Speaker
Mr
Masayoshi Kozai
(Department of Physics, Shinshu University)
Description
Galactic cosmic ray (GCR) depleted regions behind the interplanetary shocks or disturbances cause the Forbush decreases (Fds), short term decreases of the GCR isotropic intensity (or GCR density) at the Earth. We can deduce the geometries of the depleted regions from three-dimensional GCR anisotropy associated with Fds, because the first order anisotropy reflects the spatial gradient of GCR density. Deriving the dynamic variation of GCR anisotropy using a single detector, however, has been difficult because the traditional analyses based on the diurnal variation of GCR intensity provide only the daily mean equatorial anisotropy. The present GMDN consisting of four multi-directional muon detectors in Nagoya (Japan), Hobart (Australia), São Martinho da Serra (Brazil) and Kuwait city (Kuwait) started operation in 2006 and successfully observed dynamic variations of GCR anisotropy associated with major Fd events. In this presentation, we analyze the average features of GCR anisotropy and density gradient associated with shocks identified by the geomagnetic storm sudden commencement (SSC) during a period between 2006 and 2014. We analyze about 120 SSC events classified into two groups associated with coronal mass ejections (CMEs) and corotating interaction regions (CIRs). From the first order anisotropy corrected for the solar wind convection and Compton-Getting effect arising from Earth's orbital motion around the sun, we deduce the three-dimensional density gradient on hourly basis for each SSC event. We then derive the average temporal variations of the anisotropy and density gradient by superposing variations at the SSC onset timing. In the CME event, the anisotropy vector shifts sunward before the SSC onset, implying the flow of GCRs reflected by the shock. We also confirm that the density gradient components are clearly enhanced in the both of CME and CIR events, indicating the geometry of the GCR depleted region. We discuss the physical implications of the obtained geometries.
| Registration number following "ICRC2015-I/" | 0143 |
|---|---|
| Collaboration | -- not specified -- |
Primary author
Mr
Masayoshi Kozai
(Department of Physics, Shinshu University)
Co-authors
Dr
Alisson Dal Lago
(National Institute for Space Research (INPE))
Prof.
Chihiro Kato
(Department of Physics, Shinshu University)
Prof.
Hala. K. Al Jassar
(Physics Department, Faculty of Science, Kuwait University)
Prof.
Ismail Sabbah
(Department of Natural Sciences, Collage of Health Sciences, the Public Authority of Applied Education and Training, Kuwait)
Dr
John E. Humble
(School of Physical Sciences, University of Tasmania)
Prof.
John W. Bieber
(Bartol Research Institute and Department of Physics and Astronomy, University of Delaware)
Prof.
Kazuoki Munakata
(Department of Physics, Shinshu University)
Prof.
Madan M. Sharma
(Physics Department, Faculty of Science, Kuwait University)
Dr
Marcus L. Duldig
(School of Physical Sciences, University of Tasmania)
Dr
Marlos Rockenbach
(Southern Regional Space Research Center (CRS/INPE))
Prof.
Munetoshi Tokumaru
(Solar-Terrestrial Environment Laboratory, Nagoya University)
Dr
Nelson J. Schuch
(Southern Regional Space Research Center (CRS/INPE))
Prof.
Paul Evenson
(Bartol Research Institute and Department of Physics and Astronomy, University of Delaware)
Dr
Takao Kuwabara
(International Center for Hadron Astrophysics, Chiba University)
