Poker flat incoherent scatter radar investigations of the nighttime E-region

Abstract

Plasma within the ionosphere affects technology, such as long distance communications and satellite navigation, by scattering and altering the propagation of radio waves sent through the ionosphere. Understanding the structure and dynamics of the ionosphere that may interfere with modern technology is therefore an important aspect of Space Weather research. In this thesis, the average characteristics and dynamics of the nighttime E-region (90-150 km in altitude) are investigated during auroral disturbances and near extreme solar minimum. The near-continuous data on electron density obtained with the Poker Flat Incoherent Scatter Radar (PFISR) near Fairbanks, Alaska are utilized. A number of correlation analyses between E-region electron content and AE index are performed in order to examine the influence of geomagnetic conditions on the E-region in relation to time of the day as well as seasonal and solar cycle effects. It is shown that E-region electron content and AE index exhibit significant positive correlation, particularly near local magnetic midnight, with greater correlation generally occurring in spring and autumn. The midnight feature is interpreted as an indication that the electrojet system near midnight is mostly controlled by electric conductance. The presented statistical results on the current-conductance relationship utilizing a new dataset strengthen conclusions derived from previous studies. The extent of E-region contribution to the total electron content (TEC) is also estimated and investigated for various conditions for the first time using the full altitude profile of PFISR. The estimates ranged between 5%-60% and more active periods generally displayed a more significant contribution from the E-region to TEC. Additionally, using the AE index as an indicator of auroral disturbance onset, the evolution of auroral density enhancements is explored using the superposed epoch analysis technique. The behavior of E-region electron content, peak density, height of peak density, and layer thickness is considered and three discernible phases in response of the thick E-layer to auroral disturbances are found. The observations are consistent with a scenario in which an initially soft and broad auroral electron energy spectrum quickly hardens and narrows during the main response and then slowly softens and becomes more broad during recovery.