A comparison of velocity measurements from the CUTLASS Finland radar and the EISCAT UHF system

The CUTLASS Finland radar, which comprises an integral part of the SuperDAR N system of HF coherent radars, provides near continuous observations of hi gh-latitude plasma irregularities within a field-of-view which extends over some four million square kilometres. Within the Finland radar field-of-vie w lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar commenced operation, in Februa ry 1995, the mainland EISCAT UHF radar has been run in common programme 1 a nd 2 modes for a total duration exceeding 1000 h. Simultaneous and spatiall y coincident returns from these two radars over this period provide the bas is for a comparison of irregularity drift velocity and F-region ion velocit y. Initial comparison is limited to velocities from four intervals of simul taneous radar returns; intervals are selected such that they exhibit a vari ety of velocity signatures including that characteristic of the convection reversal and a rapidly fluctuating velocity feature. Subsequent comparison is on a statistical basis. The velocities measured by the two systems demon strate reasonable correspondence over the velocity regime encountered durin g the simultaneous occurrence of coherent and incoherent scatter; differenc es between the EISCAT UHF measurements of F-region ion drift and the irregu larity drift velocities from the Finland radar are explained in terms of a number of contributing factors including contamination of the latter by E-r egion echoes, a factor which is investigated further, and the potentially d eleterious effect of discrepant volume and time sampling intervals.