Skip to main content
Article thumbnail
Location of Repository

A Statistical investigation of the invariant latitude dependence of unstable magnetospheric ion populations in relation to high m ULF wave generation

By M. E. Wilson, Tim K. Yeoman, L. J. Baddeley and B. J. Kellet

Abstract

This paper was published as Annales Geophysicae, 2006, 24 (11), pp. 3027-3040. It is also available from http://www.ann-geophys.net/24/3027/2006/angeo-24-3027-2006.html. Doi: 10.5194/angeo-24-3027-2006 \ud Ann. Geophys., 24, 3027-3040, 2006\ud http://www.ann-geophys.net/24/3027/2006/\ud doi:10.5194/angeo-24-3027-2006\ud © Author(s) 2006. This work is distributed\ud under the Creative Commons Attribution 3.0 License.A statistical study is presented of the unstable proton populations, which contain the free energy required to drive small-scale poloidal mode ULF waves in the magnetosphere, observed at invariant latitudes of 60° to 80°. The data are all in the form of Ion Distribution Functions (IDFs) amassed over ~6 years using the CAMMICE (MICS) instrument on the Polar spacecraft, and cover proton energies of 1 keV to 328 keV. The free energy contained in the unstable, positive gradient regions of the IDFs is available to drive resonant wave growth. The results show that positive gradient regions in IDFs on magnetic field lines corresponding to the lower invariant latitudes in the range under study occur predominantly in the afternoon sector at proton energies of 5 keV to 20 keV. In the morning and dawn sectors positive gradient regions are seen with a typical proton energy range of 5 keV to 45 keV. While the proton energy peaks in the afternoon sector at around ~7 keV the morning sector has two peaks occurring at ~10 keV and ~20–30 keV. The technique of Baddeley et al. (2004), employed to quantify the free energy in each IDF, found that as invariant latitude increased the free energy contained in the positive gradient regions fell. Positive gradient regions in the afternoon sector decrease in number with invariant latitude at a faster rate than those in the morning sector. The majority of positive gradient regions had free energy values of >1010 J with many at the lowest invariant latitudes having free energies of in excess of 1011 J. Positive gradient regions at proton energies of >100 keV are rarely observed, and have free energies of typically <10 J, which is too small to produce high m ULF waves of significant amplitude

Publisher: Copernicus Publications on behalf of the European Geosciences Union (EGU)
Year: 2006
DOI identifier: 10.5194/angeo-24-3027-2006
OAI identifier: oai:lra.le.ac.uk:2381/8114
Journal:

Suggested articles

Citations

  1. (1976). A general approach to low-frequency instability in the ring current plasma, doi
  2. (1999). A statistical study of Pc3-Pc5 magnetic pulsations observed by the AMPTE/Ion Release Module satellite, doi
  3. (2004). A statistical study of unstable particle populations in the global ringcurrent and their relation to the generation of high ULF waves, doi
  4. (1992). A study of Pc5 hydromagnetic waves with equatorward phase propagation, doi
  5. (1989). A.: A magnetospheric magnetic field model with a warped tail current sheet, doi
  6. (1990). A.: A statistical study of Pc 3-5 pulsations observed by the AMPTE/CCE magnetic fields experiment. doi
  7. (1976). Adiabatic plasma convection in a dipole field: Proton forbidden-zone effects for a simple electric field model, doi
  8. (1978). Alfve´n waves generated by an inverted plasma energy distribution, doi
  9. (1969). Bounce resonant interactions between pulsations and trapped particles, doi
  10. (1987). Chisham, G.: Giant pulsations: An explanation for their rarity and occurrence during geomagnetically quiet times, doi
  11. (1986). Excitation of high β plasma instabilities at the geostationary orbit – theory and observations, doi
  12. (1979). Fieldaligned structure of the storm time doi
  13. (2001). Ground-based and Polar spacecraft observations of a giant (Pg) pulsation and its associated source mechanism, doi
  14. (1997). High-latitude HF Doppler observations of ULF waves. 1. Waves with large spatial scale sizes, doi
  15. (2000). High-latitude observations of ULF waves with large azimuthal wavenumbers, doi
  16. (1997). Initial backscatter occurrence statistics from the CUTLASS HF radars, doi
  17. (1992). Magnetospheric Ion Composition Spectrometer on board the CRRES spacecraft, doi
  18. (2001). Modeling the properties of high m Alfve´n waves driven by the drift-bounce resonance mechanism, doi
  19. (2002). Morning sector drift-bounce resonance driven ULF waves observed in artificially induced HF radar backscatter, doi
  20. (2001). New Evidence for the origin of giant pulsations, doi
  21. (2005). On the coupling between unstable magnetospheric particle populations and resonant high m ULF wave signatures in the ionosphere, doi
  22. (1983). Pc5 pulsations associated with ring current proton drifts: STARE radar observations, doi
  23. (1983). SABRE – new radar-auroral backscatter experiment, doi
  24. (1991). Statistical studies of giant pulsations (Pgs): Harmonic mode, doi
  25. (1992). The spatial extent of radial magnetic pulsation events observed in the dayside near synchronous orbit, doi
  26. (1984). The spatial structure of different ULF pulsation types: A review of STARE radar results, doi
  27. (1998). The WIND-HAARP experiment: Initial results of high power radiowave interactions with space plasmas, doi
  28. (2001). ULF waves with drift resonance and drift-bounce resonance energy sources as observed in artificially-induced HF radar backscatter, doi
  29. (1997). ULF waves: doi

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