Unraveling the Atmospheric Energy Input and Ionization Due to EMIC-Driven Electron Precipitation from ELFIN Observations

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 degrees-180 degrees) 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 (similar to 200 keV-similar to 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, similar to 3.3 x 10-2 erg/cm2/s), identify its location (any longitude, 50 degrees-70 degrees 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. Energetic electron precipitation (EEP) from Earth's radiation belts is a source of energy input to the terrestrial atmospheric system and has the potential of impacting its chemistry and possibly dynamics. Available data sets of EEP are incomplete due to instrumental limitations, hindering the accurate quantification of EEP energy input, its properties, and the resulting ionization. Here, we leverage the observations of the Electron Losses and Fields InvestigatioN CubeSats which provide high-resolution data for the first time both in energy and look-direction (pitch-angle). We specifically focus on observations during electromagnetic ion cyclotron (EMIC) waves, known to precipitate the most energetic electrons, thus penetrating the atmosphere at low altitudes. We estimate the EMIC-driven EEP energy input and its resulting ion-electron production rate as a function of altitude using a sophisticated method that takes into account the EEP pitch-angle distribution. We find that 74% of the energy input ionizes the atmosphere, primarily in the mesosphere (peaking between 52 and 74 km), a region underestimated by current recommended ionization rates. We provide the region where EMIC-driven EEP is observed and the ionization rates at each location, which can be used as input to comprehensive atmospheric models to ultimately quantify the accurate impact of EMIC waves on Earth's atmosphere. Electron Losses and Fields InvestigatioN's pitch-angle resolved data provide an ideal input to the Boulder Electron Radiation to Ionization model to estimate atmospheric ionization due to electron precipitation Electromagnetic ion cyclotron-driven precipitation occurs at all longitudes and 50 degrees-70 degrees latitudes; 74% of its input energy flux efficiently ionizes the atmosphere Ionization is enhanced in the mesosphere at altitudes ranging from 52 to 74 km, with ionization rates of similar to 100-200 pairs/cm3/s