coronal faraday rotation: diagnostics of current sheets and mhd waves
DESCRIPTION
Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves. Steven R. Spangler, Laura D. Ingleby, Laura G. Spitler, Catherine A. Whiting. Scope of Talk: Observations of Extragalactic Radio Sources with Radio Interferometers. Very Large Array. Radio interferometer 27 antennas - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/1.jpg)
Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves
Steven R. Spangler, Laura D. Ingleby, Laura G. Spitler, Catherine A. Whiting
![Page 2: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/2.jpg)
Scope of Talk: Observations of Extragalactic Radio Sources with Radio Interferometers
![Page 3: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/3.jpg)
Very Large Array
• Radio interferometer• 27 antennas• B or A array• Observations taken at 1465 and 1665 MHz
![Page 4: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/4.jpg)
Advantages of Interferometric Observations of Extragalactic Radio Sources
• Simultaneous measurements on a set of lines of sight (pharetra) through the corona
• Use of “constellations” of radio sources for tomographic-like analyses
![Page 5: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/5.jpg)
Plasma Contributions to the Faraday Rotation Integral
We need enough observations to sort out various contributions to coronal density and magnetic field
![Page 6: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/6.jpg)
New Coronal Faraday Rotation Results from the VLA
• Project AS764: August, 2003; 2X10 hour sessions on source 3C228
• Project AS826: March-April 2005; 4X10 hour sessions (plus reference) for coronal “tomography”
![Page 7: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/7.jpg)
Project AS826
o Observations:•March 12
•March 19
•March 28
•April 1
•May 29 (reference)
o 19 sources, 20 lines of sight
![Page 8: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/8.jpg)
Results from Project AS764: Continuous Observations of 3C228 on August 16 and 18, 2003
• Measurement of RM(t) to source as a whole
• Measurement of “Differential Faraday Rotation”, different rotation measures along different lines of sight (A,B, and C)
![Page 9: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/9.jpg)
Faraday Rotation to 3C228 on August 16, 2003
Remarkably little differential Faraday rotation observed
![Page 10: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/10.jpg)
Modeling the Observed Rotation Measure
![Page 11: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/11.jpg)
Spatial Structure Function (no Taylor Hypothesis!)
![Page 12: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/12.jpg)
Spatial Structure Function (no Taylor Hypothesis!)
Diff. RM feature
![Page 13: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/13.jpg)
Preliminary and Tentative Rotation Measure Structure Function Results
• August 16, 15.77-18.62 UT: DRM < 0.38 rad/m2
• August 16, 20.53-23.22 UT: DRM < 4.8 rad/m2
• August 18, 20 -24 UT: DRM < 0.25 rad/m2
![Page 14: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/14.jpg)
Meaning of Result in Terms of Coronal Plasma Parameters
From Minter and Spangler (1996), magnetic field fluctuations only
Turbulence properties
![Page 15: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/15.jpg)
Quantitative Significance of Observed RM Structure Functions
August 16, 6.2R August 18, 5.2R
l=0.1R
L=1.0R
e=0.5
e=1.0
![Page 16: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/16.jpg)
How Can Faraday Rotation Observations Probe the Overall Structure of the Coronal
Plasma? (AS826)
![Page 17: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/17.jpg)
Global RM Models: How well can synoptic coronal models account for FR Measurements?
Mancuso and Spangler 2000
Residuals of ~ 2-3 rad/sq-m
![Page 18: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/18.jpg)
AS826 Preliminary ResultsSource RM Average Error
2323-033 61.068 0.9976
2325-049 6.952 0.7295
2326-020 -2.418 0.9832
2328-049 -4.163 0.65297
2331-015 -6.087 2.564
2335-015 -13.671 0.305
2337-025 -12.458 0.4514
2338-042 -4.993 0.2619
2351-012 -27.35
0.693
2352-016 -24.175 1.428
2357-024 3.145 0.202
0006-001 2.255 0.207
0023+045 5.18 0.125
0029+052 -2.515 0.196
0030+058 0.582 0.685
0034+013 1.92 0.58
0039+033 2.272 1.27
0039+033 -0.905 0.79
0041+070 -0.371 0.613
0046+067 -14.067 1.509
2RM
![Page 19: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/19.jpg)
![Page 20: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/20.jpg)
![Page 21: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/21.jpg)
![Page 22: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/22.jpg)
![Page 23: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/23.jpg)
![Page 24: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/24.jpg)
AS826: Use of Synoptic Model for Corona
These measurements of magnetic field and density at ~ 3R can be used to estimate B and n at greater distances probed by Faraday Rotation
![Page 25: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/25.jpg)
Estimating the distant coronal plasma from measurements at ~3 R
An and AB are arbitrary adjustment factors
![Page 26: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/26.jpg)
How radio line of sight probes the corona
![Page 27: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/27.jpg)
Observed and Model RM Comparison-AS826
![Page 28: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/28.jpg)
Observed and Model RM Comparison
![Page 29: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/29.jpg)
Observed and Model RM Comparison
![Page 30: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/30.jpg)
Conclusions
• Simple synoptic models of the corona roughly reproduce “Pharetrae” of Faraday Rotation measurements, but large residuals.
• Measurements consistent with coronal field of 30-80mG at r=6R. (Paetzold 1987)
• Rotation measure changes substantially on timescales of a few hours; too slow to be turbulence. Thus “Mesoscale Plasma Structures”.
• Smaller, faster fluctuations attributable to waves seen in spacecraft beacon data.
• Spatial variations in RM (differential Faraday Rotation) are small; constraints on coronal turbulence are reasonable but not decisive
![Page 31: Coronal Faraday Rotation: Diagnostics of Current Sheets and MHD Waves](https://reader035.vdocuments.net/reader035/viewer/2022062501/568167b3550346895ddd030e/html5/thumbnails/31.jpg)
Future Developments
• EVLA (Expanded VLA): Enormous increase in sensitivity of the VLA, in progress. But only if feed design prevents system temperature increase due to Sun.
• VLA at 5 GHz: Could make measurements closer to the Sun, observations have more impact.