Numerical study on the solar modulation of low-energy cosmic rays measured with CALET

JAXA Supercomputer System Annual Report February 2022-January 2023

Report Number: R22EACA51

Subject Category: JSS Inter-University Research

Responsible Representative: Shoko Miyake, Associate Professor, National Institute of Technology (KOSEN), Ibaraki College
Contact Information: Shoko Miyake(miyakesk@ee.ibaraki-ct.ac.jp)
Members: Shoko Miyake

Abstract

We reveal the solar modulation of the galactic cosmic ray that is the relationship between the solar activity and the variation of the flux of low-energy particles, performing the numerical calculation of the cosmic-ray propagation in the heliosphere and the magnetosphere.

Reference URL

N/A

Reasons and benefits of using JAXA Supercomputer System

This project needs a large amount of computational resources for the following two reasons: We have to calculate the cutoff rigidity for each event measured by CALET.; We need to iteratively calculate and be compared with observations to find the best solar modulation model that reproduce the observations.

Achievements of the Year

We have improved the drift model of the cosmic-ray modulation considering a non-linear diffusion process by introducing the variation of the fraction of the magnetic fluctuation. The variation of the fraction of the magnetic fluctuation affects the diffusion coefficient and the decay rate of drift motion. By introducing the observed fraction of the magnetic fluctuation to these terms, we have found that the monthly variation of the cosmic-ray intensity becomes larger than those without considering them. Although no clear correlation was obtained between the small-scale variation of the cosmic-ray intensity obtained by numerical calculations and those observed by AMS-02 and ground-based neutron monitors in this preliminary result, we have confirmed that details of the variation depend on how the parameters about the magnetic fluctuations are set. We will continue to investigate the best diffusion coefficient model, and also proceed with the introduction of latitudinal dependence of solar wind velocity.

In the analysis of low-energy electron and proton events observed by CALorimetric Electron Telescope (CALET), we have calculated the effective cutoff rigidity by reconstructing particle trajectories in the magnetosphere, implementing a realistic description of the geomagnetic field based on the IGRF-13 and TS05 empirical models, as in the previous year. The calculation of the cutoff rigidity up to January 2023 has been completed, and the analysis of low-energy electron and proton intensities is underway by using these results to select events that are not affected by the geomagnetic cutoff variation from low-energy particle events detected by CALET. Further refinement of the cosmic-ray modulation model is expected by using precise results of low-energy electrons and protons observed by CALET, which cover the descending and ascending phase in the solar cycle.

Publications

– Oral Presentations

1) Modeling the Solar Modulation Based on the Nonlinear Cosmic-Ray Diffusion Process, S. Miyake, 44th COSPAR Scientific Assembly, Athens Greece, July, 2022.

2) Effect of the 11-year variation of the random magnetic field on the cosmic ray modulation, JPS 2022 Autumn Meeting, Okayama, Sep., 2022.

3) Charge-sign dependence of the solar modulation observed with CALET for seven years, JPS 2023 Spring Meeting, online, March, 2023.

Usage of JSS

Computational Information

Process Parallelization Methods: N/A
Thread Parallelization Methods: OpenMP
Number of Processes: 1
Elapsed Time per Case: 24 Hour(s)

JSS3 Resources Used

Fraction of Usage in Total Resources*1(%): 0.12

Details

Please refer to System Configuration of JSS3 for the system configuration and major specifications of JSS3.

Computational Resources
System Name	CPU Resources Used (Core x Hours)	Fraction of Usage*2(%)
TOKI-SORA	0.00	0.00
TOKI-ST	986568.79	0.99
TOKI-GP	0.00	0.00
TOKI-XM	0.00	0.00
TOKI-LM	0.00	0.00
TOKI-TST	0.00	0.00
TOKI-TGP	0.00	0.00
TOKI-TLM	0.00	0.00

File System Resources
File System Name	Storage Assigned (GiB)	Fraction of Usage*2(%)
/home	10.00	0.01
/data and /data2	100.00	0.00
/ssd	100.00	0.01

Archiver Resources
Archiver Name	Storage Used (TiB)	Fraction of Usage*2(%)
J-SPACE	0.00	0.00

*1: Fraction of Usage in Total Resources: Weighted average of three resource types (Computing, File System, and Archiver).

*2: Fraction of Usage：Percentage of usage relative to each resource used in one year.

ISV Software Licenses Used

ISV Software Licenses Resources
	ISV Software Licenses Used (Hours)	Fraction of Usage*2(%)
ISV Software Licenses (Total)	0.00	0.00

*2: Fraction of Usage：Percentage of usage relative to each resource used in one year.