Comparison of Ionospheric VTEC Predictions using the Holt-Winter and IRI-2016 Model in Equatorial Region

Total Electron Content (TEC) is an important parameter that considerably affects radio waves propagating through the ionosphere, causing delay errors in GPS satellite signals. Hence, identifying an effective TEC model is important. This research presents an analysis of ionospheric vertical TEC (VTEC) modeling during geomagnetic quiet and disturbed periods. The data were recorded using the Department of Survey and Mapping Malaysia's (DSMM) dual-frequency GPS located in Kedah (geographic coordinates 4.62°N-103.21°E, geomagnetic coordinates 5.64°N-174.98°E), Terengganu (geographic coordinates 6.46°N-100.50°E, geomagnetic coordinates 3.32°S-172.99°E), and Johor (geographic coordinates 1.36°N-104.10°E, geomagnetic coordinates 8.43°S-176.53°E). The VTEC was modeled using the statistical Holt-Winter method and the most recent version of the International Reference Ionospheric model (IRI-2016), using IRI01-corr, IRI-2001, and NeQuick topside electron density options. The daily variation of the measured and modeled VTEC during quiet and disturbed periods was compared. The minimum value of the VTEC was recorded in the early morning time and the maximum was recorded during the post-noon time. The diurnal hourly variation during the quiet periods indicated that IRI01-corr, IRI-2001, and NeQuick overestimated most of the time, while the Holt-Winter method showed better agreement with the GPS-TEC. During the disturbed period, IRI-2016 (IRI01-corr, IRI-2001, and NeQuick) did not show any response to the geomagnetic storm, while the Holt-Winter method underestimated the VTEC trend. However, the Holt-Winter displayed better performance and results compared to the IRI01-corr, IRI-2001, and NeQuick during the quiet and disturbed periods in the equatorial region over Malaysia.