1. Observations of Heliospheric Faraday Rotation
of a CME Using LOFAR and Space-Based Imaging
Mario M. Bisi (1), E.A. Jensen (2), Charlotte Sobey (3)(4)(5), Richard A. Fallows (3), David Barnes (1), Alessandra Giunta (1), Bernard V. Jackson (6), P. Paul L. Hick (7)(6), Tarraneh Eftekhari (8), Hsiu-Shan Yu (6), Dusan Odstrcil (9)(10), Munetoshi Tokumaru (11), and Brian Wood (12).
(1) RAL Space, Science and Technology Facilities Council, Rutherford Appleton Laboratory, OX11 0QX,
England, UK. (2) Planetary Science Institute, Tucson, AZ , USA. (3) ASTRON, the Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands. (4) Curtain Institute of Radio Astronomy, WA, Australia. (5) CSIRO Astronomy and Space Science, WA, Australia. (6) Center for Astrophysics and Space Science, University of California, San Diego, CA, , USA. (7) San Diego Supercomputer Center, University of California, San Diego, CA , USA. (8) University of New Mexico, Albuquerque, NM 87131, USA. (9) School of Physics, Astronomy, and Computational Sciences, George Mason University, VA , USA. (10) NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. (11) Institute for Space-Earth Environmental Research/Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-Cho, Chikusa-ku, Nagoya , Japan. (12) NRL, SW Washington, DC 20375, USA.
UCSD IPS Workshop – San Diego, CA, USA – December 2016

2. Outline
CME Heliospheric FR Study
Brief Summary/Outlook

3. Overview of the Interplanetary Scintillation (IPS) and Heliospheric Faraday Rotation (FR) Experiments (Radio Heliospheric Imaging)
- e.g. see M.M. Bisi, “Planetary, heliospheric, and solar science with radio scintillation”, Chapter 13 of Heliophysics Volume IV “Active stars, their astrospheres, and impacts on planetary Environments”, Editors C.J. Schrijver, F. Bagenal, and J.J. Sojka, Cambridge University Press, 16 March 2016, and references therein.

4. CME Heliospheric FR Study

5. LOFAR Observations of Heliospheric FR
LOFAR observations of heliospheric FR to date are as follows…
Crab Nebula/3C144 (15 minutes of FR each time, plus 60 minutes of IPS on 02 July 2014 only):
02 July 2014 (10:40UT) – P-Point of 69 RS, 16.2°, Heliocentric Lat. -4.4°.
11 July 2014 (10:00UT) – P-Point of 104 RS, 24.8°, Heliocentric Lat. -2.8°.
22 July 2014 (12:00UT) – P-Point of 146 RS , 35.3°, Heliocentric Lat. -1.8°.
PSR J :
13 August 2014 (13:00UT) – P-Point of around 50 RS/13.3°, and an extended observation of 140 minutes split into 10-minute intervals with 10-minute gaps yet to be fully investigated in terms of the context of the observation.
LOFAR Pulsar Catalogue of daytime FR observations is currently being populated to extend our availability of possible case studies.

6. UCSD IPS Tomography Context (1)

7. UCSD IPS Tomography Context (2)

8. UCSD IPS Tomography Context (3)

9. Background RM Context (1)
RM values (>0.01 rad m-2) with the PSR position superimposed (left) and g-level (later) sky map (right)!

10. Background RM Context (2)
CCMC modelling of the background fields using the PFSS model: the LOFAR heliospheric FR line of sight crosses through what appears to be a HCS crossing…
Net RM contribution due to the ambient effects is very small: rad m-2 (quite similar to the tomography result).

11. The 12-13 August 2014 CME in Question… (1)

12. The 12-13 August 2014 CME in Question… (2)
Left-hand image shows the geometry of the observation from the Earth/L1 and the two STEREO spacecraft.
Right-hand image is a simple CME electron density distribution in the ecliptic using assumptions similar to Wood et al., 2009, and based on observed radiance from a single HI-1B pixel.

13. The 12-13 August 2014 CME in Question… (3)
REDACTED!

14. The 12-13 August 2014 CME in Question… (4)
REDACTED!

15. The 12-13 August 2014 CME in Question… (5)
Using a dimensional analysis calculation (but only for one approximation): RM = x ne[cm-3] x B[nT] x L[AU]° m-2 where L is the contributing integration length along line of sight = x 669 x 100 x 0.25 = 33.45° m-2 ( rad m-2) – this is very much inline with the heliospheric RM from LOFAR.
Higher time-resolution context information may be needed.

16. Contributions to the Integrated FR Signal
(Courtesy of Colin J. Lonsdale)

17. Brief Summary/Outlook

18. Heliospheric FR Moving Forward? (1)
Excellent context and modelling context is needed for the full 3-D picture, but magnetic field still an unknown from white-light imagery and magnetic field from radio-astronomy techniques seems an order of magnitude or more too low (perhaps).
Need a lot more man power – most of this work has been done on a best-efforts basis and until very recently was completely unfunded for several of the core authors involved.
Difficulties lie in the verification of the RM/FR expected from the CME as the radio astronomy techniques for density don’t tie-up well with the white-light imaging and the magnetic field within a CME that is not measured with in-situ measurements is completely undefined.
The variation Ionospheric contribution to RM/FR difficult to account for with current TEC and geomagnetic-field modelling.

19. Heliospheric FR Moving Forward? (2)
How much effort is needed – well, how long is a piece of string?
Currently we need more dedicated heliospheric FR observations which requires published papers on present work!
Need more context work for really learning what each observation is observing, more modelling work on getting a real handle on the part of the CME or solar wind being observed, good projections of magnetic fields from in-situ measurements for verification of the RM/FR received, more focussed time (i.e. less best-efforts, more paid work) to work on the problem, and a better/improved/different way of really dealing with the ionospheric RM/FR variation: perhaps FTE for three to five years but scope of work needs filling out and coordinated.

20. Brief Overall Summary/Outlook
FR on LOFAR is progressing well with good preliminary CME results including the heliospheric RM/FR determination – but much more effort is needed on verification and for ambient solar wind observations, especially on the ionospheric FR contributions.
The UCSD 3-D tomography will provide an excellent platform for obtaining 3-D magnetic-field values from combined radio observations of FR and IPS and integrating them into current IPS, closed-loop fields, and Sun-Earth L1 in-situ data tomography (and hence also as an improved input to drive ENLIL).
FR (coronal and heliospheric) are becoming more useful for space-weather science and carry huge future forecasting potential of the magnetic field if the ionospheric variation issue is resolved.