The Neutral Exosphere of the Earth Between Solar Minimum (2008-2010) and Solar Maximum (2012) Conditions Using Twins Lyman-Alpha Observations

Abstract:

The exospheric,neutral hydrogen (H) continuously appears as a source of Lyman-alpha resonance radiation at 121.5 nm. The process behind this is the resonant backscattering of solar Lyman-alpha radiation from exospheric hydrogen. Along a line of sight (LOS) above 3 Earth radii geocentric distance, the backscattered Lyman-alpha intensity is proportional to the H-column density (optically thin conditions). Based on a large number of LOSs the 3D exospheric H-density distribution is derived from exospheric Lyman-alpha observations. In the presented analysis we are using data from 2008-2010 (solar minimum) and 2012 (near solar maximum) from the Lyman-alpha detectors (LADs) on the Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission to model the 3D hydrogen density distribution under different solar conditions. We discuss the methods, the datasets, a recalibration procedure, and present structural differences of the 3D exospheric H-density distributions at solar minimum (2008-2010) and near solar maximum (2012) above 3 Earth radii.