Jianqi Qin

Radiative transfer modeling of the OI 135.6 nm emission in the nighttime ionosphere

Remote sensing of the nighttime OI 135.6-nm emissions has been a widely used method for measuring the F-region ionospheric plasma. In this work, we first develop a comprehensive radiative transfer model from first principles to investigate the effects of different physical processes on the production and transport of the 135.6-nm photons in the ionosphere, and then propose a new approach for estimating electron densities from the nightglow. The forward modeling investigation indicates that under certain conditions mutual neutralization can contribute up to ∼38% of the total production of the nighttime 135.6-nm emissions. Moreover, depending on the ionospheric conditions, resonant scattering by atomic oxygen and pure absorption by oxygen molecules can reduce the limb brightness observed by satellite-borne instuments by up to ∼40% while enhancing the brightness viewing in the nadir direction by typically ∼25%. Further analysis shows that without properly addressing these effects in the inversion process, the peak electron density in the F-region (NmF2) obtained using limb observations can be overestimated by up to ∼24%. For accurate estimation of the ionospheric electron density, we develop a new type of inverse model that accounts for the effects of mutual neutralization, resonant scattering, and pure absorption. This inversion method requires the knowledge of O and O2 densities in order to solve the radiative transfer equations. Application of the inverse model to the nighttime ionosphere in the noiseless cases demonstrates that the electron density can be accurately quantified with only ∼1% error in Nmf2 and Hmf2.

Non-thermal hydrogen atoms in the terrestrial upper thermosphere

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.

Atmospheric scattering effects on ground‐based measurements of thermospheric vertical wind, horizontal wind, and temperature

Ground-based Fabry-Perot interferometers (FPIs) routinely observe large vertical winds in the thermosphere, sometimes reaching over 100 m/s. These observations, which use the Doppler shift of the 630.0-nm airglow emission to estimate the wind, have long been at odds with theory. We present a summary of 5 years of data from the North American Thermosphere-Ionosphere Observing Network (NATION), showing that large apparent vertical winds are a persistent feature at midlatitudes during geomagnetic storms. We develop a radiative transfer model which demonstrates that these measurements can be explained as an artifact of the scattering of light in the troposphere. In addition to the example from midlatitudes, we apply the model to low latitudes, where we show that the post-sunset vertical winds routinely measured over Brazil are explained in part by atmospheric scattering. Measurements of the horizontal wind and temperature are also affected, with errors reaching 400 m/s and 200 K in the most extreme cases.

Redistribution of H atoms in the upper atmosphere during geomagnetic storms

Geocoronal H emission data acquired by NASAs Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) 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 mid 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 ∼1-2RE 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+ leads 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.

Ground-based optical measurements of quiet-time thermospheric wind and temperature: atmospheric scattering corrections†

Ground-based measurements of thermospheric wind and temperature are known to be affected by tropospheric scattering during geomagnetically active times, when horizontal airglow gradients are large. In this work, we present an analysis of the effects during quiet times, when horizontal airglow gradients can be assumed to be negligible, and we derive corrections to be applied to historical and future data sets. These corrections are easy to apply, depending only upon the optical thickness of the atmosphere and the measured wind, not the viewing direction or temperature. If these corrections are not applied, all winds estimated from ground-based observatories are underestimated by about 10% (depending on the optical thickness), and temperatures are overestimated by a couple K. We present observational evidence of the effect of atmospheric scattering on temperature measurements using five years of data from the North American Thermosphere Ionosphere Observing Network (NATION). We find that the temperature measured to the east and west are statistically larger than the temperatures measured to the zenith. This is consistent with our analysis of the effect of atmospheric scattering, though the difference in the measurements is slightly larger than the theoretical prediction.