Upper E region field-aligned echoes over Chung-Li radar
Chien-Ya Wang1, Ting-An Lin2 ,Yen-Hsyang Chu2
1Department of Optoelectric Physics, Chinese Culture University, Taipei, Taiwan, R.O.C.
2Institute of Space Science, National Central University, Chung-Li, Taiwan, R.O.C.
In this report the field-aligned echoes detected by Chung-Li VHF radar occurred at height 120~150 km, which is called the upper E region echoes, will be presented. These echoes rarely detected by Chung-Li VHF radar. In range time intensity plots the upper E echoes appeared in range 150~200 km, while the normal sporadic E echoes in range 110~150 km, sometimes associated with sporadic F region echoes (in range 300~450 km) and occurred before midnight with time duration from10~80 minutes. The statistic characteristics of 6 days upper E echoes indicate the Doppler velocities varies in -50~70 m/s with mean ~15 m/s and a secondary peak at ~55 m/s , and the spectral width varies in 3~30 m/s with mean width ~12 m/s. Interferometry analyze indicate the spatial structure are clump type irregularities [Wang et al.(2011)].
A typical event in 19 July 2009 is interesting, clump type irregularities at height 130~140 km moving cross westward in periodic about 16~18 minutes occurred in 2200~2330, simultaneously, the normal sporadic E (Es) dissipated at about 100 and 110 km. The trajectory in horizontal plane indicates a clearly periodic wave structure with average horizontal trace velocities 50~60 m/s, thus a horizontal wavelength can be estimated as about 48~65 km. Some implicit information about these echoes will be discussed.