Abstract
Several solar events with different types of negative microwave bursts have been studied using data from different spectral ranges. The total radio flux data obtained at the Ussuriysk Observatory, the Nobeyama Observatory, the US Air Force Radio Solar Telescope Network (RSTN), and the spectropolarimeter of the Institute of Solar–Terrestrial Physics, Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS) were used. The images were analyzed using data from the SDO/AIA space observatory in the 304 Å channel and the Nobeyama radio heliograph at a frequency of 17 GHz. It was shown that the “isolated” depressions of radio emission were caused by the absorption of radiation from radio sources and/or vast regions of the quiet Sun by low-temperature material of a large eruptive filament in the absence of flares. This confirmed the conclusions of the previous studies. It was revealed that the cause of negative bursts of the “pre-burst depression” type was the screening of a near-limb radio source by the material of coronal jets. In the case of a weak flare accompanying the jet, the negative burst could also be of the “isolated” type. A case of a previously unreported occurrence of a deeper depression of radio emission at high frequencies as compared to low frequencies was considered. It was shown that negative bursts are not as rare phenomena as previously thought.
Highlights
The analysis of sporadic solar activity using microwave radio emission makes it possible to study eruptive events
The analysis of images in different spectral ranges showed that the matter of jets that periodically appeared on September 7–9, 2017 in or near an active region with a complex magnetic configuration approaching the solar limb partially screened the radio sources located in it, which led to numerous depressions of radio emission at a number of microwave frequencies
If the jet material screens a gyroresonance radio source at high frequencies, the negative burst at these frequencies can be expected to be deeper. In this case, the area of the absorbing material may be insufficient for the appearance of a noticeable depression of radio emission at low frequencies, when the area of the absorber is small in comparison with the size of the radio source
Summary
The analysis of sporadic solar activity using microwave radio emission makes it possible to study eruptive events. The study of some negative burst events based on data from different spectral ranges showed that the depressions of radio emission were mainly caused by the absorption of radiation from local radio sources and vast regions of the quiet Sun by low-temperature plasma of an eruptive filament [1,2,3,4,5,6]. Recall that jets are small-scale solar plasma ejections observed in the extreme ultraviolet (EUV) and X-ray ranges Another possible cause for negative bursts is a decrease in radiation from a radio source during the development of an active region [9, 10]. The observations in the EUV range were analyzed using the images obtained by the AIA instrument of the SDO solar space observatory, and in the radio range using the images of the Nobeyama radio heliograph. Coronal ejection data were taken from the SOHO LASCO CME Catalog.
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