Response of the lower ionosphere to solar proton event on July 14, 2000. Model simulations over both poles

Response of the middle atmosphere and especially of electron and ion concentrations in the lower ionosphere to one of the strongest Solar Proton Events (SPE) of the 23rd solar cycle on July 14, 2000 is studied with the emphasis on the differences in ionosphere over the North and the South Pole. General circulation model (GCM) and 3D chemical global transport-photochemical middle atmosphere model are used for simulations of neutral composition, wind and temperature response. Using these results, concentrations of the short-living ions are calculated by 1D photochemical model of the lower ionosphere. SPE-induced ionization rates in the polar atmosphere are calculated using high time-resolution satellite measurements of solar proton fluxes provided by GOES-10. SPEs are known to produce significant amounts of odd nitrogen, odd hydrogen and ion species that affect neutral and ion constituents in stratosphere and mesosphere. Our simulations show that electron concentrations over both poles increase by several orders of magnitude. In the north polar cap (NPC) in polar summer, this enhancement lasts longer than in the south polar cap (SPC) at polar night. Contribution of the significant temperature changes after the SPE found by Krivolutsky et al. [2006. Advances in Space Research 37 (8), 1602] in north polar mesosphere to the SPE-induced electron concentration enhancement is of the order of 10% at 88–98 km on day 5–8 after the SPE onset. The present simulations show that the overall negative ion concentration increased by about 2 orders of magnitude during SPE in the sun-lit NPC and slightly less in the dark SPC ionosphere. Response of the positive clusters is found similar in both hemispheres. Calculated decrease of ion composition parameter f+=[ΣClust+]/([NO+]+[O2+]) by 2 orders of magnitude over both poles is in agreement with measurements.