Implementing the MULTI-VP coronal model in EUHFORIA: Test case results and comparisons with the WSA coronal model

Abstract

Context. In this study, we focus on improving EUHFORIA (European Heliospheric Forecasting Information Asset), a recently developed 3D MHD space weather prediction tool. EUHFORIA consists of two parts, covering two spatial domains; the solar corona and the inner heliosphere. For the first part, the semi-empirical Wang-Sheeley-Arge (WSA) model is used by default, which employs the Potential Field Source Surface (PFSS) and Schatten Current Sheet (SCS) models to provide the necessary solar wind plasma and magnetic conditions above the solar surface, at 0.1 AU, that serve as boundary conditions for the inner heliospheric part. Herein, we present the first results of the implementation of an alternative coronal model in EUHFORIA, the so-called MULTI-VP model. Aims. After we replace the default EUHFORIA coronal set-up with the MULTI-VP model, we compare their outputs both at 0.1 AU and 1 AU, for test cases involving high speed wind streams (HSSs). We select two distinct cases where the standard EUHFORIA set-up failed to reproduce the HSS plasma/magnetic signatures at Earth, in order to test the performance of MULTI-VP coupled with EUHFORIA-heliosphere. Methods. To understand the quality of modeling with MULTI-VP in comparison with the default coronal model in EUHFORIA, we considered one HSS case during a period of low solar activity and another one during a period of high solar activity. Moreover, the modeling of the two HSSs was performed by employing magnetograms from different providers; one from the Global Oscillation Network Group (GONG) and the second from the Wilcox Space Observatory (WSO). This way, we were able to distinguish differences arising not only because of the different models but also because of different magnetograms. Results. The results indicate that when employing a GONG magnetogram, the combination MULTI-VP+EUHFORIA-heliosphere reproduces the majority of HSS plasma and magnetic signatures measured at L1. On the contrary, the standard WSA+EUHFORIAheliosphere combination does not capture the arrival of the HSS cases at L1. When employing WSO magnetograms, MULTIVP+EUHFORIA-heliosphere reproduces the HSS that occurred during the period of high solar activity while it is ambiguous if it models the HSS during the period of low solar activity. For the same magnetogram and periods of time, WSA+EUHFORIAheliosphere is not able to capture the HSSs of interest. Conclusions. The results show that the accuracy of the simulation output at Earth depends on the choice of both the coronal model and the input magnetogram. Nevertheless, a more extensive statistical analysis is necessary to determine how precisely these choices affect the quality of the solar wind predictions.