The Potential for Characterizing the Heliosphere and Disturbances with LOFAR Faraday Rotation Observations

Details The Potential for Characterizing the Heliosphere and Disturbances with LOFAR Faraday Rotation Observations The Potential for Characterizing the Heliosphere and Disturbances with LOFAR Faraday Rotation Observations

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh42c0557s&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH42C-0557

Physics

2111 Ejecta, Driver Gases, And Magnetic Clouds, 2164 Solar Wind Plasma, 2169 Sources Of The Solar Wind, 6982 Tomography And Imaging, 7524 Magnetic Fields

Scientific paper

A linearly polarized radio wave propagating along a magnetic field line may be represented as a combination of two components with right and left-hand circular polarizations. In a magnetized plasma such as the heliosphere these two circular polarizations experience different indices of refraction, leading to a phase lag between the two components. This phase lag results in Faraday Rotation - an overall rotation of the angle of the original linearly polarized wave. The extent of Faraday Rotation is proportional to the component of the magnetic field along the direction of propagation, the electron number density, and the square of the wavelength of the radiation. Faraday Rotation may be used to probe the three-dimensional electron number density and magnetic field topology of both the background heliosphere and of transients such as coronal mass ejections (CMEs). It is particularly interesting to note that the rotation is proportional to the total electron number density, in contrast to the signals from Interplanetary Scintillation (IPS), which are only a function of density fluctuations. Prior work in this topic typically involves monitoring variation in the polarization of either extragalactic sources or of transmitted telemetry from spacecraft such as Helios. These observations have been successfully used to study turbulence and propagating transients in the inner heliosphere. We have begun a study of the potential for the Low Frequency Array (LOFAR) to characterize both the background heliosphere and transients. LOFAR is a possible aperture synthesis radio interferometer for the 10-240 MHz range consisting of hundreds of thousands of individual receivers. The array will operate as a fully digitally steered instrument, in which the signals from the antennae may be combined to simultaneously image multiple regions in the sky. Among the factors which make LOFAR appealing to Faraday Rotation studies are the large wavelengths of the observations, the high sensitivity of the instrument, and the ability to track multiple objects. We will present our initial work on simulations of the ability of LOFAR to observe both the background heliosphere and simple transient structures such as flux ropes. For the background heliosphere we will demonstrate how various models for extrapolating photospheric magnetic fields produce different signatures. In the case of transients we examine how clearly we can extract fundamental properties such as helicity and field strength. This work is sponsored by NSF grant ATM-0317957

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