Pulsed Ionospheric Cusp Flow: Signature of Alfvén Surface Wave Induced Reconnection?

P.PRIKRYL¹. G.PROVAN², K.A.McWILLIAMS² and T.K.YEOMAN
¹Communications Research Centre, Ottawa, Canada
² Department of Physics and Astronomy, University of Leicester, UK

Pulsed ionospheric flows (PIFs) in the cusp footprint are believed to be a consequence of magnetic reconnection on the dayside magnetopause, ionospheric signatures of quasiperiodic flux transfer events (FTEs). However, the question of what causes pulsed reconnection has remained unanswered. Here the PIFs are correlated with Alfvénic fluctuations that were observed in the upstream solar wind. It is concluded that on these occasions the FTEs were pulsed by Alfvén waves coupling to the dayside magnetosphere. The cross-correlation analysis of the IMF and the ground magnetic field near the cusp footprint indicates time lags that are several minutes longer than the propagation times estimated from multi point solar wind measurements. That is, there is a delay between the expected arrival of the Alfvén wave southward turning and the reconnection onset on the dayside magnetopause. We interpret the delay in terms of the intrinsic time scale for reconnection [1] and a model of surface-wave-induced magnetic reconnection [2]. It is argued [2] that surface waves with wavelengths larger than the thickness of the neutral layer can induce tearing-mode instability whose rise time would be the intrinsic time scale for the reconnection onset. The time scales predicted by the theory are similar to the observed delays.

[1] Russell, C.T., et al., Adv. Space. Res., 19, 1913-1917, 1997.

[2] Uberoi, C. et al., J. Geophys. Res., 104, 25153-25157, 1999.

Session Index

Proceedings Index