Comparative study of riometer absorption and GPS TEC during absorption events in the high latitude ionosphere

Regions of enhanced ionization are a frequent occurrence in the high latitude ionosphere, and can significantly affect the absorption of propagating radio waves in this region. Using Global Positioning System (GPS) receivers of the Canadian High Arctic Ionospheric Network (CHAIN) and co-located riometers at several high latitude stations, we have concurrently examined variations in ionospheric total electron content (TEC) and absorption of 30 MHz cosmic radio noise (CRN) for different types of ionospheric absorption events. A survey of 128 events including substorm injections, auroral precipitation and polar patches revealed four clear relationships between TEC and absorption. At stations close to auroral latitudes we found separate relationships for events associated with precipitation of low (<; 20 keV) and high (<; 200 keV) energy particles in addition to substorm injections. For stations located well inside the polar cap we found separate relationships associated with low energy precipitation and polar patches, while substorm injections and high energy precipitation were less frequent at these latitudes. The distinct relationships can be attributed to the nature of the absorption and TEC measurements as well as the height-dependent electron production rate for precipitating particles at a range of energies. The TEC-absorption relationships show good agreement with theoretical relationships for non-deviative absorption in the lower ionosphere and deviative absorption in the upper ionosphere.