Microwave equatorial scintillation intensity during solar maximum

Abstract

A comparison of scintillation levels at 1.5 GHz made from the Appleton anomaly region of the magnetic equator and from the region close to the magnetic equator (termed the electrojet latitudes) showed increased F region irregularity intensity over the anomaly region during years of high sunspot number. Peak to peak fading greater than 27 dB was noted from Ascension Island (through a dip latitude of 17°) in the anomaly region while only 7–9 dB from Natal, Brazil, and Huancayo, Peru, were noted, the last two paths being close to the magnetic equator. The hypothesis advanced is that the dominant factor responsible for the intense gigahertz scintillation is the traversal of the propagation path through the anomaly region. During years of high sunspot numbers the high levels of ΔN constituting the F region irregularity structure are due to (1) very high electron density in the anomaly region (compared to the electrojet region) and (2) the late appearance of these high electron densities (to 2200 local time) in the anomaly region. The patches or plumes of irregularities seen in the postsunset time period then produce high ΔN; scintillation excursions are proportional to this parameter. The postulation of vertical irregularity sheets in the patches was examined to determine the possibility of this being an important factor in the difference between electrojet and anomaly scintillation levels. Older gigahertz data from the sunspot maximum years 1969–1970 were reanalyzed, and more recent observations from other studies were also reviewed. It was found that through the anomaly region, high scintillation indices were noted at a variety of azimuths of the propagation path rather than just along a path closely aligned with the magnetic meridian. A more complete evaluation of the geometrical factor, which must be of considerable importance in determining the absolute value of the scintillation intensity, awaits further observations.