Skip to main content
Article thumbnail
Location of Repository

Latitudinal and seasonal variations of quasiperiodic and periodic VLF emissions in the outer magnetosphere

By M.J. Engebretson, J.L. Posch, A.J. Halford, G.A. Shelburne, A.J. Smith, M. Spasojević, U.S. Inan and R.L. Arnoldy

Abstract

We have analyzed ELF-VLF receiver and search coil magnetometer data from five Antarctic stations from 1998 and 1999 to study quasiperiodic emissions (QPs) and periodic emissions (PEs), which occur as ULF-range modulations of ELF-VLF signals between 0.5 kHz and similar to4 kHz. QPs are modulated at frequencies of similar to20-50 mHz, and PEs are modulated at frequencies of similar to200-500 mHz. The stations used covered a range of magnetic latitudes from -62degrees (Halley) to -74degrees (South Pole Station); three automated geophysical observatories (AGOs) were located at intermediate latitudes. Consistent with earlier studies, most QPs were observed with magnetic pulsations of identical period in the Pc3 range ( type I QPs). Of those QPs not observed with simultaneous magnetic pulsations ( type II QPs), nearly all were accompanied by PEs. Type I QPs, PEs, and events during which both appeared together (QPPEs) were found to have different latitudinal, seasonal, and diurnal occurrence patterns: QPs of both types were more likely to occur between -65degrees and -70degrees magnetic latitude, while PEs occurred more often around -60degrees magnetic latitude. QPs were more common during the months of October though March, while PEs were more common during the months of May through September. QPs, whether with or without simultaneous PEs or magnetic pulsations, were predominantly a dayside phenomenon, with a broad maximum near local noon. The occurrence of QPs unaccompanied by PEs was restricted to the dayside, however, while a small number of QPPEs appeared even during nighttime hours. PEs, on the other hand, could be seen at all local times, but with latitudinally dependent diurnal patterns. Most higher-latitude QPs were type I events (observed with magnetic pulsations), while type II QP events (without simultaneous magnetic pulsations) occurred relatively more often at lower latitudes. A case study from 1 August 1999 using wideband data from South Pole and Halley provides evidence of a transition from echoing whistler activity to PE activity and then to QP activity and suggests a causal relationship

Topics: Atmospheric Sciences
Publisher: American Geophysical Union
Year: 2004
DOI identifier: 10.1029/2003JA010335
OAI identifier: oai:nora.nerc.ac.uk:12160
Download PDF:
Sorry, we are unable to provide the full text but you may find it at the following location(s):
  • http://www.agu.org/journals/ja... (external link)
  • https://doi.org/10.1029/2003JA... (external link)
  • https://doi.org/10.1029/2003JA... (external link)
  • http://nora.nerc.ac.uk/id/epri... (external link)
  • http://nora.nerc.ac.uk/id/epri... (external link)
  • Suggested articles


    To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.