Climatological features of electron density in the polar ionosphere from long-term observations of EISCAT/ESR radar

Abstract

Abstract. In this paper, climatological features of the polar F2-region electron density (N e ) 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. Fieldaligned 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 N e 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 daytime ionization peak around magnetic noon observed by ESR can be attributed to soft particle precipitation in the cusp region, whereas the pre-midnight N e 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.

Monitoring the F-region peak electron density using HF backscatter interferometry

“…While a more detailed analysis of N mF 2 variations lies outside of the scope of this letter, it should be quite clear already from our figure that our results are providing a very good match to expectations based on both solar UV/EUV flux variations and changes in the solar zenith angle. In addition, we should note that, all other things being equal, our retrieved daytime electron density tends to maximize at equinoxes rather than at summer solstices, in agreement with previous observations [see, e.g., Cai et al , 2007]. We conclude that Figure 4 therefore conclusively validates our new technique.…”

Meteorological effects of ionospheric disturbances from vertical radio sounding data

“…The absence of winter anomaly at low solar activity is a typical phenomenon at high latitudes. This feature of the winter anomaly at high latitudes agrees with the EISCAT observations (Cai et al, 2005(Cai et al, , 2007, and is reproduced by the IRI-2007 model (Bilitza and Reinisch, 2008). We analyzed which of the stratospheric JS dynamical characteristics (e.g., the Eliassen-Palm flux, horizontal gas velocities at 10 mb) correlated well with the amplitude and occurrence time of ionospheric wave disturbances in the case of the mid-latitude Irkutsk station.…”

F region ionosphere effects on the mapping accuracy of SuperDARN HF radar echoes

“…Considering the relationship between a raypath and the ground range [e.g., Chisham et al ., ], the high coefficient is thought to be related to a large elevation angle of the raypath. As the ionospheric electron density is typically higher at solar maxima than minima [e.g., Cai et al ., ], the increased SWB‐AEB offset strongly relies on the increasing ground range at solar maxima, which implies that the enhanced ionospheric density modulates the HF radar raypath more strongly.…”

“…The electron density and peak height in the high‐latitude F region is typically higher at solar maxima than minima [e.g., Cai et al ., ], to achieve that the maximum HF radio wave returns, the ionospheric refraction index must be stronger at solar maxima than minima [ Gillies et al ., ], giving an increase in the returned ionospheric backscatter at higher elevation angles [ Ponomarenko et al ., ]. This is also reflected in the observations that the rate of increase of SWB‐AEB offset versus AEB latitude is higher at solar maxima than minima (see Figure coefficients, 11:00–14:00 MLT).…”