Ann. Geophysicae 18, 1172±1181 �2000) Ó EGS ± Springer-Verlag 2000 Auroral E-region electron density gradients measured with EISCAT
Abstract. In the theory of E-region plasma instabilities, the ambient electric ®eld and electron density gradient are both included in the same dispersion relation as the key parameters that provide the energy for the generation and growth of electrostatic plasma waves. While there exist numerous me...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.210.1454 http://www.ann-geophys.net/18/1172/2000/angeo-18-1172-2000.pdf |
| Summary: | Abstract. In the theory of E-region plasma instabilities, the ambient electric ®eld and electron density gradient are both included in the same dispersion relation as the key parameters that provide the energy for the generation and growth of electrostatic plasma waves. While there exist numerous measurements of ionospheric electric ®elds, there are very few measurements and limited knowledge about the ambient electron density gradients, rNe, in the E-region plasma. In this work, we took advantage of the EISCAT CP1 data base and studied statistically the vertical electron density gradient length, Lz ˆ Ne=…dNe=dz†, at auroral E-region heights during both eastward and westward electrojet conditions and di€erent ambient electric ®eld levels. Overall, the prevailing electron density gradients, with Lz ranging from 4 to 7 km, are found to be located below 100 km, but to move steadily up in altitude as the electric ®eld level increases. The steepest density gradients, with Lz possibly less than 3 km, occur near 110 km mostly in the eastward electrojet during times of strong electric ®elds. The results and their implications are examined and discussed in the frame of the linear gradient drift instability theory. Finally, it would be interesting to test the implications of the present results with a vertical radar interferometer. Key words: Ionosphere �auroral ionosphere; ionospheric irregularities; plasma waves and instabilities) 1 |
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