Is an unusual large enhancement of ionospheric electron density linked with the 2008 great Wenchuan earthquake?

On 12 May 2008 at 0628 UT a major earthquake M-s = 8.0 struck Wenchuan County (31.0 degrees N, 103.4 degrees E) in southwest China. The maximum ionospheric electron density at F-2 peak (NmF2) recorded an unusual large enhancement during the afternoon-sunset sector by the Chinese ionosondes over Wuhan (30.5 degrees N, 114.4 degrees E) and Xiamen (24.4 degrees N, 123.9 degrees E), which are close to the earthquake epicenter. An averaged increase at these two stations is about 2 times on a geomagnetic quiet day, 9 May (Kp <= 2), 3 days prior to the earthquake, relative to the median value of 1-12 May, whereas the increase was much less significant over Yamagawa (31.2 degrees N, 130.6 degrees E) and Okinawa (26.7 degrees N, 128.2 degrees E) in Japan. Combining the data from the network of 58 global positioning system receivers around China and the global ionospheric map, the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90 degrees-130 degrees E. Our results suggest that this abnormal enhancement is most possibly a seismo-ionospheric signature.