Bibliography

Quantifying the Impact of Dynamic Storm-Time Exospheric Density on Plasmaspheric Refilling

As soon as the outer plasmasphere gets eroded during geomagnetic storms, the greatly depleted plasmasphere is replenished by cold, dense plasma from the ionosphere. A strong correlation has been revealed between plasmaspheric refilling rates and ambient densities in the topside ionosphere and exosphere, particularly that of atomic hydrogen (H). Although measurements of H airglow emission at plasmaspheric altitudes exhibit storm-time response, temporally static distributions have typically been assumed in the H density in plasmasphere modeling. In this presentation, we evaluate the impact of a realistic distribution of the dynamic H density on the plasmaspheric refilling rate during the geomagnetic storm on March 17, 2013. The temporal and spatial evolution of the plasmaspheric density is calculated by using the Ionosphere-Plasmasphere Electrodynamics (IPE) model, which is driven by a global, 3-D, and time-dependent H density distribution reconstructed from the exospheric remote sensing measurements by NASA’s TWINS and TIMED missions. We quantify the spatial and temporal scales of the refilling rate and its correlation with H densities.

Waldrop, Lara; Cucho-Padin, Gonzalo; site, this; Maruyama, Naomi; site, this;

Published by: Earth and Space Science Open Archive ESSOAr      Published on: jan

YEAR: 2021     DOI: 10.1002/essoar.10505771.1

Atmospheric Sciences; Atmospheric Sciences / Magnetospheric Particles

Understanding the role of exospheric density in the ring current recovery rate

Atomic Hydrogen (H) is the most abundant constituent of the terrestrial exosphere. Its charge exchange interaction with ring current ions (H+ and O+) serves to dissipate magnetospheric energy during geomagnetic storms, resulting in the generation of energetic neutral atoms (ENAs). Determination of ring current ion distributions through modeling depends critically on the specification of the exospheric H density distribution. Furthermore, theoretical studies have demonstrated that ring current recovery rate after the storm onset directly correlates with the H density. Although measurements of H airglow emission at altitudes [3,6] Re exhibit storm-time variations, the H density distributions used in ring current modeling are typically assumed to be temporally static during storms. In this presentation, we will describe the temporal and spatial evolution of ring current ion densities in response to a realistically dynamic exospheric H density distribution using the Comprehensive Inner Magnetosphere-Ionosphere Model (CIMI). The exospheric densities used as input to the model are fully data-driven, derived as global, 3D, and time-dependent tomographic reconstructions of H emission data acquired from Lyman-alpha detectors onboard the NASA TWINS satellites during the geomagnetic storm that occurred on March 17, 2013. We will examine modeled ring current recovery rates using both dynamic and static reconstructions and evaluate the impact of realistic storm-time exospheric variability on the simulations.

Cucho-Padin, Gonzalo; site, this; Ferradas, Cristian; Waldrop, Lara; Fok, Mei-Ching; site, this;

Published by: Earth and Space Science Open Archive ESSOAr      Published on: jan

YEAR: 2021     DOI: 10.1002/essoar.10505770.1

Atmospheric Sciences; Atmospheric Sciences / Magnetospheric Particles

Quantification of the vertical transport and escape of atomic hydrogen in the terrestrial upper atmosphere

Measurements of the limiting escape rate of atomic hydrogen (H) atoms at Earth, and the relative significance of thermal evaporation and non-thermal escape mechanisms, such as charge exchange and polar wind, have long been lacking. Our recent development of sophisticated radiative transport analysis techniques now enables the reliable interpretation of remotely-sensed measurements of optically-thick H emission, such as those acquired along the Earth\textquoterights limb by the Global Ultraviolet Imager (GUVI) onboard the NASA TIMED spacecraft, in terms of physical parameters such as exobase density and, crucially, vertical diffusive flux. In this work, we present results from a systematic investigation of H Ly_α emission measured by TIMED/GUVI along the Earth\textquoterights dayside limb from 2002-2007, which we use to derive the vertical H flux and associated density distribution from 250 km out to 1 earth radius. Our analysis reveals that the vertical flux of thermospheric H is nearly constant ver a large range of solar activity and typically exceeds the calculated thermal evaporative flux, suggesting that terrestrial H escape is indeed limited by its vertical diffusion. The excess supply of H atoms to the exobase associated with large observed vertical fluxes requires that non-thermal escape mechanisms be operative for steady-state continuity balance. We find that such non-thermal processes are a particularly significant component of total H escape during low solar activity, when thermal evaporation is weakest.

Joshi, P.P.; Phal, Y.D.; Waldrop, L.S.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2019

YEAR: 2019     DOI: 10.1029/2019JA027057

Time-Dependent Response of the Terrestrial Exosphere to a Geomagnetic Storm

Recent observations of significant enhancements in exospheric hydrogen (H) emission in response to geomagnetic storms have been difficult to interpret in terms of the evolution of the underlying global, 3-D exospheric structure. In this letter, we report the first measurement of the timescales and spatial gradients associated with the exospheric response to a geomagnetic storm, which we derive from a novel, time-dependent tomographic analysis of H emission data. We find that global H density at 3 R_E begins to rise promptly, by \~15\%, after storm onset and that this perturbation appears to propagate outward with an effective speed of \~60\ m/s, a response that may be associated with enhanced thermospheric temperature and vertical neutral wind. This effective upwelling has significant implications for atmospheric escape as well as for charge exchange reaction rates, which drive important space weather effects such as plasmaspheric refilling and ring current decay.

Cucho-Padin, Gonzalo; Waldrop, Lara;

Published by: Geophysical Research Letters      Published on: 09/2019

YEAR: 2019     DOI: 10.1029/2019GL084327

Nonparametric H Density Estimation Based on Regularized Nonlinear Inversion of the Lyman Alpha Emission in Planetary Atmospheres

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\textquoterights 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.

Qin, Jianqi; Harding, Brian; Waldrop, Lara;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2018

YEAR: 2018     DOI: 10.1029/2018JA025954

Empirical quantification of the vertical transport and escape of atomic hydrogen in the terrestrial upper atmosphere

Waldrop, Lara; Phal, Yamuna; Kerr, Robert; Qin, Jianqi;

Published by:       Published on:

YEAR: 2018     DOI:

Parametric estimation of neutral hydrogen density under charge exchange and quantification of its effect on plasmasphere-ionosphere coupling

Joshi, Pratik; Waldrop, Lara;

Published by:       Published on:

YEAR: 2018     DOI:

Redistribution of H atoms in the upper atmosphere during geomagnetic storms

Geocoronal H emission data acquired by NASA\textquoterights 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\textendash2\ R_E 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.

Qin, Jianqi; Waldrop, Lara; Makela, Jonathan;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2017

YEAR: 2017     DOI: 10.1002/jgra.v122.1010.1002/2017JA024489

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.

Qin, Jianqi; Waldrop, Lara;

Published by: Nature Communications      Published on: 12/2016

YEAR: 2016     DOI: 10.1038/ncomms13655

Thermal structure of the ITM: old challenges and new insights

Waldrop, Lara; Qin, Jianqi;

Published by:       Published on:

YEAR: 2016     DOI:

Climatology of neutral hydrogen in the terrestrial thermosphere

Qin, Jianqi; Waldrop, Lara;

Published by:       Published on:

YEAR: 2016     DOI:

Hydrogen in the Upper Atmosphere II Posters

Paxton, Larry; Waldrop, Lara; Mierkiewicz, Edwin; Mlynczak, Martin;

Published by:       Published on:

YEAR: 2015     DOI:

Quantification of upper thermosphere composition and its dynamic charge exchange coupling to the mid-latitude topside ionosphere

Waldrop, Lara; Paxton, Larry; Aponte, Nestor; Gonzalez, Sixto;

Published by:       Published on:

YEAR: 2014     DOI:

Lyman $\alpha$ airglow emission: Implications for atomic hydrogen geocorona variability with solar cycle

Satellite-based measurements of geocoronal Lyman α (Ly_α) emission at 121.6 nm, created through multiple scattering of solar Ly_αphotons by atomic hydrogen, offer a valuable means of inferring the hydrogen abundance, [H], in the terrestrial thermosphere and exosphere on a global, long-term basis. We present initial results from an analysis of Ly_α radiance measurements acquired across the Earth\textquoterights limb from 2002 to 2007 by the Global UltraViolet Imager (GUVI) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft. This data spans nearly half of a solar cycle, and both the absolute Ly_α radiance as well as its relative variation across the limb are shown to exhibit a significant dependence on solar activity. We describe sensitivities of a forward radiative transport (RT) model to key parameters governing the [H] distribution in order to assess implications for [H] estimation from the GUVI limb scan data throughout the solar cycle. Based on data-model comparisons, we conclude that the observed solar cycle variability is indicative of a decrease in dayside H density at the exobase with increasing solar activity. These results, along with additional forward RT modeling based on NRLMSISE-00 model specification of [H], are also used to assess contemporary semiempirical model accuracy.

Waldrop, L.; Paxton, L.;

Published by: Journal of Geophysical Research: Space Physics      Published on: Jan-09-2013

YEAR: 2013     DOI: 10.1002/jgra.50496

atmospheric escape; hydrogen geocorona; radiative transport

Global Spatial and Climatological Dependencies of the Hydrogen Geocorona Inferred From TIMED/GUVI Measurements of Lyman $\alpha$ Radiance

Space-based measurements of geocoronal Lyman-α (Ly-α) emission at 121.6 nm, created through multiple scattering of solar Ly-α photons by atomic hydrogen, offer a

Waldrop, LS; Paxton, LJ;

Published by:       Published on:

YEAR: 2010     DOI: