Sapna Shekhar

PhD Student in Physics and Astronomy

My research revolves around the plasma physics of the magnetosphere. There are several theories about what drives the precipitation of relativistic electrons into the atmosphere from the Van Allen radiation belts. To study this, Robyn Millan's group at Dartmouth College launched an array of balloon borne payloads that include particle detectors and magnetometers. I mostly work with low Earth Orbiting polar satellites ( POES, SAMPEX and DMSP) observations of the Relativistic Electron precipitation (REP)  events and compare them with balloon observations. Using these data, I am interested in estimating the spatial and temporal evolution of these events which remains largely unexplored.The REP's are characterized by enhancements in the relativistic electrons population at lower altitudes along the field lines that contain the radiation belts i.e L~3-8. These events are known to last from minutes to hours. Early observations have suggested scattering by EMIC (Electromagnetic Ion Cyclotron) waves as a possible mechanism of energization to relativistic energies. Recently it has also been found that these events have MLT (Magnetic Local Time ) and L-Shell dependence. Some of the open ended questions I am trying to answer are :    •    Where are these events concentrated in L and MLT?    •    How long do they last?    •    What is the energy spectrum of precipitation like, and how does it evolve with time?

B.S. in Physics, Miranda House, New Delhi, India
M.S. in Physics, Indian Institute of Technology Madras, Tamil Nadu, India