| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | June 3, 2020 |
| Latest Amendment Date: | August 24, 2022 |
| Award Number: | 2031024 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Chia-Lin Huang
chihuang@nsf.gov (703)292-7544 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | August 1, 2018 |
| End Date: | December 31, 2022 (Estimated) |
| Total Intended Award Amount: | $228,137.00 |
| Total Awarded Amount to Date: | $228,137.00 |
| Funds Obligated to Date: |
FY 2018 = $99,004.00 FY 2019 = $106,942.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
4765 WALNUT ST STE B BOULDER CO US 80301-2575 (720)974-5888 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
4750 Walnut Street Boulder CO US 80301-2532 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | MAGNETOSPHERIC PHYSICS |
| Primary Program Source: |
01001819DB NSF RESEARCH & RELATED ACTIVIT 01001920DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
This project will investigate the generation, propagation and dissipation of magnetosonic waves in the inner region of the magnetosphere as well as the energization of radiation belt electrons interacting with them. In the space environment near Earth, the plasma is so tenuous that plasma particles (ions and electrons) rarely collide. However despite this, some portion of the electrons in the magnetosphere reach dangerously high energies exceeding a million electron volts. This energy is high enough to pose a risk to satellites orbiting within the inner regions of the magnetosphere, a preferred location for communications, navigation, search-and-rescue, weather prediction and national security satellites. Plasma waves are mainly responsible for the acceleration of radiation belt electrons to these high energies but they can also contribute to the scattering of radiation belt particles into the Earth's atmosphere. Many types of plasma waves are generated in a collisionless plasma in the presence of a magnetic field and each has its own set of interactions with the charged particles in the plasma. These waves play a significant role in the dynamics of the inner magnetosphere and radiation belts. Magnetosonic waves, the focus of the proposed investigation, are found in the vicinity of the magnetic equatorial plane in a wide region near the dayside portion of the magnetosphere. The component of the wave electric field, which is aligned along a magnetic field line, can continuously accelerate electrons traveling near the speed of the wave in much the same way that a surfer is pushed forward by an ocean wave. This is termed Landau damping. Magnetosonic waves are thought to be generated by ring current protons, and dissipated in accelerating radiation belt electrons, in effect acting as intermediaries in the collisionless transport of energy between different particle populations. As a broader impact, this project is led by an early-career scientist thus contributing to the training of the next generation of scientists.
The primary goal of this research is to use linear theory and kinetic particle-in-cell (PIC) simulations to explore the excitation and propagation of fast magnetosonic waves driven by observed types of ring-like proton velocity distributions and to use insights gathered to interpret the observed wave measurements, both datasets from the twin Van Allen Probes. Furthermore, scattering of radiation belt electrons will be quantified using test-particle computations, providing clear criteria as to whether and under what conditions the conventional quasi-linear approach can be applied. Two fundamental science questions will be addressed: (1) how does the excitation and propagation of fast magnetosonic waves produce the complex pattern of the observed wave frequency spectra? and (2) how important to the evaluation of radiation belt electron scattering are the complex kinetic dispersion properties of the waves compared to the commonly assumed cold plasma dispersion used in quasi-linear theory? The generalization of the full kinetic PIC code to account for the dipole magnetic field in an inhomogeneous medium will be an additional valuable resource for the radiation belt community enabling a whole spectrum of new studies not previously possible.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
A major goal of the project was to analyze fundamental properties of several specific types of waves that are present in the Earth?s magnetosphere. Such waves are known to play an important role in the overall behavior of the magnetosphere. For example, they are responsible for both energization of charged particles to high energies and for scattering of energetic particles into the Earth?s atmosphere. The latter process may manifest itself as the famous aurora borealis. But the same energetic particles that give rise to that beautiful phenomenon may also pose danger to spacecraft and humans in space. The study of waves in the Earth?s magnetosphere is thus an inherent part of the efforts to understand so called space weather ? the overall behavior of the Earth?s magnetosphere. In fact, the Earth?s magnetosphere is often thought of as a complex, intertwined ?system of systems? comprised of different populations of particles (such as particles of different origin, different energies, etc.) and of the waves.
One of the most interesting outcomes of the project is the identification and classification of a new process by which waves of different origin can couple to each other in the presence of cold and dense plasma. In the Earth?s magnetosphere, such cold plasma populations originate in the ionosphere and are routinely present. They are, in fact, the dominant populations by density in the inner regions of the magnetosphere. Previously, the influence of cold plasma on the waves was thought to be somewhat passive ? in some sense the cold and dense plasma was thought to simply to provide the background in which the waves interact with high-energy particles. In this work, sophisticated first-principle computer simulations and theory were used to show that the influence of cold plasma populations on waves may be more nuanced. Specifically, large-amplitude waves propagating through regions of cold plasma may experience an instability that causes their decay, while transferring a significant portion of the wave energy to other types of waves and to heating of the cold plasma. Overall, the findings indicate the need for more sophisticated models of waves? propagation and evolution in the Earth?s magnetosphere that take into account the newly identified physical processes.
To summarize, the project results have important implication for space weather studies. Crucially, the same fundamental physical processes identified in this work affect both the waves naturally present in the environment and the waves artificially injected into the magnetosphere from the ground or from spacecraft. Consequently, the project findings may also have an impact on so-called radiation belt remediation efforts that seek to control population of energetic particles in the Earth?s radiation belts in order to enable safe operation of crucial space-borne infrastructure.
Last Modified: 05/15/2023
Modified by: Vadim Roytershteyn
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