
NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
Recipient: |
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Initial Amendment Date: | April 18, 2011 |
Latest Amendment Date: | May 2, 2012 |
Award Number: | 1102863 |
Award Instrument: | Standard Grant |
Program Manager: |
Carrie E. Black
cblack@nsf.gov (703)292-2426 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
Start Date: | May 1, 2011 |
End Date: | April 30, 2015 (Estimated) |
Total Intended Award Amount: | $120,000.00 |
Total Awarded Amount to Date: | $120,000.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
1109 GEDDES AVE STE 3300 ANN ARBOR MI US 48109-1015 (734)763-6438 |
Sponsor Congressional District: |
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Primary Place of Performance: |
1109 GEDDES AVE STE 3300 ANN ARBOR MI US 48109-1015 |
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: |
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Program Reference Code(s): |
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Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.050 |
ABSTRACT
This is a three-year project to investigate a remarkable new finding, that the intensity of geomagnetic storms displays distinct universal time dependence, and that it varies in concert with middle latitude ionospheric plasma abundance during storms. Geomagnetic indices provide our most consistent measure of physical processes occurring in geospace since their creation over the last century. The strength of geomagnetic storms, most notably, is captured in the so-called Dst index, calculated from a set of four ground-based magnetometer measurements located strategically around the Globe. This project will utilize a newly derived, improved Dst index dataset to carry out a detailed examination of trends in the storm-time Dst with UT, season and solar cycle. Ionospheric plasma adds greatly to the pressure, pressure gradients, and currents in the magnetosphere, the last of which are measured on the ground to indicate magnetic storm strength. Ion outflow in the auroral zone, particularly in the dayside ?cusp? and nightside tail-reconnection region, provides most of this plasma. The abundance of ionospheric plasma at high latitudes has recently been shown to be a more complex process than previously thought, with a number of processes delivering plasma from middle to high latitudes in rapid fashion during periods of enhanced magnetic activity. A UT-dependent modulation of outflow during enhanced magnetic activity is one possible explanation for the observed variation in magnetic storm strength. The examination of how ionospheric ion outflow into the magnetosphere may vary during different storms and impact the UT dependence of the Dst index is the main overarching objective for this project. A parallel effort will examine whether the UT dependence in the observations is also reproduced by first-principles models of the coupled physical system. The project will use the suite of ionosphere-thermosphere-magnetosphere models that make up the University of Michigan Space Weather Modeling Framework.
The project has impacts beyond the immediate benefits of improved scientific understanding. Students will participate in all aspects of the work, both at U. Michigan and Berkeley, results will be submitted to widely-read publications, and the team will work with the Center for Science Education at Berkeley to make the findings accessible to the network of teachers that it works with around the country on magnetometer data and magnetism. The importance of determining whether magnetic storms are indeed more powerful in the afternoon in the United States during summer can hardly be overstated, particularly in light of recent National Academy findings of the likely economic costs to the U.S.A. of a truly major geomagnetic storm.
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.
Our society is increaseingly reliant on systems that are subjected to adverse space weather effects, including communication satellites, GPS satellite signals, and electrical power grids. A better understanding of the physical processes controlling severe space weather is necessary for accurate prediction and mitigation strategies.
In particular, it has been noticed that geomagnetic activity is more intense at particular times of the day than at others. There are several hypotheses attempting to explain this universal-time dependence of the response of near-Earth space to similarly-sized solar driving forces. This study examined a few key aspects of these possible explanations.
Specifically, we conducted a large-scale statistical analysis of solar wind observations against the geospace response indices to determine which parts of near-Earth space show the most sensitivity to universal-time effects. We considered 30+ years of space observations, grouping the activity according to space storm intensity and universal time of the space storm peak. A technique called superposed epoch analysis was used to average the results of similar activity intervals together, shifting the timelines to line up on a common reference moment within each storm sequence. In this case, we used the time of the storm peak as our reference marker for lining up the data. Statistical tests were then conducted to determine if the averages were similar or different between the different universal-time groupings.
We found that there is a systematic preference for "zero universal time," when Greenwich, England is at midnight, as a time when activity is more severe than a similar driving condition peaking at some other time. There is also a progression from high to low latitude in the universal-time sensitivity throughout the storm sequence. That is, high-latitude regions will experience geomagnetic activity before the storm peak, during what is called the main phase of the space storm.
An implication of this finding is that it is more likely to see aurora in, say, Moscow, Russia (where we gave a presentation on this work at a scientific meeting), than in Ann Arbor, MI (where the researchers are located), even though the two cities are at nearly identical magnetic latitudes. This influence is the effect of the universal-time sensitivity of the geospace system. Moscow is near midnight before Greenwich, England reaches that local time, and so it is more likely to experience the preferential "high-latitude" sensitivity of increased aurora during the main phase. Ann Arbor, arriving at local midnight many hours after Greenwich, is preferentially excluded from good auroral viewing conditions. It doesn't mean that aurora is never visible, it just means that, on average, aurora is visible more often near Moscow than near Ann Arbor.
The physical reason for the sensitivity is, we think, linked to a process called ionospheric outflow. The magnetic field of the Earth is not exactly aligned with the rotational axis of the planet, and this means that magnetic latitude is different in the northern and southern hemispheres at the same geographic latitude. There are certain orientations of the magnetic field, which is a function of annual season and daily universal time, that make the high-latitude upper atmosphere emit more charged particles into deep space. This release of electrically charged gas, called ionospheric outflow, loads near-Earth space with particles and helps to make the subsequent space storm more intense. The preferential outflow time is when the American sector is on the dayside. Because aurora is only seen at night, this means that the opposite side of the world, say, near Moscow, gets the better aurora light display during the stronger storm.
Last Modified: 08/0...
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