Poleward-moving HF radar flow bursts in the cusp: Transient changes in flow speed or direction?

Poleward-moving line-of-sight velocity "flow bursts" have been observed in the cusp by two southern hemisphere SuperDARN HF radars with overlapping fields-of-view. This has allowed the estimation of unambiguous awe-dimensional velocity vectors in the vicinity of the "flow bursts". Rather than showing enhancements in the flow magnitude, the velocity vectors suggest that the line-of-sight velocity enhancements are a result of a change in the direction of the flow associated with latitudinal motion of the convection reversal boundary. These observations may have important implications for understanding the ionospheric footprint of flux transfer events, and also illustrate that caution is needed when interpreting line-of-sight velocity data from single radars.