| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | February 17, 2012 |
| Latest Amendment Date: | January 24, 2014 |
| Award Number: | 1156094 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Ilia Roussev
AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | March 1, 2012 |
| End Date: | February 29, 2016 (Estimated) |
| Total Intended Award Amount: | $382,341.00 |
| Total Awarded Amount to Date: | $382,341.00 |
| Funds Obligated to Date: |
FY 2013 = $127,423.00 FY 2014 = $132,200.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
550 S COLLEGE AVE NEWARK DE US 19713-1324 (302)831-2136 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
DE US 19716-2553 |
| 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): | SOLAR-TERRESTRIAL |
| Primary Program Source: |
01001314DB NSF RESEARCH & RELATED ACTIVIT 01001415DB NSF RESEARCH & RELATED ACTIVIT |
| 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
As the scientific motivation for this project, the principal investigator (PI) and his team note that the space physics community currently relies on solar magnetic field models that assume it is meaningful to represent flux tubes as coherent objects that extend over distances ranging from fractions of a solar radius to many Astronomical Units. In order to place this fundamental assumption on a firmer basis, the PI's team will examine the limitations of this "coherent flux tube" paradigm when magnetic fluctuations are present and they will study how to extend beyond this conceptual framework using several approaches.
The team will apply magnetic field models and nonlinear transport theory to quantify Field Line Random Walk effects, as well as the flux tube meandering and "shredding" that causes the eventual breakdown of the standard flux tube scenario. The team will investigate these phenomena using "Reduced Magnetohydrodynamics" (Reduced MHD) physics models, an approach that is well tested in solar corona studies. The PI's team will also study the often neglected implications of isotropic field line and particle transport, where particle trapping becomes very important. The team will examine the relationship between field line transport and the intermittent character of real turbulent fields, and apply this knowledge to examine the well-known "dropouts" and "channeling" of solar energetic particles (SEPs) that have been observed. The team will investigate the time-dependent interaction of flux tubes by introducing the concept of "component interchange reconnection" and exploring its consequences for the topological structure of magnetic fields in the solar wind and in dynamical simulations of MHD turbulence.
The broader impacts of this effort include improving our recognition of the limitations of existing flux tube models, and how these limitations apply to research areas ranging from astrophysics to space weather forecasting. In particular, this work will have an immediate impact on our understanding of the propagation of SEPs in a space weather context. The PI will also provide mentoring for several postdoctoral fellows and widely disseminate these research results at solar physics community workshops.
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.
We have been studying nonlinear effects of turbulence on observable properties in space plasmas, and in particular in the solar wind, where these effects influence the radiation and energy environment of the earth. An important feature of turbulence is the formation of structures, sometimes called coherent structures, which are distinctive and persistent features such as sheets of strong electric current density. These form dynamically, as can be seen in a variety of different types of numerical simulations (see attached figure 1). Our research has shown that these features occur, and also described a number of their observable consequences.
One impact of coherent structures is the phenomenon called "dropouts" in solar energetic particle observations. These bursty signals in the particle data seen by satellites (see attached figure 2) can be understood as consequences of temporary trapping of energetic particles by three dimensional magnetic "flux tubes" that have boundaries often associated with current sheets. These act to confine the particles.
Another impact that we have been describing is the enhancement of kinetic heating in or near coherent current structures. This has been seen in several plasma simulations, and also in solar wind observations. (see attached figure 3). A convenient way to identify coherent structures is the so-called "PVI index" that we introduced in 2008. In the Figure, one sees that for stronger PVI, which means stronger coherent structures, one sees significantly hotter protons.
The coherent structures we are studying have major impact on observed properties of the solar wind and the energetic particles that come from the sun or from the galaxy. There are many other examples besides the few shown here. But it is becoming clear that such structures are a manifestations of what is called "intermittency" in classical hydrodynamic turbulence, which we now see occurs in plasmas as well. Furthermore the indications so far are that the plasma intermittency has significant effects on what we see in space and the "bursty" environment that sattelites and human explorers will experience.
Last Modified: 03/21/2016
Modified by: William H Matthaeus
