1. Acharya B L, Yagnik H K, Bansal T C, Vijayvargia S K and Rai R K 1982Proc. Indian Natl. Sci. Acad. A48 Suppl. 3 388
2. Bischoff K and Taubenheim J 1967J. Atmos. Terr. Phys. 29 1063
3. Chandra H, Sethia G, Vyas G D, Deshpande M R and Vats H O 1981Indian J. Rad. Space Phys. 10 45
4. Datta G, Pradhan S N and Kotadia K M 1983Adv. Space Res. 10 209
5. Davies K 1956Solar eclipses and the ionosphere (eds) W J G Beynon and G M Brown (London: Pergamon Press) p. 40