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Title: Night-time Changes in Field Strength of 11.8 MHz Radio Signals over Coldmbo-Ahmedabad Transmission Path
Authors: Chhipa, G. M.
Patel, B. M.
Issue Date: Jun-1973
Publisher: NISCAIR-CSIR, India
Abstract: The results of a study of night-time records of the field strength of radio signals on 11.8 MHz transmitted from Colombo (6.9N, 79.9E, I=5S) and obtained at Ahmedabad (23N, 72.6E, I=34N) are reported. It is shown that the maximum strength is observed an hour after sunset in summer and almost at sunset in winter. This maximum is most pronounced in equinoctial months. The records show a fast fading of small amplitude on quiet day’s characteristic of spread-F. On magnetically disturbed days, the field strength under-goes large fluctuations with reduced fading rate and absence of flutter-type fading. On some occasions of high magnetic activity, signals become very weak. Such changes are believed to be caused by large-scale movements in the F2-layer and the accompanying changes in the electron density during the magnetic storm. Several instances of temporary sharp increases of field strengths over duration of about 10 min have been recorded in the post-sunset to pre-midnight interval. Most of these are found to occur after solar radio bursts with a lag of 12-17 min. The observed effect of increased field strength may be due to a transient disturbance produced in the F2-layer due to the burst.
Page(s): 148-152
ISSN: 0975-105X (Online); 0367-8393 (Print)
Appears in Collections:IJRSP Vol.02(2) [June 1973]

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