Identification of TIDs and plasma depletions using the LISN observatory

The Low-latitude Ionospheric Sensor Network (LISN) is a distributed observatory designed to nowcast the state and dynamics of the low latitude ionosphere. The LISN observatory is comprised of GPS receivers, flux-gate magnetometers and Vertical Incidence Pulsed Ionospheric Radar (VIPIR) ionosondes. LISN strives to measure the day-to-day variability of the low-latitude ionosphere with a regional scope (50° in longitude), and to conduct investigations of the low latitude ionosphere to develop forecasts of the electric fields, densities and equatorial spread F (ESF) over the South American continent. During the first years of operations the following tasks have been conducted: (1) Maps of total electron content (TEC) over South America. (2) Maps of TEC depletions and TEC perturbations associated with the passage of traveling ionospheric disturbances (TID). (3) Campaigns to detect medium-scale (~100 km) TIDs using 3 GPSs separated by 5-20 km. This presentation shows initial results on the seasonal/ longitudinal distributions of TEC depletions over South America and the relationship of these distributions with the variability of TEC and the occurrence of TEC perturbations associated with gravity waves.