A spherical cap model of the geomagnetic field over southeast Asia from CHAMP and Swarm satellite observations

In this paper, Spherical Cap Harmonic Analysis (SCHA) method was applied to model the geomagnetic field over Vietnam and adjacent area between 15°S and 25°N latitude and 90°E and 130°E in longitude by using magnetic data recorded on CHAMP and Swarm satellites. The characteristic parameters of the method were set at the maximum index K int = 8 for internal fields, the spherical cap half-angle θ 0 = 20°. The regional geomagnetic field over Vietnam and adjacent areas are modelled for the two epochs (2007.0 and 2015.0). Comparison between the SCHA regional geomagnetic field intensity and its time variation with those from IGRF was carried out. The geomagnetic field intensity ( E F SCHA ) from SCHA model varies between −90 and 98 nT for epoch 2007.0 and between −139 and 143 nT for epoch 2015.0; however, the trends of their time variations are the same over Vietnam. The RMS between the magnetic components from SCHA model and ground observations are in the same order. The amplitude of time variation of total field intensity from SCHA model is about tens nT greater than from IGRF over Vietnam. Highlights The SCHA has been used for modeling the magnetic field in Vietnam and adjacent area at the epochs 2007.0 and 2015.0 from CHAMP and Swarm data. The regional geomagnetic field intensity E F SCHA varies between −90 and 98 nT for epoch 2007.0 and between −139 and 143 nT for epoch 2015.0, which consists of a crustal field and a party of the core field. The time variation of the regional total magnetic field intensity in the period 2007–2015 from the SCHA method has the amplitude larger than the one from IGRF of about 10 nT in the territory of Vietnam.