SuperDARN Observations of Semidiurnal Tidal Variability in the MLT and the Response to Sudden Stratospheric Warming Events

Abstract

Using meteor wind data from the Super Dual Auroral Radar Network (SuperDARN) in the Northern Hemisphere, we (1) demonstrate that the migrating (Sun‐synchronous) tides can be separated from the nonmigrating components in the mesosphere and lower thermosphere (MLT) region and (2) use this to determine the response of the different components of the semidiurnal tide (SDT) to sudden stratospheric warming (SSW) conditions. The radars span a limited range of latitudes around 60°N and are located over nearly 180° of longitude. The migrating tide is extracted from the nonmigrating components observed in the meridional wind recorded from meteor ablation drift velocities around 95‐km altitude, and a 20‐year climatology of the different components is presented. The well‐documented late summer and wintertime maxima in the semidiurnal winds are shown to be due primarily to the migrating SDT, whereas during late autumn and spring the nonmigrating components are at least as strong as the migrating SDT. The robust behavior of the SDT components during SSWs is then examined by compositing 13 SSW events associated with an elevated stratopause recorded between 1995 and 2013. The migrating SDT is seen to reduce in amplitude immediately after SSW onset and then return anomalously strongly around 10–17 days after the SSW onset. We conclude that changes in the underlying wind direction play a role in modulating the tidal amplitude during the evolution of SSWs and that the enhancement in the midlatitude migrating SDT (previously reported in modeling studies) is observed in the MLT at least up to 60°N.

High‐Order Solar Migrating Tides Quench at SSW Onsets

“…This minimum was also reported in a case study on SSW 2009 at high latitude and a multiyear statistical study at midlatitude (He et al, ; He & Chau, ), which was attributed to energy exports in nonlinear interactions with planetary waves through the mechanism of planetary wave amplification by stimulated tidal decay. While our S2 weakening result is consistent with some abovementioned observational studies (He et al, ; He & Chau, ; Hibbins et al, ), it looks contrary to some reports of S2 enhancements during SSWs (e.g., Sridharan et al, ). The contradiction is potentially due to the fact that the enhancement and weakening are referring to different SSW stages, and time scales.…”

Climatological Westward‐Propagating Semidiurnal Tides and Their Composite Response to Sudden Stratospheric Warmings in SuperDARN and SD‐WACCM‐X

“…Hence, our results complement and extend the observational study of Hibbins et al. (2019) using SuperDARN and the model study of Limpasuvan et al. (2016) based on WACCM as well as the work of He and Chau (2019) using SMR.…”

“…Recently, Hibbins et al. (2019) combined multiple, simultaneous single‐station radar observations to separate longitudinal from temporal variations and to explicitly extract SW1, SW2, and SW3. Clustered around 60°N, these stations measure horizontal winds around 95 km as part of the Super Dual Auroral Radar Network (SuperDARN).…”

Migrating tide climatologies measured by a high-latitude array of SuperDARN HF radars

“…For comparison with ground-based instruments, vertical profiles of NAVGEM-HA analyzed winds and temperatures are converted from the model vertical grid in geopotential altitude to a geometric altitude grid. To date, NAVGEM-HA winds and tides have been shown to be in good agreement with ground-based meteor radar observations (McCormack et al, 2017;Eckermann et al, 2018;Laskar et al, 2019;Stober et al, 2020) and with independent satellite-based wind observations as reported in Dhadly et al (2018). In the present study we employ NAVGEM-HA analyzed winds at 82.5 km altitude, staying below altitudes where effects of increased numerical diffusion imposed at the NAVGEM-HA upper boundary may impact the tides, to validate the method of extracting migrating tidal signatures from the SD meteor wind data.…”