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Latitude corrected hemispheric mean poleward of 45°S for the eight ionization rate estimates produced by the different processing techniques, shown at two distinct pressure surfaces 0.01 hPa (∼80 km) (upper panel) and 0.1 hPa (∼64 km) (lower panel). Note that 0.1 hPa is outside of the nominal pressure range of AIMOS and AISstorm as shown in Figure 2.
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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 High Energy Particle Precipitation in the Atmosphere III intercomparison experiment is a collective effort to address th...
Citations
... The Medium Energy Proton and Electron Detectors (MEPED) aboard the Polar Operational Environmental Satellites (POES) and European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) MetOp have the advantage of observing within the bounce loss cone (BLC) at polar latitudes, with several operational satellites over multiple solar cycles. Nonetheless, due to instrumental challenges and different data handling within the community, parameterization of MEE leads to a large range of ionization and electron flux estimates Sinnhuber et al., 2022) and is currently a highly active field of research (Beharrell et al., 2015;van de Kamp et al., 2016;van de Kamp et al., 2018;Mironova et al., 2019;Pettit et al., 2019;Tyssøy et al., 2019;Duderstadt et al., 2021;Partamies et al., 2021;Tyssøy et al., 2021;Tyssøy et al., 2021;Babu et al., 2022;Nesse Tyssøy et al., 2022;Zúñiga López et al., 2022;Babu et al., 2023;Nesse et al., 2023;Salice et al., 2023). Other initiatives, such as the UARS satellite (Winningham et al., 1993) and the ELFIN twin CubeSats , have also monitored high-energy EEP within the BLC but not with the same coverage. ...
... One of the advantages of this model is that the Ap index can be reconstructed back until 1850 (Matthes et al., 2017), allowing for MEE parameterization way beyond satellite measurements. However, the accuracy of the model's representation of flux and ionization rate levels is a highly active discussion (Mironova et al., 2019;Pettit et al., 2019;Tyssøy et al., 2019;Nesse Tyssøy et al., 2022;Sinnhuber et al., 2022), and improvements are suggested by the community for CMIP7 . Tyssøy et al. (2019) compared the CMIP6 Ap-based model with estimates of loss cone fluxes using both the 0°and 90°F rontiers in Astronomy and Space Sciences 02 frontiersin.org ...
... The overarching objective of this study is to unravel the characteristics of solar wind properties and geomagnetic indices associated with the high-energy tail of MEE precipitation, enabling a better parameterization of the full energy range of EEP. This implies a parameterization that can determine the true range of flux variability, not averaging out strong events as demonstrated in Nesse Tyssøy et al. (2022) and Sinnhuber et al. (2022). Such parameterization will allow for an understanding of the importance of EEP's direct effect on the lower mesosphere and upper stratosphere chemistry, which further affects both the strength and timing of the subsequent impact on atmospheric dynamics. ...
Compositional NOx changes caused by energetic electron precipitation (EEP) at a specific altitude and those co-dependent on vertical transport are referred to as the EEP direct and indirect effect, respectively. The direct effect of EEP at lower mesospheric and upper stratospheric altitudes is linked to the high-energy tail of EEP (≳ 300 keV). The relative importance of this direct effect on NOx, ozone, and atmospheric dynamics remains unresolved due to inadequate particle measurements and scarcity of polar mesospheric NOx observations. An accurate parameterization of the high-energy tail of EEP is, therefore, crucial. This study utilizes EEP flux data from MEPED aboard the POES/Metop satellites from 2004–2014. Data from both hemispheres (55–70° N/S) are combined in daily flux estimates. 164 peaks above the 90th percentile of the ≳ 30 keV flux are identified. These peaks are categorized into absolute E1 and E3 events representing weak and strong ≳ 300 keV responses, respectively. A subset of absolute E1 and E3 events with similar ≳ 30 keV responses is termed overlapping events. Additionally, relative E1 and E3 events are determined by the relative strength of the ≳ 300 keV response, scaled by the initial ≳ 30 keV flux. A comparison between E1 and E3 events aims to identify solar wind and geomagnetic conditions leading to high-energy EEP responses and to gain insight into the conditions that generate a high-energy tail, independent of the initial ≳ 30 keV flux level. Superposed epoch analysis of mesospheric NO density from SOFIE confirms an observable direct impact on lower mesospheric chemistry associated with the absolute E3 events. A probability assessment based on absolute events identifies specific thresholds in the solar wind-magnetosphere coupling function (epsilon) and the geomagnetic indices Kp*10 and Dst, capable of determining the occurrence or exclusion of absolute E1 and E3 events. Elevated solar wind speeds persisting in the recovery phase of a deep Dst trough appear characteristic of overlapping and relative E3 events. This study provides insight into which parameters are important for accurately modeling the high-energy tail of EEP.
... In the High Energy Particle Precipitation in the Atmosphere (HEPPA) III-based intercomparison study of different atmospheric ionization rate models due to MEE precipitation, Nesse found that the van deKamp et al. (2016) model estimates a narrower extent of the precipitation region compared to the other MEE estimates, including the BLC flux used in this study. This finding suggests that differences in the hemispheric energy deposition of MEEs are not solely attributed to variations in the intensity and duration of MEE events, but also to the underestimation of the spatial extent of MEE precipitation(Nesse Tyssøy et al., 2022). van de Kamp et al. ...
Energetic Electron Precipitation (EEP) from the Earth's plasma sheet and the radiation belts is an important feature of atmospheric dynamics through their destruction of ozone in the lower thermosphere and mesosphere. Therefore, understanding the magnitude of the atmospheric impact of the Sun‐Earth interaction requires a comprehensive understanding of the intensity and location of EEP. This study improves the accuracy of a previous pressure‐corrected Dst model that predicts the equatorward extent of >43, >114, and >292 keV EEP using the measurements from the Medium Energy Proton Electron Detector detector of six National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites and EUMETSAT/METOP satellites. The improvement is achieved through multiple linear regression of pressure‐corrected Dst and pressure‐corrected Ring Current (RC) indices. The RC index mitigates the baseline variation of the Dst index that created an inherent solar cycle bias in the previous model. The new model is then extended to the Southern Hemisphere (SH) after removing the South Atlantic Anomaly longitudes from the data. More than 80% of the residuals lie within ±1.8° Corrected Geomagnetic Latitude (CGMLat) in the Northern Hemisphere and within ±1.98° CGMLat in the SH.
... Ozone plays an important role in linking EPP to climate variability (Andersson, Verronen, Rodger, Clilverd, & Seppälä, 2014;Seppälä et al., 2014). Due to a lack of EEP observations, proxies using Dst and Ap indices have been developed for inclusion of EPP in atmospheric and climate modeling (i.e., Matthes et al., 2017;Nesse Tyssøy et al., 2022;van de Kamp et al., 2016). The inclusion of substorm induced precipitation into the proxies is limited to few models (Nesse Tyssøy et al., 2022). ...
... Due to a lack of EEP observations, proxies using Dst and Ap indices have been developed for inclusion of EPP in atmospheric and climate modeling (i.e., Matthes et al., 2017;Nesse Tyssøy et al., 2022;van de Kamp et al., 2016). The inclusion of substorm induced precipitation into the proxies is limited to few models (Nesse Tyssøy et al., 2022). As a result, their impact on mesospheric ozone levels may be underestimated in long term simulation studies. ...
Several drivers cause precipitation of energetic electrons into the atmosphere. While some of these drivers are accounted for in proxies of energetic electron precipitation (EEP) used in atmosphere and climate models, it is unclear to what extent the proxies capture substorm‐induced EEP. The energies of these electrons allow them to reach altitudes between 55 and 95 km. EEP‐driven enhanced ionization is known to result in production of HOx and NOx, which catalytically destroy ozone. Substorm‐driven ozone loss has previously been simulated, but has not been observed before. We use mesospheric ozone observations from the Microwave Limb Sounder and Global Ozone Monitoring by Occultation of Stars instruments, to investigate the loss of ozone during substorms. Following substorm onset, we find reductions of polar mesospheric (∼76 km) ozone by up to 21% on average. This is the first observational evidence demonstrating the importance of substorms on the ozone balance within the polar atmosphere.
... Finally, EEP via production of ion pairs impacts middle atmosphere chemistry and dynamics and leads to ozone depletion [8][9][10][11][12][13]. To better understand this relationship, it is important to have realistic observations to properly characterize energetic electron precipitation [14] and atmospheric ionization rates [15,16], which are incorporated into chemistry-climate models. ...
... The comparison of balloon observations with satellite measurements was made for 2003, when there were three satellites (NOAA POES 15,16,and 17) in orbit in near-Earth space, separated by ∼100 degree in longitude. The sun-synchronous orbit inclination angle was 98.7, altitude 822 km, and orbital period 101.5 min (mean values). ...
Information about the energetic electron precipitation (EEP) from the radiation belt into the atmosphere is important for assessing the ozone variability and dynamics of the middle atmosphere during magnetospheric and geomagnetic disturbances. The accurate values of energetic electron fluxes depending on their energy range are one of the most important problems for calculating atmospheric ionization rates, which, in turn, are taken into account for estimating ozone depletion in chemistry–climate models. Despite the importance of these processes for the high latitudes of middle atmosphere, precipitation of energetic electrons is still insufficiently studied. In order to better understand EEP and related processes in the atmosphere, it is important to have many realistic observations of EEP in order to correctly characterize their spectra. Invading the atmosphere, precipitating energetic electrons, in the range from tens of keV to relativistic energies of more than 1 MeV, generate bremsstrahlung, which penetrates into the stratosphere and is recorded by detectors on balloons. However, these observations can be made only when the balloon is at stratospheric heights. Near-Earth satellites, such as the polar-orbiting operational environmental satellites (POES), are constantly registering precipitating electrons in the loss cone, but are moving too fast in space. Based on a comparison of the results of EEP measurements on balloons and onboard POES satellites in 2003, we propose a criterion that makes it possible to constantly monitor EEP ionization at stratospheric heights using observations on POES satellites.
... As electron events are also occurring without solar energetic protons (see e.g. Nesse Tyssøy et al., 2022), the particular PC size can be determined from those electron events. ...
Context: The main challenge in atmospheric ionisation modelling is that sparse measurements are used to derive a global precipitation pattern. Typically this requires intense interpolation or scaling of long-term average maps. In some regions however, the particle flux might be similar and a combination of these regions would not limit the results even though it would dramatically improve the spatial and temporal data coverage.
Aims: The paper intends to statistically analyse the particle flux distribution close to the geomagnetic poles labelled as Polar Particle Flux Distribution (PPFD) and identify similar distributions in neighbouring bins. Those bins are grouped and the size of the PPFD area is estimated. The benefit is that single measurements within the PPFD area should be able to represent the particle flux for the whole area at a given time.
Methods: We use spatially binned energetic particle flux distributions measured by POES and Metop spacecraft during 2001–2018 to identify a Kp-dependent area with a similar flux distribution as the one found close to the geomagnetic poles (|magn.lat| > 86°). First, the particle flux is mapped on a magnetic local time (MLT) vs. magnetic latitude grid. In the second step, the gridded data is split up according to Kp levels (forming the final bins). Third, the particle flux in every bin has been recalculated in order to replace zero-count rates with rates based on longer measurement periods which results in a more realistic low flux end of the particle distribution. Then the binned flux distributions are compared to the PPFD. A “Δ-test” indicates the similarity. A threshold for the Δ-test is defined using the standard deviation of Δ-test values inside the (|magn.lat| > 86°) area. Bins that meet the threshold are attributed as PPFD area.
Results: PPFDs and the corresponding PPFD areas have been determined for all investigated particle channels, covering an energy range of 154 eV–300 keV for electrons and 154 eV–2.5 MeV for protons. Concerning low energy channels a gradual flux increase with rising Kp has been identified. High energy channels show a combination of background population and solar particle event (SPE) population that adds up with increasing Kp. The size of the PPFD area depends on particle species, energy and geomagnetic disturbance, as well as MLT. The main findings are: a) There are small but characteristic hemispheric differences. b) Only above a certain energy threshold do the PPFD areas increase with particle energy. c) A clear enlargement with rising Kp is identified – with exceptions for very low Kp. d) The centre of the PPFD area is shifted towards midnight and moves with Kp. Asymmetries of the boundaries could be explained by auroral intensity. e) For low-energy particles the main restriction of the PPFD area seems to be the auroral precipitation.
... In the first paper, eight different ionization rate data-set. all using POES/MEPED data were compared for a geomagnetically disturbed period in April 2010, and their differences were analyzed in detail (Nesse Tyssøy et al., 2021). A main result of the first paper is that ionization rates differ by up to an order of magnitude as well as in their penetration depths depending on the choices made in their derivation even when using the same data-set of electron fluxes. ...
... Here, we investigate the respective atmospheric impact of these ionization rates and their spread by analyzing results from chemistry-climate models driven by three of these ionization rate data-sets for the same period of time in April 2010. To account for the large differences between ionization rates, we choose three data-sets that represent the full range of the spread discussed in Nesse Tyssøy et al. (2021). To evaluate the model response, results of the model experiments are compared with satellite observations of nitric oxide (NO) from three instruments complementary in vertical, spatial, and temporal coverage (SOFIE/AIM as well as MIPAS and SCIAMACHY on 3 of 34 ENVISAT). ...
... We use four different high-top coupled chemistry-climate models extending into the lower thermosphere to evaluate the electron ionization rate data-sets in the mesosphere and lower thermosphere. Model runs are carried out covering the same period of enhanced geomagnetic activity in April 2010 already described by Smith-Johnsen et al. (2018) and in the companion paper, Nesse Tyssøy et al. (2021). This period follows a geomagnetically very quiet period in early 2010. ...
Precipitating auroral and radiation belt electrons are considered to play an important part in the natural forcing of the middle atmosphere with a possible impact on 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.
In this study, we apply electron ionization rates from three data‐sets in four chemistry‐climate models during a geomagnetically active period in April 2010. Results are evaluated by comparison with observations of nitric oxide (NO) in the mesosphere and lower thermosphere. Differences between the ionization rate data‐sets have been assessed in a companion study. In the lower thermosphere, NO densities differ by up to one order of magnitude between models using the same ionization rate data‐sets due to differences in the treatment of NO formation, model climatology, and model top height. However, a good agreement in the spatial and temporal variability of NO with observations lends confidence that the electron ionization is represented well above 80 km. In the mesosphere, the averages of model results from all chemistry‐climate models differ consistently with the differences in the ionization‐rate data‐sets, but are within the spread of the observations, so no clear assessment on their comparative validity can be provided. However, observed enhanced amounts of NO in the mid‐mesosphere below 70 km suggest a relevant contribution of the high‐energy tail of the electron distribution to the hemispheric NO budget during and after the geomagnetic storm on April 6.
Energetic electron precipitation (EEP) from the radiation belts into Earth's atmosphere leads to several profound effects (e.g., enhancement of ionospheric conductivity, possible acceleration of ozone destruction processes). An accurate quantification of the energy input and ionization due to EEP is still lacking due to instrument limitations of low‐Earth‐orbit satellites capable of detecting EEP. The deployment of the Electron Losses and Fields InvestigatioN (ELFIN) CubeSats marks a new era of observations of EEP with an improved pitch‐angle (0°–180°) and energy (50 keV–6 MeV) resolution. Here, we focus on the EEP recorded by ELFIN coincident with electromagnetic ion cyclotron (EMIC) waves, which play a major role in radiation belt electron losses. The EMIC‐driven EEP (∼200 keV–∼2 MeV) exhibits a pitch‐angle distribution (PAD) that flattens with increasing energy, indicating more efficient high‐energy precipitation. Leveraging the combination of unique electron measurements from ELFIN and a comprehensive ionization model known as Boulder Electron Radiation to Ionization (BERI), we quantify the energy input of EMIC‐driven precipitation (on average, ∼3.3 × 10⁻² erg/cm²/s), identify its location (any longitude, 50°–70° latitude), and provide the expected range of ion‐electron production rate (on average, 100–200 pairs/cm³/s), peaking in the mesosphere—a region often overlooked. Our findings are crucial for improving our understanding of the magnetosphere‐ionosphere‐atmosphere system as they accurately specify the contribution of EMIC‐driven EEP, which serves as a crucial input to state‐of‐the‐art atmospheric models (e.g., WACCM) to quantify the accurate impact of EMIC waves on both the atmospheric chemistry and dynamics.
The Earth’s atmosphere is influenced by energetic electrons coming from the magnetosphere. This energetic electron precipitation (EEP) is energized by the solar wind and directly affects in the high‐latitude mesosphere and lower thermosphere (MLT). EEP forms odd nitrogen (NOx) and hydrogen oxides (HOx) which destroy ozone. During winter EEP‐NOx descends to the stratosphere, establishing the indirect EEP effect. Several studies have found that EEP is related to changes in temperature and winds in the northern winter stratosphere. One of the most prominent effects of EEP is the influence on the northern polar vortex, a westerly wind system surrounding the winter pole in the middle atmosphere. Most studies of the EEP effect on dynamical features of the middle atmosphere have relied on either model simulations or reanalysis datasets which are mainly limited to stratospheric heights. We study here EEP effects on chemical and dynamical properties of the stratosphere and mesosphere in the northern hemisphere by using EOS Aura satellite’s measurements of atmospheric properties and POES satellites' measurements of precipitating electrons. We confirm earlier results showing that EEP decreases ozone and affects the temperature in the polar middle atmosphere and strengthens the stratospheric polar vortex. We show that EEP weakens the mesospheric polar vortex in late winter. This effect on polar vortex is partly due to changes in propagation and convergence of planetary waves. Accordingly, the EEP effect on the northern polar vortex depends on planetary waves not only in the stratosphere, as found in earlier studies, but also in the mesosphere.
