Detection and tracking of IP disturbances using interplanetary scintillation

Abstract

A well known method of probing large portions of the interplanetary medium (IPM) is by observations of interplanetary scintillations of a large number of spatially well-distributed compact extragalactic radio sources at meter wavelengths. For this purpose large dipole arrays operating as transit instruments are used. Such telescopes generally observe a source only once a day and detect IP disturbance (IPD) travelling outward from the sun by recording the enhancement of the scintillation indices in certain regions of IPM due to the IPD. The use of a steerable radio telescope with large collecting area, such as the Ooty Radio Telescope (ORT), enables not only the detection of scintillation enhancements due to travelling IPD but also the determination of the velocity of the disturbance. Based on such data one could select a set of appropriately located scintillating sources so that the set of lines of sight to these sources is used as a "picket fence' to intercept the oncoming disturbance. The concept was tested successfully on four occasions when the times of occurrence and the travel paths of the IPD were predicted in advance by a theoretical model of generation and propagation IPD driven by solar flares. The paper describes the method and its advantages and disadvantages when adopted for predicting geomagnetic disturbances triggered by solar transients