First HF radar measurements of summer mesopause echoes at SURA

A N Karashtin,E B Eryshev,I F Belov,I V Berezin,Y V Shlyugaev,V V Bychkov,V I Abramov,G P Komrakov

doi:10.1007/s005850050512

Abstract

HF sounding of the mesosphere was first carried out at SURA in summer 1994 at frequencies in the range 8â9 MHz using one of the sub-arrays of the SURA heating facility. The observations had a range resolution of 3 km. Almost all measurements indicated the presence of strong radar returns from altitudes between 83 and 90 km with features very similar to VHF measurements of mesopause summer echoes at mid-latitudes and polar mesopause summer echoes. In contrast to VHF observations, HF mesopause echoes are almost always present.

Highlights

Considerable attention has been paid to the anomalously high power radar returns from the mesopause region in summer at high latitudes: the so-called polar mesospheric summer echoes (PMSE)
Strong VHF radar echoes from the mid-latitude mesopause region have been observed in summer and are called mesospheric summer echoes (MSE) due to their similarity to PMSE (Reid et al, 1989; Thomas et al, 1992)
PMSE are centered at an altitude of about 86 km and spread over several kilometers width; they are observed at frequencies in the VHF and UHF bands corresponding to the viscous subrange of neutral turbulence at altitudes where it should be strongly damped and undetectable under normal conditions

Summary

Introduction

Considerable attention has been paid to the anomalously high power radar returns from the mesopause region in summer at high latitudes: the so-called polar mesospheric summer echoes (PMSE) (see for example, the recent review paper Cho and Kelley, 1993). PMSE are centered at an altitude of about 86 km and spread over several kilometers width; they are observed at frequencies in the VHF and UHF bands corresponding to the viscous subrange of neutral turbulence at altitudes where it should be strongly damped and undetectable under normal conditions Such behavior is observed at low latitudes during non-summer periods at mid- and polar latitudes when much weaker radar returns appear only from altitudes below 80 km (Ecklund and Balsley, 1981) centered at about 70 km, where operating frequencies correspond to inertial subrange of the turbulence. This means that PMSE are caused by an abnormal enhancement of small-scale plasma turbulence under summer conditions in polar regions.

SURA radar for atmospheric studies

Echo characteristics and structure

Conclusions