Excitation thresholds of field-aligned irregularities and associated ionospheric hysteresis at very high latitudes observed using SPEAR-induced HF radar backscatter

D M Wright,L J Baddeley,T R Robinson,S Imber,E C Thomas,R S Dhillon,T K Yeoman

doi:10.5194/angeo-27-2623-2009

D M Wright, L J Baddeley + Show 5 more

Open Access

https://doi.org/10.5194/angeo-27-2623-2009

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Abstract

Abstract. On 10 October 2006 the SPEAR high power radar facility was operated in a power-stepping mode where both CUTLASS radars were detecting backscatter from the SPEAR-induced field-aligned irregularities (FAIs). The effective radiated power of SPEAR was varied from 1–10 MW. The aim of the experiment was to investigate the power thresholds for excitation (Pt) and collapse (Pc) of artificially-induced FAIs in the ionosphere over Svalbard. It was demonstrated that FAI could be excited by a SPEAR ERP of only 1 MW, representing only 1/30th of SPEAR's total capability, and that once created the irregularities could be maintained for even lower powers. The experiment also demonstrated that the very high latitude ionosphere exhibits hysteresis, where the down-going part of the power cycle provided a higher density of irregularities than for the equivalent part of the up-going cycle. Although this second result is similar to that observed previously by CUTLASS in conjunction with the Tromsø heater, the same is not true for the equivalent incoherent scatter measurements. The EISCAT Svalbard Radar (ESR) failed to detect any hysteresis in the plasma parameters over Svalbard in stark contract with the measurements made using the Tromsø UHF.

Highlights

The artificial modification of the Earth’s ionosphere was first noted in the 1930s when newly built broadcast radio stations began operations
Was that shown not to be the case by Robinson et al (2006) but the results presented here indicate that SPEAR effective radiated powers (ERPs) of only 1/30th of its nominal maximum capability can excite the field-aligned irregularities (FAIs)
The SPEAR high power radar performed a power stepping experiment to investigate the properties of the ionospheric plasma over Spitsbergen, Norway

Summary

Introduction

The artificial modification of the Earth’s ionosphere was first noted in the 1930s when newly built broadcast radio stations began operations. The TOTSI causes a linear conversion of electromagnetic pump wave energy into upper hybrid waves (Vaskov and Gurevich, 1977; Dysthe et al, 1983; Robinson, 1988) This coupling requires the presence of plasma density gradients (pre-existing FAIs) and leads to an increase in the FAI amplitude. 0P2 where P1 and P2, respectively, are the required power thresholds for the initial and explosive stages of FAI growth, 0 is the level of anomalous absorption before the heater was activated and a is a factor relating to the field parallel scale length of the FAIs (see Robinson, 1989). Stark differences are apparent in the incoherent scatter measurements provided by the EISCAT UHF radars

The SPEAR high power facility

The CUTLASS radars

Observations

Discussion

Power Up-cycle

Conclusion