The use of interplanetary scintillation maps in the prediction of geomagnetic activity

Abstract

Interplanetary scintillation (IPS), the twinkling of small angular diameter radio sources, arises from the interaction of the signal with small-scale plasma irregularities in the solar wind. The technique may be used to sense remotely the near-Earth heliosphere and has potential for tracking large-scale interplanetary disturbances from close to the Sun to the Earth. Such observations might be useful within routine geomagnetic forecasts, and we use data from the Mullard Radio Astronomy Observatory to test this suggestion. A forecast was based on the visual evaluation of each daily map. If an IPS event was observed then we proposed that any associated geomagnetic activity would occur either on that day, or during the following two days. We consider the success of these forecasts in predicting days when either an SSC/SI or an <i>Ap</i> value exceeding 30 were recorded. The identification of IPS events is necessarily subjective and so two observers compiled independent events lists, and the results were compared. Approximately half of the IPS events in each list were followed by a geomagnetic signature but comparison of the two lists showed that different days were being chosen. We also found that the forecasts had very high false alarm rates. Since IPS is sensitive to a volume we did not expect all events to be associated with a geomagnetic signature. However, the technique failed to forecast a large proportion of geomagnetic events and the association between IPS events and geomagnetic activity is not much better than would be expected by chance. Comparing the IPS forecasts with forecasts of <i>Ap</i> released by the Space Environment Services Center (SESC) we found that SESC correctly predicted a similar proportion of days when <i>Ap</i>geq30, but that the performance was significantly better than would be expected by chance, and had a much lower false alarm rate. We conclude that these IPS data cannot be used alone to produce reliable geomagnetic activity forecasts.