Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Abstract

We investigated characteristics of mesosphere echoes over Syowa Station (69S) in the Antarctic, which were detected by the Program of the Antarctic Syowa Mesosphere, Stratosphere and Troposphere/Incoherent Scatter (PANSY) radar (47 MHz) and Medium Frequency (MF) radar (2.4 MHz). Winter echoes from the PANSY radar and low altitude MF echoes below approximately 70−75 km mostly coexisted, appearing during the daytime as well as for a few hours post sunset. Summer echoes in the lower height region were absent in both radar observations, suggesting a close relationship in the generation mechanisms of these two radar echoes. High correlation between local K-index and the occurrence of winter echoes suggested that electron density enhancement due to ionized particle precipitation was one of the triggers of echo generation. Angles of arrival of the MF echoes were more isotropic in winter. Because gravity wave activity is much higher in winter over Syowa, higher turbulence energy caused by gravity wave breaking may also be responsible for the generation of the winter echoes and their isotropic behavior. The horizontal wind velocities of the two systems were further compared and agreed well throughout the height region of 60−90 km.

A Statistical Analysis of the Energy Dissipation Rate Estimated From the PMWE Spectral Width in the Antarctic

“…The minimum η with a detectability threshold of 3 taken for the present radar observations was approximately 1 × 10 −18 m −1 . Note that since previous studies of PMWE using the PANSY radar (Nishiyama et al, 2015(Nishiyama et al, , 2018Tsutsumi et al, 2017) are based on observations using the above-mentioned partial system, the minimum detectable η for these studies is approximately 10 times larger than that of the present study. We assumed that the scattering volume is filled by turbulence although the sparsity of PMWE might cause underestimation of η of the PMWE (Kirkwood, Chilson, et al, 2006).…”

“…Note that the effect of partial reflection is considered negligible in the mesosphere (Fukao et al, 2014; Hocking et al, 2016). The analyses were made for the height range of 55 to 82 km, where most PMWEs are observed (e.g., Tsutsumi et al, 2017). The number of vertical profiles of PMWE was ~12,000 per month on average during the analyzed period.…”

“…The local time dependence of the height distribution of PMWE is well reproduced by the theoretical calculation of the radar volume reflectivity associated with turbulence in the ionized atmosphere (Latteck & Strelnikova, 2015). Previous studies have reported PMWE occurrence in association with ionospheric disturbances, including geomagnetic disturbances, solar proton events, and auroral breakups (e.g., Kataoka et al, 2019; Nishiyama et al, 2018; Tsutsumi et al, 2017).…”

“…The mechanism of PMWE is not fully understood since these echoes are less frequent and weaker than the polar mesosphere summer echoes (PMSEs) that are observed mainly in the 80–92 km height region. Several mechanisms for PMWE that have been previously suggested include strong air turbulence (Lübken, 2014; Lübken et al, 2006, 2007; Tsutsumi et al, 2017) and highly damped ion‐acoustic waves (Kirkwood, 2007; Kirkwood, Belova, et al, 2006) in the ionized atmosphere. Recent studies have suggested that the large Schmidt number associated with charged meteor smoke particles may be responsible for the appearance of PMWE (e.g., Kavanagh et al, 2006; La Hoz & Havnes, 2008).…”

Frequency spectra of horizontal winds in the mesosphere and lower thermosphere region from multistatic specular meteor radar observations during the SIMONe 2018 campaign

“…Another technique to observe mesospheric GWs is the imaging of airglow emission layers, which provides information about spatial and temporal characteristics of the GWs (e.g., Swenson and Mende 1994;Medeiros et al 2003;Espy et al 2004;Vargas et al 2007Vargas et al , 2016Wüst et al 2017;Taylor et al 2019;Vargas 2019). Mesospherestratosphere-troposphere (MST), medium frequency (MF), incoherent scatter and specular meteor radars (SMRs) are some of the various types of radars utilized to estimate mean winds and correlations, from which it is possible to examine GWs and turbulence in the MLT region (e.g., Gage and Balsley 1984;Reid 1990;Nakamura et al 1993;Zhou 2000;Antonita et al 2008;Fritts et al 2010;Placke et al 2011aPlacke et al ,b, 2015Yasui et al 2016;Tsutsumi et al 2017;Reid et al 2018).…”