eng Ansari Education and Research Society Journal of Ultra Scientist of Physical Sciences April 2010 22 1 37 42 juc 895 article D.P. Singh Chauhan 1 D.P. Tiwari 2 S. K. Pandey 3 A.K. Tripathi 3 S.C. Dubey 3 Department of Physics, A.P.S., University, Rewa - 486 003 (INDIA) Department of Physics, Rewa Engineering College, Rewa - 486 003 (INDIA) Department of Physics, S.G.S., Govt. P.G. College, Sidhi -486 661 IINDIA) <p style="text-align: justify;">A set of 90 large geomagnetic storms, associated with D_st (decreases of more than 100 nT) observed during 1997-2007, have been analysed. The analysis included various characteristics features as well as seasonal and solar cycle dependence of these storm events. Out of selected 90 large geomagnetic storm events, 57% are sudden commen-cement type and rest 43% are gradual commencement type. In the present investigation, we have analyzed in detail all halo CMEs occurred during solar cycle 23. On the basis of investigation of 354 halo CMEs and 90 large geomagnetic storms (D_st &pound; -100 nT), it is concluded that population of halo CMEs and their average speed increases during solar maximum and their occurrence generally follow the phases of solar cycle. Out of selected 90 large geomagnetic storms occurred during solar cycle 23, 56 large geomagnetic storms are associated with halo coronal mass ejections. Long-term variations of flare index variability and global Ap have also been discussed during present analysis.<br /> &nbsp;</p> https://ultraphysicalsciences.org/paper/895/ Geomagnetic storms Coronal mass ejection Disturbance storm time Solar cycle