The zonal electric field is the primary driver of two important features of the equatorial ionosphere: (1)The Equatorial Ionization Anomaly (EIA), and (2) plasma density irregularities, also known as spread‐F. During propagation through the ionosphere, communication and navigation radio signals are attenuated, delayed and scattered by these ionospheric features. Prediction of the zonal electric field is therefore a key to the real‐time specification of the ionosphere. We divide the zonal electric field into a climatological contribution plus the prompt‐penetration contribution predicted by a transfer‐function model applied to the interplanetary electric field measured by the Advanced Composition Explorer (ACE) satellite. The zonal electric field is predicted about one hour in advance, covering all local times and longitudes. The real‐time prediction is available as a Google application at http://www.geomag.us/models/PPEFM/RealtimeEF.html. The benefit of this application to space weather forecasting is twofold: As the driver of the equatorial plasma fountain, the predicted zonal electric field is a leading indicator by 2–3 h of the EIA and the Total Electron Content (TEC) of the equatorial ionosphere. Second, rapid uplift of the ionosphere by strong eastward electric field is known to induce spread‐F. Prediction of enhanced prompt penetration electric field in the eastward direction therefore enables the forecast of radio communication and navigation outages in the equatorial region.
