Letter | Published:

Possibility of detecting Ionospheric Drifts from the Occurrence of Spread F Echoes at Low Latitudes

Naturevolume 187page927 (1960) | Download Citation



DURING the course of an investigation concerning the geographical extent of the scattered and diffuse echoes frequently observed during the night hours at high and low magnetic latitudes (spread F) an interesting phenomenon was observed. Times of occurrence of spread F echoes on ionospheric soundings taken every 15 min. during September and October 1957 at four stations in Peru (Talara, Chiclayo, Chimbote and Huancayo—average separation about 350 km., magnetic dip from 2° to 13°) strongly suggested that the patches of irregularities thought to be producing the spread F were often observed successively at each of the four stations. For example, an occurrence of spread F might be observed to begin at, say, 0015 hr. at Talara, the north-westernmost station, at 0045 at Chiclayo, at 0100 at Chimbote and at 0145 at Huancayo, the south-easternmost station. This tendency was particularly marked for the relatively short occurrences (less than about 2 hr. in duration) that were commonly observed during the latter half of the night. As the stations were located approximately along a straight line, it is not possible to deduce unambiguously the magnitude and direction of the suggested drift. It has been shown, however, that the geographic north–south component of the night F region drift is usually small at these latitudes1. Therefore, on the assumption that the drift was wholly in the magnetic east–west direction, magnitudes of the geographic east–west component of the apparent drifts indicated by the spread F occurrences during September and October have been estimated. A mean apparent drift velocity of 135 m./s. towards the east was obtained for period 0000–0400 hr. Skinner, Hope and Wright, using the Mitra technique at another equatorial location (Ibadan) during the same period, observed a mean east–west component of F region drift of about 110 m./s. towards the east2. The degree of agreement suggests that drifts, either of the patches of irregularities giving rise to the spread F echoes or of the disturbance producing the irregularities, may play an important part in the occurrence of spread F at low latitudes.

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  1. 1

    Purslow, B. W., Nature, 181, 35 (1958).

  2. 2

    Skinner, N. J., Hope, J., and Wright, R. W., Nature, 182, 1363 (1958).

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  1. R. W. KNECHT: On leave at the Cavendish Laboratory, Cambridge, England.


  1. National Bureau of Standards, Boulder, Colorado

    • R. W. KNECHT


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