Validation of coronal mass ejection arrival-time forecasts by magnetohydrodynamic simulations based on interplanetary scintillation observations

Kazumasa Iwai,Munetoshi Tokumaru,Mitsue Den,Yûki Kubo,Ken’Ichi Fujiki,Daikou Shiota

doi:10.1186/s40623-020-01345-5

Abstract

Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrival time is very important. However, forecasting accuracy is hindered by limited CME observations in interplanetary space. This study investigates the accuracy of CME arrival times at the Earth forecasted by three-dimensional (3D) magnetohydrodynamic (MHD) simulations based on interplanetary scintillation (IPS) observations. In this system, CMEs are approximated as spheromaks with various initial speeds. Ten MHD simulations with different CME initial speed are tested, and the density distributions derived from each simulation run are compared with IPS data observed by the Institute for Space-Earth Environmental Research (ISEE), Nagoya University. The CME arrival time of the simulation run that most closely agrees with the IPS data is selected as the forecasted time. We then validated the accuracy of this forecast using 12 halo CME events. The average absolute arrival-time error of the IPS-based MHD forecast is approximately 5.0 h, which is one of the most accurate predictions that ever been validated, whereas that of MHD simulations without IPS data, in which the initial CME speed is derived from white-light coronagraph images, is approximately 6.7 h. This suggests that the assimilation of IPS data into MHD simulations can improve the accuracy of CME arrival-time forecasts. The average predicted arrival times are earlier than the actual arrival times. These early predictions may be due to overestimation of the magnetic field included in the spheromak and/or underestimation of the drag force from the background solar wind, the latter of which could be related to underestimation of CME size or background solar wind density.

Highlights

Coronal mass ejections (CMEs) are eruptions of magnetized plasma structures generated by solar eruptive phenomena such as flares
The real-time forecast result using the WSA-ENLIL-Cone model is archived in the Community Coordinated Modeling Center (CCMC) CME Scoreboard
If the CME with the initial speed estimated from Large Angle and Spectrometric Coronagraph (LASCO) or Computer-aided CME tracking software (CACTus) shows the best match to the interplanetary scintillation (IPS), IPS- and LASCO- or CACTus-based forecasting will exhibit the same arrival time

Summary

Introduction

Coronal mass ejections (CMEs) are eruptions of magnetized plasma structures generated by solar eruptive phenomena such as flares. Many studies have attempted to forecast CME arrival using empirical models (e.g., Gopalswamy et al 2001), and global magnetohydrodynamic (MHD) simulations of the heliosphere such as ENLIL (Odstrcil 2003), SUSANOO (Shiota et al 2014; Shiota and Kataoka 2016), and EUHFORIA (Pomoell and Poedts 2018). These simulations calculate the background solar wind from magnetic field data of the solar surface and empirical models of the solar wind speed The modeled CMEs are placed at the inner boundary, which is approximately a few tens of solar radii (Rs), and their propagation is simulated to 1 AU

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