Observations of PW activity in the MLT during SSW events using a chain of SuperDARN radars and SD-WACCM

Abstract

Abstract. This study investigates the effect of Stratospheric Sudden Warmings (SSWs) on Planetary Wave (PW) activity in the Mesosphere-Lower Thermosphere (MLT). PW activity near 95 km is derived from meteor wind data using a chain of 8 SuperDARN radars at high northern latitudes that span longitudes from 150° W to 25° E and latitudes from 51 to 66° N. Zonal wave number 1 and 2 components were extracted from the meridional wind for the years 2000–2008. The observed wintertime PW activity shows common features associated with the stratospheric wind reversals and the accompanying stratospheric warming events. Onset dates for seven SSW events accompanied by an elevated stratopause (ES) were identified during this time period using the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM). For the seven events, a significant enhancement in wave number 1 and 2 PW amplitudes near 95 km was found to occur after the wind reversed at 50 km, with amplitudes maximizing approximately 5 days after the onset of the wind reversal. This PW enhancement in the MLT after the event was confirmed using SD-WACCM. When all cases of polar cap wind reversals at 50 km were considered, a significant, albeit moderate, correlation of 0.4 was found between PW amplitudes near 95 km and westward polar-cap stratospheric winds at 50 km, with the maximum correlation occurring ~3 days after the maximum westward wind. These results indicate that the enhancement of PW amplitudes near 95 km are a common feature of SSWs irrespective of the strength of the wind reversal.

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

“…The WAF then continues to propagate upward and equatorward, converging in the middle mesosphere. The presence of wintertime QSPW1 in the MLT has been readily observed in satellite observations (e.g., Smith, 1997), SuperDARN observations (e.g., Stray et al., 2015a, 2015b), and model simulations (e.g., Smith, 2003), particularly in association with SSW (e.g., Limpasuvan et al., 2016). These waves may be associated with the longitudinally varying gravity wave drag due to the underlying planetary‐scale wind variation (Smith, 2003).…”

“…The amplitude and phase of planetary‐scale tidal winds can be obtained by fitting daily winds as a function of longitude. By similar fitting techniques, observations from the same eight SuperDARN stations have been used to infer PW climatology and variability (Kleinknecht et al., 2014; Stray et al., 2015a, 2015b). Here, we utilize the derived SuperDARN data between 1995 and 2016, as in Hibbins et al.…”