Study On Conjugate Features Of Polar Ionospheric F2 Layer Peak Electron Density In Both Hemisphere

In this paper, climatological features and solar activity dependences of ionospheric F2 layer peak electron density(Nm F2) at cusp/aurora latitude are investigated and compared using long-term observations among the Arctic and Antarctic stations of Tromso, Longyearbyen and Zhongshan. Data are also compared with the International Reference Ionosphere(IRI-2012). In the end, numerical simulation method is used to analyze the diurnal variations of Nm F2 at cusp latitude at solar minimum. The main results are summarized as follows:For the first time, diurnal and annual variations of Nm F2 at geomagnetic/geographic conjugate stations at cusp/aurora latitude are investigated and compared. It is found that the peak time of Nm F2 at three stations are different, indicating the importance of soft particle precipitation and ionospheric convection in the cusp region. In addition to the daytime peak, there is another peak just before magnetic midnight at Longyearbyen in winter during solar maximum years, which is attributed to the cross-polar transport of EUV ionization from day side to night side. An enhancement of Nm F2 is detected at magnetic midnight in winter at Tromso. It may be caused by the nighttime substorms. On the seasonal variability, there is normal variability during solar minimum years and semiannual anomaly during solar maximum years for all three stations. The well-known winter anomaly is also evident at both Tromso and Zhongshan, but does not exist at Longyearbyen during solar maximum years.Solar activity dependences of Nm F2 are also investigated. It is found that Nm F2 is increasing linearly with solar activity indices F10.7P at most of the time at all three stations. Also, there exits an apparent “saturation effect” at Zhongshan in the Southern Hemisphere summer, but an “amplification effect” at Tromso and Longyearbyen in the Northern Hemisphere winter. The linear relationship between Nm F2 and solar activity indices is the best at Tromso, and it is the worst at Longyearbyen. At magnetic midnight in winter, Nm F2 has the lowest sensitivity to solar activity and the linear relationship between Nm F2 and F10.7P is the worst at Tromso, but Nm F2 still has a strong sensitivity to solar activity before magnetic midnight in winter at Longyearbyen, indicate that the aforementioned analyses about the nighttime peak at the two stations is reasonable.The prediction accuracies of Nm F2 from IRI-2012 model at all three stations are studied under different solar activity conditions. The differences between observed and predicted results are studied using error analysis. The IRI predictions are the best agree with observations at Tromso, followed by Zhongshan, and the worst at Longyearbyen. Also IRI predictions represent Nm F2 variation features better in summer than in winter at all three stations. At Tromso, the IRI predictions have better agreement with observations during solar maximum years than solar minimum years. At Zhongshan and Longyearbyen, the predicted results represent Nm F2 variation features better during solar minimum years than solar maximum years. In winter at Longyearbyen, IRI predictions have great differences with observations. It is concluded that more factors, such as plasma convection, particle precipitation and the high latitude trough should be taken into account in the IRI model.Diurnal variation curves of Nm F2 at cusp latitude stations of Zhongshan and Longyearbyen are studied with the help of High Latitude Ionosphere Model. It is shown that the simulations are well consistent with observations. Simulations are carried out by changing geomagnetic conditions, we found that the different behaviors of Nm F2 at the two stations is caused by the different locations of the polar convection patterns relative to the terminator line. Based on the simulation of electron density in E and F layer, it is found that the aurora particle precipitation has a contribution to the electron density of both E and F layer at two stations. Take the particle precipitation and photoionization as a single input parameters respectively, the results show that the enhancement of Nm F2 in cusp region not only depends on the soft electron precipitation, the interaction of horizontal transport processes and photoionization also has a great contribution to it.