One glaring issue in solar-terrestrial research is to understand the loss of water, via hydrogen (H) escape, to space and its impact on the atmospheric evolution of planets. The maximum rate of terrestrial hydrogen escape is limited by its rate of upward transport through Earth's lower atmospheric layers including the mesosphere and the thermosphere. After it reaches the Earth’s upper atmosphere, known as the exosphere, the hydrogen is lost to space through thermal and suprathermal mechanisms such as H-H+ charge exchange at middle latitudes and polar wind outflow at the poles.
Advised by CSL Assistant Professor Lara Waldrop, Y.T. Lo Fellow in Electrical and Computer Engineering, the goal of their award-winning proposal is to quantify the total limiting flux of terrestrial hydrogen and its thermal and non-thermal escape rates by constraining the theory of hydrogen transport using state-of-the-art measurements from NASA's TIMED and CLUSTER missions, and specification from ionospheric model SAMI3, NASA's polar wind outflow model (PWOM), and neutral atmosphere model NRLMSISE-00.
This work will yield: 1) unprecedented quantification of the limiting hydrogen flux and its partitioning between thermal and charge-exchange driven escape rates and, 2) comprehensive characterization of the solar cycle variation of H escape mechanisms and their effect on the structure and dynamics of the terrestrial hydrogen geocorona. The scientific results and estimation techniques from this research will be reported in conferences and high-impact journal publications over the next two years.
Joshi's research will not only advance the understanding of crucially important space weather, but also improve the estimation techniques and quantitative understanding of the physical processes which govern the evolution of planets in our solar system. His work will contribute directly to NASA's Strategic Plan Objective: "Understand the Sun, Earth, Solar System, and Universe."
Read NASA's public announcement for more details on the selection process.