An investigation of the nature of a Pc5 pulsation event using SuperDARN and magnetometer data

Zolile Mtumela,Judy A.E Stephenson,Anthony D.M Walker

doi:10.17159/sajs.2015/20130391

Abstract

Pc5 pulsations are global magnetohydrodynamic events in the magnetosphere. We employed an Automated Pulsation Finder program to identify significant Pc5 pulsation events in SuperDARN radar data. The event presented here was visible in the Goose Bay, Saskatoon and Þykkvibaer high-frequency radars, located in the northern polar region. These observations were coordinated with magnetometers within their field of view. These two instrument types – radars and magnetometers – complement each other. These observations represent a significant fraction of the globe in longitude. Pulsation studies of this nature are rare in the literature. Combining these two instrument types, we investigated the nature of the pulsation and determined its qualitative polarisation characteristics. A complex demodulation technique was employed to determine amplitude and phase relationships between field components observed by the radars and magnetometers, which, in turn, afforded resolution of other characteristics of pulsations, such as wave number and phase velocity. The results are discussed in the context of the magnetohydrodynamic theory of magnetic pulsations, speculating on its generation mechanism. Investigation of this mechanism will be the subject of a future publication.

Highlights

Ultra-low frequency (ULF) hydromagnetic waves, often referred to as geomagnetic pulsations, have been observed for many years in magnetometer data as well as by very high frequency (VHF) and high-frequency (HF) radars, and are endemic within the magnetosphere
The quantisation of the resonance frequencies is predicted by the cavity mode theory which was first developed by Kivelson and Southwood[1] and later modified into waveguide theory[1,6] to account for the azimuthal propagation of the compressional mode
We focused on a Pc5 pulsation event occurring between 20:00 and 22:00 UT on 6 October 2006 observed by the Saskatoon, Goose Bay, and Þykkvibaer HF radars

Summary

Introduction

Ultra-low frequency (ULF) hydromagnetic waves, often referred to as geomagnetic pulsations, have been observed for many years in magnetometer data as well as by very high frequency (VHF) and high-frequency (HF) radars, and are endemic within the magnetosphere. All the mechanisms mentioned above have been shown to be present Another type of pulsation in the Pc5 band can be generated by drift-bounce resonance with energetic ring current particles. We focused on a Pc5 pulsation event occurring between 20:00 and 22:00 UT on 6 October 2006 observed by the Saskatoon, Goose Bay, and Þykkvibaer HF radars These three radars are part of the SuperDARN international network of HF radars that monitor ionospheric plasma convection over an extensive area of mid- and high latitudes in both hemispheres. HF radars operate by utilising coherent scatter from fieldaligned irregularities of electron density in the E- and F-regions of the ionosphere They ‘see’ the electric field perturbation associated with the pulsation and not the magnetic field. These magnetometer arrays give exceptionally high quality data and they all have a good temporal resolution

Findings

Observations and discussion

Conclusions