Response of the magnetic field and plasmas at the geosynchronous orbit to interplanetary shock

Interplanetary shock can greatly disturb the Earth’s magnetosphere and ionosphere, causing the temporal and spatial changes of the magnetic field and plasmas at the geosynchronous orbit. In this paper, we use the magnetic field data of GOES satellites from 1997 to 2007 and the plasma data of MPA on the LANL satellites from 1997 to 2004 to study the properties of magnetic field and plasma (0.03–45 keV) at the geosynchronous orbit (6.6 R _E) within 3 hours before and after the arrival of shock front at the geosynchronous orbit through both case study and superposed epoch analysis. It is found that following the arrival of shock front at the geosynchronous orbit, the magnetic field magnitude, as well as GSM BZ component increases significantly on the dayside (8–16 LT), while the B _Y component has almost no change before and after shock impacts. In response to the interplanetary shock, the proton becomes much denser with a peak number density of 1.2 cm⁻³, compared to the typical number density of 0.7 cm⁻³. The proton temperature increases sharply, predominantly on the dusk and night side. The electron, density increases dramatically on the night side with a peak number density of 2.0 cm⁻³. The inferred ionospheric O⁺ density after the interplanetary shock impact reaches the maximum value of 1.2 cm⁻³ on the dusk side and exhibits the clear dawn-dusk asymmetry. The peak of the anisotropy of proton’s temperature is located at the noon sector, and the anisotropy decreases towards the dawn and dusk side. The minimum of temperature anisotropy is on the night side. It is suggested that the electromagnetic ion cyclotron (EMIC) wave and whistler wave can be stimulated by the proton and electron temperature anisotropy respectively. The computed electromagnetic ion cyclotron wave (EMIC) intense on the day side (8–16 LT) with a frequency value of 0.8 Hz, and the wave intensity decreases towards the dawn and dusk side, the minimum value can be found on the night side. The computed electron whistler wave locates on the day side (8–16 LT) with a value of 2 kHz.