562 research outputs found
Diffusion coefficient and radial gradient of galactic cosmic rays
We present the temporal changes of the diffusion coefficient K of galactic
cosmic rays (GCRs) at the Earth orbit calculated based on the experimental data
using two different methods. The first approach is based on the Parker
convection-diffusion approximation of GCR modulation [1]: i.e. K~Vr=dI where dI
is the variation of the GCR intensity measured by neutron monitors (NM),V is
the solar wind velocity and r is the radial distance. The second approach is
based on the interplanetary magnetic field (IMF) data. It was suggested that
parallel mean free path can be expressed in terms of B as in [2]-[4]. Using
data of the product of the parallel mean free path and radial gradient of GCR
calculated based on the GCR anisotropy data (Ahluwalia et al., this conference
ICRC 2013, poster ID: 487 [5]), we estimate the temporal changes of the radial
gradient of GCR at the Earth orbit. We show that the radial gradient exhibits a
strong solar cycle dependence (11-year variation) and a weak solar magnetic
cycle dependence (22-year variation), being in agreement with the previous
other calculations and with PIONEER/VOYAGER observations
Three dimensional solar anisotropy of galactic cosmic rays near the recent solar minimum 23/24
Three dimensional (3D) galactic cosmic ray (GCR) anisotropy has been studied
for 2006- 2012. The GCR anisotropy, both in the ecliptic plane and in polar
direction, were obtained based on the neutron monitors (NMs) and Nagoya muon
telescopes (MT) data. We analyze two dimensional (2D) GCR anisotropy in the
ecliptic plane and north-south anisotropy normal to the ecliptic plane. We
reveal quasi-periodicities - the annual and 27-days waves in the GCR anisotropy
in 2006-2012. We investigate the relationship of the 27-day variation of the
GCR anisotropy in the ecliptic plane and in the polar direction with the
parameters of solar activity and solar wind.Comment: 8 pages, 10 figures, paper presented on 24th European Cosmic Ray
Symposium 201
A stochastic method of solution of the Parker transport equation
We present the stochastic model of the galactic cosmic ray (GCR) particles
transport in the heliosphere. Based on the solution of the Parker transport
equation we developed models of the short-time variation of the GCR intensity,
i.e. the Forbush decrease (Fd) and the 27-day variation of the GCR intensity.
Parker transport equation being the Fokker-Planck type equation delineates
non-stationary transport of charged particles in the turbulent medium. The
presented approach of the numerical solution is grounded on solving of the set
of equivalent stochastic differential equations (SDEs). We demonstrate the
method of deriving from Parker transport equation the corresponding SDEs in the
heliocentric spherical coordinate system for the backward approach. Features
indicative the preeminence of the backward approach over the forward is
stressed. We compare the outcomes of the stochastic model of the Fd and 27-day
variation of the GCR intensity with our former models established by the finite
difference method. Both models are in an agreement with the experimental data.Comment: 8 pages, 7 figures, presented on 24th European Cosmic Ray Symposium
201
Numerical methods for solution of the stochastic differential equations equivalent to the non-stationary Parker's transport equation
We derive the numerical schemes for the strong order integration of the set
of the stochastic differential equations (SDEs) corresponding to the
non-stationary Parker transport equation (PTE). PTE is 5-dimensional (3 spatial
coordinates, particles energy and time) Fokker- Planck type equation describing
the non-stationary the galactic cosmic ray (GCR) particles transport in the
heliosphere. We present the formulas for the numerical solution of the obtained
set of SDEs driven by a Wiener process in the case of the full
three-dimensional diffusion tensor. We introduce the solution applying the
strong order Euler-Maruyama, Milstein and stochastic Runge-Kutta methods. We
discuss the advantages and disadvantages of the presented numerical methods in
the context of increasing the accuracy of the solution of the PTE.Comment: 4 pages, 2 figures, presented on 4th International Conference on
Mathematical Modeling in Physical Sciences, 201
Stochastic approach to the numerical solution of the non-stationary Parker's transport equation
We present the newly developed stochastic model of the galactic cosmic ray
(GCR) particles transport in the heliosphere. Mathematically Parker transport
equation (PTE) describing non-stationary transport of charged particles in the
turbulent medium is the Fokker-Planck type. It is the second order parabolic
time-dependent 4-dimensional (3 spatial coordinates and particles
energy/rigidity) partial differential equation. It is worth to mention that, if
we assume the stationary case it remains as the 3-D parabolic type problem with
respect to the particles rigidity R. If we fix the energy it still remains as
the 3-D parabolic type problem with respect to time. The proposed method of
numerical solution is based on the solution of the system of stochastic
differential equations (SDEs) being equivalent to the Parker's transport
equation. We present the method of deriving from PTE the equivalent SDEs in the
heliocentric spherical coordinate system for the backward approach. The
obtained stochastic model of the Forbush decrease of the GCR intensity is in an
agreement with the experimental data. The advantages and disadvantages of the
forward and the backward solution of the PTE are discussed.Comment: 4 pages, 2 figures, presented on International Conference on
Mathematical Modeling in Physical Sciences, 201
On the relationship of the 27-day variations of the solar wind velocity and galactic cosmic ray intensity in minimum epoch of solar activity
We study the relationship of the 27-day variation of the galactic cosmic ray
intensity with similar changes of the solar wind velocity and the
interplanetary magnetic field based on the experimental data for the Bartels
rotation period 2379 of 23 November 2007-19 December 2007. We develop a three
dimensional (3-D) model of the 27-day variation of galactic cosmic ray
intensity based on the heliolongitudinally dependent solar wind velocity. A
consistent, divergence-free interplanetary magnetic field is derived by solving
Maxwells equations with a heliolongitudinally dependent 27-day variation of the
solar wind velocity reproducing in situ observations. We consider two types of
3-D models of the 27-day variation of galactic cosmic ray intensity - (1) with
a plane heliospheric neutral sheet, and (2)- with the sector structure of the
interplanetary magnetic field. The theoretical calculation shows that the
sector structure does not influence significantly on the 27-day variation of
galactic cosmic ray intensity as it was shown before based on the experimental
data. Also a good agreement is found between the time profiles of the
theoretically expected and experimentally obtained first harmonic waves of the
27-day variation of the galactic cosmic ray intensity (correlation coefficient
equals 0.98 0.02). The expected 27-day variation of the galactic cosmic ray
intensity is inversely correlated with the modulation parameter z (correlation
coefficient equals -0.91 0.05) which is proportional to the product of the
solar wind velocity V and the strength of the interplanetary magnetic field B
(z VB). The high anticorrelation between these quantities indicates that the
predictable 27-day variation of the galactic cosmic ray intensity mainly is
caused by this basic modulation effect.Comment: article published in Solar Physics (2011
Modeling and experimental study of the 27-day variation of galactic cosmic-ray intensity for a solar-wind velocity depending on heliolongitude
We develop a three dimensional (3-D) model of the 27-day variation of
galactic cosmic ray (GCR) intensity with a spatial variation of the solar wind
velocity. A consistent, divergence-free interplanetary magnetic field is
derived by solving the corresponding Maxwell equations with a variable solar
wind speed, which reproduces in situ observed experimental data for the time
interval to be analyzed (24 August 2007-28 February 2008). We perform model
calculations for the GCR intensity using the variable solar wind and the
corresponding magnetic field. Results are compatible with experimental data;
the correlation coefficient between our model predictions and observed 27-day
GCR variation is 0.80 0.05.Comment: article published in Advances in Space Research (2010
Annual Variations of the Galactic Cosmic Ray Intensity and Seasonal Distribution of the Cloudless Days and Cloudless Nights in Abastumani (41.75oN, 42.82oE; Georgia): (1) experimental study and (2) theoretical modeling
We study a possible relationships between seasonal distributions of the
visually observed cloudless days (CD) and cloudless nights (CN) at Abastumani
Astrophysical Observatory (41.75N, 42.82E; Georgia) in 1957-1993. The annual
variations of monthly numbers of CD and CN have been observed, with maximum in
August for CD and in September for CN. During geomagnetic disturbances it is
also observed the growth of number of CD in September andMarch (equinoctial
months), and for CN, together with September, in June, April and February. We
assume that this phenomenon indicates an influence of cosmic factors on
cloudiness, as well as the existence of semiannual and possibly
shorter-periodicity variations. This cosmic factor can be the manifestation of
different rates of the galactic cosmic rays (GCRs) flux variations in CD and CN
periods. The influence of GCR flux on ionization of lower atmosphere and
variations of density of cloud condensation nuclei also can be connected to the
annual and seasonal changes of temperature at Earth surface of this region. To
comprehend behaviors of the annual and semi-annual variations of the GCR
intensity and their possible relationships with the seasonal distributions of
CD and CN we compose and numerically solve two dimensional (2-D) time dependent
transport equation including all important processes in the heliosphere. An
analysis of experimentally observed and theoretically obtained results have
been carried out.Comment: 9 pages, 6 figures, presented on 34th International Cosmic Ray
Conference 2015. Proceedings of Science 201
27-day variation of the GCR intensity based on corrected and uncorrected for geomagnetic disturbances data of neutron monitors
We study 27-day variations of the galactic cosmic ray (GCR) intensity for
2005- 2008 period of the solar cycle #23. We use neutron monitors (NMs) data
corrected and uncorrected for geomagnetic disturbances. Besides the limited
time intervals when the 27-day variations are clearly established, always exist
some feeble 27-day variations in the GCR 5 intensity related to the constantly
present weak heliolongitudinal asymmetry in the heliosphere. We calculate the
amplitudes of the 27-day variation of the GCR intensity based on the NMs data
corrected and uncorrected for geomagnetic disturbances. We show that these
amplitudes do not differ for NMs with cut-off rigidities smaller than 4-5 GV
comparing with NMs of higher cut-off rigidities. Rigidity spectrum of the
27-day variation of the GCR intensity found in the uncorrected data is soft
while it is hard in the case of the corrected data. For both cases exists
definite tendency of softening the temporal changes of the 27-day variation's
rigidity spectrum in period of 2005 to 2008 approaching the minimum of solar
activity. We believe that a study of the 27-day variation of the GCR intensity
based on the data uncorrected for geomagnetic disturbances should be carried
out by NMs with cut-off rigidities smaller than 4-5 GV.Comment: 8 pages, 6 figures, presented on 24th European Cosmic Ray Symposium
201
On the 27-day Variations of Cosmic Ray Intensity in Recent Solar Minimum 23/24
We have studied the 27-day variations and their harmonics of the galactic
cosmic ray (GCR) intensity, solar wind velocity, and interplanetary magnetic
field (IMF) components in the recent prolonged solar minimum 23 24. The time
evolution of the quasi-periodicity in these parameters connected with the Suns
rotation reveals that their synodic period is stable and is aprox 26-27 days.
This means that the changes in the solar wind speed and IMF are related to the
Suns near equatorial regions in considering the differential rotation of the
Sun. However, the solar wind parameters observed near the Earths orbit provide
only the conditions in the limited local vicinity of the equatorial region in
the heliosphere (within in latitude). We also demonstrate that the observed
period of the GCR intensity connected with the Suns rotation increased up to
aprox 33-36 days in 2009. This means that the process driving the 27-day
variations of the GCR intensity takes place not only in the limited local
surroundings of the equatorial region but in the global 3-D space of the
heliosphere, covering also higher latitude regions. A relatively long period (
aprox 34 days) found for 2009 in the GCR intensity gives possible evidence of
the onset of cycle 24 due to active regions at higher latitudes and rotating
slowly because of the Suns differential rotation. We also discuss the effect of
differential rotation on the theoretical model of the 27-day variations of the
GCR intensity.Comment: article published in Solar Physics (2013
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