Observations of Reduced Turbulence and Wave Activity in the Arctic Middle Atmosphere Following the January 2015 Sudden Stratospheric Warming

Abstract

Measurements of turbulence and waves were made as part of the Mesosphere‐Lower Thermosphere Turbulence Experiment (MTeX) on the night of 25–26 January 2015 at Poker Flat Research Range, Chatanika, Alaska (65°N, 147°W). Rocket‐borne ionization gauge measurements revealed turbulence in the 70‐ to 88‐km altitude region with energy dissipation rates between 0.1 and 24 mW/kg with an average value of 2.6 mW/kg. The eddy diffusion coefficient varied between 0.3 and 134 m2/s with an average value of 10 m2/s. Turbulence was detected around mesospheric inversion layers (MILs) in both the topside and bottomside of the MILs. These low levels of turbulence were measured after a minor sudden stratospheric warming when the circulation continued to be disturbed by planetary waves and winds remained weak in the stratosphere and mesosphere. Ground‐based lidar measurements characterized the ensemble of inertia‐gravity waves and monochromatic gravity waves. The ensemble of inertia‐gravity waves had a specific potential energy of 0.8 J/kg over the 40‐ to 50‐km altitude region, one of the lowest values recorded at Chatanika. The turbulence measurements coincided with the overturning of a 2.5‐hr monochromatic gravity wave in a depth of 3 km at 85 km. The energy dissipation rates were estimated to be 3 mW/kg for the ensemble of waves and 18 mW/kg for the monochromatic wave. The MTeX observations reveal low levels of turbulence associated with low levels of gravity wave activity. In the light of other Arctic observations and model studies, these observations suggest that there may be reduced turbulence during disturbed winters.

RC1 Author's Response

“…Characterizing the large features of the profile, we observe a relatively warm winter mesosphere up to 80 km, a quasi-adiabatic region between 80 and 88 km, another stable region up to 95 km, followed by a second quasi-adiabatic region up to the mesopause at 170 K and 102 km. The two bottommost regions agree well with the Rayleigh lidar temperatures (Triplett et al, 2018). The lower thermosphere is highly structured; the upleg profiles have temperature excursions up to 60 K warmer than MSIS between 105 and 110 km.…”

“…Consecutive lidar profiles showed that the wave activity, based on the lidar temperatures during the night, was relatively weak and at the time of the launches only small inversion layers near 61 and 70 km were present over the launch site. The nightly lidar average also reproduces the strongly negative temperature gradient above 80 km (Triplett et al, 2018).…”

“…Our method to calculate atmospheric densities using calibration data and ram correction follows the standard pro- cedure (Rapp et al, 2001) and is independent from external data sets (except the start temperature). An alternative method is to use the relative density profile from the nightly averaged Rayleigh lidar signal to normalize the CONE current data, which results in smoother density gradients and temperatures (Triplett et al, 2018).…”

“…A payload description and first results have been provided by Collins et al (2015). The atmospheric conditions during the launch night, the change in lidar temperatures and sodium densities throughout the night, which includes a large overturning structure in the sodium layer during the rocket launches are described by Triplett et al (2018). This paper also puts the MTeX results in the larger context of the prevailing stratospheric conditions and provides an analysis of the gravity wave activity based on lidar observations.…”

PMC Turbo: Studying Gravity Wave and Instability Dynamics in the Summer Mesosphere Using Polar Mesospheric Cloud Imaging and Profiling From a Stratospheric Balloon

“…Instabilities arising due to GWs take various forms, depending on the GW character, amplitude, and environment (Lombard & Riley, 1996;Sonmor & Klaassen, 1997;Staquet & Sommeria, 2002). Observations have provided evidence of overturning and breaking of GWs having relatively high intrinsic frequencies at altitudes from the troposphere into the MLT (Eckermann et al, 2016;Franke & Collins, 2003;Fritts et al, 1993Fritts et al, , 2017Fritts, Vosper, et al, 2018;Hecht et al, 1997;Lilly & Kennedy, 1973;Swenson & Mende, 1994;Triplett et al, 2018;Whiteway et al, 2003;Witt, 1962). In contrast, GWs having near-inertial frequencies are expected and observed to exhibit Kelvin-Helmholtz instabilities (KHI; Lelong & Dunkerton, 1998a, 1998bPavelin et al, 2001;Stober et al, 2018).…”