THE USE OF VARIOUS INTERPLANETARY SCINTILLATION INDEXES WITHIN GEOMAGNETIC FORECASTS

Interplanetary scintillation (IFS), the twinkling of small angular dia meter radio sources, is caused by the interaction of the signal with s mall-scale plasma irregularities in the solar wind. The technique may be used to sense remotely the near-Earth heliosphere and observations of a sufficiently large number of sources may be used to track large-s cale disturbances as they propagate from close to the Sun to the Earth . Therefore, such observations have potential for use within geomagnet ic forecasts. We use daily data from the Mullard Radio Astronomy Obser vatory, made available through the World Data Centre, to test the succ ess of geomagnetic forecasts based on IFS observations. The approach d iscussed here was based on the reduction of the information in a map t o a single number or series of numbers. The advantages of an index of this nature are that it may be produced routinely and that it could id eally forecast both the occurrence and intensity of geomagnetic activi ty. We start from an index that has already been described in the lite rature, INDEX35. On the basis of visual examination of the data in a f ull skymap format modifications were made to the way in which the inde x was calculated. It was hoped that these would lead to an improvement in its forecasting ability. Here we assess the forecasting potential of the index using the value of the correlation coefficient between da ily Ap and the IFS index, with IFS leading by 1 day. We also compare t he forecast based on the IFS index with forecasts of Ap currently rele ased by the Space Environment Services Center (SESC). Although we find that the maximum improvement achieved is small, and does not represen t a significant advance in forecasting ability, the IFS forecasts at t his phase of the solar cycle are of a similar quality to those made by SESC.