The high energetic plasma and the embedded magnetic field of coronal mass ejections interact with planetary magnetospheres giving rise to transient perturbations such as geomagnetic storms. Predicting the geomagnetic impact of such interplanetary coronal mass ejections (ICME) is of utmost importance for the protection of our technological infrastructure that is affected by space weather. We use 3D compressible magnetohydrodynamic simulation of a star-planet system to model and study an ICME-Earth interaction event of 20th November 2003. In the modelled interaction, we observe a change in magnetopause shape and stand-off distance on ICME impact, day and night side reconnections and induction of high currents in the magnetosphere. We also notice the formation of a ring of strong equatorial current around the Earth, leading to a reduction of the geomagnetic field. We calculate the simulated reduction in the magnetic field and compare that to the observed geomagnetic indices in order to establish a predictive approach for geomagnetic storms. These simulations are expected to illuminate the physical processes that result in space weather impacts of stellar magnetic storms in planetary and exoplanetary systems.

Coronal mass ejections (CMEs), the large scale transient eruptions from the Sun, interact with the Earth’s magnetosphere while travelling into the heliosphere. The energetic interplanetary CME (ICME) at 1AU not only creates geomagnetic storms and disrupts the magnetic field structure around the Earth but also impacts the plasma environment, causes strong aurorae, and disturbs the radio and electrical transmission massively. We use 3D compressible magnetohydrodynamic simulation of a star-planet system and study the interesting magnetohydrodynamic processes like bow-shock, magnetopause, magnetotail, planet-bound current sheets, magnetic reconnections, atmospheric mass loss as well as particle injection, etc., when an ICME flux rope crosses the Earth at 1 AU. We use the uniformly twisted force-free flux rope model proposed by Gold and Hoyle in 1960 to initiate the ICME and vary the flux rope properties using actual observational data. We observe a change in magnetopause’s shape and the stand-off distance to the magnetopause. We notice twist helicity injection inside the magnetotail current system. We discover comparative increment in both the rates of atmospheric mass out-flow and solar wind in-flow in the vicinity of Earth during the geo-storm. Such studies will help us understand how energetic magnetic storms from a host star impact planetary magnetospheres and atmospheres with implications for planetary and exoplanetary habitability.