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تسجيل مستخدم جديدForbush decreases and solar events seen in the 10 - 20GeV energy range by the Karlsruhe Muon Telescope
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Since 1993, a muon telescope located at Forschungszentrum Karlsruhe (Karlsruhe Muon Telescope) has been recording the flux of single muons mostly originating from primary cosmic-ray protons with dominant energies in the 10 - 20 GeV range. The data are used to investigate the influence of solar effects on the flux of cosmic-rays measured at Earth. Non-periodic events like Forbush decreases and ground level enhancements are detected in the registered muon flux. A selection of recent events will be presented and compared to data from the Jungfraujoch neutron monitor. The data of the Karlsruhe Muon Telescope help to extend the knowledge about Forbush decreases and ground level enhancements to energies beyond the neutron monitor regime.
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After a prolong and deep solar minimum at the end of solar cycle 23, the current cycle 24 is one of the lowest cycles. The two periods of deep minimum and mini-maximum of the cycle 24 are connected by a period of increasing solar activity. In this wo
rk, the Forbush decreases of cosmic ray intensity during the period from January 2008 to December 2014 are studied. A statistical analysis of 749 events using the IZMIRAN database of Forbush effects obtained by processing the data of the worldwide neutron monitor network using the global survey method is performed. A further study of the events that happened on the Sun and affected the interplanetary space, and finally provoked the decreases of the galactic cosmic rays near Earth is performed. A statistical analysis of the amplitude of the cosmic ray decreases with solar and geomagnetic parameters is carried out. The results will be useful for space weather studies and especially for Forbush decreases forecasting.
We seek to estimate the average level of MHD turbulence near coronal mass ejection (CME) fronts as they propagate from the Sun to the Earth. We examine the cosmic ray data from the GRAPES-3 tracking muon telescope at Ooty, together with the data from
other sources for three well observed Forbush decrease events. Each of these events are associated with frontside halo Coronal Mass Ejections (CMEs) and near-Earth magnetic clouds. In each case, we estimate the magnitude of the Forbush decrease using a simple model for the diffusion of high energy protons through the largely closed field lines enclosing the CME as it expands and propagates from the Sun to the Earth. We use estimates of the cross-field diffusion coefficient $D_{perp}$ derived from published results of extensive Monte Carlo simulations of cosmic rays propagating through turbulent magnetic fields. Our method helps constrain the ratio of energy density in the turbulent magnetic fields to that in the mean magnetic fields near the CME fronts. This ratio is found to be $sim$ 2% for the 11 April 2001 Forbush decrease event, $sim$ 6% for the 20 November 2003 Forbush decrease event and $sim$ 249% for the much more energetic event of 29 October 2003.
Forbush decreases (FDs), which are short-term drops in the flux of galactic cosmic rays, are caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, especially interplanetary coronal mass ejections (ICMEs) and thei
r associated shocks, as well as corotating interaction regions. Such events can be observed at Earth, for example, using neutron monitors, and also at many other locations in the solar system, such as on the surface of Mars with the Radiation Assessment Detector instrument onboard Mars Science Laboratory. They are often used as a proxy for detecting the arrival of ICMEs or corotating interaction regions, especially when sufficient in situ solar wind measurements are not available. We compare the properties of FDs observed at Earth and Mars, focusing on events produced by ICMEs. We find that FDs at both locations show a correlation between their total amplitude and the maximum hourly decrease, but with different proportionality factors. We explain this difference using theoretical modeling approaches and suggest that it is related to the size increase of ICMEs, and in particular their sheath regions, en route from Earth to Mars. From the FD data, we can derive the sheath broadening factor to be between about 1.5 and 1.9, agreeing with our theoretical considerations. This factor is also in line with previous measurements of the sheath evolution closer to the Sun.
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