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Highlights of Solar Radio Physics 1/2009:

Sixty-five years of solar radioastronomy - review paper published

A review paper presenting the input of 65 years of radio observations has been published in the journal Astronomy and Astrophysics Review, October 2008 issue. The authors, Monique Pick and Nicole Vilmer, present first the historical context starting from the early 1940s and then proceed to show how radio astronomy has contributed to our knowledge in solar and solar-terrestrial physics. The review is focused on radio emission from flares and coronal mass ejections (CMEs), and their association with interplanetary magnetic structures (ICMEs). Radio diagnostics of energetic particle acceleration in the corona and in the IP medium are discussed. Space Weather studies that use radio observations as a tool of forecasting the arrival times of shocks near Earth are also reviewed, among other things.

Examples from the paper:

Radio images have shown that the observed emission is consistent with a magnetic loop configuration, and that the microwave radio emission from flares is reasonably well interpreted with simple models of gyrosynchrotron radiation from energetic electrons. The figure from Nindos et al. (2000) shows how at 15 GHz the flare emission is optically thin and comes from the footpoints of the flaring loop, while at 5 GHz the loop itself is outlined. (Radio observations from VLA, Fig. 43 in the review paper.)

Comparisons of hard X-ray (HXR) sources and radio emission sources suggest common acceleration/injection sites for HXR and decimetric radio emitting electrons. The event analysed by Vilmer et al. (2002) shows a close correspondence between the changes in the HXR 25-40 keV sources and the decimetric radio sources at 410 MHz, on the time scale of a few seconds. (Radio observations from NRH, shown in white contours, and HXR observations from RHESSI, shown in black contours, Fig. 39 in the review paper.)

The kinematics of filament activation, detected first at 17 GHz on the disk and then at 34 GHz above the solar disk. The event presented by Kundu et al. (2004) shows an abrupt acceleration phase coincident with the impulsive phase of the flare and the launch of a fast CME. (Radio observations from NoRH, Fig. 67 in the review paper.)

The famous May 2, 1998 event shows a spatial and temporal link between the propagating EIT wave and an H-alpha Moreton wave (Pohjolainen et al., 2001). Moreover, the radio type II-like burst sources (labeled M1, M2, and M3 in the lower-left corner plot) were found to be located near the wave fronts. (Radio images are from NRH, Fig. 75 in the review paper.)

Continuous frequency coverage is essential in analysing shock-related CME events where radio emission is observed from meter to decameter - hectometer waves. Cane and Erickson (2005) found in their study many examples of two shock-like phenomena, with different characteristics that occurred simultaneously in the metric and decametric/hectometric bands, but no clear example of a metric type II burst that extends continuously down in frequency to become an IP type II event. (This radio dynamic spectrum has been combined from the Wind WAVES, BIRS, and Culgoora data, Fig. 84 in the review paper.)

A series of NRH images show the progression of a radio CME (Maia et al., 2007). The event was associated with an electron event measured in situ by the ACE satellite. Analysis of the event revealed that the particles inside the radio-emitting CME loops and the particles detected in situ had comparable energies. (Radio images from NRH, Fig. 105 in the review paper.)

March 18, 2009

Monique Pick () and Nicole Vilmer (), with some help from the editor

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