Incoherent scatter radar observations of spread-F producing ionospheric structures at arecibo

Range spreading type spread-F observed during the night of 7-8 January 1971 at Arecibo, Puerto Rico is shown to be associated with tilts in the ionosphere which occurred when a region of increased total electron content drifted by in a southerly direction. This conclusion is reached by using the incoherent scatter radar to measure electron densities, vertical and horizontal ion velocities, and total content. Also used for analysis of ionogram data is a spread-F intensity index and a method of applying the time development of spread-F to estimate the vertical and horizontal velocity of the reflector producing the spread-F trace. It is also suggested that frequency spreading at Arecibo is due for the most part to overlapping of four or more range spreading type ionogram traces having different critical frequencies since each trace comes from different regions of the ionosphere.