CASCADES-II sounding rocket study of auroral poleward boundary intensifications

1. CASCADES-II sounding rocket study of auroral poleward boundary intensifications Meghan Mella, Kristina Lynch Dartmouth College Contact: Meghan.Mella@Dartmouth.edu Paul Kintner, Erik Lundberg Cornell University Marc Lessard University of New Hampshire Don Hampton, Hans Stenbaek-Nielsen University of Alaska Fairbanks Nickolay Ivchenko, Hanna Dahlgren KTH Abstract Three Events from Full Flight Event 1: Top panel shows total electrons in all directions, second panel is up-going electrons, third panel is precipitating electrons, and fourth panel is perpendicular electrons The CASCADES-II sounding rocket was launched on 20 March 2009 at 11:04:00UT from the Poker Flat Research Range. The payload had five sub-payloads for multipoint measurements of auroral dynamics and structure. The ground-based cameras under the rocket trajectory show auroral signatures that can be described as a series of Poleward Boundary Intensifications, which are repeated brightenings along the poleward edge of the auroral oval that may move equatorward [Lyons et al. 1999]. In a case study by Zesta et al. [2002] PBIs are split into two categories: equatorward extending or nonequatorward extending, based on MSP observations. The rocket is seen to fly through both types of PBIs, which show fundamental differences in the in situ and allsky image data, ranging from inverted-V type aurora in the equatorward extended events to alfvenic aurora in the nonequatorward extending events. This would suggest that each type relates to different magnetotail dynamics. The CASCADES-II rocket study will serve as a detailed case study of the relation between equatorward extending PBIs and Bursty Bulk Flows (BBFs) in the tail, which are seen in THEMIS data from satellites conjugate with the rocket footpoint. This study will also provide a detailed analysis of the less-studied nonequatorward extending PBIs and their association to instabilities at the separatrix boundary by comparing particle data from multiple payloads as well as ground optical data. • The Cascades2 flight encountered three distinct auroral events. The type of aurora seen from the ground is shown below for each time, similar to an event study by Semeter [2003]. Additionally, the electron spectrograms (1-3keV), split into precipitating, up-going, and perpendicular components, are shown, along with spectral line plots. • Event 1 is a classic Inverted-V type event, as seen from the electron population with a fairly constant energy over all pitch angles. • Event 2 is also like an Inverted-V, but there is a greater spread in energy, and the visible aurora is not a stable east-west aligned arc, but rather a north-south aligned arc, which is more distinctive of a PBI. • Event 3, which corresponds to the tall, rayed aurora, is widely spread in energy and can be described as a non-equatorward-extending PBI event. Event 2: Electron temperatures suggest plasmaspheric source (see “equatorward arc” on poster by Hampton) 2 3 1 Total e- Payload Concept Precipitating • 5 subpayloads for multipoint measurements, all with GPS and magnetometers Event 3: Alfvenic aurora, corresponding to tall rays (see “poleward arc” on poster by Hampton) Perp • Two payloads (with electron detectors) ejected across field lines separated from main payload (with two electron detectors, an ion detector, and an imager) by 500m at apogee • Subpayloads (with electric field booms and thermal electron detectors) ejected along magnetic field lines separated by 4km at apogee Up-going In Event 3, note the alternating precipitating and up-going electron populations observed around 600s. Also at the time of Event 3 a separate electron detector, which measures only precipitating electrons, shows very dispersive signatures, from which source altitudes can be calculated, varying from 100-300km above the payload. Launch Conditions Conclusions and Questions: • The Cascades2 data gives a good case study for three distinct types of aurora, as first pointed out by Semeter in 2003. From our data set, we can look at the types of aurora seen from ground observations and compare to the spectrograms from flight, as well as THEMIS and PFISR data. We will continue to explore the following questions: • Does the sequence of Events 1, 2, and 3 correspond to the temporal evolution of auroral structuring? • How does the camera structure align to the particle data? • Do the observed electric fields accelerate the observed electrons? This case study can be used to look at the correlation among flows in the magnetotail, auroral intensifications detected on ground-based instruments, and Alfvén waves on the rocket. These figures from Nakamura et al. (2001) show the spatial relationship between the BBF footpoint and the associated ionospheric auroral signature. During our event, the THEMIS footpoint is within one hour east of the rocket trajectory, which matches this picture. • Launched 20 March 2009 at 1104:00 UT • Apogee of 564km • Negative bay in H seen by ground magnetometers • PBI signatures seen in keograms • Dipolarization and earthward flows seen by THEMIS Map from John Bonnell References and Acknowledgements Nakamura, R., W. Baumjohann, R. Schödel, M. Brittnacher, V. A. Sergeev, M. Kubyshkina, T. Mukai, and K. Liou (2001), Earthward flow bursts, auroral streamers, and small expansions, J. Geophys. Res., 106(A6), 10,791-10,802. Liu, W. W., B.-L. Xu, J. C. Samson, and G. Rostoker, Theory and observation of auroral substorms: A magnetohydrodynamic approach, J. Geophys. Res.,100, 79, 1995. Lyons, L., T. Nagai, G. Blanchard, J. Samson, T. Yamamoto, T. Mukai, A. Nishida, and S. Kokubun (1999), Association between Geotail plasma flows and auroral poleward boundary intensifications observed by CANOPUS photometers, J. Geophys. Res., 104(A3), 4485-4500. Zesta, E., E. Donovan, L. Lyons, G. Enno, J. S. Murphree, and L. Cogger (2002), Two-dimensional structure of auroral poleward boundary intensifications, , 107, 1350, doi:10.1029/2001JA000260. Semeter, J., C. J. Heinselman, G. G. Sivjee, H. U. Frey, and J. W. Bonnell (2005), Ionospheric response to wave‐accelerated electrons at the poleward auroral boundary, J. Geophys. Res., 110, A11310, doi:10.1029/2005JA011226. From Zesta, 2002: Equatorward extending -represent modes of energy and momentum transfer from the separatrix toward the earth and through the plasma sheet Non-equatorward extending -represent dynamic structures, such as result from instabilities, along the separatrix without propagation in the plasma sheet AGU, 17 December 2009