Remote sensing of ion-neutral charge exchange and diffusive transport in planetary atmospheres

Joshi, Pratik Prasad

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https://hdl.handle.net/2142/115938 Copy

Description

Title

Remote sensing of ion-neutral charge exchange and diffusive transport in planetary atmospheres

Author(s)

Joshi, Pratik Prasad

Issue Date

2022-07-15

Director of Research (if dissertation) or Advisor (if thesis)

Waldrop, Lara

Doctoral Committee Chair(s)

Waldrop, Lara

Committee Member(s)

• Kudeki, Erhan
• Makela, Jonathan
• Oelze, Michael
• Glocer, Alex

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• exosphere
• optical remote sensing
• UV emission
• Lyman alpha
• radiative transfer modeling
• atomic hydrogen
• atomic oxygen
• Martian atmosphere
• plasmasphere-ionosphere coupling
• proton transport
• mesophere and lower thermosphere (MLT)
• H escape
• planetary evolution

Abstract

Planetary atmospheres are the envelope of gases that encircle a planet. This region is constantly interacting with energy and particles from the Sun and exhibits variability in its composition, structure, and evolution over periods ranging from hours to years. Through the loss of water to space, these dynamic interactions affect the evolution and habitability of planets. At Earth, these interactions also drive power outages, radiation hazard to humans, safety concerns for airplanes, satellite drag, and disruptions in radio communication. To better safeguard our technological assets in space, increase human safety, and understand the evolution of habitable worlds, it is very important to understand the structure and processes that govern planetary atmospheres. The underlying physical processes can be investigated through the solution of aeronomical equations governing the conservation of momentum, energy, and mass, using radio and optical measurements of bulk atmospheric state parameters, such as densities, temperatures, and velocities. The research presented in this thesis advances the understanding of the upper atmospheres of the habitable planets Earth and Mars, through the de- sign of novel remote sensing techniques for estimation of key ion and neutral state parameters. First, this thesis determines a new aeronomical standard for the cross section for in-neutral charge-exchange between the major upper atmospheric species at Earth, namely neutral and ionized atomic oxygen, O and O+, by resolving the long standing discrepancy between its quantum mechanical, theoretical, and aeronomical specification. This work enables long overdue routine estimation of O density in the Earth’s upper atmosphere using empirical constraints on the momentum and energy transfer between these key species. This thesis also presents a new technique to estimate atomic H density [H], and H+ flux φH+, in Earth’s thermosphere and exosphere, using empirical constraints on H+ mass conservation (continuity) driven by the reactions between H+, O, O+ and H. The resulting estimates of [H] and φH+ enable the investigation of diurnal variability of the ionosphere and plasmasphere, the ionized regions of the Earth’s upper atmosphere, and also indicate over- estimation of [H] by the widely used neutral atmosphere model, MSIS00. Furthermore, this thesis presents a novel parametric technique to quantify the height-resolved limiting H flux, φlimiting, throughout the Earth’s mesosphere, by empirically constraining the gradient-driven transport (diffusion) of all hydrogenated species in the presence of imbalances in their chemical sources and sinks. Application of this technique to space-based data yields the first ever quantification of the diurnal and solar cycle asymmetry of φlimiting, which indicates that the Earth is losing ∼124,000-186,000 tons of water from its oceans each year, a rate which is ∼3-4 times faster than current estimates. In addition, this thesis develops an independent inverse-theoretic technique to estimate Earth’s H distribution above 80 km using observations of its ultraviolet (UV) emission, and co-incident constraints on the peak mesospheric [H] and φlimiting. The results provide the first ever quantification of solar cycle and local time asymmetry of [H] along with the partitioning of its escape to space via thermal evaporation, non-thermal charge-exchange between H and H+, and non-escaping flows. Thermal H escape is found to dominate during solar maximum and at dusk owing to a warmer H atmosphere, whereas the non-thermal H − H+ escape dominates during the solar minimum and at twilight, owing to the increased ratio of H and H+ temperatures. Lastly, this thesis presents a novel technique to retrieve the H density distribution as governed by imbalances in its chemical production and loss in the Martian thermosphere, using a non-parametric inversion of observations of its UV emission. When solar flux is known, the optimal solution from this technique provides independent estimate of the UV instrument calibration. The findings present the first ever quantification of H distribution in the Martian thermosphere under diffusive non-equilibrium and indicate that Mars is losing water from its atmosphere at the rate of ∼2,654 tonnes/sol, which is ∼50% slower than its currently accepted rate. This thesis advances the fields of heliophysics and planetary science by developing a suite of new techniques to estimate the density distributions of H and O and by quantifying their charge-exchange interactions with H+ and O+ in the coupled planetary regions of the mesosphere, thermosphere, ionosphere, plasmasphere and exosphere. The presented techniques have a generic utility with any measurement and model source and are applicable to investigate every planetary atmosphere consistent with the underlying physics. The scientific findings from this thesis advance our knowledge of the rate and drivers of atmospheric evolution and habitability of Earth-like planets, and provide unique and valuable constraints on Earth’s upper atmospheric state that are needed to advance capabilities for space weather prediction and mitigation of its harmful effects.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Pratik Prasad Joshi

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