Space-based ultraviolet (UV) optical signatures of equatorial ionospheric bubbles have been computed from a first-principles time-dependent physical mesoscale ionospheric simulation model. We find that for nadir-viewing geometry, extreme UV signatures at 911 ¿ of equatorial ionospheric bubble structures contain large bite-outs in intensity, are structured over tens of kilometers scales, and are distinctly different from the signatures of the quiet ionosphere. ¿ 2001 American Geophysical Union