Constructing a global ionospheric TEC map with a high spatial and temporal resolution by spherical harmonic functions

Abstract

The Massachusetts Institute of Technology (MIT) Haystack Observatory provides the ionospheric Total Electron Content (TEC) data with a temporal resolution of 5 minutes and limited spatial coverage, as they do not provide data where there are no TEC measurements. To improve the spatial coverage of MIT-TEC, we have proposed an approach for constructing a global ionospheric map of TEC with a time resolution of 5 minutes and a grid spacing of 1° × 1° in latitude and longitude. The global ionospheric TEC map constructed by the spherical harmonic (SH) function and MIT-TEC (SHMIT-TEC) is compared with the original MIT-TEC data. The results show that SHMIT-TEC can clearly present the properties of the ionospheric distribution. The average values of Standard Deviations (STDs) between SHMIT-TEC and MIT-TEC are about 4.1448 TECU and 3.1382 TECU in the high solar activity year (2003) and low solar activity year (2008), respectively. Compared to TECs provided by the Center for Orbit Determination in Europe (CODE), SHMIT-TEC can also accurately reflect the diurnal and latitudinal variations of the ionospheric TEC. Furthermore, SHMIT-TEC is utilized to investigate the ionospheric response to the solar flare on 28 October 2003. The results show that the SHMIT-TEC updated in 5 minutes can accurately detect the time of obvious TEC enhancement (11:07 universal time, UT) induced by the solar flare, which is in accordance with the peak times of X-ray flux in 0.1–0.8 nm (11:10 UT) measured by the Geostationary Operational Environment Satellite and extreme ultraviolet (EUV) fluxes (11:06 UT) observed from the solar EUV monitor experiment. In contrast to MIT-TEC and CODE-TEC, SHMIT-TEC with global coverage and high temporal and spatial resolution can monitor the ionospheric TEC response to space weather events quickly and effectively.