Middle-Latitude Ionospheric Irregularities and Scintillation During Geomagnetic Storms

Abstract

An investigation of mid-latitude ionospheric irregularities and scintillation (MIDLIIS) during geomagnetic storms is presented. Significant MIDLIIS events are revealed in Regional or Global maps of ionospheric irregularities and scintillation (RMIIS and GMIIS [1][2]). GMIIS are produced using GPS measurements from thousands of globally distributed stations. We intend to add MIDLIIS as a new element to the classical picture of global ionospheric scintillation and irregularities because the observed MIDLIIS events occurred in vast regions. To understand underlying physics mechanisms, the MIDLIIS development is compared with space weather conditions and geomagnetic data as well as auroral observations made by global ultraviolet imager (GUVI) onboard a Defense Meteorology Satellite Program (DMSP) satellite. The GUVI images show auroral oval expansion when MIDLIIS are observed. Our study leads to an assessment that MIDLIIS events are driven by auroral oval expansion to middle latitudes and possible ring current inward expansion to the plasmasphere with associated penetration of the magnetospheric electric field. Before presenting the MIDLIIS investigation, measurements of ionospheric scintillation and irregularities, namely S4, Sigma_Phi, and ROTI, are reviewed. A comparison is made to distinguish differences and emphases between these indices.