Fig. 5 shows the IMF Bz and IEF Ey measured by
the ACE satellite, the Dst index, and the ionospheric
plasma E B drift velocities and penetration
electric field at magnetic equator simulated for the
magnetic storm of 31 March 2001 with the CTIPe and RCM models. Initial results from simulation of
this event were presented in Maruyama et al. (2005).
The vertical dotted lines indicate the main phase of
the magnetic storm between 0400 and 0800 UT with
continuously southward IMF. Fig. 5d shows the
equatorial ionospheric plasma velocities caused by
different processes. The blue line represents the
vertical plasma E B drift velocity driven by the
penetration electric field (PEF) alone, the green line
represents the drift velocity driven by neutral wind
disturbance dynamo (DD) alone, the red line
represents the total drift velocity that is obtained
from a simulation including the effects of disturbance
dynamo and penetration electric fields
together, and the black line represents the quiettime
reference plasma drift velocity. These simulated
data are taken at geographic longitude 122,
and local time (LT) at this longitude is about
UT þ 9 h. An important result is that the penetration
electric field is dominant during the main phase
of the storm and lasts for 4 h until the IMF turns
northward. The contribution from the neutral disturbance dynamo is much smaller than that of
penetration electric field during the main phase of
the storm and during daytime (Maruyama et al.,
2005, 2007). The disturbance dynamo tends to
reduce the daytime drift velocity. The disturbance
dynamo effect becomes increasingly important after
0900 UT. Huang et al. (2005b) show that the IEF
can penetrate to the low-latitude ionosphere without
obvious decay for several hours during the main
phase of magnetic storms as long as the IMF
remains southward. The simulations reproduce the
occurrence of long-duration penetration electric
fields and are very consistent with the observations
of Huang et al. (2005b).