Ionospheric F2-Layer response to sudden and gradual commencement geomagnetic storms over the European mid-latitude sector

Abstract

This paper investigates the effects of the geomagnetic storms of 25_27 September 2011, 16_18 March 2013, and 6_8 September 2015 over five mid-latitude stations located in Eu- rope: Dourbes (Belgium), Fairford (United Kingdom), Moscow (Russia), Rome (Italy), and Roquetes (Spain), and performs a cross-correlation analysis of ionospheric and solar parameters during these storms. We observed the highest fluctuations in ionospheric variables during the main phase of the storms. In addition, there is strong evidence of pre storm enhancement occurring at least a few hours and more than 24 hours prior to the main phase of the geomagnetic storms. We found that the TEC and foF2 parameters have a strong dependence with latitude for the events with Sudden Storm Commencement (SSC) in mid-latitude regions. Relatively low TEC and foF2 is observed in the higher-latitude stations, in particular at Moscow, which is at the highest latitude among the five stations, because of a decrease in the n(O)/n(N2) ratio throughout the storm event. However, for the event with gradual storm commencement, there is no evidence of such dependence. The high correlation of Symmetric-H and Auroral Electrojet indices with ionospheric parameters indicates that the coupling mechanism between magnetosphere and ionosphere produces intense electric field disturbances in the middle-low latitudes. The storms drive intense solar wind energy into the auroral and mid-latitude upper atmosphere. This triggers rapid fluctuations in electron density, enhanced Joule heating and particle precipitation. The F2 layer is uplifted by up to ∼200 km and TEC is enhanced by up to ∼200% as compared to the quiet time. Such disturbances degrade HF radio communication and GNSS positioning, increase satellite drag and induce geomagnetically induced currents (GICs) in ground level conductor systems like power transmission lines. So, the lead and lag relationships obtained in this work can be used to protect sensitive devices on the ground and in space.