Ab. Bhattacharya et al., A COMPARATIVE-STUDY OF THE SUNRISE AND SUNSET EFFECTS ON THE INTEGRATED FIELD INTENSITY OF VLF ATMOSPHERICS, Annales geophysicae, 13(9), 1995, pp. 976-980
A comparative study is made of the stepped structure of atmospherics d
uring sunrise and sunset hours at three harmonically related frequenci
es in the VLF band, observed at the coast of the Bay of Bengal. The oc
currences of the steps, their duration, time sequence and amplitudes a
re critically examined. Our analysis reveals that the start times of t
he third and second steps of the sunrise effect are always before grou
nd sunrise, while the start of the main step is distributed on both si
des of it. During sunset hours, the onset time of the main step is bef
ore the local ground sunset, but for the second and third steps, the o
nset times are after that. The results are interpreted by considering
the multi-hop propagation as well as the distributed noise sources sur
rounding the observing site.