A COMPARATIVE STUDY OF Es-LAYER AT KARACHI DURING THE SOLAR MAXIMUM (1989-90) AND SOLAR MINIMUM (1996-97)

摘要

A careful study of quarter hourly ionograms at Karachi (24.95°N, 67.14°E, Dip=36°N), located near the crest of equatorial anomaly region, for Solar Maximum (1989-90) and Solar Minimum (1996-97) years has revealed that there exists a negative correlation between the frequency of occurrence of Blanketing Es-layer at Karachi and the solar activity. However, a reverse trend (i.e. a positive correlation) has been clearly observed in case of Non-Blanketing Es-layer at Karachi, which is similar to the trend reported by the previous investigators regarding the occurrence of Es at mid-latitudes. As far as the seasonal behaviour of the occurrence of Es is concerned, it shows maxima in summer and minima in winter at the two solar conditions. The specific cases of Blanketing Es-layer producing total Blanketing of the overlying F_1 and F_2 -layers, hence causing failure of HF communications, are observed to be greater in all seasons at solar minimum than at solar maximum. During both the solar conditions, it (i.e. the Blanketing Es) occurs maximally in summer and minimally in winter.