[P-EM09] Space Weather and Space Climate

[PEM09-P09] Fundamental research for the reanalysis data of the space weather based on the global MHD simulation

*Shigeru Fujita¹, Shin ya Nakano², Akira Kadokura³, Yoshimasa Tanaka³, Ryuho Kataoka⁴, Aoi Nakamizo⁵, Keisuke Hosokawa⁶, Satoko Saita⁷ (1.Research Organization of Information and Systems, Joint Support-Center for Data Science Research/The Institute of Statistical Mathematics, 2.Research Organization of Information and Systems, The Institute of Statistical Mathematics/Joint Support-Center for Data Science Research, 3.Research Organization of Information and Systems, Joint Support-Center for Data Science Research/National Institute of Polar Research, 4.Research Organization of Information and Systems, National Institute of Polar Research, 5.National Institute of Information and Communications Technology, 6.The University of Electro-Communications, 7.National Institute of Technology, Kitakyushu College)

Keywords:Space Weather, Data Assimilation, global MHD simulation

Introduction: It is almost impossible to obtain an accurate 3-D image of the magnetospheric phenomena only from the observations because the direct (in-situ) observations in the magnetosphere are quite sparse. Numerical simulations that accurately solve the physical first principles are powerful tools for studying phenomena occurring in the magnetosphere. When we can provide the grid-point-values of the plasmas in the magnetosphere-ionosphere system obtained from the simulation to the public, it may be very useful to the space weather society. These grid-point data can be called the “reanalysis data of the space weather” from the analogy of the meteorological reanalysis data. Therefore, we have started fundamental research on whether it is possible to create “space weather reanalysis data”. The final goal of the present research is to produce the grid-point values of the magnetosphere-ionosphere plasma processes and to make them publicly available.

Improvement of REPPU: For the purposes stated above, we, at first, improved the conventional global magnetosphere-ionosphere simulation code (this is REPPU by Tanaka [2015]) to include both the effect of the inclined rotation axis of the Earth and the effect of the discrepancy between the rotational axis and the magnetic axis. In addition, the improved REPPU utilizes all three components of the IMF and solar wind velocity from the quality-controlled OMNI database.

Feasibility study: To create the reanalysis data, we need to utilize the data assimilation technique to assure that the numerical data are realistic because REPPU employs several empirical parameters. For this purpose, we performed the feasibility study of the improved REPPU by comparing the simulation results and observations. So we evaluated how the improved REPPU reproduces the observations by using SuperDARN electric potential data, AMPERE field-aligned current data, and AE indices. It is noted that the magnetospheric observations cannot be used for the evaluation because the data distribution is too sparse. As a result, we confirmed that the improved REPPU reproduces considerably observed ionospheric potential and AE indices. Finally, we conclude that the improved REPPU reasonably reproduces plasma processes of the real magnetosphere-ionosphere phenomena.

Determination of the ionospheric conductivity by data assimilation: The improved REPPU assumes the ionospheric conductivities controlled by electron precipitation, the ion precipitation, and the ratio between the Pedersen conductivity and the Hall conductivity. The ionospheric electric potential and the current in the ionosphere in the simulation are dependent on arbitrary factors that determine the ionospheric conductivities. Then, by using the DP2 event that occurred in 2015 09 06, we determined the factors by the four-dimensional ensemble-based variational method [Lorenc, 2003]. We confirmed that the data assimilation technique works well and determined the suitable ionospheric conductivity distribution. Finally, we obtained the “reanalysis space weather data” of this DP2 event.

URL of the “reanalysis space weather data”: The “reanalysis space weather data” including the IDL codes that handle these data are open to the public now at https://github.com/iugonet/Udas/tree/master/iugonet/tools. We intend to add more events to this site soon.

Acknowledgments
This research was supported by "Challenging Exploratory Research Projects for the Future" grant from ROIS (Research Organization of Information and Systems).

References
Lorenc, A. C., (2003), The potential of the ensemble Kalman filter for NSP: A comparison with 4D-Var., Quart. J. Roy. Meteor. Soc., 129, 3183-3203
Tanaka, T. (2015), Substorm auroral dynamics reproduced by the advanced global M-I coupling simulation, In Auroral dynamics and space weather, Geophys. Monogr. Ser., vol. 215, edited by Y. Zhang and L. J. Paxton, p. 177, doi: 10.1002/9781118978719, AGU, Washington D. C.