Monitoring the solar activity is of paramount importance for understanding and modelling the ionospheric behaviour/effects since the ionosphere is produced mainly via the ionisation effect of the solar electromagnetic radiation (Akasofu and Chapman, 1972; Hargreaves, J.K., 1992). Since the intensity of the solar emissions varies with time, quantification of the solar activity is therefore required for research purposes and development of ionospheric models. Solar activity indices are produced (and also needed) by various ionosphere/space weather monitoring services. Currently we use the solar 10.7 cm radio flux index (F10.7) as provided by the NOAA Space Weather Prediction Center.
The interplanetary space is continuously traversed by energetic nuclear particles called cosmic rays (Akasofu and Chapman, 1972). The origin of the cosmic rays is still not definitely determined - some certainly originate from the Sun and other stars but others are believed to be associated with various energetic processes in the galaxy. Cosmic rays consist mostly of protons (~94%) and helium nuclei (~5.5%), with few nuclei of heavier elements (galactic component of the cosmic rays). The cosmic ray intensity varies regularly and inversely to the solar activity cycle and depends also on magnetic latitude and longitude.
At the RMI Geophysical Centre in Dourbes, a standard 9-NM64 neutron monitor (3 units of 3 counters) has been in operation since 1965, providing measurements of the secondary neutron component of the cosmic rays on the ground. After pressure correction, this component would follow closely the primary cosmic rays intensity, i.e. would reproduce the variations of the cosmic rays intensity high above the station. However, before any useful information can be extracted from the raw neutron monitor measurements, missing records need to be recovered and the data has to be filtered and corrected. For space weather applications, all these steps has to be carried out in real time and answer to a strong requirements among which – to minimize the introduction of spurious data (spikes) and to eliminate any possibility for removal of correct original data. For the purpose, a Real Time Automatic Data Correction (RTADC) algorithm has been developed (Sapundjiev et al., 2014). RTADC has utilized the entire dataset available in Dourbes and is currently implemented for reduction of the neutron monitor data measurements at the site. The reduced real-time data can be used for identification of solar proton events with energies which may inflict material damage and/or impose health hazards due to elevated radiation levels. The neutron monitor measurements respond unambiguously to such events by showing a peak in the monitored intensity of the secondary radiation (Ground Level Enhancement) or by suppression of the intensity (Forbush decrease).
Akasofu, S.I., Chapman, S. (1972): Solar-Terrestrial Physics. Oxford University Press, Oxford, UK.
Hargreaves, J.K. (1992): The solar-terrestrial environment. Cambridge University Press, Cambridge, UK.
Sapundjiev, D., M. Nemry, S. M. Stankov, J.C. Jodogne (2014): Data reduction and correction algorithm for digital real-time
processing of cosmic ray measurements: NM64 monitoring at Dourbes. Advances in Space Research, Vol.53, No.1, pp.71-76, (doi:10.1016/j.asr.2013.09.037). (view at publisher) (download)