Small Radio Interferometer Arrays in Solar Physics
The radio Sun offers both opportunities and challenges for small radio interferometer arrays. The radio window in the Earth’s atmosphere allows the solar corona to be viewed from the ground, where both thermal and nonthermal phenomena can be studied simultaneously. Radio emission also provides the only viable means to measure the all-important coronal magnetic fields that drive the activity and atmospheric structure of the Sun. At the same time, the Sun presents observational challenges due to its time variability, large dynamic range in flux and in spatial scales, and in the variety of radio emission mechanisms that can be active at anyone time.
The Owens Valley Solar Array was designed to meet these challenges, with its capability to image the Sun over a broad range of frequencies (1-18-GHz) with high frequency resolution. It has grown from a two-element interferometer operating at a single frequency in 1980 to its present status as a multi-element array operating at up to 86 frequencies. The unique contributions of the array to our present understanding of the Sun and solar activity are reviewed. Other small, solar-dedicated interferometer arrays exist in other countries, with different capabilities, but together they have provided a large share of our current understanding of coronal solar physics, as well as providing places where students and researchers gain first-hand experience in instrument development.
The experience gained with these small instruments has been used to define the directions needed to make further progress in solar radio physics. New solar arrays operating at decimetric and microwave frequencies can be produced cheaply in the “small instrument” model, with the help of advances in technology, that can further revolutionize our understanding of the Sun.
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