For the period July 2003 to August 2010 , the interplanetary coronal mass ejection ( ICME ) catalogue maintained by Richardson and Cane lists 106 Earth-directed events , which have been measured in-situ by plasma and field instruments on–board the ACE satellite .
We present a statistical investigation of the Earth ’ s thermospheric neutral density response by means of accelerometer measurements collected by the GRACE satellites , which are available for 104 ICMEs in the data set , and its relation to various geomagnetic indices and characteristic ICME parameters such as the impact speed ( v _ { max } ) , southward magnetic field strength ( B _ { z } ) .
The majority of ICMEs causes a distinct density enhancement in the thermosphere , with up to a factor of eight compared to the pre–event level .
We find high correlations between ICME B _ { z } and thermospheric density enhancements ( \approx 0.9 ) , while the correlation with the ICME impact speed is somewhat smaller ( \approx 0.7 ) .
The geomagnetic indices revealing the highest correlations are Dst and SYM-H ( \approx 0.9 ) , the lowest correlations are obtained for k _ { p } and AE ( \approx 0.7 ) , which show a nonlinear relation with the thermospheric density enhancements .
Separating the response for the shock sheath region and the magnetic structure of the ICME , we find that the Dst and SYM-H reveal a tighter relation to the B _ { z } minimum in the magnetic structure of the ICME , whereas the polar cap indices show higher correlations with the B _ { z } minimum in the shock sheath region .
Since the strength of the B _ { z } component—either in the sheath or the magnetic structure of the ICME—is highly correlated ( \approx 0.9 ) with the neutral density enhancement , we discuss the possibility of satellite orbital decay estimates based on magnetic field measurements at L1 , i.e .
before the ICME hits the Earth magnetosphere .
These results are expected to further stimulate progress in space weather understanding and applications regarding satellite operations .