Direct measurements of the ionospheric convection variability near the cusp/throat

[1] For the first time precise measurements obtained using Super Dual Auroral Radar Network (SuperDARN) radars are used to quantify the temporal variability in the convection velocity and identify the cause of the variations for a particular event located in the vicinity of the cusp. Using SuperDARN line-of-sight (LOS) Doppler velocities near 1200 magnetic local time and a standard fitting technique, the observed temporal variability is related to dayside convection features such as the cusp, convection throat, and convection reversal boundaries (CRBs). Two distinct regions of variability are observed: a region of high (often >500 m s ) hourly temporal variability occurring near the dayside CRB of the dusk convection cell during interplanetary magnetic field (IMF) By < 0, and a region of very low (<100 m s ) temporal variability in the convection throat. The source of the high variability near the dayside dusk CRB is caused primarily by motion of the large-scale convection pattern most likely due to the variable IMF. The line-of-sight velocities in this region fluctuate between sunward and antisunward directed flow depending on the position of the CRB relative to the radar observation area. In the convection throat, however, steady antisunward directed flow exceeding 500 m s 1 is observed despite the variable IMF. Based on these observations it is expected that increased Joule heating due to variability in the electric field occurs near the dayside CRB of the crescent-shaped convection cell and little additional Joule heating occurs in the convection throat.