SM21B-01 

Statistical Comparison of Conjugate Auroras Seen From Space

Deverapalli, C (deverapallic@cspar.uah.edu), Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35899, United States * Germany, G A (Glynn.Germany@uah.edu), Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35899, United States Spann, J F), NASA/MSFC VP60, National Space Science and Technology Center 320 Sparkman Drive, Huntsville, AL 35805, United States Chua, D), Space Science Division, Naval Research Laboratory 4555 Overlook Ave SW, Washington, DC 20375, United States Fillingim, M), Space Sciences Lab, University of California 7 Gauss Way, Berkeley, CA 94720, United States Joshi, N

Perez-Silva, C), Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35899, United States

Conjugate studies of high-latitude geomagnetic activity provide understanding of the global magnetospheric reaction to external perturbations and the role of the ionosphere in modulating and coupling with the magnetosphere. Interhemispheric asymmetries as manifested in auroral emissions have been observed for over 40 years. Until recently, the nature of the problem limited the type and extent of studies that can be performed to either conjugate ground based observations or comparison of space based images from all-sky cameras. With the availability of multiple space-based observing platforms, observations of conjugate aurora have been performed, primarily on an event basis. In this paper, initial results are presented of a statistical comparison of conjugate auroras as seen by Polar/UVI and IMAGE/FUV between 2001 and 2003. A database of over 900 potential conjugate observing periods is used to select auroral images for study. Comparisons include statistical intensity distributions, auroral power and relative substorm onset timing and substorm evolution.

SM21B-02 

Plasma Transport Along Discrete Auroral Arcs

* Kullen, A (kullen@irfu.se), IRF Uppsala, Box 537, Uppsala, SE-75121, Sweden Buchert, S (scb@irfu.se), IRF Uppsala, Box 537, Uppsala, SE-75121, Sweden Lileo, S (sonia.lileo@ee.kth.se), Alfven Laboratory, KTH, Teknikringen 31, Stockholm, SE-10044, Sweden Johansson, T (tommy.johansson@ee.kth.se), Alfven Laboratory, KTH, Teknikringen 31, Stockholm, SE-10044, Sweden

We study with help of strong E-field events the contribution of discrete auroral arcs to the total plasma flux in the high-latitude ionosphere. Common features of such arcs are a field-aligned potential drop and strong perpendicular E-field above. Due to parallel E-fields, the region above the acceleration region is partly decoupled from the ionosphere and strong, local plasma flows along the auroral arc are the consequence. As these plasma flows are directed in opposite directions on the different sides of the arc, a net plasma transport occurs only when the connected E-field is monopolar or the arc is located at a steep density gradient. For this case, it is proposed that the locally enhanced plasma convection helps to remove stresses in the magnetosphere that have built up due to friction in the ionosphere. 32 strong E-field events found in Cluster data are used. They all appear in the boundary region between polar cap and central plasma sheet. Most events appear during substorm expansion or recovery. For a large majority of the E-field events, a net plasma flux occurs. The plasma transport connected to strong E-field peaks is in two third of the cases in the same direction as the background flow within the boundary region. In one third of the cases the contribution of the E-peak is high enough to enhance the plasma flux in the boundary region considerably. Interestingly, in most expansion cases the E-peak related and background plasma transport in the boundary region is sunward, in most recovery cases the average plasma transport has an anti-sunward direction.

SM21B-03 

Azimuthal evolution of the aurora in tens of seconds around the expansive phase onset

* Liang, J (jun.liang@space.gc.ca), Space Science Branch, Canadian Space Agency, St-Hubert, QC J3Y 8Y9, Canada Donovan, E (edonovan@ucalgary.ca), Department pf Physics & Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada Liu, W (william.liu@space.gc.ca), Space Science Branch, Canadian Space Agency, St-Hubert, QC J3Y 8Y9, Canada Jackel, B (brian.jackel@ucalgary.ca), Department pf Physics & Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada Spanswick, E (emma@phys.ucalgary.ca), Department pf Physics & Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada Syrjaesuo, M (mikko.syrjaesuo@fmi.fi), Department pf Physics & Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada Partamies, N (noora.partamies@fmi.fi), Department pf Physics & Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada Voronkov, I (igor@phys.ucalgary.ca), Department pf Physics & Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada Connors, M (martinc@athabascau.ca), Atabasca University, 1 University Drive, Athabasca, AB T9S 3A3, Canada Mende, S (mende@ssl.berkeley.edu), Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 94720-7450, United States Angelopoulos, V (vassilis@ucla.edu), : Institute of Geophysics & Planetary Physics, University of California, Los Angeles, Los Angeles, CA 90095-1567, United States Frey, H (hfrey@ssl.berkeley.edu), Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA 94720-7450, United States Ge, Y (ysge@ucla.edu), : Institute of Geophysics & Planetary Physics, University of California, Los Angeles, Los Angeles, CA 90095-1567, United States Russell, C (ctrussel@igpp.ucla.edu), : Institute of Geophysics & Planetary Physics, University of California, Los Angeles, Los Angeles, CA 90095-1567, United States Rae, J (jrae@phys.ualberta.ca), Department of Physcis, University of Alberta, Edmonton, AB T6G 2J1, Canada Mann, I (imann@phys.ualberta.ca), Department of Physcis, University of Alberta, Edmonton, AB T6G 2J1, Canada

Using data from the implementation phase (2004-2007) of the THEMIS All-Sky Imager (ASI) array, we carry out a study of the temporal evolution and fine structure of the substorm onset arc in the tens of seconds around expansive phase (EP) onset. The continent-wide array provides an unprecedented combination of mesoscale imaging with relatively high time resolution (3 second cadence), subject to the limitations imposed by viewing conditions. We have identified eight events in which we have excellent viewing of the onset aurora. Our results show the following salient features: 1. The initial brightening occurs along an azimuthally extended region of the arc. This brightening typically spans ~1 hour of MLT. In cases that the camera provides ideal coverage of the arc, the length of the brightening does not noticeably change during the first tens of seconds of EP. 2. Periodic structures along the arc emerge from ~10 s before the EP onset, and significantly brightens within ~10 s after the onset, constituting the most unambiguous and prominent feature from the optical auroral aspects of the substorm EP onset. Those periodic "wave" structure, on its initial formation and brightening, are usually well aligned (<15 deg) with the L-shell. The wavelength is about 40-130 km. These structures either remain stationary or propagate east or west during the initial brightening. 3. About 20-30 s after the onset, the brightening arc is no longer aligned with the L-shell. Titled structure, typically appears as a "bifurcation" of the initial onset arc, starts to develop and leads the poleward progression of the substorm auroras. We interpret these results as follows. First, the auroral breakup is on field lines connected to a region in the CPS that is unstable over an extended azimuthal range, but in a limited radial range (the latter a conclusion based on contemporaneous riometer observations). Second, the instability grows very rapidly across this initially unstable region but the region itself does not grow in size for tens of seconds after the initial onset. Third, the alignment between the onset-associated periodic structures and the magnetic L-shell gives strongly hints that they are controlled by near-Earth magnetotail dynamics. If that is true, then waves associated with the breakup in the CPS appear to have no preferred propagation direction. We finish by discussing the implications of these results for substorm onset mechanism theories.

SM21B-04 

ROPA (Rocket Observations of Pulsating Aurora) and AMISR Observations of Precipitation and Ionospheric Conductivity During Pulsating Aurora

* Fernandes, P A (par9@unh.edu), Space Science Center, University of New Hampshire 39 College Rd., Durham, NH 03857, United States Lessard, M R (marc.lessard@unh.edu), Space Science Center, University of New Hampshire 39 College Rd., Durham, NH 03857, United States Jones, S L (sarah.jones@unh.edu), Space Science Center, University of New Hampshire 39 College Rd., Durham, NH 03857, United States Lynch, K A (kristina.lynch@dartmouth.edu), Dartmouth College, Dept. of Physics and Astronomy 6127 Wilder Lab., Hanover, NH 03755, United States Kintner, P M (pmk1@cornell.edu), Dartmouth College, Computer and Electrical Engineering 302 Rhodes Hall, Ithaca, NY 14853, United States Stenbaek-Nielsen, H C (hnielsel@gi.alaska.edu), Geophysical Institute, University of Alaska - Fairbanks 903 Koyukuk Drive, Fairbanks, AK 99775, United States Heinselman, C (craig.heinselman@sri.com), SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025, United States Lummerzheim, D (lumm@gi.alaska.edu), Geophysical Institute, University of Alaska - Fairbanks 903 Koyukuk Drive, Fairbanks, AK 99775, United States

The ROPA (Rocket Observations of Pulsating Aurora) sounding rocket was launched on February 12, 2007 at 12:45:04 UT from Poker Flat Research Range into a region of pulsating aurora. At least three electron precipitation populations were measured (including a uniform, diffuse background), with the AMISR radar acquiring supporting data. Previous studies of pulsating aurora showed the presence of thin (~2 km) patches of luminosity. During the ROPA campaign, however, first-ever AMISR observations of the ionospheric signature of pulsating aurora revealed relatively thin conductivity enhancements, but the order of 10- 20 km. In addition, the observations show conductivity enhancement peaks ranging from 95 to 105 km altitude and with significant vertical structure at times. The widely varying AMISR observations are consistent with likewise varying reports in the literature regarding in-situ measurements of the precipitating electron populations. In this presentation, AMISR observations of pulsating auroral events are presented and discussed, with a particular emphasis on the event that occurred during the launch of ROPA.

SM21B-05 

Pulsating Aurora and Associated Particle Precipitation as Observed by the Rocket Observations of Pulsating Aurora Mission

* Jones, S L (sarah.jones@unh.edu), Space Science Center, University of New Hampshire 39 College Rd., Durham, NH 03824, United States Lessard, M R (marc.lessard@unh.edu), Space Science Center, University of New Hampshire 39 College Rd., Durham, NH 03824, United States Lynch, K A (kristina.lynch@dartmouth.edu), Dartmouth College, Department of Physics and Astronomy 6127 Wilder Lab., Hanover, NH 03755, United States Kintner, P M (pmk1@cornell.edu), Cornell University, Electrical and Computer Engineering 302 Rhodes Hall, Ithaca, NY 14853, United States Stenbaek-Nielsen, H C (hnielsen@gi.alaska.edu), Geophysical Institute, University of Alaska - Fairbanks 903 Koyukuk Drive, Fairbanks, AK 99775, United States

The Rocket Observations of Pulsating Aurora sounding rocket was launched on February 12, 2007 at 12:45:04UT from Poker Flat Research Range into a region of pulsating aurora. Approximately 4.5 minutes into flight, the rocket crossed the well-defined, high latitude boundary of the pulsating aurora into a region of diffuse, non- pulasting aurora. Previous measurements of electron precipitation associated with pulsating aurora have varied with many showing high energy, tens to hundreds of keV, modulated populations. The ROPA particle instruments measured at least three distinct populations of precipitating electrons and a lack of the higher energy electrons often observed. Several parameters that have been modeled for this event using Open-GGCM show the pulsating aurora to have developed within a larger region of widespread diffuse aurora, as was observed from the Poker allsky camera images. The Poker MSP keogram shows proton aurora in the poleward region, as observed previously by Viereck and Stenbaek-Nielsen [1979]. Observations of the development of pulsating aurora within a region of diffuse plasma sheet electron precipitation and the correlation of the pulsating aurora with the diffuse proton aurora provides information about the relationship between the precipitation mechanisms involved. In this presentation, we discuss the transition from diffuse to pulsating aurora and the possible role of protons in regulating the characteristics of the pulsating aurora.

SM21B-06 

A laboratory search for plasma erosion by Alfven waves

* Vincena, S (vincena@physics.ucla.edu), UCLA Department of Physics and Astronomy, 1000 Veteran Avenue Room 15-70, Los Angeles, CA 90095-1696, United States Gekelman, W (gekelman@physics.ucla.edu), UCLA Department of Physics and Astronomy, 1000 Veteran Avenue Room 15-70, Los Angeles, CA 90095-1696, United States Pribyl, P), UCLA Department of Physics and Astronomy, 1000 Veteran Avenue Room 15-70, Los Angeles, CA 90095-1696, United States

Obliquely propagating shear Alfven waves with transverse wavelengths on the order of the electron inertial length or even the ion gyro-radius are commonly observed in the earth's low-altitude auroral zones. These regions are also replete with observations of electron beams and transversely heated ions. A kinetic treatment of shear Alfven wave-particle interaction reveals how these waves can be responsible for some of the observed particle acceleration. The auroral plasma environment is further enriched by the presence of field-aligned depletions in plasma density, and it has been suggested* that the Alfven waves may, in fact, be the cause of the erosion of ionospheric density. In this laboratory experiment, shear waves will be launched using a variety of proven antennas, and also allowed to grow spontaneously as Drift-Alfven modes in seeded density depletions**. Detailed measurements of the wave magnetic fields in the perpendicular density gradient regions will be presented which demonstrate the generation of short perpendicular wave scales due to the perpendicular gradient in parallel wave phase speed. Miniature in-situ particle diagnostics will also be used to look for electron and ion acceleration. The waves will also be launched into an increasing region of background magnetic field in an attempt to model the ratios of Alfven speed to electron thermal speed, and density gradient scale length to electron inertial length appropriate to the earth's auroral zone. Preliminary results will be presented on the efficacy of shear Alfven waves to self-generate plasma density depletions, or deepen ambient density inhomogeneities. The experiments are conducted at UCLA's Basic Plasma Science Facility in the Large Plasma Device. *Chaston, et al., "Ionospheric erosion by Alfven Waves," JGR, V 111, A03206, 2006. **Penano, et al., "Drift-Alfven fluctuations associated with a narrow pressure striation," Phys. Plasmas, V 7, Issue 1, pp. 144-157 (2000).

SM21B-07 

Hemispheric Asymmetries in the Afternoon Aurora due to Solar Wind and IMF Variations

* Nord, S (sanord@ssl.berkeley.edu), Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States Fillingim, M O (matt@ssl.berkeley.edu), Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States Parks, G K), Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States Mende, S B), Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States

Using global auroral images from Polar UVI in the southern hemisphere and IMAGE FUV in the north, we have analyzed the conjugacy of the afternoon aurora over a five-month period. From over 50 concurrent intervals we observe several asymmetries, periods for which auroral structure at one pole diverges from the other. Initial results suggest that this is due to the interplanetary magnetic field (IMF) and the solar wind velocity. Should the velocity fall below a certain threshold (~ 500 km/s), any fluctuation or discontinuity in the IMF appears to have no affect on auroral activity. Above this threshold, however, when the IMF is southward and a significant dawnward component exists, there is an enhancement in the afternoon aurora in the northern hemisphere. If, on the other hand, there is a significant duskward component to the IMF, then an enhancement in the afternoon aurora in the southern hemisphere is observed. The results of this study indicate that these features are driven by an instability at the magnetopause (such as a Kelvin-Helmholtz instability). In addition, these findings show that the dayside magnetosphere can respond asymmetrically to discontinuities in the IMF.

SM21B-08 

Statistical Relationship between Large-scale Field-aligned Currents and Particle Precipitation

* Ohtani, S (Shin.Ohtani@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Wing, S (Simon.Wing@jhuapl.edu), The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Ueno, G (gen@ism.ac.jp), Institute of Statistical Mathematics, 4-6-7 Minami-Azabu, Tokyo, 106-8569, Japan Higuchi, T (higuchi@ism.ac.jp), Institute of Statistical Mathematics, 4-6-7 Minami-Azabu, Tokyo, 106-8569, Japan

In this study we statistically examine how large-scale field-aligned currents (FACs) and particle precipitation are related. We use magnetic-field and particle data obtained from the DMSP-F7 and F12-15 spacecraft during a few hundreds of thousands of auroral oval crossings at various local times. It is found that the average electron energy is well correlated with the FAC density, especially for upward FACs. This is what one might expect from the well-known relationship between the upward FAC and auroral acceleration (Knight relation), but the present result suggests that a similar relationship also holds on a larger scale, that is, for R1 and R2 currents. In certain MLT sectors the average ion energy is positively correlated with the FAC intensity, rather than with the FAC density, irrespective of the polarity of FACs, which might be puzzling from the viewpoint of the M-I coupling. This result, however, can be attributed to the fact that both the FAC intensity and the average energy of magnetospheric ions are correlated with geomagnetic activity. We seek to examine systematically the relationship between the FAC density/intensity and the average energy and energy flux of precipitation in terms of local time and particle species..

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.