SHORT TERM SOLAR CYCLE INDEX · Geomagnetic Index Daily average of maximum variation in the earths surface magnetic field at mid lattitude(units of 2×10-9T Ap=o quiet l5 to 30 active >50 major solar stormSHORT TERM SOLAR CYCLE INDEX • Geomagnetic Index Ap – Daily average of maximum variation in the earth’s surface magnetic field at mid lattitude (units of 2 u 10-9 T) Ap = 0 quiet Ap = 15 to 30 active Ap > 50 major solar storm 6