Aims. Continuous measurements of ground-based neutron monitors (NMs) form the main data source for studying high-energy high-intensity solar energetic particle (SEP) events that are called ground-level enhancements (GLEs). All available data are collected in the International GLE Database (IGLED), which provides formal NM count-rate increases above the constant pre-increase level which is due to galactic cosmic rays (GCR). This data set is used to reconstruct the energy spectra of GLE events. However, the assumption of a constant GCR background level throughout GLE events is often invalid. Here we thoroughly revise the IGLED and provide a data set of detrended NM count-rate increases that accounts for the variable GCR background. Methods. The formal GLE count-rate increases were corrected for the variable GCR background, which may vary significantly during GLE events. The corresponding integral omnidirectional fluences of SEPs were reconstructed for all GLEs with sufficient strength from the detrended data using the effective rigidity method. Results. The database of the detrended NM count rate is revised for GLE events since 1956. Integral omnidirectional fluences were estimated for 58 GLE events and parametrised for 52 sufficiently strong events using the modified Ellison-Ramaty spectral shape. Conclusions. The IGLED was revised to account for the variable GCR background. Integral omnidirectional fluences reconstructed for most of GLE events were added to IGLED. This forms the basis for more precise studies of parameters of SEP events and thus for solar and space physics.

Aims. Sunspot number series are composed from observations of hundreds of different observers that requires careful normalization of the observers to the standard conditions. Here we present a new normalized series of the number of sunspot groups for the period 1749-1996. Methods. The reconstruction is based on the active day fraction (ADF) method, which is slightly updated with respect to the previous works, and a revised database of sunspot group observations. Results. Stability of some key solar observers has been evaluated against the composite series. The Royal Greenwich Observatory dataset appears fairly stable since the 1890s but is about 10% too low before that. A declining trend of 10-15% in the quality of Wolfer's observation is found between the 1880s and 1920s, suggesting that using him as the reference observer may lead to additional uncertainties. Wolf (small telescope) appears fairly stable between the 1860s and 1890s, without any obvious trend. The new reconstruction reflects the centennial variability of solar activity as evaluated using the singular spectrum analysis method. It depicts a highly significant feature of the Modern grand maximum of solar activity in the second half of the 20th century, being a factor 1.33-1.77 higher than during the 18-19th centuries. Conclusions. The new series of the sunspot group numbers with monthly and annual resolution, available also in the electronic format, is provided forming a basis for new studies of the solar variability and solar dynamo for the last 250 years.

Nearly 70 Ground Level Enhancements (GLEs) of cosmic rays have been recorded by the worldwide neutron monitor network since the 1950s depicting a big variety of energy spectra of solar energetic particles (SEP). Here we studied a statistical relation between the event-integrated intensity of GLEs (calculated as count-rate relative excess, averaged over all available polar neutron monitors, and expressed in percent-hours) and the hardness of the solar particle energy spectra. For each event the integral omnidirectional event-integrated fluences of particles with energy above 30 MeV (F 30 ) and above 200 MeV (F 200 ) were computed using the reconstructed spectra, and the ratio between the two fluences was considered as a simple index of the event's hardness. We also provided a justification of the spectrum estimate in the form of the Band-function, using direct PAMELA data for GLE 71 (17-May-2012). We found that, while there is no clear relation between the intensity and the hardness for weak events, all strong events with the intensity greater 100 %*hr are characterized by a very hard spectrum. This implies * Corresponding author Email address: ilya.usoskin@oulu.fi (I.G. Usoskin) December 9, 2016 that a hard spectrum can be securely assumed for all extreme GLE events, e.g., those studied using cosmogenic isotope data in the past. Preprint submitted to Advances in Space Research