[1] Concurrent type 1 and type 2 radar returns from sporadic E (Es) irregularities detected by the Chung-Li VHF radar are analyzed and discussed in this paper. For the present case the mean Doppler velocities of the type 1 echoes lasting similar to8 min are between similar to250 and 302 m/s, smaller than those observed in equatorial and auroral regions. The backscatter from type 1 irregularities is greater than that from type 2 irregularities by similar to6-8 dB. Interferometry analysis indicates that the echo patterns of the type 1 and type 2 irregularities projected in mutually orthogonal planes are striation-like, strongly suggesting that the plasma structure associated with the irregularities is in a form of thin slab. The plasma slab with thickness of similar to1-2.5 km locates in the height range from similar to104 to 107 km. The horizontal extents of the type 1 irregularities in the striation-like echoing region range from 12.7 to 6.8 km in the east-west direction and from at least 7.2 to 5.1 km in the north-south direction. The observational evidences that the slab structure has sharp edges in lateral edges and the type 1 irregularities drift in the meridional direction favor the slab model proposed by Haldoupis et al. [1996] to account for the excitation of the midlatitude type 1 irregularities. However, the other observations, including considerably large zonal extent of type 1 irregularities in the plasma slab and wide coverage of zonal polarization electric field, are unfavorable to the slab model. In addition, we present conclusive evidence in this article to show that the range variation of backscatter from Es irregularities may result directly from the zonal bulk movement of the Es irregularities in the echoing region rather than from the height variation of the irregularities. Therefore great caution should be taken in analyzing the dynamic behavior of Es irregularities from range-time-intensity plot.
