AO Callisto


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AO Callisto Solar Radio Spectrometer

The AO Callisto radio spectrometer system started the regular observations of the Sun from 10 October 2021. It is is a dual-channel programmable heterodyne receiver, equipped with a Long Wavelength Array (LWA) antenna, to record the circular polarization of the solar bursts in the frequency range of 10-90 MHz. The AO Callisto is part of the world-wide e-Callisto network, which provides a full 24-h coverage of the radio observations of the Sun ( It is fully automated to record the daily solar radio spectrum, at a sampling rate of ~250 millisecond per 200-channel wide of the spectrum. Everyday observation is made in the time interval of 06:30 AM to 05:30 PM Puerto Rico time. The AO Callisto spectra are available from 10 October 2021. Everyday spectra are made accessible in real time to the international research community at an interval of 15-min at the website:

On 28 October 2021, an intense flare (X-ray class X1.0) occurred on the Sun and it was followed by a fast and wide coronal mass ejection (CME) as well as an energetic particle event. The radio manifestations associated with the above flare/CME were recorded by the AO Callisto.

Figure 1: The radio spectrum observed by the AO Callisto spectrometer on 28 October 2021. It shows the fast drifting of type II radio bursts (fundamental and second harmonic emission) centered around 15:30 UT in the frequency range of 30-70 MHz. Groups of fast drifting type III radio bursts have also been observed in the plotted time range.

Senior Observatory Scientist
Dr. Periasamy K. Manoharan
Arecibo Observatory
787-878-2612 ext. 617