Bi-modal distribution of substorm intensity

Akira Morioka; Yoshizumi Miyoshi; Masahito Nose

Presentation information

Oral

Symbol P (Space and Planetary Sciences) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM18] Dynamics in magnetosphere and ionosphere

Wed. May 25, 2016 10:45 AM - 12:15 PM 103 (1F)

Convener:*Tomoaki Hori(Institute for Space-Earth Environmental Research, Nagoya University), Yoshimasa Tanaka(National Institute of Polar Research), Aoi Nakamizo(Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology), Mitsunori Ozaki(Faculty of Electrical and Computer Engineering, Institute of Science and Engineering, Kanazawa University), Shin'ya Nakano(The Institute of Statistical Mathematics), Yoshizumi Miyoshi(Institute for Space-Earth Environmental Research, Nagoya University), Chair:Yukinaga Miyashita(Institute for Space-Earth Environmental Research, Nagoya University), Keisuke Hosokawa(Department of Communication Engineering and Informatics, University of Electro-Communications), Yoshimasa Tanaka(National Institute of Polar Research), Shin'ya Nakano(The Institute of Statistical Mathematics)

12:00 PM - 12:15 PM

[PEM18-06] Bi-modal distribution of substorm intensity

*Akira Morioka¹, Yoshizumi Miyoshi², Masahito Nose³ (1.Planetary Plasma and Atmosphere Recearch Center,Guraduate School,Tohoku University, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.Graduate School of Science, Kyoto University)

Keywords:substorm, intensity distribution, lognormal distribution

One of the essential issues in substorm study is how is the substorm intensity distributed and what determines the distribution. In this study, the substorm intensity (AL index at substorm) distribution is statistically studied using the Wp index provided by WDC for Geomag, Kyoto University and OMNI data base. The results showed that substorm intensity distribution is composed of bi-modal peaks with lognormal distribution. The major peak is in small AL range around 100 nT (named group-S substorm) and the secondary peak is around 300 nT (named group-L substorm). The bi-modal distribution of substorm intensity means that substorm is not a continuum state between pseudo-substorms and full substorms as has been discussed. The solar cycle variation of the substorm intensity distribution showed that group-S substorms occure rather constantly during a solar cycle, whereas the appearance of group-L substorms is strongly dependent with the solar activity. These observations suggest that two different substorm processes are working in the magnetosphere or different solar wind-magnetosphere interaction processes are operating.