clouds (NLCs). For large ice particles sizes and relatively high ice densities, PMSEs at 3 m Bragg wavelengths are known to be good tracers of the atmospheric wind dynamics and to be highly correlated with NLC occurrence. Combining the Middle Atmosphere ALOMAR Radar System (MAARSY) and the Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA), i.e., monostatic and bistatic observations, we show for the first time direct evidence of limited-volume PMSE structures drifting more than 90 km almost unchanged. These structures are shown to have horizontal widths of 5–15 km and are separated by 20–60 km, consistent with structures due to atmospheric waves previously observed in NLCs from the ground and from space. Given the lower sensitivity of KAIRA, the observed features are attributed to echoes from regions with high Schmidt numbers that provide a large radar cross section. The bistatic geometry allows us to determine an upper value for the angular sensitivity of PMSEs at meter scales. We find no evidence for strong aspect sensitivity for PMSEs, which is consistent with recent observations using radar imaging approaches. Our results indicate that multi-static all-sky interferometric radar observations of PMSEs could be a powerful tool for studying mesospheric wind fields within large geographic areas.

Are mean vertical velocities from PMSE a good representation of mean vertical winds?

“…The increase of variances of the radar Doppler velocities and measurement uncertainties is expected while observing the stronger turbulent air. The weakening of PMSE at the large spectral width conditions is also known from the literature (Stober et al, 2018b;Chau et al, 2018). Hence, the explained mechanism of downward bias in PMSE vertical velocity is realistic.…”

“…Kiliani et al (2013) have shown that the westward zonal transport of the NLC is connected to cloud forming under GW influence. The horizontal advection of the PMSE patches has also been recently observed using bi-static radar measurements by Chau et al (2018). Besides theoretical and model expectations (Lindzen, 1981;Holton, 1982;Garcia and Solomon, 1985), the mean values of the vertical velocities measured by radars have shown contradicting, downward behaviour (Balsley and Riddle, 1984;Fritts et al, 1990; Hoppe and Fritts, 1995a).…”

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

“…PMSEs are considered to be an inert tracer and used to study the ambient dynamical processes in the summer polar mesosphere (Stober et al, 2013(Stober et al, , 2018a. Detailed progress in PMSE physics since the first observations by Czechowsky et al (1979) and later Ecklund and Balsley (1981) can be found in the review papers of Cho and Röttger (1997) and Rapp and Lübken (2004). Required ice clouds with particle sizes from a few to sometimes 100 nm form under dramatically low temperatures at polar mesospheric altitudes (Lübken, 1999).…”

Enhancing the spatiotemporal features of polar mesosphere summer echoes using coherent MIMO and radar imaging at MAARSY

“…PMSEs are strong echoes, more than 50 dB stronger than expected echoes from free electrons in the D region, and there is a consensus that they are generated by atmospheric turbulence and require the presence of free electrons and charged ice particles (e.g., Rapp et al, 2002;Varney et al, 2011, and references therein). Although PMSEs have been studied since the late 1970s (e.g., Ecklund and Balsley, 1981;Hoppe et al, 1988;Kelley and Ulwick, 1988;Havnes et al, 1996;Rapp and Lübken, 2004), until recently they have been considered very aspect-sensitive and homogeneous on scales of a few tens of kilometers, at least when observed at very high frequencies (VHFs) (e.g., Czechowsky et al, 1988;Zecha et al, 2001;.…”