Solar-Heliospheric-Ionospheric (SHI)

The MWA holds great promise for innovative contributions to solar, heliospheric and ionospheric (SHI) science and to space weather applications. The key features of MWA which make it well adapted for these research areas are:

Most of what we know about the Sun and heliosphere comes from either observations of the solar disk over a large range of frequencies using a variety of instruments including imaging devices like coronographs and spectrometers. Once the solar wind moves out of the field of view of the coronographs it remains essentially unobservable till it reaches space-based observatories near Earth which directly sample the plasma and provide a wealth of information about solar wind parameters like velocity, density, magnetic field, and composition at that location. Most of the satellite observatories tend to be in Earth orbit around 1 AU, and until the recent launch of STEREO, are unable to sample the vast intervening region from close to solar surface to 1 AU. This region is crucial to improving our understanding of the solar wind and supporting space weather predictions particularly if essential information about heliospheric magnetic fields is obtained. The MWA seeks to help fill this large gap in our observations through the application of remote sensing radio techniques.

The overarching goal of the MWA for SHI science is to conduct observations from the Sun, through the heliosphere, to the near-Earth environment, thus providing measurements of the Sun and Earth as a coupled system. Using various radio techniquesthat will be outlined, the MWA seeks to observe and locate radio bursts on the Sun that lead to Coronal Mass Ejections (CME), determine the density, velocity and magnetic fields of the CMEs as well as the background heliosphere, and measure fluctuations in the Earth's ionosphere during quiet and geomagnetically disturbed conditions. The MWA goals and approaches for SHI science are described by Salah et al. (2005).

Briefly, the Interplanetary Scintillation (IPS) technique will be used to measure solar wind density and velocity, and the Faraday rotation technique will be used to estimate heliospheric magnetic fields that are crucial to the determination of the CME geo-effectiveness, i.e. whether a particular CME will couple with the Earth's magnetic field when it impinges on the magnetosphere thereby resulting in space weather effects. Knowledge of the magnetic field evolution at the earliest time in the CME trajectory is important for space weather prediction. Another technique will rely on high-fidelity imaging of solar radio bursts in order to couple their occurrence, particularly Type II bursts, to the development of CMEs. The final technique which will contribute to studies of ionospheric structure will be based on the required calibration of the MWA since observations by the low frequency array must be precisely corrected for the effects of the Earth's ionosphere in order for the MWA to operate successfully as a radio imaging array. The results of that correction, both on a relative and absolute level, will therefore be a useful by-product for ionospheric science at a southern hemisphere site. Each of these techniques and applications is summarized briefly in the following sections:

Coordination of SHI activities

Coordination of SHI activities within the MWA project is conducted by an international committee of researchers associated with the project. Community involvement is encouraged, and collaborations with other projects and researchers are coordinated through this group. Interested scientists should contact the MWA project office for further information.

References

Salah, J. E., C. J. Lonsdale, D. Oberoi, R. J. Cappallo, J. C. Kasper, "Space weather capabilities of low-frequency radio arrays", Proc. SPIE on Solar Physics and Space Weather Instrumentation, 5901, 59010G 1-10, doi:10.1117/12.613448, 2005.