Small Scale Structures and Motions ofAuroral Signatures as Observed From the

Ground: a Planned Field Study UsingCamera and Radar Observations

Preliminary Results for Return Current Region Structures

R.G. Michell, K.A. Lynch: Dartmouth CollegeH.C. Stenbaek-Nielsen, T.J Hallinan: UAF

D.L. Hysell, M.C. Kelley: Cornell UnivereityM. Lessard: UNHYosemite 7-10 February, 2006

AbstractAs a continuation of the CASCADES (the Changing Aurora: in Situ and Cameraanalysis of Electron precipitation Structures) sounding rocket campaign, a groundbased study of auroral structures and motions will be conducted this coming winter fromPoker Flat, AK. A major goal of this study is to examine the small-scale perpendicularmotions of auroral features in the context of auroral poleward boundary activityassociated with substorm breakup. The use of an all-sky camera and a narrow-fieldcamera at Poker Flat will allow for a 2-D image of the auroral structures. The narrow-field camera has a 12 X 16 degree field of view and allows for viewing of sub-kilometerscale structures at 100 km altitude, and the all-sky camera provides a large scaleauroral context. The 30 MHz imaging radar located in Anchorage will be used to imagethe same area that is being observed with the narrow-field camera. The AMISR that iscurrently being constructed at Poker Flat will give high time and space resolutioninformation on the auroral plasma structures present.The main science questions to beaddressed with this array of instruments are: How intense are small-scale structureswhen viewed with high resolution? What wave modes and auroral electrodynamicscause ion outflow? What is the distribution of auroral arcs widths, and their relation toarc lifetime? What differences are observed between the motions of adjacent light anddark auroral signatures, and what can this tell us about ionospheric electric fields andplasma density.Preliminary results comparing ground camera observations of return current region(RCR) auroral signatures to in situ observations of similar RCR structures from theCluster spacecraft will be presented.

Outline

• Introduction and Motivation.

• Four open questions.

• Morphology of RCR “black” aurora.

• Comparison of camera data to typical Clustermeasurements.

• Instrumentation and plans for this winter

Background and MotivationMotivation: To understand how the aurora works and itsinteractions with the magnetosphere.

In-situ:FAST data

Lynch, et. al., 2002Ground Based:Narrowfield camera

Auroral Morphology

Diffuse aurora

Black aurora

Return current region (RCR) “black”aurora

Discrete aurora

Stormer, 1955

T. Trondsen

Focus on this type

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

Return current region “black” aurora morphology--Little attention has been paid to these blackstructures that occurs alongside the discrete aurora(return current region aurora)

--Specifically excluded in previous optical studies of black aurorawhich focused on the black aurora embedded in the diffuse aurora.

Example from Poker all-sky camera

--From in-situmeasurements: it is nowbelieved that this type isof interest.

--Return current regions (RCR) andAlfven waves (AW) play a majorrole in auroral electrodynamics andM-I coupling.

--RCR and AW are associated withion outflow and e- evacuation.

--RCR and AW don’t producesignificant visible signature.

--Ground-based studies have notyet focused on these regions

Paschmann, et al.

Auroral Regions

Return current region “black” aurora morphologyPoker Flat all-sky example of RCR auroral structure

1 2 3

4 5 6

10 seconds between images North East

Return current region “black” aurora morphology

RelativeIntensity

Pixel number (related to distance)

Time

12

3456

--Physical picture: 1) Magnetosphere drives a current requirement on the ionosphere.2) Causing the ionosphere to become evacuated of electrons, therefore the currentchannel 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 darkstripe.

(~7 km wide)

(~16 km wide)

Assumed 100 km altitude

(Marklund, et. al., 2001)

Return current region “black” aurora morphology

1 6

--Ground magnetometerdata from Kaktovik

--Deflections indicateionospheric currents.

--Black stripe formedbetween times 1 and 6:

--This time correspondsto a localized deflectionof 60 nT in themagnitude of themagnetic field on theground.

N

EJ

e-

Hall currentsignature (alongarc direction)

Black stripe

From ground-basedinductionmagnetometerobservations:

The black stripeformed a fewminutes after onsetof, and duringintense Pi2pulsations.

Return current region “black” aurora morphology

Marklund, et. al., 2001

N

RumbaSambaSalsaTango

22,000 km5,000-8,000 km

1,500-3,000 km

0 s. +105 s.-90 s.

-182 s.

Comparison to similar Cluster event

Marklund, et. al., 2001

--Downward FAC channel widens from ~15 km to ~25 kmmapped to ionospheric altitudes, on a timescale of about 2-3minutes (Marklund, et. al., 2001)

--Widened duringthe first threecrossings.

--Mostly gone bythe fourth crossing

Comparison to similar Cluster event Cluster data showing downward FAC measured by the 4 s/c

0 s.

180 s.

45 s.

Streltsov, and Marklund

Modeling of the Cluster event shows thewidening of the decreased conductivity regionfrom ~20 km to ~50 km, in about 2-3 minutes.(Streltsov, and Marklund).

Comparison to theory

Cluster: (14 January 2001)

--Scale sizes:Grows from~15 to 25 km

--Formation times:~1 to 3 minutes

--Current systems evolveabout 1-2 minutes after theonset of Pi2 pulsations(6 February 2001 event).(Aikio, et. al., 2001)

Camera: (6 March 2005)

--Scale sizes:Grows from ~10 to 20 km

--Formation times:~1 minute

--Black stripe formed a fewminutes after onset of, andduring intense Pi2pulsations.

Comparison to similar Cluster event

Summary

Instrumentation

1

6

3

54

2

• Imagers:-All-sky-Narrow-field (12x16 Deg)(H. Stenbaek-Nielsen, T. J Hallinan)-Intermediate FOV camera(M. Lessard)

• Radars-Anchorage 30 MHz coherent radar-Kodiak Island superDARN station-Poker AMISR

Plans for this winter

• Optical measurements during 2 two-week fieldcampaigns 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 ispossible 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.