Research On The Effect Of Geomagnetic Storms On The Orbit Variations Of SWARM Satellites

Thermospheric density changes caused by solar radiation or solar storms are considered to be the largest factors affecting the operation of low-orbit satellites.This paper studies the effects of thermospheric density changes on SWARM satellite orbits caused by space weather events.Using the orbit data of the SWARM satellite from GPS,the thermospheric neutral density data derived from the precision orbit counter,the model of the semi axis variation of the low-orbit satellite calculated by Chen(2014),the GOCOO1 S gravity field model with the 80 th order input as well as the intensity of the Dst index which is a measure of the intensity of magnetic storms,we calculated the mean semi-major axis,mean semi-major axis orbital decay rate and satellite mechanical energy loss of the two different altitude flying SWARM satellites under different intensities of magnetic storms.The results show that the orbital physical parameters such as the mean semi-major axis are positively correlated with the intensity of the magnetic storm.The orbital variation of the SWARM satellite at low altitude is much more obvious than that orbiting at high altitude during the same magnetic storm event.The time when the satellite orbit begins to decay is significantly ahead of the time when the Dst index starts decreasing negative.The correlation of orbit decaying with the Ap and AE indices is much better,indicating that the geomagnetic activity at the middle and high latitudes is an important factor for the thermospheric density change.Finally,the physical mechanism of upper atmosphere changes during geomagnetic storms is discussed.We find that the correlation between the increase of atmospheric density at the satellite altitude and the southward component of the interplanetary magnetic field is better.It indicates that particles are injected into the ionosphere and the thermosphere from the magnetosphere accompanying the solar wind particle injections during the period of solar storm.The solar wind particles then collide with thermospheric molecules to heat the atmosphere,causing the increase of neutral density.Using the empirical relationship between the convective electric field model of the Weimer 1996 and the height integrated Pedersen conductivity,the Joule heating of the thermosphere and ionosphere is calculated during the magnetic storm.We find that the Joule heating is obviously enhanced during the storm interval.This means that,during the interval of solar storm,the increase of the dissipation caused by the Pedersen conductivity along the direction of electric field releases a large amount of heat energy.These energy drives the expansion of the thermosphere,causing the density at the satellite altitude to rise suddenly.Then the drag of the satellite is increased And the energy of the satellite in the whole system is continuously reduced.Finally,with the continuous accumulation of small changes,it causes obvious orbit decay of the mean semi-major axis and the energy loss.