Spatial observations by the CUTLASS coherent scatter radar of ionospheric modification by high power radio waves

G E Bond,P Eglitis,A J Stocker,T B Jones,T R Robinson,M T Rietveld,D M Wright

doi:10.1007/s00585-997-1412-4

Abstract

Abstract. Results are presented from an experimental campaign in April 1996, in which the new CUTLASS (Co-operative UK twin-located Auroral Sounding System) coherent scatter radar was employed to observe artificial field aligned irregularities (FAI) generated by the EISCAT (European Incoherent SCATter) heating facility at Tromsø, Norway. The distribution of backscatter intensity from within the heated region has been investigated both in azimuth and range with the Finland component of CUTLASS, and the first observations of artificial irregularities by the Iceland radar are also presented. The heated region has been measured to extend over a horizontal distance of 170±50km, which by comparison with a model of the heater beam pattern corresponds to a threshold electric field for FAI of between 0.1 and 0.01V/m. Differences between field-aligned and vertical propagation heating are also presented.

Highlights

When high power radio waves, operating in ordinary polarisation, are beamed vertically and at an angle within a few tens of degrees of the geomagnetic ®eld, they strongly excite plasma density irregularities in regions where the wave frequency is close to the local upper-hybrid frequency (Stubbe et al, 1982; Robinson, 1989 and references therein)
In this study we present CUTLASS observations of FAI produced by the EISCAT heater, during an experimental campaign in April 1996
CUTLASS spatial plots of returned power taken at 1324 UT on 24 April 1996, during a heater-on period. a Iceland radar operating at 15 MHz in 45 km range mode. b Finland radar operating at 12X4 MHz in 15 km range mode

Summary

Introduction

When high power radio waves, operating in ordinary polarisation, are beamed vertically and at an angle within a few tens of degrees of the geomagnetic ®eld, they strongly excite plasma density irregularities in regions where the wave frequency is close to the local upper-hybrid frequency (Stubbe et al, 1982; Robinson, 1989 and references therein). In early ionospheric modi®cation experiments using the high power radio transmitter at Boulder, Colorado, Thome and Blood (1974) detected strong coherent backscatter at both VHF and HF frequencies. The arrangement facilitates simultaneous observations to be made with the EISCAT incoherent scatter radars (Rishbeth and Williams, 1985) Both CUTLASS sites make use of 16 antennas in their main arrays, which are each connected to separate 600 W RF power ampli®ers. This gave a heater ERP of just under 70 MW, neglecting losses Both the Iceland and Finland components of the CUTLASS system were operational, and transmitted frequencies between 8 and 20 MHz, along up to ®ve adjacent beam directions positioned to intercept the heated region over Tromsù. The six transmitters operated at 90 kW each, and the gain of the array was 21 dB, compared to Observations

CUTLASS observations of the horizontal extent of the heated region

Estimating the size of the heated region

CUTLASS spatial measurements

Summary