Solar proton event database

This product provides a database of solar proton events observed above 300 MeV during solar cycles 22-24, i.e., between September 1986 and December 2019. In total, the database includes 68 events: 33 ground level events (GLEs 40-72), which have been detected with neutron monitors (NMs), and 35 events (referred to as solar proton events, SPEs) which have been detected with space-borne detectors above 300 MeV, but have not produced sufficient fluxes at high energies to be detected with ground level NMs.

The database includes differential fluence (time-integrated flux) and peak flux spectra in ten energies between 200 MeV and 7690 MeV for all of the events. In addition, flux spectra at 5-minute resolution around the high-energy peak of the event are provided for six of the well-observed GLEs (namely, GLEs 59, 60, 67, 70, 71 and 72). The full event list is given below.

Note '*' = 5-min spectra available

The fluence spectra are based on analyses of space-borne (GOES EPS + HEPAD) and NM observations, in which integral proton fluences were fitted with a Band function (BF; Tylka and Dietrich, 2009; Atwell et al., 2016; Raukunen et al., 2018). The Band function (Band et al., 1993) is a double power law function with four parameters: two spectral indices γ₁ and γ₂, roll-over rigidity R₀ and fluence normalization factor J₀. More recently, the GLE spectra were revised by Koldobskiy et al. (2021) using an updated NM yield function. The revised spectra were fitted with a modified Band function (MBF), which differs from the Band function by an additional exponential roll-over at high rigidities. Thus, the MBF has five fitted parameters: two spectral indices γ₁ and γ₂, roll-over rigidities R₁ and R₂ and a high-rigidity fluence normalization factor J₂.

In the database, the fluence spectra of GLEs have been calculated by numerically differentiating the MBF representations, with the exception of GLEs 51, 54, 57 and 68, for which the BF representations were used. The spectra of all SPEs have been calculated by numerically differentiating the BF representations. The parameters of all spectral representations can be found in Vainio et al. (2017), Raukunen et al. (2018) and Koldobskiy et al. (2021).

As the available space-borne observations reach only ~600 MeV (Raukunen et al., 2020), and detailed, time-resolved fluxes from NM observations are available for only a few events, extrapolation is required to calculate the peak flux spectra. In the database we calculate the peak flux spectra by scaling the fluence spectra. More precisely, we first calculate the integral peak fluxes I(>E) for all events at >100 MeV and >400 MeV using the >100 MeV GOES/EPS channel and integral bow-tie analysed GOES/HEPAD channels P9 and P10. Then we select events where the >400 MeV peak flux is greater than two times the background flux, and compare the ratios R_I = I(>100) / I(>400) with the corresponding fluence ratios, i.e., R_F = F(>100) / F(>400). We find that, on average, R_F = 1.591 · R_I, meaning that the peak flux spectra are harder with a difference of log(1.591) / log(4) = 0.335 in spectral index. The scaling coefficient is calculated as c = I(>E₀) / F(>E₀), where E₀ = 400 MeV if the background condition is fulfilled and E₀ = 100 MeV otherwise. Thus, we calculate the scaled and corrected integral peak flux spectra as I_corr(>E) = c · F(>E) · (E/E₀)^0.335.

The flux spectra for the selected, well-observed GLEs are based on the inversion method described in Mishev et al. (2014). The method depends on detailed modeling of the particle transport in the geomagnetic field and the Earth’s atmosphere as well as the detection efficiency of NMs to determine the spectral and angular characteristics of solar energetic particles (SEPs) near Earth.

User instructions

Proton event spectrum tool

This tool lets the user plot and download the spectrum of a selected data type and event. First, the user selects the data type (either Fluence, Peak flux or Flux). That selection determines the list of events available for plotting: for Fluence and Peak flux, the full list of >300 MeV proton events observed during solar cycles 22-24 is available. For flux, the event list narrows down to six well-observed GLEs, and after selecting an event, an additional selection of a time interval becomes available.

When selecting, for example, peak flux spectrum for GLE 72, the result should look like this:

The user can hover over the plot area and read the values of the points closest to the cursor on the screen. The plot, once created, can also be saved as a PNG file using the button on the right. Alternatively, the raw data of the plot in numeric format can be copied and pasted out from the text field below the plot area, or downloaded as a text file using the "Save as text"-button.

In case the user clicks the green button to save the PNG file, either a file download dialog appears or the plot is downloaded automatically into the default download folder, depending on the browser settings. The saved plot should look like this:

Proton event time series tool

This tool lets the user plot and download the differential flux time series at a selected energy for a selected event. For example, selecting the flux time series for GLE 72 at 450 MeV should produce results like this:

Machine-to-machine interfaces

The machine-to-machine interface (API) to the product is provided as a web page located at

https://r-esc.utu.fi/api/R.166/<tool>?<parameter_list>

Here <tool> is either the string ‘spectrum’ or the string ‘timeseries’ for accessing the spectrum tool or the time series tool, respectively. The <parameter_list> depends on the chosen tool, as explained below.

The spectrum tool has two parameters:

Parameter name	Type	Range / allowed values	Description
type	string	"fluence" or "peakflux"	Data type selector between fluence or peak flux
event	string	"1989-05-20", "1989-07-25", "1989-08-12", "1989-08-16", "1989-09-29", "1989-10-19", "1989-10-22", "1989-10-24", "1989-10-29", "1989-11-15", "1989-11-30", "1990-05-21", "1990-05-24", "1990-05-26", "1990-05-28", "1991-03-23", "1991-05-13", "1991-06-04", "1991-06-11", "1991-06-15", "1991-10-30", "1992-03-07", "1992-06-25", "1992-11-02", "1997-11-04", "1997-11-06", "1998-05-02", "1998-05-06", "1998-08-24", "1998-09-30", "1998-11-14", "2000-07-14", "2000-11-08", "2001-04-02", "2001-04-12", "2001-04-15", "2001-04-18", "2001-08-16", "2001-09-24", "2001-10-22", "2001-11-04", "2001-11-22", "2001-12-26", "2002-04-21", "2002-08-24", "2003-10-28", "2003-10-29", "2003-11-02", "2004-11-01", "2004-11-10", "2005-01-17", "2005-01-20", "2005-06-16", "2005-09-08", "2006-12-06", "2006-12-13", "2012-01-23", "2012-01-27", "2012-03-07", "2012-03-13", "2012-05-17", "2013-05-22", "2014-01-06", "2014-01-07", "2014-02-25", "2014-09-01", "2015-10-29" or "2017-09-10"	Event selector

The list of events available in the spectrum tool can also be acquired by accessing the following web page:

https://r-esc.utu.fi/api/R.166/spectrum/eventlist

The output of the API spectrum tool for an event is identical to the GUI except for the header part, which is omitted.

For example, acquiring the peak flux spectrum of GLE 72 on September 10, 2017, access the following web page:

https://r-esc.utu.fi/api/R.166/spectrum?type=peakflux&event=2017-09-10

The time series tool has one mandatory and one optional parameter:

Parameter name	Type	Range / allowed values	Description
event	string	"2000-07-14", "2001-04-15", "2003-11-02", "2006-12-13", "2012-05-17" or "2017-09-10"	Event selector (mandatory)
energy_channel	integer	1 — 10	Energy channel (optional) (see below for corresponding MeV values)

energy_channel value index correspondence to energy value:

energy_channel	Description
1	200 MeV
2	300 MeV
3	450 MeV
4	675 MeV
5	1012.5 MeV
6	1518.8 MeV
7	2278.1 MeV
8	3417.2 MeV
9	5125.8 MeV
10	7688.7 MeV

If the energy channel parameter is omitted, the tool returns the time series for all 10 channels; in this case, the output has 11 columns: column 1 gives the time stamp and columns 2-11 give the flux time series for energy channels 1-10.

The list of events available in the time series tool can also be acquired by accessing the following web page:

https://r-esc.utu.fi/api/R.166/timeseries/eventlist

The output of the API time series tool for an event and an energy channel is identical to the GUI except for the header part, which is omitted.

For example, acquiring the 200 MeV flux time series of GLE 72 on September 10, 2017, access the following web page:

https://r-esc.utu.fi/api/R.166/timeseries?event=2017-09-10&energy_channel=1

References

Atwell W. et al., 2016, In Proc. 46th International Conference on Environmental Systems
Band D. et al., 1993, Astrophysical Journal, 413, 281, DOI: 10.1086/172995
Koldobskiy S. et al., 2021, Astronomy & Astrophysics, 647, A132, DOI: 10.1051/0004-6361/202040058
Mishev, A. et al., 2014, Journal of Geophysical Research: Space Physics, 119, 2, DOI: 10.1002/2013JA019253
Raukunen, O. et al., 2018, Journal of Space Weather and Space Climate, 8, A04, DOI: 10.1051/swsc/2017031
Raukunen, O. et al., 2020, Journal of Space Weather and Space Climate, 10, 24, DOI: 10.1051/swsc/2020024
Tylka A.J. and Dietrich W.F., 2009, In Proc. 31st International Cosmic Ray Conference
Vainio R. et al., 2017, Astronomy & Astrophysics, 604, A47, DOI: 10.1051/0004-6361/201730547