[1] Centre for Atmospheric Sciences, 92, A.P.C. Road, Calcutta-700009, India
[2] Department of Mathematics, S.A. Jaipuria College, 10, R.N.K. Street, Calcutta-700005, India
[3] c/o Prof. D. K. Sinha, 22/1A, Ballgunge station road, Calcutta-19, Pin-700 001, India