This Task investigates the properties of the solar proton events in three aspects. For the protons we use ~20 MeV SOHO/ERNE adopted as a reference channel under this project (see Task 1.1) over the period 1996÷2016. The used solar flares (SFs) and coronal mass ejections (CMEs) are the identified solar origin of these proton events.
Timing study
For the timing behavior we calculated the offset between the identified proton event onset and the reported in catalogs SF onset (Fig. 1) or the CME time of first appearance or onset (Fig. 2). The mean and median values for the offset (usually about several hours after the SF or CME) are given in the respective plot.
Fig. 1 Time offset between protons and SFs.
Fig. 2 Time offset between protons and CMEs.
Fig. 3 Longitudinal dependence of the proton origin.
Spatial study
For the spatial trend we used the longitudinal and latitudinal position (in degrees) of the reported location of the SF active region. The well-known preference to western longitudes is also obtained here (with a peak at W60) when using the entire event sample to improve the event statistics, see Fig. 3. Northern preference is obtained for events in solar cycle (SC) 24, whereas Southern preference for SC 23, Fig. 4, respectively.
Fig. 5 Proton spectral index for the entire sample.
Spectral study
The proton spectral index is defined as the declining slope of the dependence between the peak proton intensity and the mean energy of the proton channel.
We use the results where proton enhancements are clearly seen in five of the energy channels, in MeV: 17÷22, 26÷32, 40÷51, 64÷80, 101÷131. In this first approach a single power law is applied for all events.
The histogram in Fig. 5 is for the entire sample. The majority of the proton events have intermediate spectral index, with a broad distribution peak at about 3÷4 and longer tail to larger values. Values below 2 (so-called hard spectral index) and above 5÷6 (soft spectra) could be an artifact from the two-channel analysis.
Additional analysis shows that there is neither a clear, strong trend in the correlations between the proton spectral index with the parameters of the SFs, nor with the CMEs.
When a subset of the proton sample that are accompanied with well-observed prominences is selected, the obtained range of spectral indices is 2.95 ≤ γ ≤ 6.08, which is a wider range than previously reported.
Publications
Miteva, R., Tsvetkov, Ts., Spectral analysis of SOHO/ERNE protons in solar cycles 23 and 24,
AIP Conference Proceedings, Vol. 2075, 090014 (2019) 
Tsvetkov, Ts., Miteva, R., Petrov, N., Filaments Related to Solar Energetic Particles,
AIP Conference Proceedings, Vol. 2075, 090013 (2019)
