Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 25, 2561-2569, 2007
https://doi.org/10.5194/angeo-25-2561-2007
© Author(s) 2007. This work is distributed under
the Creative Commons Attribution 3.0 License.
 
02 Jan 2007
Climatological features of electron density in the polar ionosphere from long-term observations of EISCAT/ESR radar
H. T. Cai2,1, S. Y. Ma2,1, Y. Fan2,1, Y. C. Liu1, and K. Schlegel3 1School of Electronics Information, Wuhan University, 430079, China
2Key Lab of Geospace Environment and Geodesy, CNEM
3Max Planck Institute for Solar System Research(MPS), 37191 Katlenburg-Lindau, Germany
Abstract. In this paper, climatological features of the polar F2-region electron density (Ne) are investigated by means of statistical analysis using long-term observations from the European Incoherent Scatter UHF radar (called EISCAT in the following) and the EISCAT Svalbard radar (ESR) during periods of quiet to moderate geomagnetic activity. Field-aligned measurements by the EISCAT and ESR radars operating in CP-1 and CP-2 modes are used in this study, covering the years 1988–1999 for EISCAT and 1999–2003 for ESR. The data are sorted by season (equinox, summer and winter) and solar cycle phase (maximum, minimum, rising and falling). Some novel and interesting results are presented as follows: (1) The well-known winter anomaly is evident during the solar maximum at EISCAT, but it dies out at the latitude of the ESR; (2) The daytime peaks of Ne at EISCAT for all seasons during solar maximum lag about 1–2 h behind those at ESR, with altitudes about 10–30 km lower. (3) In addition to the daytime peak, it is revealed that there is another peak just before magnetic midnight at ESR around solar maximum, especially in winter and at equinox. The day-time ionization peak around magnetic noon observed by ESR can be attributed to soft particle precipitation in the cusp region, whereas the pre-midnight Ne maximum seems likely to be closely related to substorm events which frequently break out during that time sector, in particular for the winter case. (4) Semiannual variations are found at EISCAT during solar minimum and the falling phase of the solar cycle; at the rising phase, however, the EISCAT observations show no obvious seasonal variations.

Citation: Cai, H. T., Ma, S. Y., Fan, Y., Liu, Y. C., and Schlegel, K.: Climatological features of electron density in the polar ionosphere from long-term observations of EISCAT/ESR radar, Ann. Geophys., 25, 2561-2569, https://doi.org/10.5194/angeo-25-2561-2007, 2007.
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