Coordinated cluster and ground-based instrument observation of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: Relation to reconnection pulses and FTE signatures

Lockwood, M. and Fazakerley, A. N. and Opgenoorth, H. J. and Moen, J. and van Eyken, A. P. and Dunlop, M. W. and Bosqued, J. M. and Lu, G. and Cully, C. and Eglitis, P. and McCrea, I. W. and Hapgood, M. A. and Wild, M. N. and Stamper, R. and Denig, W. F. and Taylor, M. G. G. T. and Wild, J. A. and Provan, G. and Amm, O. and Kauristie, K. and Pulkkinen, T. I. and Strömme, A. and Prikryl, P. and Pitout, F. and Balogh, A. and Rème, H. and Behlke, R. and Hansen, T. L. and Greenwald, R. A. and Frey, H. U. and Morley, S. K. and Alcaydé, D. and Blelly, P.-L. and Donovan, E. F. and Engebretson, M. J. and Lester, M. and Watermann, J. F. and Marcucci, M. F. (2001) Coordinated cluster and ground-based instrument observation of transient changes in the magnetopause boundary layer during an interval of predominantly northward IMF: Relation to reconnection pulses and FTE signatures. Annales Geophysicae, 19 (10). pp. 1613-1640. ISSN 0992-7689

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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 well-defined 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 deg. 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 Alfvenic 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.

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Journal Article
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Annales Geophysicae
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?? clustereiscatsuperdarnmagnetometeramie dcs-publications-idart-682dcs-publications-creditssamnetdcs-publications-personnel-id104earth and planetary sciences (miscellaneous)astronomy and astrophysicsatmospheric sciencegeologyspace and planetary science ??
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24 Jun 2008 17:23
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15 Mar 2024 00:39