Observations of the Tongue of Ionization with GPS TEC and SuperDARN.

摘要

Tongue of ionization (TOI) events in both the northern and southern hemisphere have been identified with polar maps of total electron content (TEC) derived from the global network of GPS receivers. The TOI, as observed by GPS, extends through the dayside cusp, across the polar cap to the nightside, in both hemispheres. The TOI is a source of ionospheric irregularities. Its distribution across the high latitude ionosphere is believed to be controlled by plasma convection. The GPS maps show the development of TOI from mid- latitude plumes of ionization known as storm enhanced density (SED). The SED feature is observed to be magnetically conjugate, although data coverage is considerably more sparse in the southern hemisphere. In this paper, SuperDARN HF radar observations of the high-latitude convection pattern have been overlaid onto the GPS TEC polar plots for multiple TOI events. It is observed quantitatively that the GPS TEC observations of the TOI match the SuperDARN estimates of the convection pattern. Using SuperDARN observations of the evolving convection pattern, we study the evolution of the TOI and the associated redistribution of plasma structure. The locations and conditions under which HF backscatter occurs in the vicinity of the TOI plumes are examined. We explore the similarities between TOI events observed simultaneously in the two hemispheres and look especially for the impact of convection-induced asymmetries. Gradients, irregularities, and velocities are examined between the two hemispheres. Spatial and temporal estimates of the TEC at individual locations along the SED plume and the TOI are studied in an attempt to quantify the percentage of the TEC that enters into the trans-polar convection pattern.