Solar Eclipses and Ionospheric Effects: Some Historical Perspectives

The upper most part of the Earth's atmosphere consists of the gas molecule and atoms which interact with the ultraviolet and Xray radiations coming from the Sun. This interaction results in the ionization of gases resulting in the creation of large number of free negatively and positively charged particles. Such a region of the atmosphere, where ionization of gases takes place is called the Ionosphere. The ionization phenomena vary with solar intensity, solar cycle and season. Apart from external factors like solar disturbances the dynamics of ionosphere is also controlled by internal processes taking place within the ionospheric plasma itself. Since the internal and external disturbances take place simultaneously it really becomes very difficult to isolate the effect due to a single factor. Since during total solar eclipses major portion of solar radiation is blocked therefore such events provide us unique opportunity to study the internal dynamics of ionosphere in the absence of external factors. In this article we review the various studies that have been carried out to study the effect of solar eclipses and behavior of ionosphere during these events.