arXiv subjects

Thomas J. Immel

Publications and source records attributed to Thomas J. Immel.

3 recordsLinked to original sources

arXiv2026

Design and Performance of the Carruthers Geocoronal Imager

The GeoCoronal Imager (GCI) onboard the Carruthers Geocorona Observatory is the primary scientific instrument of the mission. It is designed to measure far ultraviolet light at 121.6 nm (Lyman-alpha) emitted by hydrogen (H) atoms in Earth's exosphere with the sensitivity, accuracy and precision to meet the mission's scientific objectives regarding the nature of terrestrial exospheric structure and dynamics on both global and regional scales. The GCI is comprised of two co-aligned UV imaging systems. The Narrow Field Imager (NFI) acquires nearly continuous images of exospheric Lyman-alpha radiance near and above the Earth's limb at relatively high spatial and temporal resolution, while the Wide Field Imager (WFI) uses relatively higher optical sensitivity and a wider field of view to detect faint Lyman-alpha emission from the exosphere's outermost extent. Both imaging channels feature identical active pixel sensor cameras, gain-intensifiers, and 6-position optical filter wheels. This paper outlines the instrument design requirements, informed by mission science goals, as well as its performance as measured in the vacuum ultraviolet laboratory test and calibration.

astro-ph.IM↗

arXiv2022

Characterization of the Thermospheric Mean Winds and Circulation during Solstice using ICON/MIGHTI Observations

Using the horizontal neutral wind observations from the MIGHTI instrument onboard NASA's ICON (Ionospheric Connection Explorer) spacecraft with continuous coverage, we determine the climatology of the mean zonal and meridional winds and the associated mean circulation at low- to middle latitudes ($10^\circ$S-40$^{\circ}$N) for Northern Hemisphere {summer} solstice conditions between 90 km and 200 km altitudes, specifically on 20 June 2020 solstice as well as for a one-month period from 8 June-7 July 2020 {and for Northern winter season from 16 December 2019-31 January 2020, which spans a 47-day period, providing full local time coverage}. The data are averaged within appropriate altitude, longitude, latitude, solar zenith angle, and local time bins to produce mean wind distributions. The geographical distributions and local time variations of the mean horizontal circulation are evaluated. The instantaneous horizontal winds exhibit a significant degree of spatiotemporal variability often exceeding $\pm 150 $ m s$^{-1}$. The daily averaged zonal mean winds demonstrate day-to-day variability. Eastward zonal winds and northward (winter-to-summer) meridional winds are prevalent in the lower thermosphere, which provides indirect observational evidence of the eastward momentum deposition by small-scale gravity waves. The mean neutral winds and circulation exhibit smaller scale structures in the lower thermosphere (90-120 km), while they are more homogeneous in the upper thermosphere, indicating the increasingly dissipative nature of the thermosphere. The mean wind and circulation patterns inferred from ICON/MIGHTI measurements can be used to constrain and validate general circulation models, as well as input for numerical wave models.

physics.space-ph↗

arXiv2015

Hemispheric Differences in the Response of the Upper Atmosphere to the August 2011 Geomagnetic Storm: A Simulation Study

Using a three-dimensional nonhydrostatic general circulation model, we investigate the response of the thermosphere-ionosphere system to the 5-6 August 2011 major geomagnetic storm. The model is driven by measured storm-time input data of the Interplanetary Magnetic Field (IMF), solar activity, and auroral activity. Simulations for quiet steady conditions over the same period are performed as well in order to assess the response of the neutral and plasma parameters to the storm. During the storm, the high-latitude mean ion flows are enhanced by up to 150-180%. Largest ion flows are found in the main phase of the storm. Overall, the global mean neutral temperature increases by up to 15%, while the maximum thermal response is higher in the winter Southern Hemisphere at high-latitudes than the summer Northern Hemisphere: 40% vs. 20%increase in high-latitude mean temperature, respectively. The global mean Joule heating increases by more than a factor of three. There are distinct hemispheric differences in the magnitude and morphology of the horizontal ion flows and thermospheric flows during the different phases of the storm. The largest hemispheric difference in the thermospheric circulation is found during the main and recovery phases of the storm, demonstrating appreciable geographical variations. The advective forcing is found to contribute to the modeled hemispheric differences.

physics.space-ph↗