ULF HIGH-M AND LOW-M FIELD LINE RESONANCES OBSERVED WITH THE SUPER DUAL AURORAL RADAR NETWORK

Numerous field line resonance events have been observed with three HF radars (Saskatoon, Kapuskasing, and Goose Bay) of the Super Dual Auror al Radar Network (SuperDARN). The field line resonances cause oscillat ions in the F region plasma flows which are detected in the measured l ine of sight Doppler velocities. After analysis, it was found that the resonances were of two types: those with low azimuthal wave number, l ow-m, and those with high azimuthal wave number, high-m. The high-m ev ents showed many similarities with high-m pulsations of previous repor ts including local time of most occurrences (noon-dusk), pulsation fre quencies, westward propagation, increase in phase with latitude, and n orth-south polarization. The low-m events exhibited typical field line resonance characteristics and were found near dusk and dawn with anti -Sunward propagation. The most notable result was the fact that the hi gh- and low-m events shared many common features. They both were found to occur at the same discrete and stable frequencies. The most common frequencies were 1.3, 1.9, and 2.5-2.6 mHz, which have previously bee n associated with magnetospheric waveguide modes. They also occurred a t other less common frequencies, such as 1.5-1.6 mHz. Both types of ev ents were localized in latitude with an inverse relation between frequ ency and latitude. Both were characterized by a wave packet structure with a duration of approximately 1 hour. The numerous features shared by the high- and low-m resonances strongly suggest that they are cause d by the same source mechanism. A dispersive waveguide model as a sour ce for the field line resonances is discussed.