Interplanetary Medium

The Earth is immersed in a soup of hot and tenuous plasma flowing out from the Sun, referred to as the solar wind. The surface features on the Sun modify the energy and magnetic field content and composition of this turbulent magnetized plasma, and its coupling to the Earth's magnetosphere leads to an impact on the space weather, the ionosphere and the geo-magnetic conditions observed on Earth. The aurora are the most familiar manifestations of solar energetic electrons which enter the Earth's magnetic field.

Most of what we know about the Sun and heliosphere comes from either observations of the solar disk over a large and impressive range of frequencies (from Gamma rays to very low frequency radio waves) using a variety of instruments ranging from imaging devices like coronographs to spectrometers. Once the solar wind moves out of the field of view of the cornographs it remains essentially unobservable till it reaches the in-situ satellite based observatories which directly sample the solar wind and provide a wealth of data about solar wind plasma like velocity, density, magnetic field, composition etc. Most of our satellite based observatories tend to be in Earth orbit around 1 AU. In the vast intervening region from close to solar surface out to 1 AU, which is crucial to understanding the solar wind and space weather, it evolves and propagates largely unobserved. It is therefore important to fill this large gap in our observations.

The Mileura Widefield Array – Low Frequency Demonstrator (MWA-LFD), being developed by Haystack astronomers and engineers will provide a new and very efficient tool for studying the interplanetary medium. The MWA-LFD characteristics are very well matched to the needs of studying the interplanetary medium.

(*) The naturally wide field-of-view of the array provide simultaneous access to a large part of the sky.
(*) Being a digital instrument, it allows multiple simultaneous beams allowing multiple objects to be monitored simultaneously.
(*) The solar wind is optically too thin to observe in direct emission or absorption, except very close to the Sun. However, the frequency range of the MWA-LFD is very well suited to observing propagation effects due to the passage of radio waves from distant background objects through the turbulent and magnetized plasma of solar wind.
(*) The rapid high dynamic range capability of the MWA-LFD will make it an ideal instrument for providing images of the solar bursts. To date high fidelity, and high time and spectral resolution radio images of solar bursts have not been available. These images are expected to help fill many of missing links in our knowledge of solar bursts , Coronal Mass Ejections (CMEs) and the relationship between them.

In addition to imaging, the astronomers at Haystack Observatory plan to use the techniques of Interplanetary Scintillation and Faraday Rotation for investigating the heliosphere.