Proceedings with Extended Abstracts (single PDF file) - Radio ...

1996 and high in 2002). The electric field observed during the downleg is shown in Figure 2.The electric field seems to have a offset directed to westward with an amplitude of 2 to 3mV/m. A similar offset during the downleg is also found in the SEEK observation. The reasonof the offset is not clear, but the wake of the rocket may cause this type of offset because thewake is larger during the downleg than the upleg and the nearly eastward rocket trajectoryproduce the wake at the west side of the rocket. Except the offset, 10 km-scale modulation ofelectric field was still observed above 110 km, and the peak of the magnitude exists at 103 km.The results below 100 km are not reliable because of the unstable rocket attitude.(a) (b) (c) (d)Figure 1. Electric field measured by EFD during the upleg.(a) (b) (c) (d)Figure 2. Electric field measured by EFD during the downleg.3. NUMERICAL SIMULATIONYokoyama et al. [2003a, b] showed with 2-D and 3-D numerical simulation models thatintense polarization electric fields can be generated in association with inhomogeneous Eslayer. One of the results is shown in Figure 3. The plasma cloud that has a Gaussiandistribution in the meridional plane with a maximum density of 4 x 10 5 cm -3 is assumed at 100km. The half width of the distribution is 3.3 km and the zonal elongation is 15 km. Ahorizontal Es layer with a maximum density of 1.1 x 10 5 cm -3 is assumed at the same altitude.The conductivity integrated over the F-region is added at the top boundary. As an externalforce, we apply a southward neutral wind which has a Gaussian distribution with themaximum amplitude of 70 m/s at 100 km. In response to the southward neutral wind,polarization electric fields of northward/upward direction are generated to maintain the127