Data assimilation for three-dimensional modelling of the ionosphere in Brazil

Abstract

Spatial and temporal variation of the electron density in the atmosphere makes the ionosphere a difficult region to model. Many models were developed using the GNSS (Global Navigation Satellite System) observation to represent the ionosphere in Vertical Total Electron Content (VTEC) maps. However, errors in the VTEC modeling occur due to the consideration of the ionosphere as a thin shell with constant height. By contrast, ionosphere is a layer with 1000 km thickness. The ionospheric profile can be calculated using tomographic reconstruction techniques, which are based on TEC (Total Electron Content) observations from GNSS to map the ionosphere in three dimensions. However, performing tomographic reconstructions using only TEC measurements shows deficiencies in vertical representations of the ionosphere. To overcome this geometric deficiency, data assimilation can be performed including ionospheric profiles in the tomographic reconstruction. In addition, a relevant peculiarity of the Brazilian region is the fact that some ionospheric dynamics over the region are not completely understood and it is affected by strong vertical drifts in the evening pre-reverse period. In this way, the research project aims to study tomographic reconstruction methods of the ionosphere using data assimilation including TEC observations and ionospheric profiles. The experiments will be conducted with GNSS data from global and regional networks, as well as using ionosondes installed around the world and in Brazil. Furthermore, Radio-Occultation techniques will be included in the tomographic reconstruction. The results will be validated using the Root Mean Square Error (RMSE) of the critical frequency and peak elevation of the F2 layer of the ionosphere (foF2 and hmF2). Also, we will calculate the RMSE of the slant TEC (STEC) and STEC will be applied in GNSS positioning to evaluate the improvement in Precise Point Positioning (PPP). Finally, possible representations of the ionosphere in the Brazilian region will be assessed from TEC assimilation with the ionospheric profiles.