Effects of ionospheric disturbances on GPS observation in low latitude area

In this paper, ionospheric disturbance data from a local GPS network in Hong Kong (low latitude region) are studied in the solar maximum period (2001-2003). The spatial and temporal distributions of the disturbances in Hong Kong are investigated. It is found that strong ionospheric disturbances occur frequently during the solar maximum period, particularly around March and September, and concentrate at the region around geographic latitude 22 degrees N (geomagnetic latitude 12 degrees N). The effects of the disturbances on GPS geodetic receivers, such as loss of lock and measurement noise level, are also analyzed for the 3-year period. It shows that the measurement noise level and the number of losses of lock in GPS data increase dramatically during ionospheric disturbance periods. The behaviors of different types of GPS receivers during the disturbances are also compared.