Development of a formalism for computing in situ transits of Earth-directed CMEs. Towards a forecasting tool II

Abstract. Earth-directed coronal mass ejections (CMEs) are of an important interest for space weather purposes, because they are precursors of the major geomagnetic storms. The geoeffectiveness of a CME mostly relies on its physical properties like magnetic field and speed. There are multiple efforts in the literature to estimate in situ transit profiles of CMEs, most of them based on numerical codes. In this work we present a semi-empirical formalism to compute in situ transit profiles of Earth-directed fast halo CMEs. Our formalism combines analytic models and empirical relations to approximate CME properties as would be seen by a spacecraft near the Earth's orbit. We use our formalism to calculate synthetic transit profiles for 10 events, including the Bastille day event and three varSITI Campaign events. Our results showed qualitative agreement with in situ measurements. Synthetic profiles of speed, magnetic intensity, density and temperature of protons had average errors of 10 %, 27 %, 46 % and 83 %, respectively. Additionally, we also computed the travel time of CME centers, with an average error of 9 %. We found that compression of CMEs by the surrounding solar wind significantly increased our uncertainties. We also outline a possible path to apply this formalism into a space weather forecasting tool.