| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | February 17, 2012 |
| Latest Amendment Date: | March 19, 2014 |
| Award Number: | 1155841 |
| 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: | $288,831.00 |
| Total Awarded Amount to Date: | $288,831.00 |
| Funds Obligated to Date: |
FY 2013 = $100,188.00 FY 2014 = $98,408.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
10889 WILSHIRE BLVD STE 700 LOS ANGELES CA US 90024-4200 (310)794-0102 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
3845 Slichter Hall Los Angeles CA US 90095-1567 |
| 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) explains that the magnetic Eulerian Correlation Function (ECF) is a measure of the temporal decorrelation of particle transport in the solar wind due to interplanetary magnetic field fluctuations, and he notes that the ECF is directly invoked in particle scattering theory, as well as in fundamental turbulence theory, dynamo theory, and plasma physics.
In order to provide accurate observations of solar wind decorrelation functions for space physics modelers who rely heavily on ECF estimates, the PI will provide observationally based measurements of ECF parameters for magnetic field fluctuations in both the slow and fast solar wind, using data from multiple spacecraft. This study will address questions concerning how the ECF varies with solar wind speed and the role that turbulence geometry plays in how the ECF varies with respect to the mean magnetic field. The answers to these questions will, for the first time, provide detailed scale-dependent constraints on theoretical models relevant to solar wind turbulence and cosmic ray transport. Better knowledge of the ECF will also provide better estimates of the temporal ranges over which solar wind propagation can be reliably simulated.
These results will have beneficial applications to space weather forecasting, and will contribute to enhanced planning and data analysis for observations from NASA's future "Solar Probe" spacecraft. These findings will also benefit ongoing studies of interplanetary magnetic field turbulence which are applicable to a much more extensive range of astrophysical and space research topics than this effort alone addresses. This research project will also support one undergraduate summer student. The PI will disseminate his research findings to the community at international meetings, in conference presentations, and in journal publications.
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.
Fluctuations in the magnetic field and plasma flowing away from our Sun display turbulent properties. Weygand et al. [2011] demonstrated how these turbulent properties decayed across space in the solar wind using observations from pairs of spacecraft for many events. What was not known at the time was how these turbulent fluctuations decayed over time. Weygand et al. [2013] demonstrated how turbulent magnetic field fluctuations in the solar wind decayed with time in both the slow (< 450 km/s) and fast (>600 km/s) solar wind. Figures 1 and 2 show this decay and indicate that in the slow solar wind the decorrelation time is 215 ± 43 min, and in fast solar wind, the decorrelation time scale is 114 ± 23 min, which indicates that decorrelation times vary with the nature of the turbulence. It has been previously shown that there are two different types of turbulence within the solar wind. The slow solar wind is dominated by quasi two dimensional turbulence and the fast solar wind consists mainly of Alfvenic turbulence. Until Weygand et al. [2013] no empirical model for slow and fast solar wind turbulence decay was available. These results will be useful in magnetohydrodynamic modeling of the solar wind and space weather predictions. Accurate space weather predictions are important for protecting our power grids and spacecraft.
In addition to our temporal decorrelation functions we have also produced the first space-time correlation function for the slow and fast solar wind. As discussed, the spatial and temporal correlation functions have been previously produced, however, many models of solar and galactic cosmic ray scattering use a single space-time correlation functions and not separate functions for space and time. Until recently the model space-time correlation functions have been theoretical in nature. In Matthaeus et al. [2016] we have developed the first empirical space-time correlation function. See Figure 3. This function is expected to improve our models of solar and galactic cosmic ray scattering and diffusion in the heliosphere. Accurate models of solar and galactic cosmic ray scattering are important for estimating the effects of energetic particles on spacecraft and the Earth’s atmosphere.
Last Modified: 05/14/2016
Modified by: James M Weygand
