Arrival Time Estimates of Earth-Directed CME-Driven Shocks

Abstract

We report on the travel times of 19 interplanetary (IP) shocks driven by Earth-directed coronal mass ejections (CMEs) that occurred from 2010 to 2017. We track the shocks ahead of CMEs using the graduated cylindrical shell (GCS) model constructed from multiple-view observations from the Solar TErrestrial RElations Observatory (STEREO) and Solar and Heliospheric Observatory (SOHO) coronagraphs. We calculate the Earthward speed of the shocks from the height-time data obtained from the GCS fit that we use as input to the Empirical Shock Arrival (ESA) model to predict the shock travel times to 1 AU. We find that the mean absolute deviation (MAD) of the predicted IP shock travel time from the observed travel time is about 6.1 hours. The prediction error ranges from −14.3 hours to +13.1 hours with a standard deviation of 7.5 hours. The MAD and RMS errors are significantly smaller than those in the previous report (Gopalswamy et al., Space Weather11, 661, 2013), which used SOHO-STEREO quadrature observations to obtain the Earthward speed of halo CMEs. The χ²-test confirms the high consistency level between predicted and observed travel times. These results suggest that the three-dimensional speeds of shocks can be derived using the GCS model outside of quadrature intervals and can be used in the determination of shock travel times.