Small Scale Structures and Motions of Auroral Signatures as Observed From the Ground: a Planned Field Study Using Camera and Radar Observations

Transcription

1 Small Scale Structures and Motions of Auroral Signatures as Observed From the Ground: a Planned Field Study Using Camera and Radar Observations Preliminary Results for Return Current Region Structures R.G. Michell, K.A. Lynch: Dartmouth College H.C. Stenbaek-Nielsen, T.J Hallinan: UAF D.L. Hysell, M.C. Kelley: Cornell Univereity Yosemite 7-10 February, 2006 M. Lessard: UNH

2 Abstract As a continuation of the CASCADES (the Changing Aurora: in Situ and Camera analysis of Electron precipitation Structures) sounding rocket campaign, a ground based study of auroral structures and motions will be conducted this coming winter from Poker Flat, AK. A major goal of this study is to examine the small-scale perpendicular motions of auroral features in the context of auroral poleward boundary activity associated with substorm breakup. The use of an all-sky camera and a narrow-field camera at Poker Flat will allow for a 2-D image of the auroral structures. The narrowfield camera has a 12 X 16 degree field of view and allows for viewing of sub-kilometer scale structures at 100 km altitude, and the all-sky camera provides a large scale auroral context. The 30 MHz imaging radar located in Anchorage will be used to image the same area that is being observed with the narrow-field camera. The AMISR that is currently being constructed at Poker Flat will give high time and space resolution information on the auroral plasma structures present.the main science questions to be addressed with this array of instruments are: How intense are small-scale structures when viewed with high resolution? What wave modes and auroral electrodynamics cause ion outflow? What is the distribution of auroral arcs widths, and their relation to arc lifetime? What differences are observed between the motions of adjacent light and dark auroral signatures, and what can this tell us about ionospheric electric fields and plasma density. Preliminary results comparing ground camera observations of return current region (RCR) auroral signatures to in situ observations of similar RCR structures from the Cluster spacecraft will be presented.

3 Outline Introduction and Motivation. Four open questions. Morphology of RCR black aurora. Comparison of camera data to typical Cluster measurements. Instrumentation and plans for this winter

4 Background and Motivation Motivation: To understand how the aurora works and its interactions with the magnetosphere. Ground Based: Narrowfield camera In-situ: FAST data Lynch, et. al., 2002

5 Auroral Morphology Discrete aurora Diffuse aurora Black aurora T. Trondsen Focus on this type Stormer, 1955 Return current region (RCR) black aurora

6 Four open questions for ground-based studies I. Evolution in space / time of auroral features 1. Arc width distributions 2. Return current region black aurora morphology II. Ionospheric response to optical signatures 3. Ionospheric feedback 4. Ion outflows

7 Return current region black aurora morphology --Little attention has been paid to these black structures that occurs alongside the discrete aurora (return current region aurora) --Specifically excluded in previous optical studies of black aurora which focused on the black aurora embedded in the diffuse aurora. --From in-situ measurements: it is now believed that this type is of interest. Example from Poker all-sky camera

8 Auroral Regions --Return current regions (RCR) and Alfven waves (AW) play a major role in auroral electrodynamics and M-I coupling. --RCR and AW are associated with ion outflow and e- evacuation. --RCR and AW don t produce significant visible signature. --Ground-based studies have not yet focused on these regions Paschmann, et al.

9 Return current region black aurora morphology Poker Flat all-sky example of RCR auroral structure seconds between images North East

10 Return current region black aurora morphology Assumed 100 km altitude Relative Intensity (~16 km wide) Time (~7 km wide) Pixel number (related to distance) --Physical picture: 1) Magnetosphere drives a current requirement on the ionosphere. 2) Causing the ionosphere to become evacuated of electrons, therefore the current channel must widen with time to supply enough electrons to meet current requirement. --Very stationary structure. --1-D cut of the width, but the length also changes, changing the 2-D area of dark stripe. (Marklund, et. al., 2001)

11 Return current region black aurora morphology --Ground magnetometer data from Kaktovik --Deflections indicate ionospheric currents. J E --Black stripe formed between times 1 and 6: --This time corresponds to a localized deflection of 60 nt in the magnitude of the magnetic field on the ground. e- N Hall current signature (along arc direction) 1 6

12 Return current region black aurora morphology From ground-based induction magnetometer observations: Black stripe The black stripe formed a few minutes after onset of, and during intense Pi2 pulsations.

13 Comparison to similar Cluster event -182 s. Tango -90 s. Salsa 0 s. Samba +105 s. Rumba N 5,000-8,000 km 22,000 km 1,500-3,000 km Marklund, et. al., 2001

14 Comparison to similar Cluster event Cluster data showing downward FAC measured by the 4 s/c --Widened during the first three crossings. --Mostly gone by the fourth crossing Marklund, et. al., Downward FAC channel widens from ~15 km to ~25 km mapped to ionospheric altitudes, on a timescale of about 2-3 minutes (Marklund, et. al., 2001)

15 Comparison to theory 0 s. 45 s. 180 s. Streltsov, and Marklund Modeling of the Cluster event shows the widening of the decreased conductivity region from ~20 km to ~50 km, in about 2-3 minutes. (Streltsov, and Marklund).

16 Comparison to similar Cluster event Summary Camera: (6 March 2005) --Scale sizes: Grows from ~10 to 20 km --Formation times: ~1 minute --Black stripe formed a few minutes after onset of, and during intense Pi2 pulsations. Cluster: (14 January 2001) --Scale sizes: Grows from~15 to 25 km --Formation times: ~1 to 3 minutes --Current systems evolve about 1-2 minutes after the onset of Pi2 pulsations (6 February 2001 event). (Aikio, et. al., 2001)

17 Instrumentation Imagers: -All-sky -Narrow-field (12x16 Deg) (H. Stenbaek-Nielsen, T. J Hallinan) -Intermediate 1 FOV camera (M. Lessard) 2 3 Radars -Anchorage 30 MHz coherent radar -Kodiak Island superdarn station 4 5 -Poker AMISR 6

18 Plans for this winter Optical measurements during 2 two-week field campaigns this coming winter at Poker Flat, AK. (21 February - 6 March and 22 March - 5 April, 2006) Collect AMISR and coherent radar data whenever it is possible to be conjugate with the camera data. Use this data to address: 1. Evolution in space / time of auroral features. 2. Ionospheric response to optical signatures.