The primary goal of this project is to determine the characteristics of the response of the ionospheric total electron content (TEC) to geomagnetic storms. The study will utilize the extensive ground-based, dual-frequency, Global Positioning System (GPS) measurements of TEC. A recent study has shown that by sorting F-region ionosonde data (NmF2) as a function of a new index of storm magnitude, a consistent repeatable picture begins to emerge in each season and latitude. The PIs will perform a similar analysis of total electron content, and compare and contrast the geophysical response with NmF2. This study will contribute to the understanding of the ionospheric response to geomagnetic storms. In the context of the National Space Weather Program, the work will provide the information to hopefully lead to an operational product for the benefit of a range of single frequency GPS users.