Characteristics of Equatorial Electrojet Derived From MSS1A Observation: Initial Result

In this study, we use the magnetic field data from the Coupled Dark State Magnetometer (CDSM) aboard the Macau Science Satellite-1A (MSS1A) to calculate and analyze the equatorial electrojet (EEJ) in the period between November 2023 and December 2024. The inverse method, initially developed for polar-orbiting satellites, is evaluated for its applicability to the MSS1A, which features a distinct 41° orbital inclination. For the observational time window, there are 6251 electrojet events selected for analysis. We find that the median current density profile peaks at the magnetic equator, with a median peak value of 35 mA/m. The current density distribution is relatively concentrated, with a half-maximum width of approximately 5° in magnetic latitude. The data set comprises the eastward and westward EEJ events in a ratio between 79% and 21%, respectively. We also have examined the EEJ dependence on solar activity level, local time, longitude, season, and magnetic activity. The peak current density of the EEJ increases as the P10.7 index rises from 140 to 220 solar flux units. The peak density of EEJ is mostly pronounced around noon and varies with season, with high amplitudes observed during equinoxes and low values during solstices. The averaged peak current density of the EEJ displayed a distinct longitudinal wave number 4 pattern, which should be attributable to non-migrating tides originating from the lower atmosphere. In general, from both event-based and statistical analyses, the EEJ characteristics observed by MSS1A agree well with that observed by previous satellites, for example, Swarm, suggesting that the magnetic measurements from the newly launched MSS provide a new data set for monitoring the ionospheric currents.