Summary
Auroral westward flow channels (A WFCs) are intense, narrow channels of westward drift overlapping the equatorward edge of the auroral oval in the pre-magnetic midnight sector. They are a close relative of the sub-auroral polarisation stream which encompasses polarisation jets, a phenomenona lso known as sub-aurorali on drift events.R ecento bservationsm ade with the TasmanG eospaceE nvironment Radar (TIGER) (147.2°E,4 3.4°SG eodetic; 55.0° Geomagnetich) ave revealedc lose associationsb etweent he appearanceo f A WFCs and substormo nset,a nd their subsequendt ecayt oward the end of recoveryp hase.I n fact, in terms of electricf ield strength, they are the strongest signatures of substorms in the ionospheric convection (>50 mV m-I). In terms of electric potential difference (> I 0 kV), they also represent a substantial fraction of the total potential difference generated during substorms. The A WFCs exhibit a diverser ange of behaviour,t hereb eing no typicale vent.T he radar observationss howt hat radial polarisationf ields sometimeso scillate towards and away from the Earth, and bifurcate, within regions of closed flux in the magnetotail throughout substorm evolution. We have identified every A WFC observed by TIGER during the first year of operation, 2000. Simple statistical arguments imply that one, if not more, A WFC probably occurs during every substorm. A WFCs are a fundamental aspect of substorm evolution.