全球电离层分布特别是f₀F₂和h_mF₂对雷达探测、无线电通信以及卫星导航等有非常大的影响，为研究全球f₀F₂和h_mF₂的时空分布，利用全球导航卫星定位系统（GNSS）掩星数据统计分析了全球f₀F₂和h_mF₂的周年变化特性、日变化特性以及季节变化特性，并通过与日本地区测高仪站f₀F₂数据进行对比，分析了两种探测方式获取电离层参数的相关性。结果表明，全球f₀F₂和h_mF₂周年变化与太阳活动和地磁活动具有明显的正相关性，f₀F₂和h_mF₂还具有明显的空间分布特性。此外，全球f₀F₂和h_mF₂峰值出现在LT 14：00—16：00期间，且h_mF₂出现明显的日落后赤道电离异常复苏现象。全球f₀F₂具有比较明显的季节变化特性，f₀F₂峰值出现在春秋季中低纬地区，在夏冬季较小，且出现比较明显的冬季异常现象，而h_mF₂季节分布相比f₀F₂并不明显。通过和日本地区Wakkanai、Kokubunji、Yamagawa以及Okinawa测高仪站f₀F₂数据对比，发现两种探测手段获取的电离层参数具有较好的相关性。初步研究表明，全球f₀F₂和h_mF₂分布受到多种因素的影响，其中太阳活动和地磁活动占主要地位，其次是电场、热层风以及高能粒子沉降等。

The ionosphere is an atmospheric region ionized by solar radiation, cosmic rays, and various particle radiations ranging from 60 km to 1000 km above the earth. Numerous free electrons and ions in the ionosphere can interfere with radio signals. Ionospheric parameters, especially F₂ layer critical frequency (f₀F₂) and electron density peak height (h_mF₂), play an important role in the propagation of HF waves. Therefore, the study of f₀F₂ and h_mF₂, especially its global distribution, is important.
The overall objective of this paper is to study the annual, diurnal, and seasonal variations of f₀F₂ and h_mF₂ in the world on the basis of GNSS occulation datasets and to compare the values f₀F₂ obtained by GNSS occultation and digisondes from all stations in Japan.
COSMIC, GRACE, and CHAMP electron density profile datasets and digisonde datasets in Wakkanai, Kokubunji, Yamagawa, and Okinawa for 2002—2016 are selected as the data sources. The maximum electron density N_mF₂ and h_mF₂ is obtained by using the electron density profile. Compared with ionosonde f₀F₂ datasets, the latitude and longitude of the selected N_mF₂ are within 5 degrees of ionosondes, and the time of the selected N_mF₂ is within 15 minutes of ionosondes.
Results show that the annual variation of f₀F₂ and h_mF₂ has a significant positive correlation with solar activity and geomagnetic activity and significant spatial distribution characteristics. The maximum value of f₀F₂ distribution on both sides of the magnetic equator is approximately 15 degrees, and the maximum value of h_mF₂ distribution in the equatorial region and the northern and southern hemisphere peak heights is not symmetrical. In addition, the peak value of f₀F₂ and h_mF₂ appears during LT 14:00—16:00, and h_mF₂ exhibits significant equatorial ionization anomaly recovery after sunset. The f₀F₂ has obvious seasonal characteristics; the peak value of f₀F₂ appears in spring and autumn at middle and low latitudes, and is evident in abnormal winter phenomenon. However, the seasonal distribution of h_mF₂ evidently change. The values f₀F₂, which were obtained by occultation and digisondes from all stations in Japan, were compared, and results indicate that the ionospheric parameters obtained by the two detection methods have acceptable correlation. The correlation in the Okinawa station is the best, with a correlation coefficient of 0.88. The correlation in the Wakkanai station is poor, with a correlation coefficient of 0.75. The correlation between Yamagawa and Kokubunji stations is close at 0.84 and 0.85, respectively.
The preliminary study shows that the global f₀F₂ and h_mF₂ distribution is affected by many factors, including solar activity, geomagnetic activity, electric field, and wind and high-energy particle sedimentation.
The values f₀F₂ obtained by occultation and digisondes from all stations in Japan were compared, and results show that the ionospheric parameters obtained by the two detection methods have acceptable correlation. However, some evident differences were observed; these differences may be due to the electron density gradient and satellite retrieval technology.