RESEARCH FOCUS

Our research focuses on modeling the trapped radiation environment in near-Earth space. Earth is surrounded by two Van Allen radiation belts containing energetic electrons and protons that are trapped by the geomagnetic field. The radiation belts present a hazardous radiative environment for spacecraft operating within. Therefore, since their discovery in 1958, understanding the governing processes, and simulating and eventually predicting the dynamics of radiation belt particles have been the research targets that space physicists have long pursued.

Van Allen Probes
Recent Media Coverage
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West Virginia University (WVU) TODAY’s E-News: ''WVU physicist receives prestigious NSF CAREER Award'' 

 

In the heat of the space race in 1958 between the United States and the Soviet Union, James Van Allen discovered Earth’s radiation belt. The belt is located at 500 to 60,000 kilometers above Earth’s surface and is populated with energetic “killer” electrons that create a hazardous environment for satellites and other spacecrafts operating within this zone ...

Radiation Belts

EOS Research Spotlight on our 2017 JGR Paper: ''How Earth’s Outer Radiation Belts Lose Their Electrons'' 

 

A new analysis of three space storms reveals the mechanisms of particle loss from the Van Allen belts. The Van Allen belts are massive, donut-shaped rings of radiation that encircle Earth, extending up to 58,000 kilometers into space. Held in place by Earth’s magnetic field, the belts shrink and expand as electrons get knocked between belts, down into the atmosphere, or out into space ...

Radiation Belts

NASA News Story on Tu et al. (2014) GRL Paper: ''New NASA Van Allen Probes Observations Helping To Improve Space Weather Models'' 

 

Using data from NASA's Van Allen Probes, researchers have tested and improved a model to help forecast what's happening in the radiation environment of near-Earth space -- a place seething with fast-moving particles and a space weather system that varies in response to incoming energy and particles from the sun ...

DREAM3D

LANL Science News on DREAM3D Model: ''Observations and simulations improve space weather models'' 

 

Researchers used data from the Van Allen Probes to improve a three-dimensional model created by Los Alamos scientists called DREAM3D. ...

The work demonstrated that DREAM3D accurately simulated the behavior of a complex and dynamic event in the radiation belt that was observed in October 2012.

Weichao Tu

Chinese Academy of Sciences News Story on Dr. Tu's Visit

 

Dr. Weichao Tu visited the National Space Science Center, the Chinese Academy of Sciences on April 28, 2010. She delivered a lecture entitled “Quantification of the Precipitation Loss of Radiation Belt Electrons Observed by SAMPEX". 50 researchers from the State Key Laboratory of Space Weather and other laboratories in NSSC attended the lecture. After the lecture, Dr. Tu answered the questions from the audience and had an insightful discussion with the young researchers ...

Recent Projects

Study the precipitation of radiation belt electrons during the rapid dropout events

 

The MeV electron flux in the Earth's outer radiation belt has been observed to drop by orders of magnitude on timescale of hours, which is called the electron ‘dropout’. Where do the electrons go? This is one of the most important outstanding questions in radiation belt studies. Radiation belt electrons can be lost either by transport across the magnetopause into interplanetary space or by precipitation into the atmosphere. In this project we will use the Drift-Diffusion model to simulate the electron dropout observed by Van Allen Probes at high altitude and the precipitating electrons observed at low altitude. The goal is to quantify the electron precipitation loss with high spatial and temporal resolution and resolve the underlying loss mechanisms for radiation belt electrons.

Electron Dropout
Electron Precipitation

Formation and decay of the inner electron radiation belt

 

The electron intensity in Earth's inner radiation belt is characterized by occasional rapid increase followed by extended periods of gradual decrease. The mechanisms of these formation and decay processes are unknown. Radial diffusion driven by interactions with Ultra Low Frequency (ULF) waves can contribute to the formation and decay of inner belt electons. Our goal in this project is to use the ULF wave measurements from the Van Allen Probes in space, supplemented by complementary analysis of ground magnetometer data, to quantify the radial diffusion coefficient of inner belt electrons.

Inner belt electrons

The Effect of Magnetic Field Line Curvature Scattering on the Loss of Ring Current Ions

 

Understanding the dynamics of ring current ions (~1-100s of keV) is crucial for modeling the highly dynamic and coupled system of the Earth’s magnetosphere. During geomagnetic storms, ring current development strongly affects the magnetic field topology in the inner magnetosphere. In turn, the distorted magnetic field modifies the ion trajectories, and may lead to non-adiabatic motion of ring current ions if the gyroradius of the ion is large compared to the radius of curvature of the magnetic field line. This effect is referred to as magnetic field line curvature (FLC) scattering, which can act as an important loss mechanism for ring current ions. In this project, we will use our newly developed particle tracing code to perform direct test particle simulations of the cumulative FLC scattering of ring current ions. By numerical simulations and model-data comparison, our goal is to quantify the effects of FLC scattering and determine its relative contribution to ring current losses.

Field line curvature scattering