High spatial resolution radar observations of ultralow frequency waves in the southern polar cap

Abstract

We present an analysis of ultralow frequency (ULF) waves detected in the southern polar cap using the Super Dual Auroral Radar Network (SuperDARN). These waves manifest as quasi‐sinusoidal oscillations in the Doppler velocity, which arise due to the oscillating ULF wave electric field in the F region ionosphere. The event reported in this study occurred during the southern polar winter under quiet geomagnetic conditions. The 1.1–1.3 mHz oscillations were observed throughout the polar cap by the McMurdo, Dome C East, and South Pole Station SuperDARN radars and also by the Dome Concordia and Scott Base magnetometers at corrected geomagnetic latitudes of ∼89°S and ∼80°S, respectively. In contrast to large‐scale toroidal field line resonances observed at auroral latitudes, we find that the magnetic perturbation vector of the polar cap oscillations did not undergo a 90° rotation upon transmission from the ionosphere to the ground and was instead rotated by about 30°. The polar cap oscillations were also accompanied by simultaneous field line resonance (FLR) activity in the dayside auroral zone, in the field of view of the Zhongshan SuperDARN radar. This FLR occurred at the same frequency and exhibited a similar azimuthal phase velocity to the polar cap oscillations, indicating that they may have been driven by the same source mechanism.

Multipoint Conjugate Observations of Dayside ULF Waves During an Extended Period of Radial IMF

“…An outstanding issue is how Pc5 waves are generated in the cusp and polar cap region on open field lines. The polar cap has generally been thought to be a quiet region, with wave power entering only from neighboring regions, such as the auroral oval (e.g., Bland & McDonald, 2016). As summarized in Engebretson et al (2006) Pc5 waves from very high latitudes can be categorized into three classes according to their potential sources: cusp-related waves (Posch et al, 2016), polar pulsations extended from the auroral region, and Pi cap 3 independent of cusp and auroral pulsations (Yagova et al, 2018).…”

“…An outstanding issue is how Pc5 waves are generated in the cusp and polar cap region on open field lines. The polar cap has generally been thought to be a quiet region, with wave power entering only from neighboring regions, such as the auroral oval (e.g., Bland & McDonald, 2016). As summarized in Engebretson et al.…”

Periodic Modulation of the Upper Ionosphere by ULF Waves as Observed Simultaneously by SuperDARN Radars and GPS/TEC Technique

“…The observed occurrence rate was very different from known geomagnetic Pc5 wave morphology. The existence of ionospheric oscillations in the Pc5/Pi3 band without a ground magnetic response were noticed in (Bland & McDonald, 2016;Kozyreva et al, 2019;Scoular et al, 2013). So far, the mechanisms of these ionospheric fluctuations and their association with geomagnetic pulsations still have not been established.…”

A case study of the spectral parameters of ULF fluctuations before substorms with no evident trigger in the interplanetary space

“…Such a value is comparable with magnitude of global ULF pulsations, which are resulting from magnetic closed field-line resonance. ULF activity is also observed in the polar caps, but oscillations are specified by lower amplitudes, and the central frequency ~ a few mHz (Bland, 2016). These pulsations are simultaneously seen in geomagnetic and radar data and might be a result of internal processes in the magnetosphere; be directly driven by perturbations in the Solar Wind (SW) or related to substorms (see references from introduction by Bland, 2016).…”