%0 Journal Article %J Journal of Geophysical Research: Space Physics %D 2018 %T Nonparametric H Density Estimation Based on Regularized Nonlinear Inversion of the Lyman Alpha Emission in Planetary Atmospheres %A Qin, Jianqi %A Harding, Brian J. %A Waldrop, Lara %X

Inversion of space‐borne remote sensing measurements of the resonantly scattered solar Lyman alpha (121.6‐nm) emission in planetary atmospheres is the most promising means of quantifying the H density in a vast volume of space near terrestrial planets. Owing to the highly nonlinear nature of the inverse problem and the lack of sufficient data constraints over the large volume of space where H atoms are present, previous inversion methods relied on physics‐based parametric formulations of the H density distributions to guarantee solution uniqueness. Those physical formulations, such as the Chamberlain model, were developed with simple assumptions of the atmospheric conditions. The use of such formulations as constraints significantly limits the range of possible solutions, which might lead to large errors in the case when those assumptions are invalid. In this study, we demonstrate for the first time the feasibility of estimating the H density through regularized nonlinear inversion of the Ly‐α emission in an optically thick atmosphere, without using parametric formulations. Specifically, Occam's inversion algorithm is used to demonstrate that the H density can be estimated in a large volume of space near the planet, with accuracy in different atmospheric regions depending on the observation scheme. Two distinctly different schemes are examined, including a low‐Earth orbit and a geostationary orbit. Modeling results show that the low‐Earth orbit is better for H density estimation in the thermosphere, while the high‐altitude orbit is better for estimation in the exosphere. Our results could provide useful information for designing the observation schemes of future missions.

%B Journal of Geophysical Research: Space Physics %V 123 %P 8641 - 8648 %8 09/2018 %G eng %U http://doi.wiley.com/10.1029/2018JA025954 %N 10 %! J. Geophys. Res. Space Physics %R 10.1029/2018JA025954 %0 Journal Article %J Journal of Geophysical Research: Space Physics %D 2017 %T Redistribution of H atoms in the upper atmosphere during geomagnetic storms %A Qin, Jianqi %A Waldrop, Lara %A Makela, Jonathan J. %X

Geocoronal H emission data acquired by NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics mission are analyzed to quantify the H density distribution over the entire magnetosphere‐ionosphere‐thermosphere region in order to investigate the response of the atmospheric system as a whole to geomagnetic storms. It is shown that at low and middle latitudes the H density averaged over storm times in the thermosphere‐exosphere transition region decreases by ∼30%, while the H density at exospheric altitudes above ∼1–2 RE increases by up to ∼40% relative to quiet times. We postulate that enhanced ion‐neutral charge exchange in the topside ionosphere and inner plasmasphere is the primary driver of the observed H redistribution. Specifically, charge exchange reactions between H atoms and ionospheric/plasmaspheric O+ lead to direct H loss, while those between thermal H and H+ yield kinetically energized H atoms which populate gravitationally bound satellite orbits. The resulting H density enhancements in the outer exosphere would enhance the charge exchange rates in the ring current and the associated energetic neutral atom production. Regardless of the underlying mechanisms, H redistribution should be considered as an important process in the study of storm time atmospheric evolution, and the resultant changes in the geocoronal H emissions potentially could be used to monitor geomagnetic storms.

%B Journal of Geophysical Research: Space Physics %V 122 %P 10,686 - 10,693 %8 08/2017 %G eng %U https://onlinelibrary.wiley.com/toc/21699402/122/10 %N 10 %! J. Geophys. Res. Space Physics %R 10.1002/jgra.v122.1010.1002/2017JA024489 %0 Journal Article %J Nature Communications %D 2016 %T Non-thermal hydrogen atoms in the terrestrial upper thermosphere %A Qin, Jianqi %A Waldrop, Lara %X

Model predictions of the distribution and dynamical transport of hydrogen atoms in the terrestrial atmosphere have long-standing discrepancies with ultraviolet remote sensing measurements, indicating likely deficiencies in conventional theories regarding this crucial atmospheric constituent. Here we report the existence of non-thermal hydrogen atoms that are much hotter than the ambient oxygen atoms in the upper thermosphere. Analysis of satellite measurements indicates that the upper thermospheric hydrogen temperature, more precisely the mean kinetic energy of the atomic hydrogen population, increases significantly with declining solar activity, contrary to contemporary understanding of thermospheric behaviour. The existence of hot hydrogen atoms in the upper thermosphere, which is the key to reconciling model predictions and observations, is likely a consequence of low atomic oxygen density leading to incomplete collisional thermalization of the hydrogen population following its kinetic energization through interactions with hot atomic or ionized constituents in the ionosphere, plasmasphere or magnetosphere.

%B Nature Communications %V 7 %8 12/2016 %G eng %U http://www.nature.com/articles/ncomms13655 %N 1 %! Nat Commun %R 10.1038/ncomms13655 %0 Journal Article %J Journal of Geophysical Research: Space Physics %D 2015 %T Radiative transfer modeling of the OI 135.6 nm emission in the nighttime ionosphere %A Qin, Jianqi %A Makela, Jonathan J. %A Kamalabadi, Farzad %A Meier, R. R. %K OI 135.6-nm Emission %K onosphere %K Radiative transfer %K remote sensing %X


%B Journal of Geophysical Research: Space Physics %V 120 %P 10116 - 10135 %8 11/2015 %G eng %U http://doi.wiley.com/10.1002/jgra.v120.11http://doi.wiley.com/10.1002/2015JA021687http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2F2015JA021687 %N 11 %! J. Geophys. Res. Space Physics %R 10.1002/jgra.v120.1110.1002/2015JA021687