Real-time magnetic activity indices : two examples in daily use

Two different examples of real-time indices that are both provided and used by the British Geological Survey (BGS) are described here. The first is a "quick-look" estimate of both the well established and much used 3-hourly planetary index (ap) and the daily planetary index (Ap). In order to mimic the definitive indices, these estimates are derived using data from as many of the official Ap magnetic observatories as possible. They are available in real-time and are currently used by BGS when making short-term forecasts of geomagnetic activity. Results are shown as to how well the BGS estimated values correspond to the definitive Ap. The second example is the hourly standard deviation (HSD) in the North (X) and East (Y) components of the geomagnetic field. This index was chosen by BGS as an appropriate measure of geomagnetic activity for work being carried out on the analysis and monitoring of geomagnetically induced currents (GIC) in power grids in the UK. Simple to compute in real-time, HSD is a realistic proxy for the power in magnetic field variations driving GIC.