Numerical Simulation of Heliospheric Transients Approaching Geospace

摘要

This one-year long project supported graduate student's participation on the verification of numerical simulations of heliospheric transients approaching geospace. Coronal mass ejections (CMEs) represent a prime causal link between solar activity and large geomagnetic storms, and numerical modeling plays a critical role in space weather research and forecasting. Numerical code ENLIL is used for heliospheric simulations at Center for Integrated Space Weather Modeling (CISM) and Community Coordinated Modeling Center (CCMC), and it was selected for transitioning to operations by NOAA Space Weather Prediction Center (SWPC). The project supported testing and verification of ENLIL in two areas. Firstly, we investigated effect of numerical resolution on interplanetary shocks. We found that while shocks are shapper and locally corrugated on very fine numerical grids, 'medium' grid (radial spacing of 0.8 Rs, angular spacing of 2 deg) is sufficient for predicting arrival time of CMEs and their strength at geospace. This enables to run four simulations per day on current 32-procs systems. Finally, we investigated accuracy of the cone model fitting technique that uses coronagraph observations of CMEs and determines the location, diameter, and initial speed of ejecta launched into the heliospheric computational domain. We used multi- perspective coronagraph observations, a unique opportunity provided by NASA twin STEREO spacecraft, to verify accuracy of cone model fitting on selected CMEs. We found large differences between the initial CME speeds fitted by cone- model and stereo-model techniques but slightly smaller differences in arrival times to geospace (due to larger deceleration of faster CMEs).