Pc3-4 ULF waves observed by the SuperDARN TIGER radar

Abstract

Abstract. Despite extensive research, the mechanisms for propagation of Pc3-4 energy from the generation region at the bow shock to the high-latitude ionosphere remain unresolved. We used high temporal (6-12 s) and spatial (45 km) resolution data from the SuperDARN TIGER radar (Tasmania) to examine Pc3-4 wave signatures at the F-region heights. We focus on a case study on 28 September 2000, when large-amplitude band-limited Pc3-4 oscillations were observed across 10-20 range gates in beam #4 (which points towards the CGM pole) for about four hours preceding MLT noon. These waves were detected in sea-scatter echoes reflected from the ionospheric footprint of the plasmatrough. Nearby ground magnetometer data from Macquarie Island showed very similar variations in both the north-south and east-west components. The radar data revealed the occasional presence of quasi-FLR (field-line resonance) spatial structures with frequencies much higher than those of the local fundamental FLR modes. Detailed spectral analysis of the ionospheric and ground data shows that these structures most probably correspond to a 3rd-harmonic, poloidal-mode FLR. Such observations suggest that compressional Pc3-4 waves produced in the upstream solar wind travel earthward from the magnetopause in the magnetic equatorial plane depositing energy into the Alfvenic modes, as either forced or 3rd-harmonic FLR that reach ionospheric heights along magnetic field lines.

A new type of Doppler velocity fluctuations in HF ground scatter from the polar cap

“…Radar echoes from these ranges were identified as GS due to their relatively low background velocity, |v D0 |, and spectral width, W, both of the order of several tens of m/s (not shown). Importantly, these fluctuations visually resemble Pc3-4 signatures observed at lower latitudes [e.g., Ponomarenko et al, 2005]. Such variations appeared to be common in the daytime GS data, especially in summer.…”

“…At auroral/magnetotrough latitudes, these waves are observed in radar data as periodic variations of f D with a spatial coherence scale of 1000 km which are accompanied by synchronous variations in the colocated ground magnetic field records and exhibit maximum power/occurrence near local magnetic noon [Ponomarenko et al, 2003[Ponomarenko et al, , 2005. Importantly, ULF wave signatures are regularly observed in both ionospheric scatter (IS) and ground scatter (GS) components, the latter being a more convenient indicator due to its insensitivity to the fast background drifts [Ponomarenko et al, 2003].…”

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…In addition to the compressed dynamic range, detrending the velocity field (bottom panel) clarifies the wave field still further unearthing a wealth of wave activity as shown by the almost continuous black and white striped regions. Using this method, Ponomarenko et al (2005) examined a specific Pc3 wave event in detail, identifying the energy source of the wave as upstream ion-cyclotron waves which passed through the magnetopause, propagating across magnetic field lines, until a resonant field line was encountered.…”

Spectral width of SuperDARN echoes: measurement, use and physical interpretation

“…To quantify the change in the experimental sea-scatter spectral width, we analysed data from TIGER beam #4 recorded on 20:00-22:00 UT on 28 September 2000, which consisted of seascatter echoes only (Ponomarenko et al, 2005). Comparing the original estimates of W with the FITACF modified to extract the zero lag noise, we found that the original algorithm incorrectly classified up to 20% of the echoes as ionospheric rather than sea scatter.…”