Investigation of Midlatitude Nighttime Ionospheric E-F Coupling and Interhemispheric Coupling by Using COSMIC GPS Radio Occultation Measurements

This study presents the statistical features of ionospheric E-F coupling and interhemispheric coupling at midlatitudes. Nighttime ionospheric E and F region irregularity occurrences are investigated by using Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation measurements during 2006-2018. We presented four typical events of simultaneous observations of E and F region irregularities in the local hemisphere and F region irregularities in both conjugate hemispheres. Results of case studies indicate the coincidence of ionospheric irregularities in both E and F regions, as well as the coincidence of ionospheric irregularities in both F regions of two conjugate hemispheres. Statistical analysis of occurrences of E and F region irregularities shows that the concurrence of ionospheric irregularities in both E and F regions reaches a maximum (nearly 70%) during June (December) solstice in the Northern (Southern) Hemisphere. Nearly 50% (45%) of the F region irregularity in the Northern (Southern) Hemisphere occurs simultaneously with F region irregularity occurrence in the Southern (Northern) Hemisphere during December (June) solstice. These results provide the observational evidences showing that the effect of E-F coupling and interhemispheric coupling may be important in generation of midlatitude nighttime F region irregularity. In addition, our results also reveal that mapping efficiency of electrodynamic coupling has a different seasonal variation in the Northern and Southern Hemispheres, which shows dependence on both the integrated Pedersen conductivity of F region (Sigma(F)(P)) and the integrated Hall conductivity of E-S layer (Sigma(ES)(H)).