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The scintillation of radio stars
Author(s) -
Palmer H. P.
Publication year - 1955
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49708134718
Subject(s) - physics , ionosphere , stars , astrophysics , zenith , scintillation , ionization , astronomy , atmospheric sciences , geology , optics , ion , quantum mechanics , detector
This note presents a brief summary of the work of Little, Maxwell and Dagg (1952, 1954) on the fluctuations of the power received from the intense sources of radio emission in the constellations of Cassiopeia and Cygnus. Receiving equipments, 4 km apart, give almost identical records of the fluctuations, but there is no correlation when the receivers are 200 km apart. The fluctuations occur mainly during the night, the degree of fluctuation varying from night to night, and showing a close correlation with the occurrence of ‘spread F’ ionospheric echoes. This evidence suggests that the fluctuations are caused by a terrestrial agency, and not by variations of the power emitted by the radio source. It is thought that the fluctuations are analogous to the ‘twinkling’ of visual stars and are caused by a diffracting screen of irregularities above the maximum of ionization in the F region of the ionosphere. When records from receivers two or three km apart are compared, small time‐differences can be detected between the records of similar fluctuations. These may be interpreted as evidence for drift motions of the diffracting screen. Records from a triangularly‐spaced set of three stations have recently given both the drift speeds and directions. For observations when the source is near the zenith, in Britain, the velocities are usually in the range 50–300 m/sec, in an east‐west direction. In the winter months, when the stars transit near midnight, the drifts are towards the west before 01 GMT. There appears then to be a fairly sharp reversal, and the drifts are predominantly towards the east thereafter. As the fluctuations rarely occur in the daytime, no other reversal has been observed. When the stars are observed near lower culmination the line of sight passes through the F region in the auroral zone. Fluctuations are observed at all times (even on magnetically quiet days), and they indicate rather higher velocities, and more variable directions of drift. The drifts are predominantly towards the west in the period 09–21 GMT and towards the SE. or SW. from 21‐06 GMT. The apparent N‐S components of these drifts might be caused by vertical movements. The appended references contain full accounts of this work.