New Index to Characterize Ionospheric Irregularity Distribution

Characterization of the global ionospheric irregularities as a function of local time, longitude, altitude, and magnetic activities is still a challenge for radio frequency operations, especially at the low-latitude region. One of the main reasons is lack of observations due to the unevenly distributed instruments. To overcome this constraint, we developed a new spatial density gradient index (DGRI) at two different scale sizes: small scale and medium/large scale. The DGRI is derived from in situ density measurements onboard recently launched constellation of low-Earth-orbiting satellites (COSMIC-2 and ICON) at the rate of 1 Hz. Hence, the DGRI appeared to be suitable parameter that can be used as a proxy to describe the essential features of ionospheric disturbances that may critically affect our radio wave application as well as to identify the "all clear" zone as a function of longitude, latitude, and local time-at a refreshment rate of 30 min or less. The presence of ionospheric small-scale (sub-km) irregularities may disturb the amplitude and phase of the radio signals that traverse through it. Radio signal scintillation strength depends on many factors, including irregularity strength, signal frequency, background density magnitude or layer thickness, local time, season, solar and magnetic activity, and the angle between the ray path and the Earth's magnetic field. The most severe irregularity environment is found in the equatorial and high-latitude regions, but mid-latitude region is not also immune from the presence of irregularities-mainly associated with geomagnetic storms. Hence, every technology that operates with radio signals that traverse through the ionosphere is vulnerable to the dynamics of ionized region and requires ionospheric corrections. Therefore, it is critically important for operations (e.g., for accurate navigation applications) to develop an ionospheric index that can accurately characterize the presence and absence of ionospheric irregularities. The gradient index that we develop from in situ density measurements onboard multiple low-Earth-orbiting satellites can describe the essential features of ionospheric perturbations that may critically affect our radio wave application. It also overcome the limited spatial coverage of ground-based receivers and characterize the location of global ionospheric irregularities at a refreshment rate of 30-min or less. Equatorial region is one of the most severe irregularity environmentsCharacterization of the global ionospheric irregularities is essential for radio signal operationsSpatial gradient index can be used as a proxy to identify scintillation "all clear" zone