Effect of Finite Larmor Radius on the Cosmic Ray Penetration into an Interplanetary Magnetic Flux Rope

We discuss a mechanism for cosmic ray penetration into an interplanetary magnetic flux rope, particularly the effect of the finite Larmor radius and magnetic field irregularities. First, we derive analytical solutions for cosmic ray behavior inside a magnetic flux rope, on the basis of the Newton-Lorentz equation of a particle, to investigate how cosmic rays penetrate magnetic flux ropes under an assumption of there being no scattering by small-scale magnetic field irregularities. Next, we perform a numerical simulation of a cosmic ray penetration into an interplanetary magnetic flux rope by adding small-scale magnetic field irregularities. This simulation shows that a cosmic ray density distribution is greatly different from that deduced from a guiding center approximation because of the effect of the finite Larmor radius and magnetic field irregularities for the case of a moderate to large Larmor radius compared to the flux rope radius.Comment: 17 pages, 14 figures, accepted for publication in The Astrophysical Journa

Prediction of the Dst index from solar wind parameters by a neural network method

Using the Elman-type neural network technique, operational models are constructed that predict the Dst index two hours in advance. The input data consist of real-time solar wind velocity, density, and magnetic field data obtained by the Advanced Composition Explorer (ACE) spacecraft since May 1998 (http://www2.crl.go.jp/uk/uk223/service/nnw/index.html). During the period from February to October 1998, eleven storms occurred with minimum Dst values below −80 nT. For ten of these storms the differences between the predicted minimum Dst and the minimum Dst calculated from ground-based magnetometer data were less than 23%. For the remaining one storm (beginning on 19 October 1998) the difference was 48%. The discrepancy is likely to stem from a imperfect correlation between the solar wind parameters near ACE and those near the earth. While the IMF Bz remains to be the most important parameter, other parameters do have their effects. For instance, Dst appears to be enhanced when the azimuthal direction of IMF is toward the sun. A trapezoid-shaped increase in the solar wind density enhances the main phase Dst by almost 10% compared with the case of no density increase. Velocity effects appear to be stronger than the density effects. Our operational models have, in principle, no limitations in applicability with respect to storm intensity

Scandinavian IMS magnetometer array data and their use for studies ofgeomagnetic rapid variations

A data set which was newly open to the public from the World Data Center C2 for Geomagnetism is introduced. It was obtained from geomagnetic observations at 36 stations in Scandinavia during the International Magnetospheric Study (1977-1979). A few examples of analysis using the data are shown

Acceleration of PIC Simulation with GPU * )

Particle-in-cell (PIC) is a simulation technique for plasma physics. The large number of particles in highresolution plasma simulation increases the volume computation required, making it vital to increase computation speed. In this study, we attempt to accelerate computation speed on graphics processing units (GPUs) using KEMPO, a PIC simulation code package [H. Matsumoto and Y. Omura, Computer Space Plasma Physics, pp.21-65 (1985)]. We perform two tests for benchmarking, with small and large grid sizes. In these tests, we run KEMPO1 code using a CPU only, both a CPU and a GPU, and a GPU only. The results showed that performance using only a GPU was twice that of using a CPU alone. While, execution time for using both a CPU and GPU is comparable to the tests with a CPU alone, because of the significant bottleneck in communication between the CPU and GPU

3-D MHD model of the Sun-solar wind system : The first results

Toward the integrated numerical space weather prediction, we have been developing a three dimensional MHD simulation model of the sun-solar wind combining system. Here we describe the overview of the model and report on the first result of the simulation. Appling the unstructured grid system, we achieved the dense grid spacing at the inner boundary, which enable us to treat the fine structure near the sun, and a size of simulation space of 1AU, simultaneously. The magnetic field at the inner boundary is prescribed with the observational data of photospheric magnetic field during a specific time period. In order to obtain the supersonic solar wind, the parametric source functions are introduced into the energy equation and momentum equation. The source functions are in the exponentially dumping form as has been widely used in previous works. However the intensities of the source functions are newly adjusted so as to reflect the topology of the coronal magnetic field. They are increased inside the magnetic flux tube in sub-radial expansion and reduced inside the magnetic flux tube in over-radial expansion. This adjustment aims to reproduce the variation of the solar wind speed according to the coronal magnetic field. It is confirmed from the data comparison that the MHD model successfully reproduced many features both of the solar coronal region and the solar wind 3-D structure. With the further improvement and refinement, the model will be applied to the integrated space weather simulation system being developed at NiCT (National institute of Information and Communication Technology), Japan