CAREER: Understanding and Modeling the Mysterious Dropout of Radiation Belt Electrons

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This project focuses modeling of the relativistic electron population dynamics in Earth's Radiation Belts. Without fully understanding the mysterious dropout of electrons, a full understanding and prediction of radiation belt dynamics cannot be reached. This is of considerable practical importance due to the hazards to space-borne systems. Many communications satellites and national security assets reside in this radiation environment and their lifetime depends on its dynamics. Advancing the science supports improvement of the predictive models and fits directly into the goals of the National Space Weather Strategy and Action Plan, which was released in 2015. The project supports a female faculty member and will train and educate graduate and undergraduate students in both research and outreach activities. The learning module will provide an unprecedented informal learning opportunity on space science to West Virginia K-12 schools. It is expected to increase the awareness and interest of middle school students in the STEM programs in the state, and inspire them to pursue STEM careers, especially the underrepresented female and lower socioeconomic status students. The opportunities to develop and deliver the learning module will also provide valuable educational and outreach experience for undergraduate and graduate students and enhance their science literacy and communication skills.Since the launch of NASA Van Allen Probes in 2012, significant progress has been achieved in understanding the strong enhancement of relativistic electrons. However, the fast and dramatic dropout of radiation belt electrons (orders of magnitudes in a few hours) remains unsolved. The open question exists: Where do the electrons go during the dropout? This award is to develop a new and comprehensive dropout model, named Relativistic Electron Dropout (RED), with physical and event-specific inputs to simulate the electron dropout and understand the governing processes. RED will include not only the traditional loss processes (pitch angle diffusion, magnetopause shadowing, and outward radial diffusion), but also the new mechanism called Drift Orbit Bifurcation (DOB). Physical quantification of these processes will be achieved based on realistic field and particle conditions. With these inputs, RED will simulate both the electron dropout observed at high altitudes and the electron precipitation observed at low altitudes to resolve the governing mechanisms. The wealth of energetic electron and wave measurements from Van Allen Probes, THEMIS, and MMS spacecraft that cover the region from the outer belt to the magnetopause and the multiple POES satellites at low altitudes will provide an excellent test base for the RED model. This model will be the first to incorporate all the major loss mechanisms during the dropout, including the new DOB process. It is capable of simulating both electron dropout at high altitudes and precipitation at low altitudes, which will make a significant contribution in understanding the governing processes during the dropout and resolving their relative importance. The physical and event-specific quantification of the magnetopause shadowing, DOB, and radial diffusion processes is new and critical for understanding the fast electron dropout as well as the overall radiation belt dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.