Abstract
Abstract. Four mesosphere–lower thermosphere temperature and turbulence profiles were obtained in situ within ∼30 min and over an area of about 100 by 100 km during a sounding rocket experiment conducted on 26 January 2015 at Poker Flat Research Range in Alaska. In this paper we examine the spatial and temporal variability of mesospheric turbulence in relationship to the static stability of the background atmosphere. Using active payload attitude control, neutral density fluctuations, a tracer for turbulence, were observed with very little interference from the payload spin motion, and with high precision (<0.01 %) at sub-meter resolution. The large-scale vertical temperature structure was very consistent between the four soundings. The mesosphere was almost isothermal, which means more stratified, between 60 and 80 km, and again between 88 and 95 km. The stratified regions adjoined quasi-adiabatic regions assumed to be well mixed. Additional evidence of vertical transport and convective activity comes from sodium densities and trimethyl aluminum trail development, respectively, which were both observed simultaneously with the in situ measurements. We found considerable kilometer-scale temperature variability with amplitudes of 20 K in the stratified region below 80 km. Several thin turbulent layers were embedded in this region, differing in width and altitude for each profile. Energy dissipation rates varied between 0.1 and 10 mW kg−1, which is typical for the winter mesosphere. Very little turbulence was observed above 82 km, consistent with very weak small-scale gravity wave activity in the upper mesosphere during the launch night. On the other hand, above the cold and prominent mesopause at 102 km, large temperature excursions of +40 to +70 K were observed. Simultaneous wind measurements revealed extreme wind shears near 108 km, and combined with the observed temperature gradient, isolated regions of unstable Richardson numbers (0<Ri<0.25) were detected in the lower thermosphere. The experiment was launched into a bright auroral arc under moderately disturbed conditions (Kp∼5).
Highlights
The structure and dynamics of the mesosphere are largely determined by atmospheric gravity waves (GWs) propagating from the lower atmosphere (e.g., Fritts and Alexander, 2003)
No attitude control system (ACS) maneuver or other payload event occurred at this time that could have perturbed both measurements, and the angleof-attack analysis performed by NASA Wallops Flight Facility showed no deviation; we suggest that a large wind may have altered the drag force
The Mesosphere Turbulence Experiment (MTeX) flights achieved a higher apogee (156 vs. 135 km) and higher Mach numbers (M ∼ 4.5 vs. 4.0) than the earlier flight, we find that extrapolating these ram factors works well for our flights
Summary
The structure and dynamics of the mesosphere are largely determined by atmospheric gravity waves (GWs) propagating from the lower atmosphere (e.g., Fritts and Alexander, 2003). Large temperature and wind amplitudes lead to GW breaking, instabilities and intermittent turbulence. Such processes are too small to be included in global atmosphere models and must be parameterized with eddy diffusion coefficients. Large and variable eddy diffusion causes enhanced transport of minor species, e.g., O and NO, which in turn modify the structure and energy balance of the upper atmosphere (Qian et al, 2009; Meraner and Schmidt, 2016).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
