A new digital spectrograph for obtaining a dynamic spectrum of radio burst emission from the Sun in the frequency range 30-80 MHz has been recently commissioned at the Gauribidanur Radio Observatory (Lat: 13 • 36 12 N and Long: 77 • 27 07 E), about 100 km north of Bangalore, India. This paper describes various aspects of the antenna system, frontend receiver and digital hardware of the spectrograph. Some of the initial results obtained with the instrument are also presented.

Aims. We study the characteristics of doublet type II radio bursts in which two type II bursts occur in sequence and investigate their drivers. Methods. 37 type II bursts reported by the Culgoora radio observatory in the Solar Geophysical data for the period September 1994-July 2004 were used to determine their time and frequency characteristics. In order to investigate their association with flares and Coronal Mass Ejections, flare data from NOAA and Coronal Mass Ejection data from Center for Solar Physics and Space weather, Catholic University of America were used. Results. The second type II burst starts at a lower frequency than to the first one. The normalized drift rate of the the first II burst is found to be nearly twice that of the second type II burst. For both the first and second type II bursts, their start frequencies and the drift rates are found to be correlated. The mean time difference between the start of the first and second type II burst is 8.1 min. There were no reports of two flares or CMEs except one case each. The first and second type II bursts start 5 and 15 min after the start of the GOES X-ray flares. The time difference between the CME onset and start of the first and second type II burst is close to the above values. The type II doublet bursts have the following association with flares: B class 11%; C class 25%; M class 40% and X class 25%. The Coronal Mass Ejections associated with type II doublet bursts have an acceleration of −10 m/s 2 and angular width of more than 270 degrees.

We report a transient intensity reduction/absorption burst observed at decameter wavelengths in close temporal association with an X2.0/3B flare near the disk center and the onset of a "halo" coronal mass ejection. The observed bandwidth of the burst was about 10 MHz. The size of the absorption region was estimated to be ≈28,000 km.

Abstract. We present metric radio observations of quasi-periodic emission from the solar corona in close association with a "halo" CME and an "EIT wave" phenomenon. The radio event lasted for about 60 s. Its mean periodicity was ≈8.8 s. The estimated Alfvén speed in the corona was 1034 km s −1 . The derived height of the source region of the observed quasi-periodic emission, and the magnetic field at the corresponding location (for emission in the fundamental mode) were ∼0.23 R and 6.3 G, respectively. The magnetic field for harmonic emission was found to be ∼3.1 G.

We investigated a peculiar metric type II solar radio burst with a broken lane structure, which was observed on November 13, 2012. In addition to the radio data, we also studied the data in the other wavelengths. The bursts were associated with two CMEs and two flares that originated from active region AR 11613. A long current sheet was developed in the first CME, and the second G. Gao Gao et al.CME collided with the current sheet first and then merged with the first one.Combing information revealed by the multi-wavelength data indicated that a coronal shock accounting for the type II radio burst, and that the collision of this shock with the current sheet resulted in the broken lane of the type II radio burst. The type II burst lane resumed after the shock passed through the current sheet. We further estimated the thickness of the current sheet according to the gap on the lane of the type II burst, and found that the result is consistent with previous ones obtained for various events observed in different wavelengths by different instruments. In addition, the regular type II burst associated with the first CME/flare was also studied, and the magnetic field in each source region of the two type II bursts was further deduced in different way.