On the characteristic feature of the electron density irregularities in the cusp

Details On the characteristic feature of the electron density irregularities in the cusp On the characteristic feature of the electron density irregularities in the cusp

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm14a..04a&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM14A-04

Computer Science

Sound

[2407] Ionosphere / Auroral Ionosphere, [2435] Ionosphere / Ionospheric Disturbances, [2439] Ionosphere / Ionospheric Irregularities, [2467] Ionosphere / Plasma Temperature And Density

Scientific paper

The ICI-2 (Investigation of Cusp Irregularities-2) sounding rocket campaign was conducted in Svalbard, Norway in late 2008. The scientific objective of ICI-2 is to investigate generation mechanism(s) of coherent HF radar backscatter targets. Strong coherent HF backscatter echoes are a well-known characteristic of the polar ionospheric cusp, and are thought to result from field-aligned plasma irregularities with decameter scale length. The ICI-2 sounding rocket was launched at 10:35:10 UT at Ny-Ålesund on December 5, 2008. Measurements of thermal plasma, low energy electrons, and AC and DC electric fields were made to conduct a comprehensive study with the aim to exploit the potential role of the gradient drift instability versus the other suggested mechanisms. We present a result obtained from a fixed-bias probe (FBP) which was installed to measure fine-scale (~1m) electron density perturbation. Our analysis of the FBP data indicates that the rocket traversed regions where the electron density perturbation is relatively large, during its flight. Characteristic features of the electron density perturbation are summarized as follows: 1) Rough correspondence in space between the electron density perturbation and the poleward moving 630 nm emission region estimated from the all-sky imager. 2) The absolute value of the electron density becomes larger in the disturbed region than in the surrounding region. 3) The degree of the electron density perturbation is remarkable in the edge, i.e., in the equatorward and poleward boundaries. 4) The electron density perturbation was identified at three different altitudes, indicating that the perturbation exists in a larger extent in the vertical direction. In this presentation, we describe two primary results; 1) a result from further analysis of spatial correspondence between the electron density perturbation region and 630 nm emission region, and 2) a result from further discussion of power spectral analysis of the electron density. As for the first subject, 630 nm emission strength at the rocket position is estimated from all-sky imager data which are obtained every 30 seconds, and it is compared with spectral power derived from FFT analysis of the electron density data. In two cases out of three in which the strong density perturbation was observed, the local increase of the 630 nm emission was observed almost in the same region. Our analysis provides the observation evidence of coexistence of the density perturbation and the optical emission. As for the second subject, spatial scale of the electron density perturbation is estimated by considering the spectral power derived from FFT analysis and the rocket speed, and it is compared with variation of the 630 nm emission strength. Our analysis confirms that the density perturbation with several 10 m scale has a similar spatial distribution with the 630 nm emission. More careful analysis is needed to determine characteristic scale length of the electron density perturbation because the FBP basically provides one-dimensional distribution along the rocket trajectory. We will discuss characteristic feature of the cusp plasma irregularities derived from the detailed analysis of the electron density perturbation.

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