Type-I ion outflow from the high latitude ionosphere

Abstract

The aim of this thesis is to study type-I ion outflows in the high latitude ionosphere. Type-I ion outflows are characterized by strong perpendicular electric fields, enhanced and anisotropic ion temperatures and low electron densities below 300 km, indicating small amounts of hard particle precipitation. We scanned data from the EISCAT Madrigal database over a period of 10 years (January 2000 - December 2010). We checked the colour plots of the field-aligned experiments ran with the UHF, the VHF and the ESR radars. Data from the type-I candidates have then been analyzed using a matlab program. Type-I ion outflows have been divided into two categories: non-continuous and continuous, depending on the temperature ratio profile. Continuous outflows have been detected with the ESR radar and only at high altitudes ( > 400 km) with the VHF radar. We suggest different ion heating mechanisms at different locations and altitudes. Type-I ion outflows have been detected only in the evening sector with the UHF and VHF radars, but both in the morning and evening sectors with the ESR radars, suggesting that particle precipitations may be of relevance to trigger these outflows. A third type of ion outflows has been identified showing a fast changing temperature ratio profile. When possible we checked the presence of naturally enhanced ion acoustic lines (NEIALs) during type-I ion outflows, 4 outflow events have been analyzed. We found NEIALs during 1 outflow event, suggesting that the proposed theories in the literature about the NEIAL generation mechanisms should be discussed in the future or other mechanisms are needed to fulfill the requirement of a temperature ratio less than 1.