Medium-scale traveling ionospheric disturbances detected with dense and wide TEC maps over North America

Nighttime and daytime medium- scale traveling ionospheric disturbances ( MSTIDs) are detected with dense and wide detrended total electron content ( TEC) maps over North America using multiple GPS receiver networks. The TEC maps cover a wide region of 60-130 degrees W and 24 - 54 degrees N (30-65 degrees N in geomagnetic latitude), and have a spatial resolution of 1.05 degrees x1.05 degrees in latitude and longitude (0.15 degrees x0.15 degrees with 7x7 pixel smoothing) and a temporal resolution of 30 seconds. The TEC maps reveal, for the first time, that the nighttime MSTIDs propagate southwestward with 200 - 500 km wavelengths over North America and have wavefronts longer than similar to 2,000 km. We also observe that daytime MSTIDs with 300 - 1,000 km wavelengths propagate southeastward until mid-afternoon and southwestward in the late afternoon. In the mid-to-late afternoon, these MSTIDs propagating in the different directions are superimposed. The TEC maps can be a new powerful tool to investigate the MSTIDs.