Chien-Chih Lee

VHF radar and MF/HF dynasonde observations during Polar Mesosphere Summer Echoes conditions at EISCAT

The EISCAT VHF radar (224 MHz) and the EISCAT dynasonde (1–10 MHz) were operated simultaneously during a Polar Mesosphere Summer Echoes (PMSE) event on 22 June 1994. We investigate the echo characteristics revealed by these two instruments. The antenna of the VHF radar was set 10° off-zenith to the north for both transmission and receiving, while the dynasonde was operated with vertical beam to record ionograms every 3 minutes. The Height-Time-Intensity (HTI) variation of the VHF radar PMSE is studied, which is characterized layered structures. The intensity profiles are quite intermittent which show similarity to those data recorded by the dynasonde. To study the ionospheric condition with the dynasonde, the quantities of signal-to-noise ratio, echo frequency, echo polarization, echolocation, and Doppler velocity are investigated. Variations in the quantities demonstrate that during the PMSE conditions, echoes of the dynasonde are mainly attributed by reflection of many small irregularities within the observed ionospheric volume.

An upward moving thin layer in the equatorial F region observed by a digisonde

[i] This study presents an observation of a thin layer motion in the equatorial F region for the first time. The thin layer is detected by the Jicamarca Digisonde from 1000 to 1230 LT (1500 to 1730 UT) on 14 October 1996. We apply the inversion and fitting processes to derive the parameters (peak density, peak height, scale heights) of a thin layer. Results show that the thin layer has a constant total content of 2.48 × 10 6 el/cm 2 that might be formed by the long-lived metallic ions. From 1000 to 1200 LT, the layer is lifted upward from 164.6 to 275.9 km height with a velocity of 15.5 m/s, where the topside and bottomside scale heights are 2.8-5.0 and 1.2-2.4 km, respectively. In addition to the characteristics of the thin layer, this observation further provides evidence for the vertical transport of metallic ions in the equatorial F region.