Modelling non-radially propagating coronal mass ejections and forecasting the time of their arrival at Earth

We present the study of two solar eruptive events observed on December 7 2020 and October 28 2021.Both events were associated with full halo CMEs and flares.These events were chosen because they show a strong non-radial direction of propagation in the low corona and their main propagation direction is not fully aligned with the Sun-Earth line.This characteristic makes them suitable for our study, which aims to inspect how the non-radial direction of propagation in the low corona affects the time of CMEs' arrival at Earth.We reconstructed the CMEs using coronagraph observations and modelled them with EUHFORIA and the cone model for CMEs.To compare the accuracy of forecasting the CME arrival time at Earth obtained from different methods, we also used so-called typeII bursts, radio signatures of associated shocks, to find the velocities of the CME-driven shocks and forecast the time of their arrival at Earth.We also estimated the CME arrival time using the 2D CME velocity.Our results show that the lowest accuracy of estimated CME Earth arrival times is found when the 2D CME velocity is used.The velocity of the typeII radio bursts provides better, but still not very accurate, results.Employing, as an input to EUHFORIA, the CME parameters obtained from the GCS fittings at consequently increasing heights, results in a strongly improved accuracy of the modelled CME and shock arrival time Delta t changes from 14h to 10min for the first event, and from 12h to 30min for the second one.This improvement shows that when we increased the heights of the GCS reconstruction we accounted for the change in the propagation direction of the studied CMEs, which allowed us to accurately model the CME flank encounter at Earth. Our results show the great importance of the change in the direction of propagation of the CME in the low corona when modelling CMEs and estimating the time of their arrival at Earth.