Tuesday, 3 May 2011

EISCAT Observations of the Quiet-Time Ionospheric Trough

It is Science Tuesday and we are happy to present the first science result in this series. If you are interested in seeing your results on-line on the EISCAT_3D blog, please send us a short text explaining the main result, one image or graph with caption, and the original article's reference. Also, please send the PDF of the article in its final layout, because that will clarify possible questions.

As an introdution to this work, the ionospheric trough is a gap of lower-than-elsewhere ionisation between the sunlit and night-time ionosphere. The solar terminator is the great-circle line on the globe, which is the separator of the sunlit and the dark hemispheres.

Data from a combined azimuth-scan and overhead-scan UHF radar experiments were used to determine the behaviour of the eveningside F-region trough on 9th November 1987. The MLT and CGMlat dependence of various ionospheric parameters at a set of F-region altitudes was determined. It was found that both ion and electron temperatures have minima within the trough region and increase at the poleward wall. The most important result was obtained by comparing the observed ion velocity and electron density to the respective parameters given by the LiMIE model (see Figure). The results suggest that the density depletion within the trough is due to recombination of F-region plasma convecting for a long time in the dusk convection cell beyond the terminator. The northern edge of the trough is associated with soft particle precipitation. The southern edge is steeper than the northern edge, and is built by sunlit plasma brought to the trough region by corotation. The trough is thus a result of a combination of transport and precipitation processes rather than stagnation.

Figure: (left) Zonal ion velocity and (right) electron density at 345 km together with the convection pattern given by the LiMIE model, positive potentials are indicated by continuous and negative potentials by dashed lines. Shown is also the position of the solar terminator as a line of different colours, chosen for the sake of a good contrast with the background.

Original article: Voiculescu, M., T. Nygrén, A. Aikio, and R. Kuula, An olden but golden EISCAT observation of a quiet-time ionospheric trough, J. Geophys. Res., 115, A10315, doi:10.1029/2010JA015557, 2010.

Thanks to Tuomo Nygrén for providing the text and the figure.

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