Half-hourly nowcast ap30 index

Half-hourly (30-minute ap-like) sub-auroral geomagnetic activity indicator provided by GFZ Potsdam, Germany. The near real-time computation is based on 1-minute geomagnetic data from the contributing observatories. The quiet magnetic field is subtracted and the remaining disturbance is translated into H30 value. The H30 values are standardized at each observatory to obtain Hs30 values, from which Hp30 value is derived as a mean. The ap30 index is obtained as a linear scale representation of Hp30 according to a mapping table.