In the outer radiation belt, electromagnetic ION cyclotron (emic) waves are mainly responsible for energetic electron precipitation, and whistler-mode chorus waves can cause both loss and acceleration…

This is a $568,771.12 federal research grant awarded by NASA's Shared Services Center to the University of Texas at Dallas (UTD). The grant supports a 3-year study on nonlinear wave-particle interactions in the Earth's outer radiation belt, with a focus on understanding the role of electromagnetic ion cyclotron (EMIC) waves and whistler-mode chorus waves in causing energetic electron scattering and precipitation. The research aims to develop improved models for simulating the kinetic evolution of the radiation belt electron population in response to these large-amplitude, coherent wave events. The work involves collaboration between researchers at UTD, Catholic University of America, and The Aerospace Corporation. This grant does not have a set-aside designation, as UTD is competing as a public research university. The grant supports NASA's broader objective of characterizing fundamental space physics processes within the heliosphere.

In the outer radiation belt, electromagnetic ION cyclotron (emic) waves are mainly responsible for energetic electron precipitation, and whistler-mode chorus waves can cause both loss and acceleration to energetic electrons [thorne, 2010]. Recent observations [e.g., fennel ET AL., 2014; zhang ET AL., 2016] reported very efficient energetic electron scattering events by intense and coherent emic waves and chorus waves that were not explained by quasi-linear wave-particle-interaction theory. The large amplitude and phase coherence of these waves cause energetic electrons to respond nonlinearly by phase-bunching and phase-trapping in the wave field [bortnik ET AL., 2008]. Theoretical studies on nonlinear wave-particle interaction [e.g., artemyev ET AL., 2017] suggest an advective fokker-planck equation to describe kinetic evolution of the energetic electron phase space density. However, event-specific solutions to such a fokker-planck equation had been unavailable due to the lack of a solver. With the recent advance in modeling techniques we developed, we are able to solve this fokker-planck equation. Therefore, using the accurate wave and particle measurements from van allen probes and the conjugate balloon array for radiation belt relativistic electron losses (barrel), we propose to investigate and understand energetic electron response due to nonlinear wave-particle interactions. Our proposal will address the following scientific goals: (1) simulating and understanding energetic electron phase space density evolution induced by large amplitude emic and chorus waves. (2) characterizing barrel observed precipitating electron energy spectrum with nonlinear wave-particle interaction model. (3) modeling nonlinear chorus wave energization events. Relevance: our proposed study will greatly advance the understanding of nonlinear wave-particle interactions, in direct relevance to a major science goal of heliophysics decadal survey: to "discover and characterize fundamental processes that occur both within the heliosphere and throughout the universe". Our proposed study will also enhance the interpretation of van allen probes and barrel data, therefore contributing to and extending the overall objective of the van allen probes mission. Methodology: year 1: we will perform parametric test-particle studies on nonlinear wave-particle interaction effects, and use these studies to calibrate our green's function and fokker-planck models. We will also use observed waveforms and background magnetic field and plasma density to calculate event-specific nonlinear diffusion and advection coefficients, and develop event-specific simulation techniques for our models. Year 2: we will identify van allen probes observed event periods of wave activity to compare with barrel, and collect nonlinear emic wave and chorus wave events by analyzing waveforms of van allen probes' emfisis instrument and particle measurements from ECT suite. We will focus on energy spectrum of precipitating energetic electrons induced by nonlinear emic waves. Using simulation results, we will calculate the resultant bremsstrahlung x-RAY intensities and compare with barrel observations. Year 3: we will identify nonlinear chorus wave events, and perform two-dimensional event-specific simulations. In particular, we will resolve both the pitch-angle signature and the acceleration effects in energetic electrons caused by nonlinear chorus waves, and compare them with van allen probes particle measurements. These results will also be compared with those predicted by quasi-linear theory to quantify its validity regime. Project team: liheng zheng (at university of texas at dallas) will act as the administrative PI. HUI ZHU and lunjin chen (at university of texas at dallas) will be CO-is. Alexa halford (at catholic university of america) will be CO-i. Seth claudepierre (at the aerospace corporation) will be CO-i.