A machine-learning-based electron density (MLED) model in the inner magnetosphere

Plasma density is an important factor in determining wave-particle interactions in the magnetosphere.We develop a machine-learning-based electron density(MLED)model in the inner magnetosphere using electron density data from Van Allen Probes between September 25,2012 and August 30,2019.This MLED model is a physics-based nonlinear network that employs fundamental physical principles to describe variations of electron density.It predicts the plasmapause location under different geomagnetic conditions,and models separately the electron densities of the plasmasphere and of the trough.We train the model using gradient descent and backpropagation algorithms,which are widely used to deal effectively with nonlinear relationships among physical quantities in space plasma environments.The model gives explicit expressions with few parameters and describes the associations of electron density with geomagnetic activity,solar cycle,and seasonal effects.Under various geomagnetic conditions,the electron densities calculated by this model agree well with empirical observations and provide a good description of plasmapause movement.This MLED model,which can be easily incorporated into previously developed radiation belt models,promises to be very helpful in modeling and improving forecasting of radiation belt electron dynamics.

Energetic Electron Pitch Angle Diffusion due to Whistler Wave during Terrestrial Storms

A concise and elegant expression of cyclotron harmonic resonant quasi-pure pitch-angle diffusion is constructed for the parallel whistler mode waves, and the quasi-linear diffusion coefficient is prescribed in terms of the whistler mode wave spectral intensity. Numerical computations are performed for the specific case of energetic electrons interacting with a band of frequency of whistler mode turbulence at L ≈ 3. It is found that the quasi-pure pitch-angle diffusion driven by the whistler mode scatters energetic electrons from the larger pitch-angles into the loss cone, and causes pitch-angle distribution to evolve from the pancake-shaped before the terrestrial storms to the flat-top during the main phase. This probably accounts for the quasi-isotropic pitch-angle distribution observed by the combined release and radiation effects satellite spacecraft at L ≈ 3.

Magnetospheric Physics in China:2020-2021

In the past two years,many progresses were made in magnetospheric physics by the data of OMNI,SuperMAG networks,Double Star Program,Cluster,THEMIS,RBSP,DMSP,DEMETER,NOAA,Van Allen Probes,GOES,Geotail,Swarm,MMS,BeiDa,Fengyun,ARTEMIS,MESSENGER,Juno,Chinese Mars ROVER,MAVEN,Tianwen-1,Venus Express,Lunar Prospector e.g.,or by computer simulations.This paper briefly reviews these works based on 356 papers published from January 2020 to December 2021.The subjects covered various sub-branches of Magnetospheric Physics,including solar wind-magnetosphere-ionosphere interaction,inner magnetosphere,outer magnetosphere,magnetic reconnection,planetary magnetosphere.