EISCAT radar reflection from the vicinity of a noctilucent cloud

The backscattered signal profile received with the EISCAT VHF radar during a noctilucent cloud event of 3-4 August 1997 is discussed. The processing o f the radar signal was standard. A strong signal reflection from 83-88 km a ltitude was observed for three hours without abnormal ionization above this layer. The layer descended with a velocity of 0.5-3 km/hr. Sometimes it wa s stratified into two layers, the ionosphere between the layers being undis turbed. The scattered signal strength was as strong as would be expected fr om an electron density of 10(11) el/cm(3). Simultaneously the MST radar at Esrange revealed the occurrence of PMSE at the same heights. A case of stro ngly reflected signals for the MST radar from 62 km altitude during the Sol ar Proton Event of 2 May 1998 is also discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.