Ionospheric corrections from a prototype operational assimilation and forecast system

This paper describes an operational system, sponsored by the US Air Force, for generating and distributing near real-time three-dimensional ionospheric electron densities and corresponding GPS propagation delays. The core ionospheric model solves plasma dynamics and composition equations governing evolution of density, velocity and temperature for ion species on a fixed grid in magnetic coordinates. It uses a realistic model of the Earth's magnetic field and solar indices obtained in real time from NOAA's Space Environment Center. At the present time the model computes real-time ion and electron densities at a grid of more than one million points. Higher resolutions are anticipated in the future. While the core model is capable of delivering realistic results, its accuracy can be significantly improved by employing a special set of numerical techniques known as data assimilation. These techniques originated and are currently used for numerical weather forecasting. The core ionospheric model is constantly fed real-time observational data from a network of reference GPS ground stations. This improves both the nowcast and the forecast of electron densities. Web-based access to the system is provided to early users for validation and exploration purposes at: http://fusionnumerics.com/ionosphere.