Satellite Traces Research Articles

Some characteristics of spread F at the magnetic equatorial station Fortaleza

Spread F in ionograms of both the range and frequency spread types is studied for the magnetic equatorial station Fortaleza (geographic coordinates 38°W, 4°S; dip latitude −1.7°) for a 1‐year period during 1978–1979). Satellite traces suggesting ionization structures with scale sizes of 100–200 km are found to be necessary precursors to the formation of the irregularities that give rise to range type spread F, whereas frequency type spread F was observed under different circumstances. Striking differences are noted in the spread F characteristics and related parameters over Fortaleza as compared with Huancayo (geographic coordinates 75.3°W, 12.05°S; dip latitude 0.6°) and Jicamarca (geographic coordinates 76.8°W, 11.95°S; dip latitude 0.9°), situated within only ∼38° in longitude west of Fortaleza. The postsunset maximum in h′F, in winter, is delayed by about 1½ hr with respect to other seasons over Fortaleza, as compared with Huancayo, where it occurs earlier in winter than in other seasons. Similar differences also exist in the prereversal peak near sunset in the vertical drift velocity (Vz) between Fortaleza and Jicamarca. The differences are attributed possibly to the large difference in the magnetic field declination and to other factors such as the difference in the magnetic field intensity and the relative separation between geographic and magnetic equators that exist between Fortaleza and the other stations.

An unusual travelling disturbance in the F-region of the ionosphere

A series of ionograms showing satellite traces has been interpreted in terms of a large in verted-trough disturbance travelling in the F-region overhead. Some details of the shape of the disturbance, which resembled a breaking wave in cross-section, have been worked out. The disturbance was approximately 100 km long, 60 km high, and was propagated at a speed of 420 km/hr. There is some evidence that it may have been associated with sunrise in the F-region.

Latitude Variations of Frequency of Occurrence of "Spread-F" Satellite Traces

Night-time "spread-F" satellites, revealed as discrete extra traces of range greater than the main F-region echo on ionograms (h'f records) have been recorded by McNicol, Webster, and Bowman (1956)? as part of the spread-F phenomenon at Brisbane. This report is an investigation of the relative frequency of occurrence of such satellites at different latitudes.