Medium Scale Structure of the F-Region

Data collected during 1980/81 at Brighton, Colorado, show clearly that the F-region variations are undersampled in space and time by standard recording procedures. Fast temporal changes, with periods as short as 10 minutes, are directly observable if ionograms are taken in rapid sequences of a least 12 ionograms per hour. In order to obtain a correct spatial sampling, the distances between observing stations should not be much larger than 100 kilometers. This conclusion is derived from the temporal variations of F-layer parameters assuming a propagation velocity typical for acoustic gravity waves. Some direct estimates of a spatial structure scale can be obtained from angle of arrival measurements. Comparisons of foF2 and MUF(3000) indicate that the main effect of gravity waves on the F-region structure is the variation of the height of the layer and to a lesser degree a variation of the maximum electron density. Keywords: F region variability; Sporadic E layer tilts. Presented at the AGARD Conference, 16-20 May 1988, Munich, Germany, F.R.