Publication Date:
2019-11-04
Description:
The variation in nighttime ionospheric E- and F-region critical frequencies (foEs and foF2) is examined for the
months of August 1988, September 1993 and May 1997 in which major earthquakes (6〈M〈6.6) occurred in Indian
seismic zones of Bihar-Nepal border, Latur in West India, and Jabalpur in Central India. The ionospheric
data are obtained from Ahmedabad (latitude 23.01°N, longitude 72.36°E). The percent deviations of foF2 and
foEs from their monthly median are determined for pre-midnight (18:00-00:00 h LT) and post-midnight (00:00-
06:00 h LT) periods and studied over a span of 20 days before the occurrence of earthquakes. The results show
that foF2 are reduced in both the time sectors prior to the occurrence of main shocks. In pre-midnight sector the
reduction is between 24 and 30%, 0 to 4 days before the main shocks and in the post-midnight sector it is between
18 and 26%, 1 to 15 days before the main shocks. The foEs show enhancements by 100 to 155% during
the same periods. The effects of magnetic storms (Kp and Dst variations) on the data are identified clearly but
they do not vitiate the effects of earthquakes. The earthquake related anomalies are interpreted in terms of electromagnetic
coupling between the lithosphere and ionosphere during earthquakes preparation processes.
Description:
JCR Journal
Description:
open
Keywords:
ionosphere
;
E- and F-layers
;
earthquakes-magnetic storm
;
foF2 and foEs
;
01. Atmosphere::01.02. Ionosphere::01.02.06. Instruments and techniques
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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