Space weather study through analysis of solar radio bursts detected by a single-station CALLISTO spectrometer

Abstract. This article summarises the results of an analysis of solar radio bursts (SRBs) detected by the Compound Astronomical Low-cost
Low-frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO) spectrometer hosted by the University of Rwanda. The data analysed were detected during the first year (2014–2015) of the instrument operation. Using quick plots provided by the e-CALLISTO website, a total of 201 intense and well-separated solar radio bursts detected by the CALLISTO station located in Rwanda, are found consisting of 4 type II, 175 type III and 22 type IV radio bursts. It is found that all analysed type II and ∼ 37 % of type III bursts are associated with impulsive solar flares, while the minority (∼ 13 %) of type IV radio bursts are associated with solar flares. Furthermore, all type II radio bursts are associated with coronal mass ejections (CMEs), ∼ 44 % of type III bursts are associated with CMEs, and the majority (∼ 82 %) of type IV bursts were accompanied by CMEs. With aid of the atmospheric imaging assembly (AIA) images on board the Solar Dynamics Observatory (SDO), the location of open magnetic field lines of non-flare-associated type III radio bursts are shown. The same images are used to show the magnetic loops in the solar corona for type IV radio bursts observed in the absence of solar flares and/or CMEs. Findings from this study indicate that analysis of SRBs that are observed from the ground can provide a significant contribution to the early diagnosis of solar transients phenomena, such as solar flares and CMEs, which are major drivers of potential space weather hazards.



Solar radio bursts
Solar radio bursts (SRBs) are Sun's EM emissions in radio band often associated with solar flares and CMEs.SRBs originate from solar atmosphere (solar corona) mainly by plasma emission mechanism.They are signatures of solar activity.SRBs are common during the years of high solar activity.

Morphology of Solar Radio Bursts in time-frequency domain
Types of Solar radio bursts Type I (storm burst): short-lived emission with duration ∼ 1 s and narrow band events.Type II: slow drift from high to low frequencies associated with fundamental-harmonic frequency structure.Type III: fast drift from high to low frequencies and often accompany the flash phase of large flares.Type IV: broadband continuum.broadband continua which may appear with type III and last 1 to 2 minutes.Type II, III & IV bursts are generated by non-thermal electrons accelerated during solar eruptions.The latter are relevant to space weather study.

Estimation of CMEs Speed from type II bursts characteristics
The drift rates df dt of type II SRBs are estimated using the relation These frequencies will be estimated from the CALLISTO spectrum.
The plasma frequency can be assumed to be Estimation of CMEs Speed from type II bursts characteristics...
Then by substituting equation (3) into equation ( 4) Knowing that dr dt = v , the above equation can be written as 1 The expression ( 1 n dn dr ) in equation ( 6) is known as the scale height, L −1 n .
Estimation of CMEs Speed from type II bursts characteristics ...
Assume a density model of the form n 0 r −α (Gopalswamy, 2009), the scale height becomes Plug equation ( 7) into (6) , we finally get

Methodology
Radio data used in this study were detected from October 2014 to September 2015 during SC 24.
Using quick plots provided by the e-CALLISTO network and by manual inspection, we made cross-checked to identify all radio bursts observed by the CALLISTO Rwanda.
Radio bursts are used as diagnostics of the level of solar activity (e.g., Salmane et al., 2018).we carefully examined their association with the solar transients.
White light coronagraph data from the LASCO C2 on board the SOHO and the SECCHI on board STEREO were analyzed.

Methodology
The association of SRBs and CMEs was confirmed upon the time coincidence (a time window of ∼ 1 h of CME from the onset of radio burst was considered).
A burst is considered as being flare associated if it appears between its onset and end times.
For some type III and type IV bursts, the AIA images on board SDO were used to indicate the possible launch sites.

Statistical Results
A total of 201 radio bursts comprising 4 type II radio bursts, 175 type III radio bursts and 22 type IV radio bursts.
All type II radio bursts are associated with solar flares, and ∼ 37% of the type III and ∼ 13% of type IV radio bursts detected are flare associated.
The remaining non-flare associated type III radio bursts may be due to small-scale reconnection events present in the solar corona.
All type II radio bursts are associated with CMEs.
∼ 44% of type III radio bursts are accompanied by CMEs.
The majority (∼ 82%) of type IV radio bursts are associated with CMEs.

Summary of Results
In this study analyzed 201 SRBs detected by the CALLISTO spectrometer installed in Kigali, Rwanda.
The obtained results show that, during its first year of operation, 4 type II, 175 type III and 22 type IV radio bursts were detected in the frequency range of 45-80.9MHz.
Analyzed data indicate that all detected type II radio bursts are flare associated; ∼ 37% of observed type III bursts are triggered by impulsive flares.We found that the remaining non-flare-related type III bursts might have been triggered by small-scale features or weak energy events present in the solar corona according to the literature and with the help of AIA/SDO images in the 171 Åbandpass.
Examples of type II and type III radio bursts observed by CALLISTO Rwanda.

Solar Activity: connection with SRBs Characteristics of SRBs Detection of SRBs and Space weather connection Statistical Analysis of SRBs by CALLISTO - Rwanda station Space weather Connections
Global Coverage of ground-based CALLISTO Spectrometers ObjectiveThe current analysis presents the trends of SRBs detected by the CALLISTO station in Rwanda and discusses their correlation with solar explosive phenomena which occurred during its first year of operation.

Characteristics of SRBs Detection of SRBs and Space weather connection Statistical Analysis of SRBs by CALLISTO - Rwanda station Space weather Connections
sample of SDA/AIA images using the 171 Å bandpass of the Sun on 3 November 2014 Maps with radio blackout on 13 January 2015 (top) and on 12 March 2015 (bottom) A