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Chlorofluorocarbon (CFC) emissions in the latter part of the 20th century reduced stratospheric ozone abundance substantially, especially in the Antarctic region. Simultaneously, polar stratospheric ozone is also destroyed catalytically by nitrogen oxides (NOx = NO + NO2) descending from the mesosphere and the lower thermosphere during winter. These are produced by energetic particle precipitation (EPP) linked to solar activity and space weather. Active chlorine (ClOx = Cl + ClO) can also react mutually with EPP-produced NOx or hydrogen oxides (HOx) and transform both reactive agents into reservoir gases, chlorine nitrate or hydrogen chloride, which buffer ozone destruction by all these agents. We study the interaction between EPP-produced NOx, ClO and ozone over the 20th century by using free-running climate simulations of the chemistry–climate model SOCOL3-MPIOM. A substantial increase of NOx descending to the polar stratosphere is found during winter, which causes ozone depletion in the upper and mid-stratosphere. However, in the Antarctic mid-stratosphere, the EPP-induced ozone depletion became less efficient after the 1960s, especially during springtime. Simultaneously, a significant decrease in stratospheric ClO and an increase in hydrogen chloride – and partly chlorine nitrate between 10–30 hPa – can be ascribed to EPP forcing. Hence, the interaction between EPP-produced NOx/HOx and ClO likely suppressed the ozone depletion, due to both EPP and ClO at these altitudes. Furthermore, at the end of the century, a significant ClO increase and ozone decrease were obtained at 100 hPa altitude during winter and spring. This lower stratosphere response shows that EPP can influence the activation of chlorine from reservoir gases on polar stratospheric clouds, thus modulating chemical processes important for ozone hole formation. Our results show that EPP has been a significant modulator of reactive chlorine in the Antarctic stratosphere during the CFC era. With the implementation of the Montreal Protocol, stratospheric chlorine is estimated to return to pre-CFC era levels after 2050. Thus, we expect increased efficiency of chemical ozone destruction by EPP-NOx in the Antarctic upper and mid-stratosphere over coming decades. The future lower stratosphere ozone response by EPP is more uncertain.

The forcing component of energetic particle precipitation (EPP) is recently added into the IPCC's official Coupled Model Intercomparison Project (CMIP) climate modelling. According to these simulations, the impact of inclusion of the medium energy electrons to the ozone variability was estimated to be 12-24% in the mesosphere and 5-7% in the stratosphere. However, to obtain a continuous particle forcing required for these multi-decadal simulations, the precipitating particle flux spectrum was parameterised by the magnetic Ap index to match statistically to the POES satellite's MEPED particle detector data. This rather simple approach has several uncertainties, but the most critical one is that the existing satellite-borne particle detectors, including the MEPED instrument, struggle to separate the loss cone populations from trapped particles, leading to biases in EPP forcing especially in the relativistic energies.In this presentation, we evaluate various EPP forcing models proposed for the future CMIP climate models against the EISCAT VHF data. This can be regarded as a ground-thruth approach for the mesospheric ionisation essential for the atmospheric consequences of the EPP.

The region separating the inner and outer radiation belt, typically devoid of energetic electrons, is termed the slot region. The outer edge of the slot region marks the equatorward edge of the energetic electron precipitation (EEP) originating from the outer radiation belt. Its varying location is strongly linked to the plasmasphere and geomagnetic activity. As such, geomagnetic indices are used to estimate the equatorward extent of the EEP region. There are, however, numerous reports where the energetic electrons cross these boundaries and fill the slot region, during which energetic electrons that can precipitate into the atmosphere long after the geomagnetic activity subsides. This is a missing source of energy input in current EEP estimates based on geomagnetic indices.This study explores the occurrence rate, reformation, local time dependence, and energy deposition of slot region filling events. Medium energy electron measurements from the NOAA/POES over a full solar cycle from 2004 to 2014 are applied. We combine observations from the MEPED 0° and 90° detectors together with theory of pitch angle diffusion by wave-particle interaction to estimate the precipitating fluxes. To explore the energy dependent characteristics, each of the MEPED energy channels, > 43, >114, and >292 keV are evaluated independently. Finally, we investigate the potential EEP impact on the NO density utilizing seven years of Envisat MIPAS NO observations from 2005 to 2011.

We investigate the connection between the interplanetary magnetic field (IMF) B$_\text{y}$-component and polar surface pressure, also known as the Mansurov effect. The aim of the investigation is to unravel potential dependencies on specific seasons and/or solar wind sector structures, and it serves as a sequel to Edvartsen et al. (2022). The mechanism for the effect includes the ability of the IMF to modulate the global electric circuit (GEC), which is theorized to impact and modulate cloud generation processes. By usage of daily ERA5 reanalysis data for geopotential height since 1968, we find no significant response confirming the current Mansurov hypothesis. However, we do find statistically significant correlations on decadal timescales in the time period March-May (MAM) in the northern hemisphere, but with an unusual timing. Similar phased anomalies are also found in the southern hemisphere for MAM, but not at a significant level. In an attempt to explain the unusual timing, heliospheric current sheet crossing events, which are highly correlated with the B$_\text{y}$-index, are used. These events result in higher statistical significance in the NH for the MAM period, but cannot fully explain the timing of the response. In general, these statistically significant correlations differ from previously reported evidence on the Mansurov effect, and suggest a revision of the Mansurov hypothesis. Our results also highlights a general feature of time-lagged cross correlation with autocorrelated variables, where the correlation value itself is shown to be a fragile indicator of robustness of a signal. For future studies, we suggest that the $p$-values obtained by modern statistical methods are considered, and not the correlation values alone.

Compositional NOx changes caused by energetic electron precipitation (EEP) at a specific altitude are called the EEP direct effect. Changes co-dependent on vertical transport are referred to as the EEP indirect effect. The relative importance of EEP’s direct and indirect effect on NO and its subsequent impact on ozone and dynamic changes remain unresolved. The challenges are partly due to inadequate particle measurement and the relative scarcity of NO observations. Moreover, lower production rates in the mesosphere make it challenging to determine EEP’s direct impact on NO. In this study, the uncertainty of EEP observations is bypassed by exclusively identifying events applying NO-observations from the SOFIE instrument on board the AIM satellite. SOFIE daily averaged data from 2007 to 2014 is used to create a climatology based on the median of the data. A direct EEP-produced NO-event at 90 km is identified when the NO density surpasses the climatology by 100%. If the NO density exceeds 25% above the climatology at 80, 70, 60, and 50 km, the event qualifies as a "50km-event”. By contrasting the 90km and 50km events, the characteristics of the solar wind and geomagnetic indices, as well as observed electron fluxes from POES, are studied. The goal is to unravel when EEP can produce NO directly in the upper stratosphere. The results will contribute to developing a parameterization of EEP from the radiation belt that includes both the direct and indirect impact of EEP and, thus, deciphering the total EEP effect on ozone and atmospheric dynamics., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Chlorofluorocarbon (CFC) emissions in the latter part of the 20th century reduced stratospheric ozone abundance substantially, especially in the Antarctic region. Simultaneously, polar stratospheric ozone is also destroyed catalytically by nitrogen oxides (NOx = NO + NO2) descending from the mesosphere and the lower thermosphere during winter. These are produced by energetic particle precipitation (EPP) linked to solar activity and space weather. NOx and active chlorine (ClOx = Cl + ClO) also react mutually and transform both reactive agents into reservoir gas chlorine nitrate, which buffers ozone destruction by both NOx and ClOx. We study the interaction between EPP produced NOx, ClO and ozone over the 20th century by using free running climate simulations of the chemistry-climate model SOCOL3-MPIOM. Substantial increase of NOx descending to polar stratosphere is found during winter, which causes ozone depletion in the upper and mid-stratosphere. However, in the Antarctic mid-stratosphere the EPP induced ozone depletion becomes less efficient after 1960s, especially during springtime. Simultaneously, significant decrease in stratospheric ClO and increase in chlorine nitrate between 10–30 hPa can be ascribed to EPP forcing. Hence, interaction between NOx and ClO likely suppressed the ozone depletion due to both EPP-NOx and ClO at these altitudes. Furthermore, at the end of the century significant ClO increase and ozone decrease is obtained at 100 hPa altitude during winter and spring. This lower stratosphere response is likely due to activation of chlorine from reservoir gases on polar stratospheric clouds. Our results show that EPP has been a significant modulator of reactive chlorine in the Antarctic stratosphere during the CFC era. With the implementation of the Montreal Protocol, stratospheric chlorine is estimated to return to pre-CFC era levels after 2050. Thus, we expect increased efficiency of chemical ozone destruction by EPP-NOx in the Antarctic upper and mid-stratosphere over coming decades. The future lower stratosphere ozone response by EPP is more uncertain.

Energetic particle precipitation (EPP) into the atmosphere, lead to chemical reactions producing NOx gases. Auroral electrons deposit their energy at altitudes throughout the upper mesosphere and lower thermosphere. During the winter the EPP-produced NOx gases can survive for months and be transported down to the stratosphere, where it can destroy ozone through catalytic reactions. Studies comparing the NO density estimated by chemistry climate models and observations suggest that the estimation of NO-production by auroral forcing is overestimated during quiet times and underestimated during active time. This study provides an intercomparison of different auroral forcing estimates. We compare fluxes from the Total energy detector (TED) onboard the NOAA Polar Orbiting Environmental Satellites (POES) and Meteorological Operational satellite (MetOp), sensor for precipitating particles (SSJ) from Defense Meteorological spacecraft Program (DMSP), alongside a Kp-driven auroral model. The data over a full year was sorted by the daily Kp and evaluated as function of geomagnetic latitude and magnetic local time. Discrepancies are evaluated in respect to geographical bias, as well as geometric factors of the satellites. Furthermore, the observations are compared to the Kp-driven auroral model.

Medium energy electron (MEE) (30-1000 keV) precipitation enhances the production of nitric (NOx) and hydrogen oxides (HOx) throughout the mesosphere, which can destroy ozone (O3) in catalytic reactions. The dynamical effect of the direct mesospheric O3 reduction has long been an outstanding question, partly due to the concurrent feedback from the stratospheric O3 reduction. To overcome this challenge, the Whole Atmosphere Community Climate Model (WACCM) version 6 is applied in the specified dynamics mode for the year 2010, with and without MEE ionization rates. The results demonstrate that MEE ionization rates can modulate temperature, zonal wind and the residual circulation affecting NOx transport. The required fluxes of MEE to impose dynamical changes depend on the dynamical preconditions. During the Northern Hemispheric winter, even weak ionization rates can modulate the mesospheric signal of a sudden stratospheric warming event. The result is a game changer for the understanding of the MEE direct effect.

Medium energy electron (MEE) (>30 keV) precipitation into the Earth's atmosphere is acknowledged as a relevant part of solar forcing as collisions between electrons and atmospheric gasses initiate several chemical reactions which can reduce ozone concentration. Ozone is critically important in the middle atmosphere energy budget as changes in ozone concentration impact temperature and winds. There is an ongoing debate to which extent the existing geomagnetic parameterizations represent a realistic precipitating flux level, especially when considering the high energy tail of MEE (>300 keV). An improved quantification might be achieved by a better understanding of the driving processes of MEE acceleration and precipitation, alongside optimized data handling. In this study, the bounce loss cone fluxes are inferred from MEE precipitation measurements by the Medium Energy Proton and Electron Detector (MEPED) on board the Polar Orbiting Environmental Satellite (POES) and the Meteorological Operational Satellite Program of Europe (METOP) at tens of keV to a couple hundred keV. It investigates MEE precipitation in contexts of different solar wind structures: corotating interaction regions (CIRs) associated with high-speed solar wind streams (HSSs), and coronal mass ejections (CMEs), during an eleven-year period from 2004 – 2014. The objective of this study is to explore general features of the MEE precipitating spectrum in the context of its solar wind driver: the intensity of MEE alongside the intensity and delayed response of its high energy tail.

The Mansurov effect is related to the interplanetary magnetic field (IMF) and its ability to modulate the global electric circuit, which is further hypothesized to impact the polar troposphere through cloud generation processes. We investigate the connection between IMF By-component and polar surface pressure by using daily ERA5 reanalysis for geopotential height since 1980. Previous studies produce a 27-day cyclic response during solar cycle 23 which appears to be significant according to conventional statistical tests. However, we show here that when statistical tests appropriate for strongly autocorrelated variables are applied, there is a fairly high probability of obtaining the cyclic response and associated correlation merely by chance. Our results also show that data from three other solar cycles produce similar cyclic responses as during solar cycle 23, but with seemingly random offset in respect to the timing of the signal. By generating random normally distributed noise with different levels of temporal autocorrelation and using the real IMF By-time series as forcing, we show that the methods applied to support the Mansurov hypothesis up to now are highly susceptible to random chance as cyclic patterns always arise as artifacts of the methods. The potential non-stationary behavior of the Mansurov effect makes it difficult to achieve solid statistical significance on decadal time scales. We suggest more research on, e.g., seasonal dependence of the Mansurov effect to understand better potential IMF effects in the atmosphere.

Energetic particle precipitation (EPP) causes ionization of the main constituents of the Earth's atmosphere which leads to the production of nitric oxide (NO) throughout the polar mesosphere and lower thermosphere (MLT). Due to the long lifetime of NO during winter, it can also be transported deeper into the atmosphere by the mesospheric residual circulation (the indirect EEP effect). This study investigates the mesospheric indirect NO response to EEP using Whole Atmosphere Community Climate Model (WACCM) version 6. In comparison to observations from the instrument Solar Occultation For Ice Experiment (SOFIE) on the AIM (Aeronomy of Ice in the Mesosphere) satellite, a wintertime underestimation is found in the modeled mesospheric NO amount. WACCM's temperature profile is found to be vertically shifted compared to observations by SOFIE and by The Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite (SABER). The discrepancies in NO are therefore attributed to the model's ability to simulate the dynamics responsible for the indirect EEP effect. The drivers of this transport are investigated by sensitivity runs of WACCM's gravity wave forcing. Changing the amplitude of the non-orographic gravity waves and the Prandtl number improves the modeled vertical distribution of NO and temperature in the MLT region. publishedVersion

Medium energy electron (MEE) (30–1,000 keV) precipitation enhances the production of nitric (NOx) and hydrogen oxides (HOx) throughout the mesosphere, which can destroy ozone (O3) in catalytic reactions. The dynamical effect of the direct mesospheric O3 reduction has long been an outstanding question, partly due to the concurrent feedback from the stratospheric O3 reduction. To overcome this challenge, the Whole Atmosphere Community Climate Model version 6 is applied in the specified dynamics mode for the year 2010, with and without MEE ionization rates. The results demonstrate that MEE ionization rates can modulate temperature, zonal wind and the residual circulation affecting NOx transport. The required fluxes of MEE to impose dynamical changes depend on the dynamical preconditions. During the Northern Hemispheric winter, even weak ionization rates can modulate the mesospheric signal of a sudden stratospheric warming event. The result provides a first step in a paradigm shift for the understanding of the MEE direct effect. publishedVersion

Energetic particle precipitation (EPP) increases the production of odd hydrogen (HOX ) species in the mesosphere, which catalytically destroy ozone (O3) in sunlight. Hence, the EPP‐HOX impact on the tertiary O3 maximum (TOM) depends on a complex geometry of a geographic‐oriented TOM, geomagnetic‐oriented auroral zone, producing short‐lived HOX species, and a destruction process depending on the solar zenith angle (SZA). Particle observations from the Medium Energy Proton and Electron Detectors telescopes aboard the Polar Orbiting Environmental Satellites, and hydroxyl (OH) and O3 mixing ratios from Aura microwave limb sounder (MLS) are used to investigate the potential limitations of using the MLS observations to study EPP‐OH impact on the TOM in the Northern Hemisphere. Our results show limited overlap between the auroral zone and the TOM at twilight conditions. A composite analysis indicates O3 mixing ratio decrease over the auroral zone lagged by ∼1 day compared to the maximum energetic electron precipitation (EEP)‐OH impact. Hence, MLS is predominantly observing a lagged and lower estimate of the response of O3 to EEP‐OH at SZA > 95°. The EEP impact region within the TOM is smaller than the overlap region, strongly modulated by the background atmospheric dynamics. The results, although limited by the satellites viewing conditions, imply that the importance of EEP upon O3 mixing ratio is strongly influenced by the background atmosphere, both in terms of chemistry and dynamics. Multisatellite observations at different solar local times are required to separate the direct from the lagged EEP‐OH impact on O3. publishedVersion

Precipitating auroral and radiation belt electrons are considered an important part of the natural forcing of the climate system. Recent studies suggest that this forcing is underestimated in current chemistry-climate models. The HEPPA III intercomparison experiment is a collective effort to address this point. Here, eight different estimates of medium energy electron (MEE) (>30 keV) ionization rates are assessed during a geomagnetic active period in April 2010. The objective is to understand the potential uncertainty related to the MEE energy input. The ionization rates are all based on the Medium Energy Proton and Electron Detector (MEPED) on board the NOAA/POES and EUMETSAT/MetOp spacecraft series. However, different data handling, ionization rate calculations, and background atmospheres result in a wide range of mesospheric electron ionization rates. Although the eight data sets agree well in terms of the temporal variability, they differ by about an order of magnitude in ionization rate strength both during geomagnetic quiet and disturbed periods. The largest spread is found in the aftermath of the geomagnetic activity. Furthermore, governed by different energy limits, the atmospheric penetration depth varies, and some differences related to latitudinal coverage are also evident. The mesospheric NO densities simulated with the Whole Atmospheric Community Climate Model driven by highest and lowest ionization rates differ by more than a factor of eight. In a follow-up study, the atmospheric responses are simulated in four chemistry-climate models and compared to satellite observations, considering both the model structure and the ionization forcing.

Energetic electron precipitation (EEP) ionizes the Earth's atmosphere and leads to production of nitric oxide (NO) throughout the polar Mesosphere and Lower Thermosphere (MLT). In this study we investigate the direct and indirect NO response to the EEP using the Whole Atmosphere Community Climate Model (WACCM) version 6. In comparison to observations from SOFIE / AIM (Solar Occultation For Ice Experiment / Aeronomy of Ice in the Mesosphere), we find that EEP production of NO in the D-region is well simulated when both medium energy electron precipitation and negative and cluster ion chemistry are included in the model. However, the main EEP production of NO occurs in the E-region, and there the observed and modeled production differ. This discrepancy impacts also the D-region due to downward transport of long lived NO. The transport across the mesopause is seasonally dependent, and WACCM’s underestimate of D-region NO is highest during winter when downwelling from above is strong. The drivers of this transport are further investigated by a sensitivity study of WACCM’s gravity wave forcing.

Energetic Electron Precipitation (EEP) from the plasma sheet and the radiation belts ionize the polar lower thermosphere and mesosphere. EEP increase the production of NOx and HOx, which will catalytically destroy stratospheric ozone, an important element of atmospheric dynamics. Therefore, measurement of the latitudinal extent of the precipitation boundaries is important in quantifying atmospheric effects of Sun-Earth interaction.This study uses measurements by Medium Energy Proton Electron Detector (MEPED) of six NOAA/POES and EUMETSAT/METOP satellites from 2004 to 2014 to determine the latitudinal boundaries of EEP and its variability with geomagnetic activity and solar wind drivers. Variation of the boundaries with respect to different particle energies and magnetic local time is studied. Regression analyses are applied to determine the best predictor variable based on solar wind parameters and geomagnetic indices. The highest correlation was found for pressure-corrected Dst index through linear regression. Although, the model has an error estimate of ±2.2° cgmlat and exhibits a solar cycle bias, it performs well in predicting the precipitation boundaries. The result will be a key element for constructing a model of EEP variability to be applied in atmosphere climate models.

Energetic electron precipitation (EEP) into the Earth's atmosphere can collide with gases and deposit their energy there. The collisions between electrons and atmospheric gasses initiate several chemical reactions which can reduce the ozone concentration. Ozone is critically important in the middle atmosphere energy budget as changes in the ozone concentration impact temperature and winds. EEP is not fully understood in terms of how much energy is being deposited and what the associated drivers are. An accurate quantification of EEP has limitations due to instrumental challenges and therefore imposes limitations of the associated EEP parameterization into climate models. A solution to this problem is a better understanding of the driver processes of energetic electron acceleration and precipitation, alongside optimized data handling. In this study the bounce loss cone fluxes are inferred from EEP measurements by the Medium Energy Proton and Electron Detector (MEPED) on board the Polar Orbiting Environmental Satellite (POES) and the Meteorological Operational Satellite Program of Europe (METOP) at tens of keV to relativistic energies. It investigates EEP in contexts of different solar wind structures: high-speed solar wind streams (HSSs) and coronal mass ejections (CMEs), during an eleven-year period from 2004 – 2014. While today's chemistry climate models only provide snapshots of EEP, independent of context, this study aims to understand the context EEP is created in, which will allow a more accurate estimate of the EEP to be applied in atmospheric climate models.

Ozone is expected to fully recover from the CFC-era by the end of the 21st century. Furthermore, because of anthropogenic climate change, a cooler stratosphere accelerates ozone production and is projected to lead to a super recovery of ozone. We investigate the ozone distribution over the 21st century with four different future scenarios using simulations of the Whole Atmosphere Community Climate Model (WACCM). At the end of the 21st century, equatorial upper startosphere has roughly 0.5 to 1.0 parts per million more ozone in scenario with the highest greenhouse gas emissions compared to conservative scenario. Polar ozone levels exceed those in the pre CFC-era in scenarios that have the highest greenhouse gas emissions. This is true in the Arctic stratosphere and the Antarctic lower stratosphere. The Antarctic upper stratosphere is an exception, where different scenarios all have similar levels of ozone during winter, which do not exceed pre-CFC levels. Our results show that this is due to excess nitrogen oxides (NOx) descending from above in the stronger scenarios of greenhouse gas emissions. NOx is formed by energetic electron precipitation (EEP) in the thermosphere and the upper mesosphere, and descends faster through the mesosphere in stronger scenarios. This indicates that the EEP indirect effect will be important factor for the future Antarctic ozone evolution, and could potentially prevent a super recovery of ozone in the upper stratosphere.

The Mansurov Effect is related to the interplanetary magnetic field (IMF) and its ability to modulate the global electric circuit, which is further hypothesized to impact the polar troposphere through cloud generation processes. In this paper we investigate the connection between IMF By-component and polar surface pressure by using daily ERA5 reanalysis for geopotential height since 1980. Previous studies have shown to produce a significant 27-day cyclic response during solar cycle 23. However, when appropriate statistical tests are applied, the correlation is not significant at the 95% level. Our results also show that data from three other solar cycles, which have not been investigated before, produce similar cyclic responses as during solar cycle 23, but with seemingly random offset in the timing of the signal. We examine the origin of the cyclic pattern occurring in the super epoch/lead lag regression methods commonly used to support the Mansurov hypothesis in all recent papers, as well as other phenomena in this community. By generating random normally distributed noise with different levels of temporal autocorrelation, and using the real IMF By-index as forcing, we show that the methods applied to support the Mansurov hypothesis up to now, are highly susceptible, as cyclic patterns always occurs as artefacts of the methods. This, in addition to the lack of significance, suggests that there is no adequate evidence in support of the Mansurov Effect.

A set of 24 isolated, 46 compound, and 36 multi-night substorm events from the years 2008–2013 have been analysed in this study. Isolated substorm events are defined as single expansion–recovery phase pairs, compound substorms consist of multiple phase pairs, and multi-night substorm events refer to recurring substorm activity on consecutive nights. Approximately 200 nights of substorm activity observed over Fennoscandian Lapland have been analysed for their magnetic disturbance magnitude and the level of cosmic radio noise absorption. Substorm events were automatically detected from the local electrojet index data and visually categorized. We show that isolated substorms have limited lifetimes and spatial extents as compared to the other substorm types. The average intensity (both in absorption and ground-magnetic deflection) of compound and multi-night substorm events is similar. For multi-night substorm events, the first night is rarely associated with the strongest absorption. Instead, the high-energy electron population needed to cause the strongest absorption builds up over 1–2 additional nights of substorm activity. The non-linear relationship between the absorption and the magnetic deflection at high- and low-activity conditions is also discussed. We further collect in situ particle spectra for expansion and recovery phases to construct median precipitation fluxes at energies from 30 eV up to about 800 keV. In the expansion phases the bulk of the spectra show a local maximum flux in the range of a few keV to 10 keV, while in the recovery phases higher fluxes are seen in the range of tens of keV to hundreds of keV. These findings are discussed in the light of earlier observations of substorm precipitation and their atmospheric effects.

Pulsating aurora (PsA) is a diffuse type of aurora with different structures switching on and off with a period of a few seconds. It is often associated with energetic electron precipitation (>10 keV) resulting in the interaction between magnetospheric electrons and electromagnetic waves in the magnetosphere. Recent studies categorize pulsating aurora into three different types – amorphous pulsating aurora (APA), patchy pulsating aurora (PPA), and patchy aurora (PA) – based on the spatial extent of pulsations and structural stability. Differences in precipitation energies of electrons associated with these types of pulsating aurora have been suggested. In this study, we further examine these three types of pulsating aurora using electron density measurements from the European Incoherent Scatter (EISCAT) VHF/UHF radar experiments and Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) cosmic noise absorption (CNA) measurements. Based on ground-based all-sky camera images over the Fennoscandian region, we identified a total of 92 PsA events in the years between 2010 and 2020 with simultaneous EISCAT experiments. Among these events, 39, 35, and 18 were APA, PPA, and PA types with a collective duration of 58, 43, and 21 h, respectively. We found that, below 100 km, electron density enhancements during PPAs and PAs are significantly higher than during APA. However, there are no appreciable electron density differences between PPA and APA above 100 km, while PA showed weaker ionization. The altitude of the maximum electron density also showed considerable differences among the three types, centered around 110, 105, and 105 km for APA, PPA, and PA, respectively. The KAIRA CNA values also showed higher values on average during PPA (0.33 dB) compared to PA (0.23 dB) and especially APA (0.17 dB). In general, this suggests that the precipitating electrons responsible for APA have a lower energy range compared to PPA and PA types. Among the three categories, the magnitude of the maximum electron density shows higher values at lower altitudes and in the late magnetic local time (MLT) sector (after 5 MLT) during PPA than during PA or APA. We also found significant ionization down to 70 km during PPA and PA, which corresponds to ∼200 keV of precipitating electrons.

In April 2010, a coronal mass ejection and a corotating interaction region on the Sun resulted in an energetic electron precipitation event in the Earth's atmosphere. We investigate direct and indirect nitric oxide (NO) response to the electron precipitation. By combining electron fluxes from the Total Energy Detector (TED) and the Medium Energy Proton and Electron Detector (MEPED) on the National Oceanic and Atmospheric Administration's (NOAA's) Polar Orbiting Environmental Satellites (POES), we obtain a continuous energy spectrum covering 1-750 keV. This corresponds to electrons depositing their energy at atmospheric altitudes 60-120 km. Based on the electron energy deposition, taking into account loss due to photolysis, the accumulated NO number density is estimated. When compared to NO measured at these altitudes by the Solar Occultation for Ice Experiment (SOFIE) instrument on board the Aeronomy of Ice in the Mesosphere (AIM) satellite, the NO direct effect was detected down to 55 km. The main variability at these altitudes is however dominated by the indirect effect, which is downward transported NO. We estimate the source of this descending NO to be in the upper mesosphere at ∼75-90 km.

Evidence are pointing to two potential links between solar wind forcing and atmospheric dynamics in polar regions. The chemical link follows from energetic particle precipitation (EPP) ionizing the higher atmosphere, leading to a production of nitrogen and hydrogen oxides (NOx and HOx), which later on participate in ozone destruction. This can lead to changes in the radiative balance of the atmosphere, followed by related changes in winds. The physical link is related to the interplanetary magnetic field (IMF) and its ability to modulate the global electric circuit (GEC), with a hypothesized link between changes in the GEC and polar tropospheric dynamics through cloud generation processes. By use of ERA-5 reanalysis data and OMNI near Earth solar wind magnetic field and plasma parameter data, we investigate these links with a multiple correlation analysis. Internal atmospheric variability is excluded before the analysis. Time period of the data is 1979-2018. Results concerning the chemical link show a significant negative correlation between EPP (geomagnetic activity index Ap used as a proxy) and pressure anomalies in the local winter inside the polar vortex. The anomaly, starting in the stratosphere, extends downwards to the surface in a matter of days. The results indicate a greater response in the north compared to the south. For the physical link, a significant correlation is seen between the IMF horizontal (By) component and lower tropospheric pressure in the south for certain months in local summer. There seems to be no correlation between the two indices, Ap and By, indicating that these mechanisms operate individually without aliasing between the two. These results imply that solar wind variability can potentially impact polar atmospheric dynamics during specific seasons in different ways. This can enhance our understanding on solar related atmospheric effects.

Energetic electron precipitation (EEP) from the plasma sheet and the radiation belts, can collide with gases in the atmosphere and deposit their energy. EEP increase the production of NOx and HOx, which will catalytically destroy stratospheric ozone, an important element of atmospheric dynamics. The particle precipitation also causes variation in the radiation belt population. Therefore, measurement of latitudinal extend of the precipitation boundaries is important in quantifying atmospheric effects of Sun-Earth interaction and threats to spacecrafts and astronauts in the Earth’s radiation belt. This study uses measurements by MEPED detectors of six NOAA/POES and EUMETSAT/METOP satellites during the year 2010 to determine the latitudinal boundaries of EEP and its variability with geomagnetic activity and solar wind drivers. Variation of the boundaries with respect to different particle energies and magnetic local time is studied. The result will be a key element for constructing a model of EEP variability to be applied in atmosphere climate models.

Quantifying the ionization rates due to medium energy electron (MEE) precipitation into the mesosphere has long been an outstanding question. It is the key to understand the total effect of particle precipitation on the atmosphere. The first MEE ionization rate was provided by the Atmospheric Ionization Module Osnabrück (AIMOS) in 2009. It applies electron measurements by the 0o electron detector on the MEPED instrument on board the NOAA/POES satellites together with geomagnetic indices. Since then several other efforts to estimate the MEE precipitation and associated ionization rates has been made taking account e.g. of cross contamination by low-energy protons; Full Range Energy Electron Spectra (FRES) and ISSI-19. Recently, a parameterization based on the same electron data, scaled by the geomagnetic index Ap, has been included in the solar-driven particle forcing in the recommendation for Coupled Model Intercomparison Project 6 (CMIP6). Another parameterization aiming to resolve substorm activity applies the SML index, AISstorm. Further, three different methods to construct the total bounce loss cone fluxes based on both MEPED detectors has been suggested by the University of Colorado, University of Oulo, and the University of Bergen. In total, the space physics community offers a wide range of mesospheric ionization rates to be used in studies of the subsequent chemical-dynamical impact of the atmosphere, which are all based on the MEPED electron measurement.Here we present a review of eight different estimates of energetic electron fluxes and the ionization rates during an event in April 2010. The objective of this comparison is to understand the potential uncertainty related to the MEE energy input in order to assess its subsequent impact on the atmosphere. We find that although the different parameterizations agree well in terms of the temporal variability, they differ by orders of magnitude in ionization strength both during geomagnetic quiet and disturbed periods and show some inconsistency in terms of latitudinal coverage.

Energetic electron precipitation (EEP) ionizes the Earth's atmosphere and leads to production of nitric oxide (NO) from 50 to 150 km altitude. In this study we investigate the direct and indirect NO response to EEP using the Whole Atmosphere Community Climate Model (WACCM). In comparison to observations from SOFIE / AIM (Solar Occultation For Ice Experiment / Aeronomy of Ice in the Mesosphere), we find that EEP production of NO in the D-region is well simulated when both medium energy electron precipitation and negative and cluster ion chemistry is included in the model. However, the main EEP production of NO occurs in the E-region, and there the observed and modeled production differ. This discrepancy impacts also the D-region, and is seasonally dependent with the highest underestimate of D-region NO occuring during winter. The modeled transport across the mesopause during winter is generally weak, but strengthens with increased gravity wave activity. Increased eddy diffusion, increases NO at all altitudes through the polar MLT region

Energetic electron precipitation (EEP) into the Earth’s atmosphere can collide with gases and deposit their energy there. The collisions between electrons and atmospheric gasses initiate several chemical reactions which can reduce the ozone concentration. Ozone is critically important in the middle atmosphere energy budget as changes in the ozone concentration impact temperature and winds. EEP is not fully understood in terms of how much energy is being deposited and what the associated drivers are. An accurate quantification of EEP has limitations due to instrumental challenges and therefore imposes limitations of the associated EEP parameterization into climate models. A solution to this problem is a better understanding of the driver processes of energetic electron acceleration and precipitation, alongside optimized measurements. In this study the bounce loss cone fluxes are inferred from EEP measurements by MEPED on board NOAA/POES and EUMETSAT/METOP at tens of keV to relativistic energies. It investigates EEP in contexts of three different solar wind structures: high-speed streams, coronal mass ejections, and ambient or slow interstream solar wind, as well as geomagnetic activity. The study will focus on the year 2010 and aim to understand the context EEP is created in, which will allow a more accurate estimate of the EEP to be applied in atmospheric climate models

Accurate specification of ionization production by energetic electron precipitation is critical for atmospheric chemistry models to assess the resultant atmospheric effects. Recent model-observation comparison studies have increasingly highlighted the importance of considering precipitation fluxes in the full range of electron energy and pitch angle. However, previous parameterization methods were mostly proposed for isotropically precipitation electrons with energies up to 1 MeV, and the pitch angle dependence has not yet been parameterized. In this paper, we first characterize and tabulate the atmospheric ionization response to monoenergetic electrons with different pitch angles and energies between ∼3 keV and ∼33 MeV. A generalized method that fully accounts for the dependence of ionization production on background atmospheric conditions, electron energy, and pitch angle has been developed based on the parameterization method of Fang et al. (2010, https://doi.org/10.1029/2010GL045406). Moreover, we validate this method using 100 random atmospheric profiles and precipitation fluxes with monoenergetic and exponential energy distributions, and isotropic and sine pitch angle distributions. In a suite of 6,100 validation tests, the error in peak ionization altitude is found to be within 1 km in 91% of all the tests with a mean error of 2.7% in peak ionization rate and 1.9% in total ionization. This method therefore provides a reliable means to convert space-measured precipitation energy and pitch angle distributions into ionization inputs for atmospheric chemistry models. publishedVersion

Energetic electron precipitation (EEP) is an important source of polar nitrogen oxides (NOx) in the upper atmosphere. During winter, mesospheric NOx has a long chemical lifetime and is transported to the stratosphere by the mean meridional circulation. Climate change is expected to accelerate this circulation and therefore increase polar mesospheric descent rates. We investigate the southern hemispheric polar NOx distribution during the 21st century under a variety of future scenarios using simulations of the Whole Atmosphere Community Climate Model (WACCM). Each future scenario has the same moderate variable solar activity scenario, where EEP activity is lower than during the 20th century. We simulate stronger polar mesospheric descent in all future scenarios that increase the atmospheric radiative forcing. By the end of 21st century polar NOx in the upper stratosphere is significantly enhanced in two future scenarios with the largest increase in radiative forcing. This indicates that the ozone depleting NOx cycle will become more important in the future, especially if stratospheric chlorine species decline. Thus, EEP-related atmospheric effects may become more prominent in the future.

High-energy electron precipitation from the radiation belts can penetrate deep into the mesosphere and increase the production rate of NOx and HOx, which in turn will reduce ozone in catalytic processes. The mechanisms for acceleration and loss of electrons in the radiation belts are not fully understood, and most of the measurements of the precipitating flux into the atmosphere have been insufficient for estimating the loss cone flux. In the present study the electron flux measured by the NOAA POES Medium Energy Proton and Electron Detectors 0° and 90° detectors is combined together with theory of pitch angle diffusion by wave-particle interaction to quantify the electron flux lost below 120 km altitude. Using this method, 41 weak and moderate geomagnetic storms caused by corotating interaction regions during 2006–2010 are studied. The dependence of the energetic electron precipitation fluxes upon solar wind parameters and geomagnetic indices is investigated. Nine storms give increased precipitation of >∼750 keV electrons. Nineteen storms increase the precipitation of >∼300 keV electrons, but not the >∼750 keV population. Thirteen storms either do not change or deplete the fluxes at those energies. Storms that have an increase in the flux of electrons with energy >∼300 keV are characterized by an elevated solar wind velocity for a longer period compared to the storms that do not. Storms with increased precipitation of >∼750 keV flux are distinguished by higher-energy input from the solar wind quantified by the ϵ parameter and corresponding higher geomagnetic activity. publishedVersion