Initial backscatter occurrence statistics from the CUTLASS HF radars

Abstract

A statistical study of the occurrence of ground and ionospheric backscatter within the ®elds-of-view of the CUTLASS HF radars, at an operating frequency of 10 MHz, during the ®rst 20 months of operation has been undertaken. The diurnal variation of the occurrence of backscatter and the range at which such backscatter is observed is found to be highly dependent on seasonal changes of the ionospheric electron density in both the E and F region, determined from ionosonde observations. In general, ionospheric backscatter is observed at far ranges during the local day in winter months and at near ranges during the local night in summer months. The Iceland radar observes more nearrange E region backscatter than the Finland radar as a consequence of its more zonal look-direction. The dependence of the occurrence of backscatter on geomagnetic activity and radar operating frequency are also investigated. The occurrence of ground and ionospheric backscatter is discussed in terms of HF propagation modes and ionospheric electron densities as well as geophysical processes. A brief assessment of the possible impact of solar cycle variations on the observations is made and frequency management is discussed. Such a study, with its focus on the`instrumental' aspect of backscatter occurrence, is essential for a full interpretation of HF coherent radar observations.

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

“…It should be reiterated that the location of the EISCAT UHF radar within the CUTLASS Finland radar ®eld-of-view is by no means optimum for such a comparison as the nature of HF propagation severely limits Finland radar returns from the vicinity of EISCAT (Milan et al, 1997); this is indeed even more applicable to the location of EISCAT within the CUTLASS Iceland ®eld-of-view. In each of the following ®gures, EISCAT ion drift velocities where any of the three UHF receiver sites has a signal-to-noise ratio of less than 2% have been excluded.…”

“…In each of the following ®gures, EISCAT ion drift velocities where any of the three UHF receiver sites has a signal-to-noise ratio of less than 2% have been excluded. Moreover, CUTLASS velocities deduced from spectra which are attributed to ground scatter (Milan et al, 1997) have been excluded and a power threshold of 3 dB has been applied to the data. Ground scatter is characterised by a combination of low line-of-sight velocity and low spectral width, roughly 50 m s A1 and 20 m s A1 respectively.…”

First results of the high-resolution multibeam ULF wave experiment at the Ekaterinburg SuperDARN radar: Ionospheric signatures of coupled poloidal Alfvén and drift-compressional modes

“…It takes into account the values of velocity and spectral broadening of the signal, as well as some additional parameters (Milan et al, 1997;Ribeiro et al, 2011). Fig.…”

A comparison of SuperDARN-derived plasma convection and DMSP ion drift measurements

“…Ref. [10] shows that SuperDARN far-range echoes (>2 500 km) can be received from the E region (not the F region as assumed) through the 1 and 1/2 hop mode. It is well known that velocities of E-region irregularities are "saturated" at a value of the ion-acoustic speed (400-600 m/s, depending on the convection magnitude), which means, for strong convection, the velocities measured by SuperDARN will not exceed the ion-acoustic speed.…”