Characteristics and Generation Mechanism of Polar Cap Patch: Multi-instrument Observations

Abstract

This dissertation includes studies on the generation mechanisms and plasma characteristics of polar cap patches and ion upflows in the high-latitude ionosphere, which is a region that involves dynamic processes reflecting the coupling of the solar wind, magnetosphere and ionosphere. Observational datasets from coherent and incoherent scatter radars (ISRs), Global Positional System (GPS) receivers and Low-Earth Orbiting (LEO) satellites were used in these studies. Polar cap “patches” are ~100 to 1,000 km islands of high-density plasma present in the polar cap, which can cause scintillation of communication and navigation signals. Using the global total electron content (TEC) maps and observations from the Sondrestrom ISR, we investigated a dynamic generation process of a polar cap patch during the geomagnetic storm on 13 October 2016. Evidence showed that the patch was segmented from the Storm-enhanced density (SED) by a transient fast flow associated with dayside magnetic reconnection. The roles of enhanced frictional heating and transport of ambient plasma in the segmentation process were discussed. In another work, based on 7-months of measurements taken by the Canadian component of the Resolute Bay ISR (RISR-C) in 2016, an automatic algorithm to identify the polar cap patch was developed and a database of 437 patches was constructed. We then studied the Magnetic Local Time (MLT) distribution of the patch occurrence frequency and also conducted a superposed epoch analysis on the altitude profiles of plasma density, temperature and field-aligned ion fluxes measured within the patches. The results showed that the patch electron temperature is typically lower than its surrounding areas, indicating their major source is the solar radiation produced plasma on the dayside mid-latitude region. When high-density plasma structures, such as the SED and polar cap patch, seed ion upflow in the F region and topside ionosphere, large ion fluxes can be produced, which may have significant impact on the distribution of ion outflow. We investigated the statistical characteristics of ion upflow and downflow using a 3-year (2011–2013) dataset from the Poker Flat ISR (PFISR). The results showed that ion upflow occurs more frequently on the nightside and when the ionospheric convection speed and the geomagnetic activity level increase. The downflow occurs most often on the dayside subauroral region when the IMF By > 10 nT and the IMF Bz < -10 nT, which we suggest is associated with enhanced plasma pressure gradient and poleward thermospheric wind during the decaying phase of the dayside SED and the SED plume. Results in this dissertation deepen our understanding of the polar cap patch and ion upflow in terms of their formation and plasma characteristics, and can be applied to studies of high-latitude high-density structure related scintillations and be used to validate and improve numerical models of the high-latitude ionosphere.