Abstract. We have combined $300 h of tristatic measurements of the ®eld-perpendicular F region ionospheric¯ow measured overhead at Tromsù by the EISCAT UHF radar, with simultaneous IMP-8 measurements of the solar wind and interplanetary magnetic ®eld (IMF) upstream of the Earth's magnetosphere, in order to examine the response time of the ionospheric ow to changes in the north-south component of the IMF (B z ). In calculating the¯ow response delay, the time taken by ®eld changes observed by the spacecraft to ®rst eect the ionosphere has been carefully estimated and subtracted from the response time. Two analysis methods have been employed. In the ®rst, the¯ow data were divided into 2 h-intervals of magnetic local time (MLT) and cross-correlated with the``half-wave recti®er'' function V 2 B s , where V is the solar wind speed, and B s is equal to IMF B z if the latter is negative, and is zero otherwise. Response delays, determined from the time lag of the peak value of the cross-correlation coecient, were computed versus MLT for both the east-west and north-south components of¯ow. The combined data set suggests minimum delays at $1400 MLT, with increased response times on the nightside. For the 12-h sector centred on 1400 MLT, the weighted average response delay was found to be 1.3 0.8 min, while for the 12-h sector centred on 0200 MLT the weighted average delay was found to increase to 8.8 1.7 min. In the second method we ®rst inspected the IMF data for sharp and enduring (at least $5 min) changes in polarity of the north-south component, and then examined concurrent EISCAT¯ow data to determine the onset time of the corresponding enhancement or decay of the¯ow. For the case in which the¯ow response was timed from whichever of the¯ow components responded ®rst, minimum response delays were again found at $1400 MLT, with average delays of 4.8 0.5 min for the 12-h sector centred on 1400 MLT, increasing to 9.2 0.8 min on the nightside. The response delay is thus found to be reasonably small at all local times, but typically $6 min longer on the nightside compared with the dayside. In order to make an estimate of the ionospheric information propagation speed implied by these results, we have ®tted a simple theoretical curve to the delay data which assumes that information concerning the excitation and decay of¯ow propagates with constant speed away from some point on the equatorward edge of the dayside open-closed ®eld line boundary, taken to lie at 77°magnetic latitude. For the combined cross-correlation results the best-®t epicentre of information propagation was found to be at 1400 MLT, with an information propagation phase speed of 9.0 km s A1. For the combined event analysis, the best-®t epicentre was also found to be located at 1400 MLT, with a phase speed of 6.8 km s A1.

Abstract. Cluster magnetic field data are studied during an outbound pass through the post-noon high-latitude magnetopause region on 14 February 2001. The onset of several minute perturbations in the magnetospheric field was observed in conjunction with a southward turn of the interplanetary magnetic field observed upstream by the ACE spacecraft and lagged to the subsolar magnetopause. These perturbations culminated in the observation of four clear magnetospheric flux transfer events (FTEs) adjacent to the magnetopause, together with a highly-structured magnetopause boundary layer containing related field features. Furthermore, clear FTEs were observed later in the magnetosheath. The magnetospheric FTEs were of essentially the same form as the original "flux erosion events" observed in HEOS-2 data at a similar location and under similar interplanetary conditions by Haerendel et al. (1978). We show that the nature of the magnetic perturbations in these events is consistent with the formation of open flux tubes connected to the northern polar ionosphere via pulsed reconnection in the dusk sector magnetopause. The magnetic footprint of the Cluster spacecraft during the boundary passage is shown to map centrally within the fields-of-view of the CUTLASS SuperDARN radars, and to pass across the field-aligned beam of the EISCAT Svalbard radar (ESR) system. It is shown that both the ionospheric flow and the backscatter power in the CUTLASS data pulse are in synchrony with the magnetospheric FTEs and boundary layer structures at the latitude of the Cluster footprint. These flow and power features are subsequently found to propagate poleward, forming classic "pulsed ionospheric flow" and "poleward-moving radar auroral form" structures at higher latitudes. The combined Cluster-CUTLASS observations thus represent a direct demonstration of the coupling of momentum and energy Correspondence to: J. A. Wild (j.wild@ion.le.ac.uk) into the magnetosphere-ionosphere system via pulsed magnetopause reconnection. The ESR observations also reveal the nature of the structured and variable polar ionosphere produced by the structured and time-varying precipitation and flow.

[1] We report an event observed by the Low-Energy Neutral Atom (LENA) imager on 18 April 2001, in which enhanced neutral atom emission was observed coming from the direction of the Sun and from the general direction of the subsolar magnetopause. The enhanced neutral atom emission is shown to be primarily a result of increased solar wind charge exchange with the Earth's hydrogen exosphere, that is, enhanced neutral solar wind formation, occurring in conjunction with a southward turning of the interplanetary magnetic field (IMF) which moves the magnetopause closer to the Earth. It is shown that the neutral atom flux under compressed magnetopause conditions is extremely sensitive to changes in the IMF north-south component.

Abstract. We perform a case study of a favourable conjunction of overpasses of the DMSP F11 and F13 spacecraft with the field of view of the Hankasalmi HF coherent scatter. At the time, pulsed ionospheric flows (PIFs) were clearly observed at a high-latitude in the radar field of view. The PIFs were associated with medium spectral width values and were identified as the fossilized signatures of pulsed dayside reconnection. Simultaneously, DMSP spectrograms from the two spacecraft showed dispersed ion signatures, observed equatorwards of the PIF signatures. We identified dayside high-latitude magnetosphere boundaries; these boundaries agreed well with those defined using the algorithm on the JHU/APL auroral particle website (Haerendel et al., 1978; Meng, 1988, 1995;Newell et al., 1991aNewell et al., , 1991bNewell et al., , 1991cTraver et al., 1991). We conclude that in this case study the dispersed ion signatures map to regions of very newly-opened flux. It is only when this flux has convected polewards that the signatures of the PIFs with medium spectral widths are observed by the HF radars. These particular PIF signatures map to regions of mantle precipitation, i.e. recently reconnected flux.

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