Spatial structure of the E region field‐aligned irregularities revealed by the MU radar

The MU radar (34.9°N, 136.1°E, geomagnetic latitude 25.0°N) is utilized to observe the spatial structures of the field‐aligned irregularities in the midlatitude E region. The multibeam observation in 12 directions has found that the “quasi‐periodic” echoes have a monochromatic wave structure propagating toward SSW. Much smaller‐scale structure of the irregularities has been observed by the interferometry techniques with three receivers. The results are consistent with a model in which a southward propagating gravity wave modulates the sporadic E layer to generate the quasi‐periodic echoes of the irregularities.