The ionospheric signature of transient dayside reconnection and the associated pulsed convection return ̄ow

Three SuperDARN coherent HF radars are employed to investigate the excitation of convection in the dayside high-latitude ionosphere in response to transient reconnection occurring in the cusp region. This study demonstrates the existence of transient antisunward-propagating backscatter features at the expected location of the ionospheric footprint of the cusp region, which have a repetition rate near 10 min. These are interpreted as the ionospheric signature of ̄ux transfer events. Moreover, transient sunward-propagating regions of backscatter are observed in the convection return ̄ow regions of both the preand post-noon sectors. These patches are observed to propagate towards the noon sector from at least as far around the auroral zone as 07 MLT in the pre-noon sector and 17 MLT in the post-noon sector, travelling with a velocity of approximately 1.5 to 2 km s. These return ̄ow patches have a repetition rate similar to that of the transient features observed at local noon. While providing supporting evidence for the impulsive nature of convection ̄ow, the observation of sunward-propagating features in the return ̄ow region is not consistent with current conceptual models of the excitation of convection.