Pitch Angle Distribution Evolution Of Radiation Belt Electrons

The Van Allen radiation belts contain energetic electrons trapped in the terrestrial magnetic field.These energetic electrons are responsible for several types of satellite malfunctions and pose a serious threat to orbiting astronauts.The electron fluxes are highly dynamic due to various acceleration,loss and transport processes acting within the magnetosphere.Pitch angle is an essential parameter to describe charged particle motions in the magnetic filed.Investigation of electron pitch angle distributions(PADs)is of great significance for understanding the radiation belt dynamics.Plasma waves in the radiation belts can resonantly interact with electrons.These interactions are pitch angle dependent and can change the electron PADs efficiently.In this thesis,we study the influence of wave-particle interactions on the evolution of energetic electron PADs.In the first chapter of this thesis,at first we briefly describe the structure of the Earth's magnetosphere,and then introduce the motion of the charged particles in the inner magnetosphere.Then we details the related features of the electron PADs,includ-ing the classification,explicit expressions,spatial distribution and association with the space weather conditions.This chapter also introduce the characteristics of whistler-mode and magnetosonic waves and their spacial distribution in the radiation belts.In chapter 2,we mainly discuss the effect of whistler-mode chorus waves on the dynamic evolution of energetic electron PADs in the outer radiation belt.Using Van Allen Probes data,we study two events of interaction between chorus waves and en-ergetic electrons.In the first event,the electron PADs present normal patterns at the initial time and gradually evolve into nearly flattop-shaped.In the second event,the initial electron PADs are butterfly-shaped.We report the rapid flattening of electron butterfly PAD patterns within one or several hours,and found that the chorus-driven acceleration can be expected to fill the concave part of butterfly PADs near 90°.Our works further confirm the importance of whistler-mode chorus waves to the dynamic evolution of electrons in the outer radiation belt.The main content in chapter 3 is about electron PADs in the radiation belt slot re-gion.Previous works suggested that the PADs of hundreds keV electrons in the slot region often exhibit butterfly patterns with shallow depressions near 90°.However,the dominant mechanism for these peculiar PADs remains unclear.We study this problem using statistical methods.At first we examen the longitudinal and latitudinal distribu-tion features of electron butterfly PADs in the slot region.And then we analyze the correlation between energetic electron butterfly PADs in the slot region and geomag-netic activities.Moreover,we statistically investigate the spatial distribution of mag-netosonic and whistler-mode waves in different L-shells,and the relationship between these waves and geomagnetic activities.Finally,we study the relationship between plasma waves and energetic electron PADs in the slot region.We find that the reso-nance with magnetosonic waves is the main mechanism for the formation of energetic electron butterfly PADs in the slot region.In summary,the dynamic evolution of energetic electrons in the Earth's radiation belts is studied through investigating the electron PADs and their variations.We mainly discuss the interactions between electrons and whistler-mode or magnetosonic waves in this thesis.Our works further confirm the important role of wave-particle interactions in the radiation belt dynamics from a new point of view.