Energetic particle precipitation into the atmosphere has been identified as a key loss process for electrons in the Earth’s outer radiation belt region. However, direct measurements of the electron flux precipitating into the atmosphere are challenging from high altitude low inclination spacecraft, such as the Van Allen Probes, due to the small angular size of the loss cone along the orbital path of these high-altitude spacecraft. Here we use data from the Polar Orbiting Environmental Satellites (POES)/Space Environment Monitor in low Earth orbit to assess the relationship between the trapped and precipitating electron flux in integral energy channels >30 keV, >100 keV, and >300 keV. Our results highlight that there is a strong non-linear relationship between the flux of trapped and precipitating electrons, with the ratio of precipitating to trapped flux only becoming significantly enhanced once the trapped flux reaches a critical level. This transition from low to high levels of precipitation is consistent with the theory proposed by Kennel and Petschek (K-P) (1966) https://doi.org/10.1029/JZ071i001p00001, whereby intense chorus waves are excited and trigger pitch angle diffusion, resulting in energetic particle precipitation and limiting the trapped flux. Using electron flux data from POES and chorus wave data from the Van Allen Probes, we further test the observations against predictions from the K-P theory. A particle tracing model is also utilized to illustrate a direct link between the drift paths of injected electrons, the occurrence of chorus waves and the spatial distribution of strong electron precipitation into the atmosphere at different energies.

How to cite: Ozeke, L., Mann, I., Olifer, L., Chakraborty, S., and Pettit, J.: The Relationship Between Electron Precipitation and the Population of Trapped Electrons in LEO: New Evidence Supporting a Natural Limit to the Flux of Energetic Electrons, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12857, https://doi.org/10.5194/egusphere-egu24-12857, 2024.

The outer Van Allen belt is home to relativistic electrons and experience large variations in electron fluxes during geomagnetic driving events. Many satellite orbits, especially geostationary ones, overlap with the radiation belts and experience high-energy electron radiation. This radiation causes surface and internal charging, accompanied by aging of satellite components. In order to determine the impact on satellites during strong and extreme geomagnetic storms, one needs to quantify the magnitude of the fluxes. In this communication, we compare two different methods for estimating large flux values at geostationary orbit. The first method is physical and relies on the Kennel-Petschek limit (Kennel&Petschek, 1966). The second method is purely statistical and originates in extreme value theory (Coles, 2001). Using extreme value theory (EVT), for electron energies of 130 keV, we find for the once in 150 years electron flux an expected value that is two orders of magnitude larger than electron flux during the Halloween storm of 2003. On the other hand, the Kennel-Petschek limit, for the 130 keV electrons at L=6.7, which corresponds to geostationary orbit, is 1/6 of the maximum of the Halloween storm flux. The EVT therefore provides much larger estimates than the Kennel-Petschek limit. We compare the two methodologies with their respective strengths and limitations and determine under which conditions they should be combined to estimate extreme fluxes in the radiation belts. 

How to cite: Savola, M., Osmane, A., Turc, L., Kilpua, E., and Palmrooth, M.: Estimation of extreme electron fluxes at geostationary orbit: a statistical and a physical approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15761, https://doi.org/10.5194/egusphere-egu24-15761, 2024.

Most studies of the geoeffectiveness of the solar wind tend to focus on coronal mass ejections (CMEs) and Corotating Interactive Regions (CIRs). By comparison, fewer studies focus on the geoeffectiveness of the solar wind directional discontinuities (DD), either tangential discontinuity (TD) or rotational discontinuity (RD).  We present two examples of solar wind DD interaction with the magnetosphere that lead to complex dayside particle precipitation structures even though the geomagnetic activities remain quiet in those two events.  In the first example, the DD leads to the formations of unusual boundary layer, overlapping mantle, and double cusp as observed by the DMSP spacecraft. The double cusp signature is consistent with simultaneous magnetic reconnection occurring at both low and high latitudes due to the dominant IMF By as confirmed in a global MHD simulation for the event. The existence of a high-latitude reconnection in this even is also supported by Cluster C2, which observes velocity fluctuations and reversals with peak-to-peak amplitudes >800 km s^–1 as C2 crosses the magnetopause.  Guided by the MHD simulation, the Cluster observation can be interpreted as the spacecraft crossing reconnection outflows while moving from one side of the X-line to the other.  In the second example, the DD leads to the unusual particle precipitation structure where three distinct ion populations can be found on the same magnetic field line.  These three populations have energies of a few hundreds eVs, a few keVs, and a few tens of keVs, suggesting that ions originating from the magnetosphere, solar wind, and ionosphere, respectively, can coexist on the same field line unthermalized.  Moreover, this unusual particle precipitation region has a spatio-temporal scale of about 1 min or 500 km in the ionosphere.

How to cite: Berchem, J., Wing, S., and Escoubet, C. P.: Complex dayside particle precipitation observed during the passage of solar wind discontinuities  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3260, https://doi.org/10.5194/egusphere-egu24-3260, 2024.

The Comprehensive Inner Magnetosphere-Ionosphere Model (CIMI) is designed by coupling the Comprehensive Ring Current Model (CRCM) and the Radiation Belt Environment (RBE) model (Fok et al., Journal of Geophysical Research: Space Physics, 119, 2014). The model provides electron and ion distribution functions in Earth’s radiation belt, ring current, estimates energies of precipitated electrons and ions in the ionosphere, calculates plasmaspheric density, ionospheric height-integrated Hall and Pedersen conductivities, ionospheric convection potentials. An important feature of CIMI model is calculation of electron precipitation from diffusion-convection equation that accounts both for particle drift in the inner magnetosphere and wave-particle interactions through various plasma waves. In this paper, the performance of the CIMI in terms of precipitating particle energy distribution is evaluated during the geomagnetic disturbed period of May 31 – June 1, 2013 (minimum Dst = -124nT). The performance of CIMI is observed in correspondence with Defense Meteorological Satellite Program (DMSP) satellite observations. Precipitated electrons (30 keV > E > 500eV) from Earth’s plasma sheet go through wave-particle interactions and produce diffuse aurora, that can be simulated with CIMI model. We compare CIMI electron precipitation energy channels for DMSP energy bins and analyze CIMI performance for different energy bins, mean energy and for the total integrated energy flux. In addition, CIMI model has different options for ionospheric conductance model: 1) empirical model of Hardy et al. (Journal of Geophysical Research: Space Physics, 92, 1987) that depends on Kp-index, and 2) Robinson's formulation (Robinson et al., Journal of Geophysical Research: Space Physics, 92, 1987) where ionospheric conductance depends on electron precipitation mean energy and total energy flux. We study CIMI model performance for two different models of ionospheric conductance and evaluate the feedback of electron precipitation on the ring current and ionospheric electric field.

How to cite: Sur, D., Dorelli, J. C., Fok, M.-C., and Buzulukova, N. Y.: Performance Assessment of CIMI Electron Precipitation During Geomagnetic Storm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6932, https://doi.org/10.5194/egusphere-egu24-6932, 2024.

Auroral precipitation plays an important role in the magnetosphere-ionosphere-thermosphere (MIT) coupling. Various precipitation spectra have been observed and they are driven by different physical mechanisms. In this study, we report the Dragon King model which is used to characterize auroral precipitation and its consequent ionospheric conductance in the Multiscale Atmosphere-Geospace Environment (MAGE) model, a newly developed whole geospace model. Mono-energetic electron precipitation is derived from large-scale field-aligned currents and drift-physics informed loss cone rate, using the linearized Fridman-Lemaire relation. Diffuse electron precipitation is derived with a drift-physics based ring current model, in which electron lifetime due to interactions with chorus and hiss waves is obtained with an empirical table and electron loss rate is informed by drift physics and IGRF magnetic field. Broadband electron precipitation is derived from a statistical relationship between field-aligned Alfvénic Poynting flux and the precipitation energy flux and number flux. The Dragon King model is validated from different perspectives with various observational data, including the statistical pattern during different categories of solar wind driving conditions, and along-trajectory comparison with satellite measurements. The Dragon King model is further used to understand the drivers of different precipitation and their relative importance with MAGE simulations.

How to cite: Lin, D., Bao, S., Wang, W., Merkin, V., Sorathia, K., Lotko, W., Wang, D., Pham, K., Ma, Q., Sotirelis, T., Shi, X., Michael, A., Sciola, A., Wiltberger, M., Toffoletto, F., Lyon, J., and Garretson, J.: Characterizing auroral precipitation and ionospheric conductance with the Dragon King model in MAGE, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4781, https://doi.org/10.5194/egusphere-egu24-4781, 2024.

Based on the multi-scale statistical observations from antarctic Zhongshan station, a rippling aurora-like optical phenomena was observed near the poleward boundary of the aurora. The lack of red emission and extremely small scale indicated the aurora ripple is not likely been the result of the electron or ion perception along the magnetic field line. Through the statistical results of appearance location, fine scale structures and the consistence to the theoretical predication, the Aurora ripple is believed to be mainly caused by the plasma gradient drift instability around aurora. Dreyer et al described this phenomena as Fragmented aurora-like emissions in 2019, considering the patterns of emergence and progression associated with this phenomenon, we suggest to name it as "Aurora ripples". This designation is inspired by the visual resemblance of the phenomenon to rippless formed when a paddle moves through a lake, signifying the interaction of auroral plasma with the atmosphere.

How to cite: Li, B.: Aurora ripples - a visual ionospheric emissions when auroral plasma sweeping through atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3868, https://doi.org/10.5194/egusphere-egu24-3868, 2024.

Solar particle events (SPEs) are short-lived bursts of high-energy particles from the solar atmosphere and are widely recognized as posing significant economic risks to modern society. Most SPEs are relatively weak and have minor impacts on the Earth’s environment but historic records contain much stronger SPEs which have the potential to alter atmospheric chemistry, impacting climate and biological life. The impacts of such strong SPEs would be far more severe when the Earth’s protective geomagnetic field weakened, such as during past geomagnetic excursions or reversals. Here we model the impacts of an extreme SPE under different geomagnetic field strengths, focusing on changes in atmospheric chemistry and surface radiation using the atmosphere-ocean-chemistry-climate model SOCOL3-MPIOM and the radiation transfer model LibRadtran. Under current geomagnetic conditions, an extreme SPE would increase NO_x concentrations in the polar stratosphere and mesosphere, causing reductions in extratropical stratospheric ozone lasting for about a year. In contrast, with no geomagnetic field there would be a substantial increase in NO_x throughout the entire atmosphere, resulting in severe stratospheric ozone depletion for several years. The resulting ground-level UV radiation would remain elevated for up to six years, leading to increases in UV index up to 20-25% and solar-induced DNA damage rates by 40-50%. The potential evolutionary impacts of past extreme SPEs remains an important question, while the risks they pose to human health in modern conditions continue to be underestimated.

How to cite: Arsenovic, P., Rozanov, E., Usoskin, I., Turney, C., Sukhodolov, T., McCracken, K., Friedel, M., Anet, J., Simic, S., Maliniemi, V., Egorova, T., Korte, M., Rieder, H., Cooper, A., and Peter, T.: Global impacts of an extreme Solar Particle Event under different geomagnetic field strengths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8910, https://doi.org/10.5194/egusphere-egu24-8910, 2024.

The SMILE mission, supported by the European Space Agency and the Chinese Academy of Sciences, is scheduled for launch in 2024. The mission is augmented by a substantial ground-based network of optical ASI's. Here, we report  progress in developing a numerical model of UV emissions to aid interpretation of images collected by the SMILE UVI.  The model calculates UV emissions produced by suprathermal electrons, accounting for prominent UV auroral and dayglow emission lines and bands, including OI 130.4/135.6nm, Lyman-Birge-Hopfield (LBH) and Vegard-Kaplan (VK) bands. It also calculates line-of-sight absorption and the integrated UV photon flux spectrum reaching each UVI-imager pixel. Photoelectron energy spectra for the UV emission module are generated using a Monte Carlo model of photoelectron propagation. This model accounts for 52 kinds of electron-neutral collisions as well as Coulomb collisions. Considering closed geomagnetic field lines in the night sector, and depending on Earth's position relative to the Sun, the model predicts the appearance of energetic photoelectrons coming from the day sector. Coulomb scattering prevents pthese hotoelectrons from reaching the opposite ionosphere [c.f., Khazanov et al, 1994]. To reveal the importance of Coulomb collisions, model photoelectron fluxes and related UV emissions were calculated with Coulomb collisions included and omitted for five locations along the orbit of the DMSP F16 satellite on UT0800 January 1, 2017, which observed anomalous UV emission induced by conjugate photoelectrons [Kil et al., 2020]. Omitting Coulomb collisions overestimates the photoelectron flux and the intensity of UV emission by up to 50% with the effect being more pronounced on longer field lines.

Solar EUV photons also produce energetic photoelectrons which ionize neutrals, heat ambient electrons, and cause UV emission. These photoelectrons can penetrate into the nightside even when connected to the day sector by geomagnetic field lines. UV emission caused by such photoelectrons in the night sector is called anomalous UV emission. knowlege of which is important for the analysis of data from the SMILE UVI. The model development for SMILE includes a module that calculates propagation of photoelectrons and related UV emission. Results from the model are benchmarked against observations by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) of the DMSP F16 spacecraft. The spacecraft was in Earths shadow, and traveling towards the equatorial plane. The observed anomalous UV emission rapidly decreases as the spacecraft approaches lower latitudes where field lines are shorter and almost completely in the shadow. Values of the UV emission at wavelengths of 135.6 nm and 130.4 nm were calculated from the model at several locations along the spacecraft orbit. Calculations performed with a tilted dipole geomagnetic field gave values that were significantly larger than the observed ones. Calculations using the International Reference Geomagnetic Field (IGRF) provided much improved agreement between the model and the observation because the IGRF places the southern ends of geomagnetic field lines farther from the sunlit hemisphere. The improved agreement suggests the model development related to the SMILE mission will aid interpretation of the data.

How to cite: Rankin, R., Sydorenko, D., Liang, J., and Donovan, E.: Calculation of photoelectron induced UV emission with application to the SMILE mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15929, https://doi.org/10.5194/egusphere-egu24-15929, 2024.