Eastward propagation of PC4‐5 range CNA pulsations in the morning sector observed with scanning narrow beam riometer at L=6.1

A new type of cosmic noise absorption (CNA) pulsation is observed with a scanning beam riometer with a spatial resolution of 10 km, at Syowa station, Antarctica (L=6.1). This type of CNA pulsation has a short azimuthal wavelength (80–600 km), corresponding to a large azimuthal m‐number (20–180). Most CNA pulsations with a period of 1 to 10 min propagate eastward at a speed of 200 m/s to 3 km/s in the morning sector (5–10 MLT). The eastward propagation direction is opposite to that of CNA pulsations with a small m‐number as reported by Olson et al. (1980). The pulsation period tends to increase, while the propagation speed decreases with increasing local time. These results suggest that the source of this new type of CNA pulsation first appears in the nightside magnetosphere and moves toward noon. It is pointed out that the finding of this new CNA pulsation is due to the high spatial resolution (10 km) and narrow antenna beam (13°) of the scanning riometer system.