Analog ionospheric forecasts: Space weather forecasts by analogy with previous events

Operational systems that take advantage of the ionosphere or for which the ionosphere is a major inconvenience require that deleterious changes to the ionosphere during geomagnetically disturbed intervals be forecast up to several days in advance, in order to allow mitigation procedures to be instituted. However, the reliability of current space weather models of the Sun, solar wind, magnetosphere and ionosphere is such that the consequential ionospheric forecasts depend too much on the uncertainties of the various models. It is no secret that the level of success of space weather forecasts is currently still a decade or two behind that achieved by the tropospheric weather forecasting community. As an interim solution to forecasting the low and midlatitude ionosphere, we propose the use of analog forecasts in which we look to the past to see what happened to the ionosphere during a historical interval for which the forecast geomagnetic conditions also applied. In order to investigate the concept of analog forecasts, we have analyzed Australian ionosonde values of NmF2 for similar to 200 disturbed intervals. While we do not expect analog forecasts to match the details of individual storms, we do expect them to provide users with the essential nature of a forecast ionospheric storm. The reliability of analog forecasts should increase as we gain experience and thus provide a standard of reliability that will eventually be reached by fully coupled space weather forecasts.