How Much Flux Does a Flux Transfer Event Transfer?

• Published in: Journal of Geophysical Research: Space Physics
• Main Authors: Fear, R. C., Trenchi, L., Coxon, J. C., Milan, S. E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU), Wiley 2018
• Subjects: reconnection; magnetopause; flux transfer event; Antarctic; Canada; Breen; Antarc*; British Antarctic Survey
• Online Access: http://onlinelibrary.wiley.com/doi/10.1002/2017JA024730/abstract; http://hdl.handle.net/2381/40998; https://doi.org/10.1002/2017JA024730

Flux transfer events are bursts of reconnection at the dayside magnetopause, which give rise to characteristic signatures observed by a range of magnetospheric/ionospheric instrumentation. One outstanding problem is that there is a fundamental mismatch between space-based and ionospheric estimates of the flux that is opened by each flux transfer event-in other words, their overall significance in the Dungey cycle. Spacecraft-based estimates of the flux content of individual flux transfer events (FTEs) correspond to each event transferring flux equivalent to approximately 1% of the open flux in the magnetosphere, whereas studies based on global-scale radar and auroral observations suggest this figure could be of the order of 10%. In the former case, flux transfer events would be a minor detail in the Dungey cycle, but in the latter they could be its main driver. We present observations of two conjunctions between flux transfer events observed by the Cluster spacecraft and pulsed ionospheric flows observed by the Super Dual Auroral Radar Network (SuperDARN) network. In both cases, a similar number of FTE signatures were observed by Cluster and one of the SuperDARN radars, but the conjunctions differ in the azimuthal separation of the spacecraft and ionospheric observations (i.e., the distance of the spacecraft from the cusp throat). We argue that the reason for the existing mismatch in flux estimates is due to implicit assumptions made about FTE structure, which tacitly ignore the majority of flux opened in mechanisms based on longer reconnection lines. If the effects of such mechanisms are considered, a much better match is found. R. C. F. was supported by the UK's Science and Technology Facilities Council (STFC) Ernest Rutherford Fellowship ST/K004298/2; L. T. and J. C. C. were supported by STFC Ernest Rutherford grant ST/L002809/1, and S. E. M. was supported by STFC consolidated grant ST/N000749/1. SuperDARN is a collection of radars funded by national scientific funding agencies of Australia, Canada, China, France, Japan, South Africa, United Kingdom, and the United States of America. Data were obtained from the British Antarctic Survey SuperDARN data hub and processed with RST v4.0 and FITACF v3.0. Cluster data were obtained from the Cluster Science Archive (https://www.cosmos.esa.int/web/csa). We are grateful to Paul Breen, Pasha Ponomarenko, Kevin Sterne, and Keith Kotyk for their assistance with the SuperDARN data hub, RST, and FITACF. Peer-reviewed Publisher Version