Radio Propagation Diagnostics of the Inner Heliosphere in the Era of the Parker Solar Probe

Tim Bastian, National Radio Astronomy Observatory

A variety of radio propagation techniques can be used to probe regions in the corona and solar wind that are otherwise inaccessible to direct observation. One of these is angular broadening observations, which allow the wave structure function D(s) of solar wind to be measured rather directly; s is the projected distance between any two antennas which, for the Jansky Very Large Array, ranges from ~0.1 up to several 10s of km. This , in turn, allows properties of the spatial spectrum of electron density fluctuations to be determined on small spatial scales, including the power law index, the degree of anisotropy, the presence of an inner scale, and the orientation of the local magnetic field. Another technique is refractive scintillation, caused by weak focusing and defocusing effects on much larger spatial scales - 100s to 1000s of km. We present pilot observations made by the JVLA in 2015 to illustrate their potential for deducing key properties of solar wind turbulence in the inner heliosphere. We discuss prospects for exploiting these techniques in a more systematic way in the era of the Parker Solar Probe and the Solar Obiter.