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 eight 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 is a common feature of SSWs irrespective of the strength of the wind reversal.
Highlights
Stratospheric sudden warmings (SSWs) are dramatic breakdowns of the polar vortex occurring in the polar wintertime that can dynamically couple the atmosphere all the way from the troposphere into the ionosphere (e.g., Limpasuvan et al, 2004; Goncharenko et al, 2010; Pancheva and Mukhtarov, 2011; Yuan et al, 2012)
Limpasuvan et al (2012) mentioned in a case study using WACCM that the elevated stratopause (ES) event was accompanied by a planetary wave (PW) in the mesosphere–lower thermosphere (MLT) region, and Chandran et al (2013a) later established a climatology of stratospheric sudden warmings (SSWs) events using WACCM
Chandran et al (2013a) reported that the majority of SSW events studied were accompanied by an increase in PW amplitudes in the MLT
Summary
Stratospheric sudden warmings (SSWs) are dramatic breakdowns of the polar vortex occurring in the polar wintertime that can dynamically couple the atmosphere all the way from the troposphere into the ionosphere (e.g., Limpasuvan et al, 2004; Goncharenko et al, 2010; Pancheva and Mukhtarov, 2011; Yuan et al, 2012). In addition to these model results, Chandran et al (2013b) observed an enhancement of PW amplitudes and a change of their longitudinal propagation speed in the MLT in connection with a strong SSW event in January 2012 using the Specified Dynamics Whole Atmosphere Community Climate Model (SD-WACCM) and temperatures from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument This event was noteworthy in that it was strong, with the total zonal-mean zonal wind at 50 km (averaged from 50–77◦ N) reaching westward wind speeds of more than 40 m s−1 during the reversal. It should be noted that no polar cap wind reversals lasting at least 4 days occurred 40 days prior to the seven SSW ES events studied, ensuring that the baseline was not disturbed by a previous event Composites of these seven SSW ES events were made for the modeled temperature, wind and PW activity using SD-WACCM and for the PW activity observed by the SuperDARN chain. The mean elevated stratopause, clearly visible at around 70 km after the warming, is not representative of the individual stratopause jumps in the composite
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