Modelling the magnetic vectors of ICMEs at different heliocentric distances with INFROS

TL;DR

This study validates the INFROS model for predicting ICME magnetic fields at different distances, showing high accuracy for isolated events and limitations during interactions with streams, emphasizing the importance of inner observations.

Contribution

The paper demonstrates the effectiveness of INFROS in forecasting ICME magnetic fields and highlights the impact of stream interactions on model accuracy and ICME evolution.

Findings

Model accurately predicts magnetic fields for isolated ICMEs.

Interactions with streams reduce model accuracy at outer distances.

Self-similar expansion assumption provides a lower limit for magnetic field strength.

Abstract

The INterplanetary Flux ROpe Simulator (INFROS) is an observationally constrained analytical model dedicated for forecasting the strength of the southward component (Bz) of the magnetic field embedded in interplanetary coronal mass ejections (ICMEs). In this work, we validate the model for six ICMEs sequentially observed by two radially-aligned spacecraft positioned at different heliocentric distances. The six selected ICMEs in this study comprise of cases associated with isolated CME evolution as well as those interacting with high-speed streams (HSS) and high-density streams (HDS). For the isolated CMEs, our results show that the model outputs at both the spacecraft are in good agreement with in-situ observations. However, for most of the interacting events, the model correctly captures the CME evolution only at the inner spacecraft. Due to the interaction with HSS and HDS, which in most cases occurred at heliocentric distances beyond the inner spacecraft, the ICME evolution no longer remains self-similar. Consequently, the model underestimates the field strength at the outer spacecraft. Our findings indicate that constraining the INFROS model with inner spacecraft observations significantly enhances the prediction accuracy at the outer spacecraft for the three events undergoing self-similar expansion, achieving a 90 % correlation between observed and predicted Bz profiles. This work also presents a quantitative estimation of the ICME magnetic field enhancement due to interaction which may lead to severe space weather. We conclude that the assumption of self-similar expansion provides a lower limit to the magnetic field strength estimated at any heliocentric distance, based on the remote sensing observations.