Reconstructing coronal hole areas with EUHFORIA and adapted WSA model: optimising the model parameters

The adopted WSA model embedded in EUHFORIA (EUropean Heliospheric FORecasting Information Asset) is compared to EUV observations. According to the standard paradigm coronal holes are sources of open flux thus we use remote sensing EUV observations and \textsc{catch} (Collection of Analysis Tools for Coronal Holes) to extract CH areas and compare them to the open flux areas modelled by EUHFORIA. From the adopted WSA model we employ only the Potential Field Source Surface (PFSS) model for the inner corona and the Schatten Current Sheet (SCS) model for the outer (PFSS+SCS). The height, $R_{\rm ss}$, of the outer boundary of the PFSS, known as the source surface, and the height, $R_{\rm i}$, of the inner boundary of the SCS are important parameters affecting the modelled CH areas. We investigate the impact the two model parameters can have in the modelled results. We vary $R_{\rm ss}$ within the interval [1.4, 3.2]$R_{\rm \odot}$ with a step of 0.1$R_{\rm \odot}$, and $R_{\rm i}$ within the interval [1.3, 2.8]$R_{\rm \odot}$ with the same step, and the condition that $R_{\rm i}<R_{\rm ss}$. This way we have a set of 184 initial parameters to the model and we assess the model results for all these possible height pairs. We conclude that the default heights used so far fail in modelling accurately CH areas and lower heights need to be considered.

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