Blobs and irregularities in the auroral ionosphere

The EISCAT BLOB experiment has been designed to study structuring of the plasma in the auroral ionosphere on scales of tens of kilometres transverse to the magnetic field. Results are presented from the initial observations that show three different types of field-aligned irregularities occurring within a time interval of about two hours. The first type appears to be a long-lived boundary blob of cold plasma convecting through the field of view. The others show evidence of in-situ formation. A narrow density enhancement, associated initially with high electron temperatures, appears to originate and develop from a localised particle precipitation event. In the third category the irregularity takes the form of a narrow trough in electron density with high ion temperatures caused by ion-frictional heating in a fast convective flow.