Latitudinal dependence on the frequency of Pi2 pulsations near the plasmapause using THEMIS satellites and Asian-Oceanian SuperDARN radars

Abstract

We herein describe a harmonic Pi2 wave that started at 09:12 UT on August 19, 2010, with data that were obtained simultaneously at 19:00-20:00 MLT by three mid-latitude Asian-Oceanian Super Dual Auroral Radar Network (SuperDARN) radars (Unwin, Tiger, and Hokkaido radars), three Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites (THEMIS A, THEMIS D, and THEMIS E), and ground-based magnetometers at low and high latitudes. All THEMIS satellites, which were located in the plasmasphere, observed Pi2 pulsations dominantly in the magnetic compressional (B // ) and electric azimuthal (E A ) components, i.e., the fast-mode component. The spectrum of Pi2 pulsations in the B // and E A components contained two spectral peaks at approximately 12 to 14 mHz (f 1 , fundamental) and 23 to 25 mHz (f 2 , second harmonic). The Poynting flux derived from the electric and magnetic fields indicated that these pulsations were waves propagating earthward and duskward. Doppler variations (V) from the 6-s or 8-s resolution camping beams of the Tiger and Unwin SuperDARN radars, which are associated with Pi2 pulsations in the eastward electric field component in the ionosphere, observed Pi2 pulsations within and near the footprint of the plasmapause, whose location was estimated by the THEMIS satellites. The latitudinal profile of f 2 power normalized by f 1 power for Doppler velocities indicated that the enhancement of the normalized f 2 power was the largest near the plasmapause at an altitude-adjusted corrected geomagnetic (AACGM) latitude of 60°to 65°. Based on these features, we suggest that compressional waves propagate duskward away from the midnight sector, where the harmonic cavity mode is generated.

Review of the accomplishments of mid-latitude Super Dual Auroral Radar Network (SuperDARN) HF radars

“…In a pair of papers, Teramoto et al (2014Teramoto et al ( , 2016 presented two further case studies of Pi2 pulsations using data from the THEMIS mode. In the first (Teramoto et al 2014), a Pi2 wave was observed by HOK in the ground/ sea scatter, which was reflected via the ionospheric F region, as well as from a sporadic E layer.…”

“…The authors suggested that the concept of a pure cavity mode is not sufficient to explain the radar and coincident magnetometer observations and that a contribution from an Alfven mode must be considered in order to explain the observations. In a second study, Teramoto et al (2016) presented observations from three radars, HOK, TIG, and UNW, together with ground magnetometer data and electric and magnetic field observations by the THEMIS A, D, and E spacecraft. Note that, to date, this represents the only study of MHD waves at any latitude which use radar data from the two hemispheres.…”

Simultaneous space and ground‐based observations of a plasmaspheric virtual resonance

“…Most highlatitude Pi2 pulsations are believed to be caused by Alfvén waves associated with the transient response of the substorm current wedge [Baumjohann and Glassmeier, 1984], while low-latitude Pi2s are often attributed to cavity mode resonance [Saito and Matsushita, 1968;Kivelson and Southwood, 1985]. An outstanding open question concerns the generation mechanisms of Pi2s at midlatitudes, especially pulsations observed near the plasmapause, where there is a marked transition between high-and low-latitude Pi2 pulsations [Teramoto et al, 2016].…”

The ARASE (ERG) magnetic field investigation

“…Coordinated observation of the phenomena by multiple satellites, (e.g., the THEMIS mission, Van Allen Probes, and the Magnetospheric Multiscale (MMS) mission) and ground facilities should be promoted to further enhance the groundwork of our project (Fujimoto et al 2012;Teramoto et al 2016 MN works for the MGF data evaluation and analysis. AF works for the initial MGF planning, hardware design and data analysis.…”