Comparison of changes in the ionospheric total electron content at mid-latitude locations few hundred kilometers apart

The changes in the ionospheric TEC (Total Electron Content) at the three North American locations Stanford (370N, 1220W), Clark Lake (330N, 1160W) and Rosman (350N, 830W) are compared for about 260 days in 1971. Apart from considerable day-to-day changes (approximately=30%) in the daily ranges of TEC even on quiet days at all the three locations, the changes at Stanford and Clark Lake differed between themselves sometimes by as much as 30% and those between this pair and Rosman by as much as 50%, indicating random components of local origin of scales as small as few hundred km. and as large as few thousand km