极区极夜期间E层占优电离层的分布特征

CHARACTERISTICS OF THE E-LAYER DOMINATED IONOSPHERE IN THE POLAR REGIONS DURING POLAR NIGHTS

E层占优电离层是指E层的峰值电子密度大于F层的峰值电子密度(NmE>NmF)时的电离层,记为ELDI(E-Layer Dominated Ionosphere)。针对ELDI,利用2007—2010年的COSMIC(Constellation Observing System for Meteorolo-gy,Ionosphere,and Climate satellite)掩星数据,在修正地磁纬度-磁地方时标系下统计分析了它在南北极区极夜期间(南北半球的冬至日前后30天)的分布特征,结果表明极夜期间电离层ELDI特征明显,其分布与极光椭圆位形基本一致,而且其在夜侧的发生率较高,特别是磁子夜之后,北极为70%左右,而南极为90%左右;另外南极的ELDI特征在磁纬度分布上要略宽于北极的分布范围。在ELDI高发区,电离层峰值电子密度要高于其两侧地区,特别是在夜侧,尤其是磁子夜前的峰值电子密度要接近甚至大于磁正午的峰值电子密度,在南极地区格外明显;而且ELDI高发区内的E层的电子含量(TECE)、电离层总电子含量(TECI)及TECE占TECI的比重(TECEI)都高于其两侧地区,北极TECE和TECI大于南极,而TECEI则是南极大于北极。这些现象主要是由于极夜期间极区高能粒子沉降引起底部电离层电离率增大所致;同时,由于地磁轴偏离地理轴的程度在南极要大于北极,使得极夜期间南极地区的电离层的电子密度,特别是在F层要相应地小于北极地区,从而导致了极夜期间南北半球极区电离层ELDI特征之间差异。

The E-Layer Dominated Ionosphere （ELDI） is defined as the ionosphere where the maximum electron density in the E-Layer is larger than that of the F-Layer. The characteristics of the ELDI in the polar region during polar nights were investigated in 2007--2010 in the Corrected Geomagnetic Latitude and Magnetic Local Time Coordi- nates, using the measurements of COSMIC （ Constellation Observing System for Meteorology, Ionosphere, and Cli- mate satellite）. The ELDI is marked in the polar region during polar nights, with a similar distribution to the auro- ral oval. The ELDI occurred more during the night than the day, especially after midnight. Maximum occurrence probability was about 70% and 90% in the Arctic and Antarctic, respectively. The ELDI appears slightly wider in the Antarctic than in the Arctic. In the area where the occurrence probability of ELDI is higher, the ionospheric maximum electron density （NmI） is larger than outside this area, especially during the night. The Nml before mid- night is close to, and even slightly larger than, the NmI at mid-day, a phenomenon which was more obvious in the Antarctic. Additionally, the electron content in the E-Layer （TECE）, the ionospheric total electron content （TE- CI） and the ratio of TECE accounting for TECI were also greater in the area where the occurrence of ELDI is lar- ger, compared with outside the area. The values of TECE and TECI were largest in the Arctic, while the values of TECEI were largest in the Antarctic. These patterns were mainly caused by the precipitation of high-energy parti- cles, which increases the ionization rate in the bottom of the ionosphere. Meanwhile, differences in ELDI features between the Arctic and Antarctic are attributed to differences in the departure of the geomagnetic pole from the geo- graphic pole in each hemisphere; this causes a greater electron density in the Arctic than Antarctic, especially in the F-layer, during polar night.