2021 Workshop: Terrestrial Hydrogen

Evaluating the distribution of hydrogen in the Earth’s atmosphere, and how that distribution responds to external forcing factors (e.g., solar activity), is important to our understanding of the mechanisms that shape the evolution of planetary atmospheres. Knowledge of this distribution can also guide atmospheric photochemical modeling of hydrogen containing species (e.g., CH4 and H2O), and be used for benchmark studies for these models. Further, hydrogen plays an important role in the mesosphere, thermosphere and exosphere as well as being the dominant species in the topside ionosphere. Hydrogen is also an indicator of whether our understanding of the processes near the turbopause is correct; the limiting flux of H into the thermosphere is established by the effective eddy mixing coefficient (Donahue, 1969). One of the most commonly used methods for investigating H from the ground is to use the H Balmer alpha line. Spacebased observations, such as those planned for the GLIDE and SIHLA mission, open new opportunities. Small optical remote sensing instruments on cubesats, commercial suborbital flight or other platforms will provide other insights. In this session we solicit contributions from the modeling and the observational community to address our current understanding, identify gaps / challenges, and establish a path forward. We look forward to contributions from across the entire spectrum of inquiry into hydrogen ranging from lower atmosphere exchange to plasmaspheric processes.