A. Kullen (1), L. Rosenqvist (1), and G. Marklund (2) (1) Swedish Institute of Space Physics, Uppsala, Sweden (2) Royal Institute of Technology, Stockholm, Sweden Large-scale auroral spirals during CIR-events Observations Global auroral images have been examined systematically for periods of CIR events in Undulations of the poleward boundary of the auroral oval are frequently observed during such high-speed solar wind conditions. Sometimes, the boundary undulations take the form of a giant auroral spiral or surge. Five such large-scale spiral/surge cases are presented in Figure 1. Typically, the event starts as a polewardly displaced auroral bulge at the pre- or postmidnight sector which further develops into a giant spiral (case 1 and 5) or surge (case 2-4) with a diameter of km. The spirals fade after some tens of minutes. Interestingly, during all auroral surge events (cases 2-4) boundary undulations and multiple bright spots can be seen on the dawn or duskside oval. Solar wind and MagnetosphereMagnetometer chain Chapman Conference on Corotating Solar Wind Streams and Recurrent Geomagnetic Activity 06 – 12 February 2005, Manaus, Brazil Possible explanations  Connection to poleward bulges during substorm recovery ? Interplanetary Magnetic Field (IMF) of average magnitude and fluctuations around zero. Case 5 is taken from another time period and occurs at the end of a Coronal Mass Ejection (CME) associated magnetic cloud during mainly northward IMF conditions. For this event no solar wind data is available but typically CME’s are connected to high solar wind speeds. Figure 3: Figure 3: Preliminary AE index data. All events appear during a prolonged period of auroral activity, resembling substorm recovery. Figure 1 : Figure 1 : IMAGE FUV (event 1-4) and Polar UVI (event 5) images. Figure 2: Figure 2: ACE solar wind data corrected for the propagation time. Common for all events are extremely high solar wind speeds of km/s. Events 1-4 occur during high speed streams related to Corotating Interaction Regions (CIRs) with an Although some of the events (case 2-4) show a high similarity with the WTS, no signatures of substorm onset are found. Thus, the auroral spiral/surge events are not correlated to a near- Earth tail current disruption. The occurrence of multiple auroral spots and boundary undulations on the dawn/dusk oval sides during the large-scale spiral/surge events (2-4) as well as the very high solar wind speed suggests the occurence The poleward bulges out of which the spirals form (1,4,5) resemble polewardly dis- placed bulges that appear typically during substorm recovery and northward IMF. Such bulges can reach very high latitudes and develop into a midnight arc. They might be caused by an interchange instability at the Rezhenov, 1995 of Kelvin-Hemholtz related boundary waves along the magnetotail flanks. However, the spirals probably do not map to the flanks. end of the tailward plasma sheet leading to a tailward stretching tongue.  Connection to the Westward Travelling Surge (WTS)?  Connection to vortices at the magnetopause flanks ? Figure 4: Figure 4: LANL and GOES data. None of the events are correlated with substorm breakup (lack of particle injections and B-field dipolarization). [Hasegawa et al., 2004] [Marklund et al., 1998]