Xiaoqing Pi, Jet Propulsion Laboratory, California Institute of Technology

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In this paper several methods are described for measuring spatial slopes of ionospheric total electron content (TEC) using ground-based GNSS observations. The following approaches are included: (1) Global Ionospheric Map (GIM) based TEC gradients (GBTG); (2) small-scale TEC slopes (SSTS); (3) averaged TEC and gradients (ATAG); (4) fitted IGP TEC and gradients (FITG). Characteristics of TEC slopes resulted from these approaches with regionally distributed GNSS data in different latitude regions are assessed and compared. In addition, a new way to measure small-scale TEC irregularities (SSTI) is defined as the standard deviation of detrended SSTS, which characterizes ionospheric irregularities at horizontal spatial scales ranging from 1.8 to 15 km approximately. Examples of global images of TEC slopes and SSTI are presented, which are obtained using data from thousands of globally distributed GNSS stations. A preliminary analysis indicates that the magnitude and direction of TEC slopes derived using these approaches are consistent in general, but differences among the approaches become noticeable when the ionosphere is perturbed either during active space weather or irregularity events. The differences between SSTS, ATAG and FITG are attributed to the data distribution and amount in the binned area that may affect 2- dimensional data fitting, errors of satellite and receiver instrumental bias estimation, and data outliers which must be detected and removed.