Giant disturbance in the ionospheric F 2 region prior to the M 8 . 0 Wenchuan earthquake on 12 May 2008

With a new factor, effective sunspot number R eff , the results show that there were giant positive disturbances of foF2 around the epicentral zone on 9 May, 3 days prior to the earthquake. Our results indicate that the observed positive ionospheric disturbances were most possibly associated with the imminent earthquake and the new analytic method has good prospects in practice.