Rocket Observations of Pulsating Aurora(ROPA)

Marc Lessard, PI Univ of New HampshirePaul Riley, Engineer

Kristina Lynch, CoI Dartmouth CollegeKevin Rhoads, Engineer

Paul Kintner, CoI Cornell UniversitySteve Powell, Engineer

Hans Nielsen, CoI Univ of Alaska

Jay Scott, Payload Manager NASA Wallops

Pulsating aurora morphology

• Patchy, with scales sizes from 10-200 km.

• Periodicities from a few to tens of seconds, most often from 5-10 seconds.

• Tendency to occur after substorms and/or post-midnight.

• Very distinct from flickering aurora, which has much higher frequencies (~7-10 Hz) and is associated with inverted-V arcs.

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

Example recorded by THEMIS camera at Whitehorse, NWT (S. Mende, PI).

“Facts” about pulsating aurora

1. Pulsating aurora is caused by the precipitation of energetic particles that presumably originate near the equatorial region.

Electron fluxes observed from a sounding rocket (upper two traces) plotted with ground-based optical data (lower trace). Eleven pulsations are clearly shown in all traces (from McEwen, Can. J. Phys., 50, 1106, 1981)

“Facts” about pulsating aurora

2. Patches are thin, the order of 2 km (Stenbaek-Nielsen et al., JGR, 84, 3257, 1979)!!!

3. Patches are associated with intense currents (Arnoldy et al. JGR, 87, 10449,1982). Current distributions within patches suggested by Oguti et al., JGR, 89, 7467,1984:

“Facts” about pulsating aurora

4. Appear to drift at EXB velocities, although results from a Barium release indicate that pulsating patches drift slower than the Barium cloud (Wescott et al., JGR, 81, 4487, 1976). An interesting, related result concludes that pulsating patched drift upwards (Winckler and Nemzek, in Auroral Plasma Dynamics, AGU Monograph, vol. 80, 1993).

5. Energetic protons? Very mixed observations.

6. Asscociation with diffuse aurora, latitudinal dependencies of periods, 3 Hz modulation, etc…

Theories about pulsating aurora

Basic idea: Energetic electrons are scattered from the equatorial region via pitch angle diffusion by VLF waves (VLF waves result from electron anisotropies in the region). This idea is driven by observations of velocity dispersion of energetic electrons. Does not address ionospheric interactions (i.e., drifts, thin patches, repeatability, etc).

See other works: Stenbaek-Nielsen and Hallinan, Pulsating Auroras: Evidence for Noncollisional Thermalization of Precipitating Electrons, JGR, 84, 3257, 1979; Stenbaek--Nielsen, Pulsating Aurora: The Importance of the Ionosphere, GRL, 7(5), 353, 1980; recent work by Jay Johnson that describes thin patches.

Important questions

1. What is the basic mechanism? How can energetic electrons be ‘delivered’ to the upper atmosphere with this distribution in space and time? Not much theory.

2. What is the nature of MI coupling in pulsating aurora? Or, how is the source mechanism related to the ionspheric footprint? Where (how) are currents returned? What is the definitive motion of the patches?

ROPA Mission

To launch a sounding rocket into a pulsating auroral event from Poker Flat, AK, in January, 2007.

Main Objectives:

1. Acquire large-scale topside images of pulsating aurora for comparison to in-situ observations and to ground data.

2. To investigate current closure associated with pulsating patches.

ROPA Mission

Secondary Objectives:

1. Directly measure the convection electric field in order to compare the ExB speed to the drift of the pulsating patches.

2. Measure distribution functions of low-energy (non-pulsating) electrons from ~6 eV to 18 keV to fully characterize the backscattered and secondary populations. Do this on spatially separated payloads to look for spatial variations.

3. Obtain spatially distributed measurements of pulsating electrons to see if the dispersion times are the same in different regions of a single patch or, perhaps, for different patches.

4. Acquire ion data for comparison to large-scale image data.

ROPA Mission

ROPA Mission

ROPA Mission Instruments

Main payload:- 2 wide fov auroral imagers, 428 and 558 nm (UNH).- High energy (up to ~30 keV) electron tophat analyzer (Dartmouth).- Solid state instrument for energetic electrons (~28-100 keV) and

protons (UNH).- Magnetomter (Dartmouth).- COWBOY electric fields (Cornell).- Low energy (thermal) electron instrument (UNH).

Fly Away Detectors (FADs, there are 2):- Electron tophat analyzer, energy up to 18 keV (Dartmouth).- Magnetometer (Dartmouth/Cornell).

Ground-based observations:- Allsky camera observations at Poker Flat, Fort Yukon and Kaktovik

(UAF).- Narrow FOV imagers at Fort Yukon and Poker Flat (UAF).

ROPA Mission Instruments

DEspun Rocket Borne Imager (DERBI) provides a means of imaging aurora from a spinning platform.

ROPA Mission Integration

AMISR support

1. Observations ionospheric conductivity enhancements in the patches; including temporal variations.

2. Measurements of convection electric field.

3. Detect indication of current closure?

4. Motion of patches?

5. Any other signature? Ion outflow?

Svalbard closely-spaced array of induction coil magnetometersM. Engebretson and M. Lessard

Data available as of Sep 16, 2006

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And in the north….And in the north….SvalbardSvalbard

Questions and comments to:Marc.lessard@unh.edu

Hornsund, Svalbard