Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm32a..01m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM32A-01
Physics
[2407] Ionosphere / Auroral Ionosphere, [2439] Ionosphere / Ionospheric Irregularities, [2463] Ionosphere / Plasma Convection, [2706] Magnetospheric Physics / Cusp
Scientific paper
High density polar cap patches are associated with enhanced backscatter power observed by the SuperDARN HF radars. How decametre scale HF radar echoing targets form is still a matter of debate. The Gradient Drift Instability (GDI) is usually regarded as the dominant mode for generating HF backscatter irregularities in the F-region cusp ionosphere. However, observations by EISCAT Svalbard Radar indicate that reversed flow events (RFEs), 100-200 km wide flow channels opposing the background convection, occur up to 40% of the time near the cusp inflow region. Here we present the first documentation of the RFE phenomenon by SuperDARN. When the RFE flow disturbance expands in longitude there is an immediate response in enhanced level of backscatter power, to within the one minute resolution of the radar. This gives experimental support to the new idea that the Kelvin-Helmholtz Instability (KHI) forms 0.1-10 km seed structures on which other instabilities like the GDI can operate more efficiently. However, high-resolution in-situ measurements by sounding rockets are really needed to reliably evaluate the relative importance of various plasma instability modes. The first results from the ICI-2 sounding rocket launched from Svalbard 5 December 2008 will be presented. The payload was equipped with Langmuir probes, AC and DC electric field experiment, plasma wave experiment, particle spectrometers for electrons (10 eV-10keV & >30keV) and ions (>30 keV). It intersected 3 regions of HF backscatter during its 10 min flight reaching an apogee of 330 km. With University of Oslo’s novel multi-Needle Langmuir probe experiment we performed absolute electron density measurements of decametre scale HF backscatter targets. Each HF backscatter region was associated with an inverted V precipitation region which opens for current driven instabilities.
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