Science goals determining the physical mechanisms that produce outer electron radiation belt enhancements is one of the most pressing questions in inner magnetospheric physics. The primary technique…

This federal contract award, valued at $276,833.00, was granted by the National Aeronautics and Space Administration (NASA) to the University of California, Los Angeles (UCLA) to conduct research on the physical mechanisms that produce outer electron radiation belt enhancements. The project aims to create a cross-calibrated estimate of electron phase space density across the outer radiation belt region by combining data from the ERG/ARASE mission (JAXA) and the Van Allen Probes mission. This combined data product will span approximately 2.5 years and provide one complete revolution around the Earth in magnetic local time from both missions, enabling researchers to unambiguously determine whether phase space density peaks were present in the outer belt. The award does not have a set-aside designation and is a grant for research with a completion date of January 31, 2026.

Science goals determining the physical mechanisms that produce outer electron radiation belt enhancements is one of the most pressing questions in inner magnetospheric physics. The primary technique for identifying and differentiating between the mechanisms is through the analysis of phase space density (PSD) distributions as a function of the 3 adiabatic invariants of the electron motion. As has been detailed in a number of recent van allen probes studies of electron enhancement events, the apogee of the probes (~5.8 RE) is too close to the earth to unambiguously identify the presence of peaks versus monotonic radial gradients in PSD, since the peak can be located outside of apogee. Some attempts have been made to address this issue, for example by using additional spacecraft that sample the belt at higher altitudes. However, all of these techniques have their shortcomings and have not led to clarity on the question at hand. What is needed is a set of reliable, clean measurements of electron PSD that span from L3 to the outer reaches of the radiation belt near L8. Van allen probes data alone simply cannot provide this measurement. We thus propose to construct a fully-cross-calibrated estimate of electron PSD across the entire outer radiation belt region by combining the high-quality ERG/arase (jaxa) and van allen probes measurements. The combined data product will span ~2.5 years and provide one complete revolution around the earth in MLT from both missions. Due to the orbital configuration of arase, this combined product will provide the necessary information on electron PSD distributions at altitudes beyond the van allen probe apogee, and thus be able to unambiguously determine whether PSD peaks were present in the outer belt or not. The following science questions (SQS) will be investigated: SQ1: what are the physical processes that produce radiation belt enhancements? SQ2: what are the interplanetary and magnetospheric conditions that lead to one mechanism dominating over the other? Methodology the proposed methodology will build on cross-calibration work that has already been initiated between the two mission teams. The specific data sets that will be used are the mageis and rept electron measurements (van allen probes), and the mepe, HEP, and XEP measurements (arase). We will perform an extensive cross-calibration of the angular distributions obtained from both missions. We will then convert the measurements from both missions into phase space density as a function of the 3 adiabatic invariants from a common set of magnetic field models. We will then combine the two into a merged PSD product on the same time cadence, adiabatic invariant grid, etc. This will be archived and freely provided to the scientific community, allowing US researchers full access to the calibrated arase dataset for the first time. We will validate the merged PSD using a novel technique to remotely infer the radial gradient in PSD at higher l using electron drift echoes. Our initial survey indicates that over 40 electron enhancement events were observed in the overlapping times between the two missions. To answer the SQS, we will analyze radial PSD profiles at various values of (fixed) first and second adiabatic invariant in all of the events and perform a superposed epoch analysis using the interplanetary conditions from the omni database. Relevance our proposed role as a CO-investigator on the arase mission addresses multiple NASA heliophysics goals. The proposed effort will include three core elements of the huspi program: calibration of several energetic particle instruments, scientific analysis and research of the data returned, and development of innovative data analysis techniques. The overarching effort has the potential to shed new light on the processes responsible for radiation belt enhancements, which will ultimately inform physics-based models of the radiation belts that are used for space weather prediction.