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Recently, observational and re‐analysis studies have outlined potentially enhanced influence of Energetic Particle Precipitation (EPP) either at times preceding Sudden Stratospheric Warmings (SSW) or when the distribution of planetary wave activity is suitable. In addition, significant correlations have been found between EPP and the occurrence rate of SSWs when the phases of the Quasi‐Biennial Oscillation (QBO) are taken into account. Here we study the influence of EPP during disturbed stratospheric polar vortex conditions using chemistry‐climate model SOCOL‐MPIOM3 over the 20th century. When classifying disturbed conditions, the definition of minor SSWs are utilized along with a temperature gradient (day‐to‐day variations) criteria at 90°N and 10 hPa acting as a measure of the strength of the events. We find no influence of EPP on the occurrence rate of disturbed conditions over the last 100 year period. However, conditions preceding and during the disturbances are significantly different when EPP forcing is included into the model. This is especially true for stratospheric disturbances occurring in February. Furthermore, there is a clear tendency that the EPP effect becomes more notable after the 1950s. Our results imply that EPP forcing could be important for the stratospheric conditions during winter and that pre‐conditioning forced by atmospheric disturbances are an important factor when considering how the mechanism operates. Plain Language Summary: Energetic particles precipitating into the atmosphere is known to produce nitric (NOx) and hydrogen (HOx) oxides. These molecules are known to be associated with ozone (O3) loss, which is further shown to impact the temperature and weather patterns of the middle atmosphere. Recently, studies have shown that this impact could potentially be largest during winter time when the polar vortex experiences disturbed and unstable conditions. To study the impact of energetic particle precipitation (EPP) during these conditions, we use model data from the chemistry‐climate model SOCOL‐MPIOM3 over the period 1900–2008. In the model runs, we have 10 experiment ensembles which include ionization rates from historical records of EPP, and eight reference ensembles excluding these ionization rates. Our results show no relationship between EPP and the rate of occurrence of disturbed polar vortex conditions. However, conditions preceding and during disturbed times are significantly different when EPP ionization rates are included. Also, the results show that this effect only becomes noticeable after the 1950s, indicating that this mechanism might become even more important in the future. Key Points: We investigate links between Energetic Particle Precipitation and atmospheric dynamics during times of disturbed stratospheric polar vortexBy usage of model data, significant temperature anomalies are observed in the middle stratosphere, consistent with observational studiesA disturbed polar vortex (enhanced planetary wave activity), favor stratospheric temperature impact by Energetic Particle Precipitation [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: During some winters the cold polar stratosphere experiences a strong and sudden warming. These sudden stratospheric warmings (SSW) can affect greatly the surface weather in northern Europe and in North America. However, the factors that contribute to the formation of sudden warmings are not entirely known. We study how the two independent solar‐related factors, energetic particles and solar irradiance, and two atmospheric internal factors, the wind in the equatorial stratosphere (QBO) and the weather system of the Pacific (ENSO), affect the occurrence of sudden warmings in the Northern Hemisphere. We confirm the earlier finding that sudden stratospheric warmings are more common in winters with an easterly QBO wind. We find that the QBO effect on SSW occurrence depends on the two solar‐related factors and ENSO. Additionally, we find that the occurrence of sudden stratospheric warmings is affected by energetic particles precipitating to the Earth's atmosphere. Sudden warmings happen more often if the number of energetic particles is small. This effect is especially clear if the QBO wind is easterly. Our study helps to understand in which circumstances sudden stratospheric warmings are more or less likely to form. This information can benefit the forecasting of northern wintertime weather. Key Points: SSWs occur more often in QBO‐E than QBO‐W winters with the largest difference found if the QBO at 30 hPa of preceding autumn is usedQBO effect on SSW occurrence strengthens (weakens) if geomagnetic or sunspot activity is low (high) or if the ENSO is in cold (warm) phaseThe highest SSW occurrence rate is found in winters with low geomagnetic activity and easterly QBO [ABSTRACT FROM AUTHOR]

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. Key Points: Energetic electron precipitation (EEP) causes ozone loss, modifies temperatures, and strengthens northern polar vortex in winterEEP effect on polar vortex is significantly larger in QBO‐E than in QBO‐W phase when using QBO at 30 hPa lagged by 6 monthsOur results suggest that QBO modulated meridional circulation affects the EEP response [ABSTRACT FROM AUTHOR]