Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)

Abstract

Abstract. Atmospheric temperatures and winds in the mesosphere and lower thermosphere have been measured simultaneously using the Aura satellite and a meteor radar at Bear Lake Observatory (42 • N, 111 • W), respectively. The data presented in this study is from the interval March 2008 to July 2011.The mean winds observed in the summer-time over Bear Lake Observatory show the meridional winds to be equatorward at meteor heights during April-August and to reach monthly-mean velocities of −12 m s −1 . The mean winds are closely related to temperatures in this region of the atmosphere and in the summer the coldest mesospheric temperatures occur about the same time as the strongest equatorward meridional winds. The zonal winds are eastward through most of the year and in the summer strong eastward zonal wind shears of up to ∼4.5 m s −1 km −1 are present. However, westward winds are observed at the upper heights in winter and sometimes during the equinoxes. Considerable inter-annual variability is observed in the mean winds and temperatures.Comparisons of the observed winds with URAP and HWM-07 reveal some large differences. Our radar zonal wind observations are generally more eastward than predicted by the URAP model zonal winds. Considering the radar meridional winds, in comparison to HWM-07 our observations reveal equatorward flow at all meteor heights in the summer whereas HWM-07 suggests that only weakly equatorward, or even poleward flows occur at the lower heights. However, the zonal winds observed by the radar and modelled by HWM-07 are generally similar in structure and strength.Signatures of the 16-and 5-day planetary waves are clearly evident in both the radar-wind data and Aura-temperature data. Short-lived wave events can reach large amplitudes of up to ∼15 m s −1 and 8 K and 20 m s −1 and 10 K for the 16-and 5-day waves, respectively. A clear seasonal and shortterm variability are observed in the 16-and 5-day planetary wave amplitudes. The 16-day wave reaches largest amplitude in winter and is also present in summer, but with smaller amplitudes. The 5-day wave reaches largest amplitude in winter and in late summer. An inter-annual variability in the amplitude of the planetary waves is evident in the four years of observations. Some 41 episodes of large-amplitude wave occurrence are identified. Temperature and wind amplitudes for these episodes, A T and A W , that passed the Student T-test were found to be related by, A T = 0.34 A W and A T = 0.62 A W for the 16-and 5-day wave, respectively.

Study of the Quasi‐5‐Day Wave in the MLT Region by a Meteor Radar Chain

“…Four approximate heights (~81, ~86, ~91, and ~97 km) are converted from the pressure levels via equation . Our conversion is consistent with a previous MLS temperature study (Day et al, ). The MLS data in the four altitudes and at the three latitude bands of ±2° latitude centered at MH (53.5°N), BJ (40.3°N), and WH (30.5°N) are used in this study.…”

“…Using meteor radar measurements at the Bear Lake Observatory (42°N, 111°W) in the period from March 2008 to July 2011, Day et al () found that 5DWs in both neutral wind components obtain the largest amplitudes in winter and late summer. The 5DW amplitudes over BJ, which has a similar latitude to the Bear Lake Observatory, are very different in different wind components.…”

Study of Mean Wind Variations and Gravity Wave Forcing Via a Meteor Radar Chain and Comparison with HWM‐07 Results

“…Placke et al () reported that the 3‐monthly mean zonal wind shows stronger interannual variability in winter than in summer based on meteor radar measurements at Collm (51.3°N) during 2004 to 2009. Day et al () observed seasonal oscillations from the mean winds at Bear Lake Observatory (42°N, 111°W). Using meteor radar measurements obtained during 2002 to 2004 at Wuhan (30.6°N), Zhao et al () demonstrated that the MLT zonal wind has a strong shear in solstices and the meridional wind is largely northward in the winter.…”

Annual and interannual variations in global 6.5DWs from 20 to 110 km during 2002–2016 observed by TIMED/SABER

“…As a kind of global wave component from the stratosphere to the MLT, 6.5DW traces have been widely detected in several atmospheric parameters, such as zonal wind (10-30 m/s) [Wu et al, 1994;Meyer and Forbes, 1997;Talaat et al, 2001;Kishore et al, 2004;Lima et al, 2005;Jiang et al, 2008;Day et al, 2012], meridional winds (10-20 m/s) [Wu et al, 1994;Talaat et al, 2001], temperature (10-15 K) [Talaat et al, 2001;Riggin et al, 2006;Day et al, 2012], atomic oxygen (~4 × 10 5 m À6 ) [Talaat et al, 2001], and occurrences of the sporadic E (Es) layer [Zuo and Wan, 2008]. In polar summer mesopause regions, 6.5DWs are even found to modulate short-term variations of polar mesospheric clouds [Merkel et al, 2003[Merkel et al, , 2008von Savigny et al, 2007;Nielsen et al, 2010] and polar mesospheric summer echoes [Kirkwood and Réchou, 1998;Kirkwood et al, 2002].…”