HF radar observation of ionospheric irregularities with unsual behaviour

HF radar ionospheric echoes have been observed at mid latitudes, exhibiting a very unusual behaviour in the RTI (Range-Time-Intensity) display with fast quasi-periodic variations of the power of the echoes in the range 1-10 seconds. A wavelet analysis reveals that periodicities are in fact present in the data ranging from 1 second up to 400 seconds, depending on the time of observation. The strongest radar echoes were recorded during the first 40 minutes of the experiment. The radar used for these observations offers the possibility to perform scanning in elevation and in azimuth by software. Elevation scans have been used to estimate the height of the echoing region. Apparently the echoes are not coming exactly from the aspect-sensitive region. This result must be considered carefully because at HF frequencies refraction of radio waves easily produces ray bending.