We present in this work the temporal evolution of the three-dimensional electron density at global scale during two ionospheric storms (October 18--19, 1995, and January 10, 1997) computed using only actual Global Positioning System data. The tomographic model is solved by means of a Kalman filtering with a filter updating time of 1 hour in a Sun-fixed reference frame, and with a resolution of 10¿10 deg in latitude/local time and 100 km in height including also a protonospheric component (eight layers). The data set contains the data from the International GPS Service IGS (with more than 100 ground GPS stations worldwide distributed) and the GPS/MET low orbiting GPS receiver (both positive and negative elevation observations are used). This means for each storm 1,000,000 of delays, 400 occultations and 3000 unknowns per batch. The International Reference Ionosphere and data coming from the ionosonde of the Ebre observatory are used to show the reliability of the results. ¿ 1998 American Geophysical Union