Data assimilation techniques for space weather are finding increasing success in ionospheric remote sensing due to the growing abundance of data from ground and space-based GPS receivers and new UV remote sensing satellites. The COSMIC 6-satellite constellation, launched in April 2006, now provides unprecedented global coverage from GPS occultation measurements (~1700 per day as of June 2007), each of which yields electron density information with up to ~1 km vertical resolution. Calibrated measurements of ionospheric delay (total electron content or TEC) from COSMIC suitable for input into assimilation models are currently made available in near real-time (NRT) with latencies between 30 and 120 minutes. Ground GPS receiver networks continue to provide near real-time (NRT) TEC data from two worldwide networks consisting of ~75 sites capable of 5-minute latency, and ~125 additional hourly sites, operated by JPL and others. Vertically-resolved NRT occultation data from COSMIC should lead to retrieved profile shapes that reproduce the hour-to-hour ionospheric “weather” much more accurately than has been possible before the COSMIC era.

In this presentation, we discuss the impact of assimilating COSMIC occultation and ground-based TEC measurements into the JPL/USC Global Assimilative Ionospheric Model (GAIM). Electron density profiles from GAIM will be compared to radar measurements obtained from the Incoherent Scatter Radar (ISR) at Jicamarca. GAIM is a physics-based three-dimensional data assimilation model that can be run at varying spatial resolutions and can work in a post-processed mode or real-time operation that generates output grids every 12 minutes. We will compare GAIM output to Jicamarca profiles and show results as a function of model spatial resolution, output latency (real-time versus post-processed) and data type used (ground alone versus ground combined with space data). COSMIC data latencies presently exceed ground network latencies, so we expect the added value of COSMIC data decays with time since the last overflight. The added value of COSMIC data will be assessed as a function of its latency assuming all ground network data are assimilated continuously as a baseline. Such an analysis permits us to estimate the configuration of radio occultation satellites that provides most value for ionospheric weather nowcasting and forecasting.