| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | August 23, 2016 |
| Latest Amendment Date: | June 13, 2018 |
| Award Number: | 1613134 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Lisa Winter
AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2016 |
| End Date: | August 31, 2019 (Estimated) |
| Total Intended Award Amount: | $382,882.00 |
| Total Awarded Amount to Date: | $382,882.00 |
| Funds Obligated to Date: |
FY 2017 = $137,581.00 FY 2018 = $125,910.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
1608 4TH ST STE 201 BERKELEY CA US 94710-1749 (510)643-3891 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
7 Gauss Way Berkeley CA US 94720-7450 |
| 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: |
01001718DB NSF RESEARCH & RELATED ACTIVIT 01001819DB 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 quantify the global distribution of Alfven waves in the polar region and its variations with solar wind conditions, geomagnetic storm conditions, and auroral substorm phase. Alfven waves are an essential component of the dynamics and associated energy transport within the Earth's magnetosphere. This has become more and more apparent with each satellite mission into the magnetosphere. Significant Alfven wave activity has been observed by satellites traveling through the plasma sheet, the plasmasphere, the tail lobes, the auroral zone, and the reconnection regions in the magnetotail. Alfven waves are oscillations traveling along magnetic field lines. Much like waves moving outward from a stone tossed into the water, the Alfven waves carry information to other locations along magnetic field lines about changes in the magnetic field or currents at the site of their generation. At these other locations, the waves can be dissipated supplying their energy to power different processes remote from the original energy source. For example, in the polar ionosphere, the dissipation of Alfven waves supplies energy to accelerate the electrons responsible for creating breathtaking auroras. These Alfven waves are thought to originate in strong plasma jets within the stretched magnetotail far from the polar ionosphere. The project will support a graduate student for the summer thus contributing to the training of the next generation scientific workforce. The advances in knowledge of an energy transport process important to the dynamics of the magnetosphere will in the long term improve models of space weather forecasting, of value to a technological society.
The project proposed here will develop statistical maps of Alfven wave power observed by the NASA Polar spacecraft and quantify how these maps vary depending on solar wind and interplanetary magnetic field parameters and storm and substorm conditions. Results from MHD modeling will be compared to the statistical maps to validate the MHD simulations. The study will use tools similar to and the methodology of earlier work by the PI, but will include 10 years of data instead of the one-year interval used previously. This will allow the statistical examination of Alfven wave power for a wide-range of different conditions and geomagnetic activity levels. New insights about energy transport and dynamics of the Geospace system are expected.
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.
The surface of the Sun is a vibrant, ever-changing landscape, which sends a continual stream of hot, charged particles (plasma) hurtling into space in every direction - a phenomenon called 'solar wind'. Occasionally, highly energetic events on the solar surface send brief yet powerful bursts of these particles, collectively known as 'coronal mass ejections', in specific directions, in episodes known as 'solar storms'. Inevitably, some of these plasma surges will stream towards Earth.
During solar storms, when the energy of the plasma hitting Earth's magnetic field is particularly strong, it can have a strong influence on the near-Earth space environment (geospace) - potentially allowing increased amounts of energy to transfer down to Earth's atmosphere. Therefore, it is vital that we understand exactly what is happening when our planet feels the effects of solar storms.
Trapped inside geospace, the energy trickles down to Earth through a sequence of energy transfer processes. Some of the energy shows up in a special kind of wave, called an Alfven wave - named after Swedish physicist Hannes Alfven. These waves travel along Earth's magnetic field, which acts like a giant 'magnetic funnel' above the polar regions. It should be noted that Alfven waves are responsible for some types of aurora.
In this study, we investigated the influence of Alfven waves on the Earth, paying particular attention to how they vary over time and space. One specific question that was addressed in this study was: how different is the impact of Alfven waves during solar storms compared to less disturbed times?
We used the NASA satellite Polar - launched specially to observe the aurora and associated phenomena - to investigate Alfven waves above Earth's poles. The satellite traversed the 'magnetic funnel' relatively close to Earth - at 20,000-30,000 km - while enabling measurements over the entire polar region. This gave us a global picture of the total energy due to Alfven waves flowing toward Earth's atmosphere during solar storms, even those that have been generated 200,000 kilometers and more away.
We analyzed Polar's measurements collected over six years, which is half a solar cycle, when many bursts of plasma originating from the Sun reached Earth's magnetosphere. For the first time, the measurements allowed us to quantify precisely how much more energy is carried toward the atmosphere in the form of Alfven waves during solar storms. It was found that the rate of energy supply is about four times higher during storms, meaning there is even more energy available from Alfven waves to power parts of the aurora. The experiment confirmed that Alfven waves do indeed play an increased role in carrying energy to Earth's atmosphere during solar storms.
It was also found that the Alfven waves occur globally in an oval-like shape above the polar region, which expands and shrinks ('breathes') with geomagnetic activity. We were able to provide a mathematical equation to estimate the amount of power flowing in this oval and how much of it is absorbed by electrons, which subsequently cause auroral luminosity. This equation also allows predicting the wave power when there are no satellites around to measure it, which is an extremely important tool for space weather applications.
Last Modified: 10/28/2019
Modified by: Andreas Keiling
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