Abstract
Abstract. An isolated plasma sheet flow burst took place at 22:02 UT, 1 September 2002, when the Cluster footpoint was located within the area covered by the Magnetometers-Ionospheric Radars-All-sky Cameras Large Experiment (MIRACLE). The event was associated with a clear but weak ionospheric disturbance and took place during a steady southward IMF interval, about 1h preceding a major substorm onset. Multipoint observations, both in space and from the ground, allow us to discuss the temporal and spatial scale of the disturbance both in the magnetosphere and ionosphere. Based on measurements from four Cluster spacecraft it is inferred that Cluster observed the dusk side part of a localized flow channel in the plasma sheet with a flow shear at the front, suggesting a field-aligned current out from the ionosphere. In the ionosphere the equivalent current pattern and possible field-aligned current location show a pattern similar to the auroral streamers previously obtained during an active period, except for its spatial scale and amplitude. It is inferred that the footpoint of Cluster was located in the region of an upward field-aligned current, consistent with the magnetospheric observations. The entire disturbance in the ionosphere lasted about 10min, consistent with the time scale of the current sheet disturbance in the magnetosphere. The plasma sheet bulk flow, on the other hand, had a time scale of about 2min, corresponding to the time scale of an equatorward excursion of the enhanced electrojet. These observations confirm that localized enhanced convection in the magnetosphere and associated changes in the current sheet structure produce a signature with consistent temporal and spatial scale at the conjugate ionosphere.
Highlights
High-speed plasma flows in the near-Earth and mid-tail plasma sheet are considered to play a key role in the flux and energy transport in the magnetotail
The flows near the boundary of the plasma sheet consist of field-aligned beams, whereas the flows in the central plasma sheet tend to have a large bulk flow component. The latter flows organize themselves in 10-min time scale flow enhancements, which are called bursty bulk flow (BBF) events, embedding velocity peaks of 1-min duration, which are called flow bursts, and have characteristics distinctly different from plasma sheet boundary layer flows (Baumjohann et al, 1990; Angelopoulos et al, 1992)
We examine the spatial and/or temporal scale of the flow burst and its relevant counterparts in the ionosphere and discuss the electrodynamics of the flow-associated disturbance in the ionosphere and the magnetosphere
Summary
High-speed plasma flows in the near-Earth and mid-tail plasma sheet are considered to play a key role in the flux and energy transport in the magnetotail Most likely, these fast flows are due to acceleration in the reconnection region. Many studies using quite different methods with single spacecraft have come to the conclusion that a BBF is expected to be limited in dawn-dusk extent with a spatial scale of 3–5 RE (Angelopoulos et al, 1997; Kauristie et al, 2000; Nakamura et al, 2001) These results were obtained by comparison between satellite and ground-based data, and low-altitude observations of convection, equivalent current, and auroral pattern. We examine the spatial and/or temporal scale of the flow burst and its relevant counterparts in the ionosphere and discuss the electrodynamics of the flow-associated disturbance in the ionosphere and the magnetosphere
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