Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 19, 1613-1640, 2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.
30 Sep 2001
Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures
M. Lockwood2,1, A. Fazakerley3, H. Opgenoorth4, J. Moen6,5, A. P. van Eyken7, M. Dunlop14, J.-M. Bosqued8, G. Lu9, C. Cully17, P. Eglitis4, I. W. McCrea1, M. A. Hapgood1, M. N. Wild1, R. Stamper1, W. Denig15, M. Taylor3, J. A. Wild10, G. Provan10, O. Amm11, K. Kauristie11, T. Pulkkinen11, A. Strømme12, P. Prikryl13, F. Pitout4, A. Balogh14, H. Rème8, R. Behlke4, T. Hansen12, R. Greenwald16, H. Frey21, S. K. Morley2, D. Alcaydé8, P.-L. Blelly8, E. Donovan17, M. Engebretson18, M. Lester10, J. Watermann19, and M. F. Marcucci20 1Solar Terrestrial Physics Division, Department of Space Science and Technology, Rutherford Appleton Laboratory, Oxfordshire, UK
2Department of Physics and Astronomy, Southampton University, Southampton, UK
3Mullard Space Science Laboratory, Holmbury St. Mary, Surrey, UK
4IRF, Swedish Institute of Space Physics, Uppsala Division, Sweden
5Department of Physics, University of Oslo, Blindern, Oslo, Norway
6Also at Arctic Geophysics, University Courses on Svalbard, Longyearbyen, Norway
7EISCAT Scientific Association, Longyearbyen, Svalbard, Norway
8CESR, Centre d’Etude Spatiale des Rayonnements, Toulouse, France
9High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, USA
10Department of Physics and Astonomy, Leicester University, Leicester, UK
11Finnish Meteorological Institute, Helsinki, Finland
12University of Tromsø, Tromsø, Norway
13Communications Research Centre, Ottawa, Ontario, Canada
14Blackett Laboratory, Imperial College, London, UK
15AFRL, Hanscom AFB, Cambridge, MA, USA
16Remote Sensing Group, Applied Physics Laboratory, John Hopkins University, Laurel, MD, USA
17University of Calgary, Calgary, Canada
18Department of Physics, Augsburg College, Minneapolis, MN, USA
19Danish Meteorological Institute, Kobenhavn, Denmark
20Istituto di Fisica dello Spazio Interplanetario – CNR, Rome, Italy
21Space Science Centre, Berkeley, USA
Abstract. We study a series of transient entries into the low-latitude boundary layer (LLBL) of all four Cluster spacecraft during an outbound pass through the mid-afternoon magnetopause ( [ XGSM, YGSM, ZGSM ] ≈ [ 2, 7, 9 ] RE). The events take place during an interval of northward IMF, as seen in the data from the ACE satellite and lagged by a propagation delay of 75 min that is welldefined by two separate studies: (1) the magnetospheric variations prior to the northward turning (Lockwood et al., 2001, this issue) and (2) the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, this issue). With an additional lag of 16.5 min, the transient LLBL events correlate well with swings of the IMF clock angle (in GSM) to near 90°. Most of this additional lag is explained by ground-based observations, which reveal signatures of transient reconnection in the pre-noon sector that then take 10–15 min to propagate eastward to 15 MLT, where they are observed by Cluster. The eastward phase speed of these signatures agrees very well with the motion deduced by the cross-correlation of the signatures seen on the four Cluster spacecraft. The evidence that these events are reconnection pulses includes: transient erosion of the noon 630 nm (cusp/cleft) aurora to lower latitudes; transient and travelling enhancements of the flow into the polar cap, imaged by the AMIE technique; and poleward-moving events moving into the polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15 satellite reveals that the open field lines near noon have been opened for some time: the more recently opened field lines were found closer to dusk where the flow transient and the poleward-moving event intersected the satellite pass. The events at Cluster have ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Event (FTE), with allowance for magnetospheric ion reflection at Alfvénic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1 RE in their direction of motion and show a rise in the magnetic field strength, but unlike FTEs, in general, they show no pressure excess in their core and hence, no characteristic bipolar signature in the boundary-normal component. However, most of the events were observed when the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge from the exterior boundary (when the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of FTEs at middle altitudes.

Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions; solar wind-magnetosphere interactions)

Citation: Lockwood, M., Fazakerley, A., Opgenoorth, H., Moen, J., van Eyken, A. P., Dunlop, M., Bosqued, J.-M., Lu, G., Cully, C., Eglitis, P., McCrea, I. W., Hapgood, M. A., Wild, M. N., Stamper, R., Denig, W., Taylor, M., Wild, J. A., Provan, G., Amm, O., Kauristie, K., Pulkkinen, T., Strømme, A., Prikryl, P., Pitout, F., Balogh, A., Rème, H., Behlke, R., Hansen, T., Greenwald, R., Frey, H., Morley, S. K., Alcaydé, D., Blelly, P.-L., Donovan, E., Engebretson, M., Lester, M., Watermann, J., and Marcucci, M. F.: Coordinated Cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to reconnection pulses and FTE signatures, Ann. Geophys., 19, 1613-1640,, 2001.
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