Interplanetary scintillation imaging of disturbances in the solar wind

Small scale turbulence in the solar wind causes radio sources to scintillate and it has been found that this effect depends upon the mean plasma density along the line of sight. Routine daily observations of interplanetary scintillation (IPS) on about 1000 sources can be used to construct whole-sky maps showing the two-dimensional projection of large scale features of enhanced, or reduced density such as corotating streams or compression zones following interplanetary shocks. This ground-based method provides a global picture of major interplanetary disturbances and gives information over a wide range of ecliptic latitude which complements the detailed sampling provided by individual spacecraft. Continuous monitoring of the interplanetary medium has been carried out at Cambridge since March 1990. The method will be described and some typical disturbances observed during this period will be shown. The results provide new insights into the nature of coronal magnetic energy releases responsible for the most powerful interplanetary shocks