We present a short overview on the results from the first association analysis between in situ observed solar energetic electrons at 1 AU using the ACE/EPAM instrument (Samwel and Miteva, 2021) and radio bursts of type II, III and IV. The statistical analysis is performed over the last two solar cycles (SCs), 23 and 24 (1997-2019). All previous research has focused on energetic protons, whereas we aimed to compare in situ electrons and remotely observed electron emission. Over the period of interest, we selected 832 electron events with identified solar origin (solar flare or/and coronal mass ejection, CME). Radio emission signatures were identified using available dynamic radio spectra from 10 ground-based radio observatories in addition to Wind/WAVES. Radio bursts that occur within about 1 hour after the reported solar origin onset time are selected as produced by the same solar eruption. Furthermore, the radio emissions are identified in 6 wavelength bands: dm-l (3-1 GHz), dm-h (1000-300 MHz), m-l (300-100 MHz), m-h (100-30 MHz), dam (30-3 MHz) and Hkm (3 MHz-20 kHz). No continuation of the burst (from the low corona to the interplanetary, IP, space) is implied, namely, the plots only show the individual burst appearance in the respective sub-bands.

Main results

Figure 1 presents the distribution of the number of type II, III and IV bursts normalized to all 832 events as a function of the radio wavelength. The wavelength trends differ among the burst types, with increasing occurrence towards the IP space for type IIIs and decreasing for type IIs and IVs. 

Figure 1 – Distribution of the occurrence rate of type II, III and IV radio bursts associated with in situ electrons as a function of radio wavelength over solar cycles 23 and 24. Color code is: black – visually confirmed radio bursts, blue – uncertain identifications or observatory reports, red – data gaps in the dynamic spectra. 

Some of the results in this work are summarized below:

• No excess SC productivity is found for the general radio burst occurrence as function of the observed wavelength;
• The Eastern helio-longitude sample is accompanied by ∼7% more IP type IIs and more dm and m-IVs, compared to the type IIIs that show no preference.
• There is a strong decline in the occurrences of type II (∼30%) and IV (∼25%) radio bursts associated with weak (in median value) electron events compared to the strong samples.
• Flare-dominated acceleration is plausible for up to 29% of the entire event sample (compared to only 19% burst association with situ proton events); CME-dominated – for 18% (vs. 42%); mixed-contribution – for 17% (vs. 32%); however the fraction of uncertain cases is large, 34% (vs. 7% for the proton sample, respectively).

Conclusions

For the first time, in situ observed electrons are compared to electron-generated radio emission signatures. The study presents the trends of type II, III and IV radio burst occurrence with respect to SC, helio-longitude, electron intensity, SF/CME properties. An alternative scenario for the solar origin and dominant acceleration of electron events is proposed here based solely on radio burst observations. 

Based on a recent paper:  Miteva, R., Samwel, S. W., Zabunov, S.: 2022, Universe, 8(5), 275, 20pp. DOI: https://doi.org/10.3390/universe8050275

Additional info

ACE/EPAM electron catalog: https://www.nriag.sci.eg/ace_electron_catalog/ 

Radio catalog: https://catalogs.astro.bas.bg/ 

References

Miteva, R., Samwel, S. W., Zabunov, S.: 2022, Universe, 8(5), 275, 20pp.

Samwel., S. W., Miteva, R.: 2021, MNRAS, 505(4), pp. 5212-5227 

*Full list if authors: Rositsa Miteva(1), Susan W. Samwel(2) and Svetoslav Zabunov(3)

1. Institute of Astronomy and National Astronomical Observatory (IANAO), Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria, rmiteva@nao-rozhen.org 
2. National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Cairo 11421, Egypt, samwelsw@nriag.sci.eg 
3. Space Research and Technology Institute (SRTI), Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria, szabunov@nao-rozhen.org