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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, A09307, doi:10.1029/2004JA010922, 2005

Modeling a large solar proton event in the southern polar atmosphere

Mark A. Clilverd

British Antarctic Survey (NERC), Cambridge, UK


Craig J. Rodger

Physics Department, University of Otago, Dunedin, New Zealand


Thomas Ulich

Sodankylä Geophysical Observatory, University of Oulu, Sodankylä, Finland


Annika Seppälä

Finnish Meteorological Institute, Helsinki, Finland


Esa Turunen

Sodankylä Geophysical Observatory, University of Oulu, Sodankylä, Finland


Aurelein Botman

British Antarctic Survey (NERC), Cambridge, UK


Neil R. Thomson

Physics Department, University of Otago, Dunedin, New Zealand


Abstract

We have modeled the effects of the Sodankylä Ion Chemistry model (SIC) electron density profiles on VLF propagation across the southern polar region during the first few days of the 4–10 November 2001 solar proton event (SPE). The results show that the SIC model is accurately reproducing the changes in ionization during the SPE. These results were obtained by approximating the SIC electron density profiles to the Wait β and h′ profiles where the densities were below 1000 el cm−3, a limitation that means during SPEs the technique is typically sensitive in the altitude range 50–60 km. The calculated values of β and h′ were applied to the part of the propagation path poleward of the L = 4 boundary for the Hawaii (NPM)–Halley great circle path. Comparing the change in amplitude of NPM at Halley during the SPE with the GOES satellite proton flux measurements, we observe a good correlation and thus conclude that the variability observed in the VLF data is primarily caused by >50 MeV proton fluxes. This suggests that the SPE produced ionization dominates all other precipitation sources at these altitudes during 4 and 5 November 2001. Consequently, these results suggest that the assumption made during the SIC modeling runs of 4–5 November 2001 of only having proton precipitation and no significant energetic electron precipitation was reasonable. Our work strongly suggests that VLF subionospheric propagation is a reliable tool for the study of SPEs and that it is particularly effective when used in conjunction with an atmospheric model such as SIC.

Received 26 November 2004; accepted 19 April 2005; published 17 September 2005.

Keywords: particle precipitation; atmospheric modeling; radio propagation; solar proton event.

Index Terms: 0340 Atmospheric Composition and Structure: Middle atmosphere: composition and chemistry; 0342 Atmospheric Composition and Structure: Middle atmosphere: energy deposition (3334); 0689 Electromagnetics: Wave propagation (2487, 3285, 4275, 4455, 6934); 1650 Global Change: Solar variability (7537); 2455 Ionosphere: Particle precipitation.

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Citation: Clilverd, M. A., C. J. Rodger, T. Ulich, A. Seppälä, E. Turunen, A. Botman, and N. R. Thomson (2005), Modeling a large solar proton event in the southern polar atmosphere, J. Geophys. Res., 110, A09307, doi:10.1029/2004JA010922.