Modeling polar ionospheric effects during the October-November 2003 solar proton events

At Ny Ålesund, Svalbard (78°54′N, 11°53′E, L ∼ 18), a narrowband VLF receiver was used to monitor the behavior of the amplitude of several high-power transmitters located in the Northern Hemisphere under the influence of the solar proton events (SPE) of October/November 2003. We have used Sodankylä ion chemistry (SIC) atmospheric model profiles calculated at the midpoint location of the propagation paths in the northern wintertime polar region to investigate the radio propagation properties of several high-latitude paths. Different paths showed different responses to the proton precipitation, but propagation modeling was broadly able to account for most of the positive and negative responses observed. Using the SIC-based electron density profiles, we have been able to develop models of ionospheric effective height (h′) and sharpness (β) in order to describe the D region behavior as a function of proton flux, extending previous work which reported β and h′ values as functions of the X-ray flux from solar flares. As a result of these models, our understanding of VLF propagation influenced by SPEs is such that VLF observations might be used to predict changes in the ionospheric D region electron density profiles during other particle precipitation events.