Energetic electron precipitation (EEP) affects the high‐latitude middle atmosphere by producing NOX compounds that destroy ozone. Earlier studies have shown that in the wintertime polar stratosphere, increased EEP enhances the westerly wind surrounding the pole, the polar vortex. This EEP effect has been found to depend on the quasi‐biennial oscillation (QBO) of equatorial winds, but the mechanism behind this modulation has so far remained unresolved. In this study we examine the atmospheric effect of EEP and its modulation by QBO using the corrected electron flux measurements by NOAA/POES satellites and the ERA‐Interim reanalysis data of zonal wind, temperature, and ozone in winter months of 1980–2016. We verify the EEP‐related strengthening of the polar vortex, warming (cooling) in the upper (lower) stratosphere and a reduction of ozone mass mixing ratio in the polar stratosphere. We also verify that the EEP effect is stronger and more significant especially in late winter, when the QBO at 30 hPa is easterly. We find here that the difference in the EEP effect between the two QBO phases is largest using a roughly 6‐month lag for QBO. We demonstrate that ozone mass mixing ratio in the lower polar stratosphere, a proxy for the strength of Brewer‐Dobson circulation, is also larger during QBO‐E than QBO‐W, with the difference maximizing when the QBO is lagged by 6 months. Our findings indicate that the modulation of the Brewer‐Dobson circulation by QBO controls how the EEP affects the polar vortex.

The Northern polar vortex experiences considerable interannual variability, which is also reflected to tropospheric weather. Recent research has established a link between polar vortex variations and energetic electron precipitation (EEP) from the near-Earth space into the polar atmosphere, which is mediated by EEP-induced chemical changes causing ozone loss in the mesosphere and stratosphere. The most dramatic changes in the polar vortex are due to sudden stratospheric warmings (SSWs). Enhanced planetary wave convergence and meridional circulation may cause an SSW, a temporary breakdown of the polar vortex. Here we study the relation of SSWs to the atmospheric response to EEP in 1957-2017 using combined ERA-40 and ERA-Interim reanalysis data and geomagnetic activity as a proxy of EEP. We find that the EEP-related enhancement of the polar vortex and other associated dynamical responses are seen only during winters when an SSW occurs and that the EEP-related changes are observed systematically slightly before the SSW onset.We show that during these times, the planetary wave activity into the stratosphere is systematically increased, thus favoring enhanced wave-mean-flow interaction, which can dynamically amplify the initial polar vortex enhancement caused by ozone loss. These results highlight the importance of considering planetary wave activity as a necessary condition for observing the effects of EEP on the polar vortex. Plain Language SummaryThe wintertime weather on the Northern Hemisphere is greatly influenced by variation of the polar vortex, which is a strong westerly wind that forms in the polar stratosphere each winter. Recent research has established a link between polar vortex variations and energetic electron precipitation from the near-Earth space into the polar atmosphere, which is mediated by electron precipitation-induced chemical changes causing ozone loss in the mesosphere and stratosphere. The most dramatic changes in the polar vortex are due to sudden stratospheric warmings, where the vortex temporarily breaks. Here we study how these warming events influence the effect of electron precipitation on the polar vortex. We find that the electron precipitation enhances the polar vortex but preferentially during times preceding the sudden stratospheric warmings. We show that during these times, the initial response to electron precipitation is efficiently amplified by the same planetary wave activity, which later breaks the polar vortex. These results highlight the importance of considering sufficiently strong planetary wave activity typically associated to sudden stratospheric warmings as a necessary condition for observing the effects of electron precipitation on the polar vortex dynamics.

A sudden stratospheric warming (SSW) is a large‐scale disturbance of the wintertime stratosphere, which occurs especially in the Northern Hemisphere. Earlier studies have shown that SSW occurrence depends on atmospheric internal factors and on solar activity. We examine SSW occurrence in northern winters 1957/1958–2016/2017, considering several factors that may affect the SSW occurrence: Quasi‐Biennial Oscillation (QBO), El Niño–Southern Oscillation (ENSO), geomagnetic activity, and solar radiation. We confirm the well‐known result that SSWs occur more often in easterly QBO phase than in westerly phase. We show that this difference depends on how the QBO phase is determined. We find that the difference in SSW occurrence between easterly and westerly QBO winters strengthens (weakens) if geomagnetic activity or solar activity is low (high), or if the ENSO is in a cold (warm) phase. In easterly QBO phase significantly more SSWs occur during low geomagnetic activity than high activity.

Energetic electron precipitation (EEP) forms ozone‐depleting nitrogen and hydrogen oxides in the high‐latitude middle and upper atmosphere, leading to ozone destruction and temperature enhancement that can strengthen the winter polar vortex. This EEP effect on polar vortex depends on quasi‐biennial oscillation and sudden stratospheric warmings, which earlier studies relate to planetary waves. We study here the possible modulation of the EEP effect by planetary waves. We perform a principal component analysis of the vertical component of Eliassen‐Palm flux (EP flux) to examine the latitudinal pattern of planetary waves. We use a multilinear regression analysis to estimate the responses of zonal wind and EP flux divergence to EEP in the northern winter stratosphere by keeping the two leading principal components of vertical EP flux as controlling factors. We find that the EEP strengthens the polar vortex most systematically when planetary wave propagation is enhanced at mid‐latitudes but reduced at polar latitudes.

Recent studies suggest a response in the North Atlantic winter circulation which lags by a couple of years with respect to sunspot maximum. This has been explained by two different top‐down mechanisms: a solar wind driven particle effect in the polar atmosphere during the declining phase of the solar cycle, and the re‐emergence and amplification of heat anomalies in the Atlantic Ocean produced by enhanced solar ultraviolet (UV). Here we study how December to February climate is affected by two solar‐related drivers: geomagnetic activity (proxy of particle precipitation) and sunspot activity (proxy of solar UV) during 1948–2017. We use reanalysis data of sea‐level pressure (SLP) and zonal wind (U) to show that both geomagnetic activity and sunspot activity independently and simultaneously produce atmospheric circulation responses in the North Atlantic whose evolutions clearly differ from each other. Geomagnetic activity produces a strengthening of the polar vortex and a negative poleward SLP gradient between mid‐ and high latitudes, resembling a positive NAO‐type circulation pattern during December to February. Solar UV produces a positive U anomaly in the low‐latitude stratosphere during December, which moves poleward and downward during the winter resulting in a negative poleward SLP gradient between mid‐ and high latitudes during February. We find the lagged sunspot activity responses in SLP to form zonal pressure patterns (wave‐train structure) resembling the Eurasian pattern. Geomagnetic activity responses remain essentially the same when we introduce the lag with respect to sunspot activity supporting its independency as a driving mechanism. Our results suggest that solar wind related particle precipitation and (lagged) solar UV mechanism provide independent, significant circulation signals in the North Atlantic winter.