Impact of Strong and Weak Stratospheric Polar Vortices on the Mesosphere and Lower Thermosphere

Abstract

The stratospheric polar vortex is associated with strong eastward winds in the high latitude, wintertime, stratosphere. The occurrence, or absence, of strong tropospheric planetary wave activity leads to large variability in the strength of the polar vortex. Upward propagating planetary waves weaken the polar vortex resulting in a deceleration, and potential reversal, of the stratospheric winds at high latitudes (Matsuno, 1971). Weakening of the polar vortex is typically associated with sudden stratospheric warming (SSW) events (Charlton & Polvani, 2007). Likewise, the absence of strong tropospheric planetary wave activity leads to a strong polar vortex (e.g., Lawrence et al., 2020). Since tropospheric planetary wave variability is stronger, and more variable, in the Northern Hemisphere (NH), the stratospheric polar vortex exhibits significantly greater variability in the NH compared to the Southern Hemisphere (SH; Waugh & Randel, 1999). Understanding the role of the polar vortex on atmospheric coupling processes has attracted considerable attention in recent decades owing to its good predictability and wide range of impacts throughout the entirety of Earth's atmosphere (Baldwin et al., 2021).The impact of the polar vortex on the middle and upper atmospheres has focused largely on SSW (i.e., weak vortex) events. Sudden stratospheric warmings lead to considerable impacts throughout the middle and upper atmospheres, including changes in: mesosphere composition, temperature, and winds; ionosphere electron densities, electrodynamics, and irregularities; and thermosphere composition, density, and temperature (see reviews

Influence of Stratosphere Polar Vortex Variability on the Mesosphere, Thermosphere, and Ionosphere

“…The temperature anomalies in the Southern Hemisphere MLT are slightly lower than those in the Northern Hemisphere MLT, which is consistent with previous results (Karlsson et al., 2009; Körnich & Becker, 2010) and attributed to hemispheric differences in the circulation and gravity wave drag. Though there are some minor differences in the equatorial upper stratosphere and lower mesosphere, the zonal mean zonal wind anomalies are also consistent with N. M. Pedatella and Harvey (2022). The 40 Northern Hemisphere winters simulated by the free‐running WACCM‐X thus reproduce the zonal mean anomalies found previously in SD‐WACCM‐X, which were also shown to be consistent with Aura Microwave Limb Sounder observations (N. M. Pedatella & Harvey, 2022).…”

“…This suggests that decreases in the semidiurnal tidal amplitude during strong stratosphere polar vortex time periods may not entirely dominate the changes in the thermosphere temperature, and that other factors may be equally as important. This is not entirely surprising as the enhancement in the semidiurnal tide during weak stratosphere polar vortex events is considerably larger than the decrease during strong stratosphere polar vortex events (N. M. Pedatella & Harvey, 2022). In the middle to upper thermosphere, the zonal mean zonal wind anomalies during weak stratosphere polar vortex time periods are westward with maxima of ∼10 m/s at middle latitudes near 10 −5 hPa.…”

“…To eliminate any influence of solar and geomagnetic activity, the simulations were performed with a constant solar flux of 70 solar flux units and a K p of 0 + . Similar to N. M. Pedatella and Harvey (2022), we use the Northern Annular Mode (NAM) at 10 hPa as a measure of the strength of the stratosphere polar vortex. The NAM is calculated based on the polar cap (>65°N) average geopotential height anomalies (Gerber & Martineau, 2018).…”

Day‐to‐Day Variability of the Semidiurnal Tide in the F‐Region Ionosphere During the January 2021 SSW From COSMIC‐2 and ICON

“…E-region dynamo modulation is also the most likely explanation for the close correspondence between the day-to-day variations in the tidal wind and plasma amplitudes. N. M. Pedatella and Harvey (2022) recently reported a high correlation between the strength of the polar vortex and mesosphere/lower thermosphere tides from analyzing Microwave Limb Sounder (MLS) data and Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (SD-WACCMX) model simulations, with a semidiurnal tidal reduction of about 25% during strong polar vortex times. Their modeled daily SW2 variability during northern hemisphere winter showed a linear correlation of −0.62 with daily variations in the strength of the polar vortex (expressed through the Northern Annular Mode).…”

CIPS Observations of Gravity Wave Activity at the Edge of the Polar Vortices and Coupling to the Ionosphere

“…Becker, Goncharenko, et al (2022) showed that this link involves the MSVC process. During strong vortex states GWs have larger amplitudes and tidal variations have smaller amplitudes in the MLT compared to during weak vortex states such as SSWs (Pedatella & Harvey, 2022). Since the strength of the polar vortex can be predicted up to 2 weeks with some accuracy (Butler et al, 2019), the relationship between vortex strength, GWs, and ionospheric phenomena may be used to better predict some ionospheric variability (Harvey et al, 2022).…”