Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsa31c..03p&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SA31C-03
Physics
[2471] Ionosphere / Plasma Waves And Instabilities, [2475] Ionosphere / Polar Cap Ionosphere, [2494] Ionosphere / Instruments And Techniques
Scientific paper
Polar cap patches are the primary source of scintillation in the high latitude region, but measurements of small-scale plasma structure produced by instabilities acting on the patches have been limited to 1-dimensional profiles from in-situ satellite instruments or beacon receivers. Optical observations typically show no small-scale structure due to thermal motion during the long (>100s) lifetime of the O (1D) state producing the 630 nm red line and convective motion during long exposures necessitated by the low emission intensities. However, when plasma densities and recombination rates are sufficiently high, structure can be observed in the O (1S) 557.7 nm green line emission, which has a much shorter lifetime (~1s) but is typically only one-fifth as bright as the red line. We present all-sky optical image data from a magnetically active period during the previous solar maximum when high plasma densities and emission intensities allowed quality imagery of patch structure to be acquired using the oxygen green line. These images show significant 2-D structuring at 20-30 km scales preferentially on the trailing edges of patches, and also reveal a potentially new class of "arc-like" patches which are very narrow in the flow direction while extending for very large distances across the flow. Satellite and TEC observations confirm the plasma density nature of the patch structures and indicate the location of smaller irregularities relative to the optical structure.
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