Ionospheric Data Assimilation Four-Dimensional (IDA4D) is an ionospheric data assimilation algorithm that has been under development for more than 15 years. It is a fully developed, mature, validated algorithm that provides global and regional 4-D distributions of electron density. IDA4D is currently being applied to space weather projects that have both a scientific and applied societal aspect to them. This paper will provide an introduction to IDA4D, including recent improvements, show results of a recent validation campaign and then present results from several space weather application projects that use IDA4D.

The space weather applications discussed in this paper include the following:

1. Estimating physical drivers such as neutral winds and electric fields from IDA4D

2. Validation of SSUSI 1356 EUV limb scans

3. Improved estimation of conductances inputs to AMIE and estimation of field aligned currents at high latitudes

4. Improved bottom-side F-region imaging of electron density and subsequent improvements to HF propagation applications

5. Using IDA4D to assist in the inversion of GPS occultations to get accurate estimates of E-region densities

6. Investigating the high-altitude redistribution of plasma during strong magnetic storms

Each of these space weather projects will be discussed, results presented and the current status and future plans described.