基于CHAMP、GRACE和COSMIC掩星数据的全球电离层h_mF_2建模研究

基于CHAMP、GRACE和COSMIC的电离层h_mF_2掩星数据,采用最小二乘法建立了一个包含地磁和太阳活动、经度、地方时、年积日和纬度信息的非线性多项式h_mF_2模型(Nonlinear Polynomial Peak Height Model—NPPHM).利用GRACE掩星数据对NPPHM与IRI2012进行了独立检验,结果显示这两个模型在2008年与GRACE数据的相关系数分别为0.798和0.532,均方根误差分别为25.97km和44.56km;在2012年,相关系数分别为0.732和0.488,均方根误差分别为31.39km和42.83km.选取全球不同地区14个测高仪站点数据,并引入相似离度对这两个模型的精度进行了评估,结果表明,NPPHM的相似离度远小于IRI2012,更加接近测高仪观测值.使用Athens站2003—2013年数据对模型进行了检验,结果显示IRI2012与Athens站测高仪数据的平均偏差达到8.11%,NPPHM则只有3.53%,并且在太阳活动低年及每年10月NPPHM的精度要明显高于IRI2012.此外,NPPHM也能够较好模拟出h_mF_2的日变化、季节变化及赤道异常等特性.

Global model of ionospheric hmF2 based on CHAMPE,GRACE and COSMIC radio occultation

For global ionospheric h_mF₂ modeling, a nonlinear polynomial model approach based on global h_mF₂ observational data form ionospheric radio occultation (IRO) measurements onboard CHAMP, GRACE, and COSMIC satellites is presented in this paper. The Nonlinear Polynomial Peak Height Model (NPPHM) is constructed by a nonlinear fit with h_mF₂ measurements in least squares sense and describes the dependencies of h_mF₂ on geomagnetic activity, solar activity, geographical longitude, local time, day of year and geographical latitude. Using independent data from CHAMP satellite, quantitative analysis is made. The correlation coefficients for proposed model NPPHM and CHAMP data are 0.798 in 2008 and 0.732 in 2012, respectively. The corresponding coefficients for IRI2012 are 0.532 and 0.488. NPPHM shows root mean squared errors (RMS) of 25.97 km and 31.39 km in 2008 and 2012, respectively. The corresponding values for IRI2012 are 44.56 km and 42.83 km. Analog deviations are calculated to compare the NPPHM with IRI2012, using data from 14 different world wide ionosonde stations. The deviation of NPPHM is much less than that of IRI2012. Using observational data from the Athens station from 2003 to 2013, the mean deviation of IRI2012 is 8.11%, more than 3.53% of NPPHM. In low solar activity years and every October during the 11 years, the accuracy of NPPHM is much higher than that of IRI2012. What's more, NPPHM can well present the daily variation, seasonal variation and equatorial ionization anomaly phenomenon of h_mF₂.