Abstract
The cosmic ray modulation in relation to solar activity indices and heliospheric parameters during the period January 1996–October 2011, covering the solar cycle 23 and the ascending phase of solar cycle 24, is studied. The new perspective of this contribution is that the CME-index, obtained from only the CMEs with angular width greater than 30 degrees, gives much better results than in previous works. The proposed model for the calculation of the modulated cosmic ray intensity obtained from the combination of solar indices and heliospheric parameters gives a very satisfactory value of the standard deviation. The best reproduction of the cosmic ray intensity is obtained by taking into account solar and interplanetary indices such as sunspot number, interplanetary magnetic field, CME-index, and heliospheric current sheet tilt. The standard deviation between the observed and calculated values is about 6.63% for the solar cycle 23 and 4.13% for the ascending part of solar cycle 24.
Highlights
The cosmic ray (CR) intensity, as it is observed from Earth and in Earth’s orbit, exhibits an approximate 11-year variation anti correlated with solar activity, with perhaps some time lag, firstly studied by Forbush [1]
Particular consideration of the cosmic ray modulation is given to the correlation of longterm cosmic ray variations with different solar-heliospheric parameters and to existing empirical models of cosmic ray intensity, as it is described in the review paper by [6]
In our last work [10], we have shown that the long-term modulation of the intensity of cosmic-rays has reproduced using sunspot number (Rz), coronal mass ejections (CMEs)-index (Pi), interplanetary magnetic field (IMF), and heliospheric current sheet (HCS) tilt
Summary
The cosmic ray (CR) intensity, as it is observed from Earth and in Earth’s orbit, exhibits an approximate 11-year variation anti correlated with solar activity, with perhaps some time lag, firstly studied by Forbush [1]. This method gives satisfactory results when applied to prediction of the dose received on-board commercial aeroplane flights He notes that prediction of the galactic cosmic ray intensity observed at a given station is preferable than prediction of the different potentials such as the modulation potential in terms of sunspot numbers [8]. Solar cycle 23 was a cycle of great interest firstly, as it was characterized by a lot of violent periods of extreme solar events mainly in the descending phase, such as OctoberNovember 2003, January 2005, July 2005, and December 2006 and secondly, it had an extraordinary and extended minimum with duration more than three years In this solar minimum, the cosmic ray intensity was much higher than in the previous cycles [11]. According to [12], slow and narrow CMEs are ineffective for modulation, and as a result, we are showing the modulation with the previous form of the index and the new one
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