Effect of temporal variation rate of cross polar cap potential on the equatorial ionospheric vertical drift: A statistical study

Based on the equatorial vertical ion drift measured by DMSP and cross polar cap potential (φ cpc) from AMIE output during 2001 to 2003, this paper investigates the relationship of φ cpc and its temporal variation rate (Δφ cpc) with the disturbed ion velocity (ΔV x ) which is the difference between the disturbed days (Kp⩾4) and quiet days (Kp<2). The statistical analysis shows: (1) The ΔV x correlates better with Δφ cpc than with ϕ cpc, indicating that the electric field penetration is more easily to occur when solar wind input rapidly varies with time. (2) The optimal delay time of electric field penetration from the high-latitude magnetosphere to equatorial ionosphere has local time dependence which is longer on the nightside than on the dayside. It may be due to more complicated electrodynamic process on the nightside. (3) With the linear relationship between Δϕ cpc and Δϕ V x , it is obtained that the penetration efficiency is about 4.5%–13.9% at day and 31%–42% at night, coinciding well with former studies.