Small Size Ground Level Enhancements During Solar Cycle 24статья
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Дата последнего поиска статьи во внешних источниках: 16 сентября 2020 г.
Аннотация:Abstract We continue the systematical empirical search for small size ground level enhancements(GLEs) (also called “hidden” or sub-GLEs) using data from ground-based instrumentsfor Solar Cycle 24. The starting point of this research is the hypothesis that smallsize GLEs may be indicative of the acceleration of solar energetic particles (SEPs) by shocksdriven by coronal mass ejections (CMEs). A crucial parameter for solving the problemseems to be the SEP energy spectrum at the Earth’s orbit measured by spacecraft detectorsand ground-based neutron monitors (NMs). We try to recover the SEP spectrum in a widerange of energies – from GOES non-relativistic energy channels to the relativistic rangefrom NM data, as well as from relevant measurements of some ground-based non-standard(mainly muon) cosmic ray detectors. The main factors that determine the SEP intensity andspectrum shape near the Earth are the source power, location, and/or shock strength. Every“suspected” small GLE is analyzed separately. Finally, we compile the list of statisticallyconfirmed small GLEs and give our interpretation within the frame of the above hypothesis.The three considered models of shock wave acceleration are not suitable to physicallyand unambiguously explain some features of the observed solar cosmic ray (SCR) spectra.The results emphasize the importance of studying the GLEs of low intensity (hidden GLEs) for better understanding the SEP spectrum formation, especially in the range of relativisticenergies. The GLE events from behind-the-limb sources are of special interest.