Study of periodicities in relative sunspot numbers and disturbance storm time indices using wavelet techniques

Various periodicities have been observed in many phenomena associated with the Sun. We investigate wavelet transform of monthly mean relative sunspot numbers (1749-2010) and disturbance storm time indices (1957-2010). Wavelet power spectrum peaks at 10.7 and 110.7 years periodicities for sunspot numbers and at 10.7 years periodicity for the said indices. Time in which each periodicity is strong and reason for maximum power are studied. Results show that around 1956 and 1987, power is maximum for a periodicity of 9.8 years. Year 1956 is neither solar maximum nor minimum. But 1987 is close to solar minimum. 10.7 years periodicity for disturbance storm time indices shows maximum power around 1964 and 2002. Year 1964 is close to sunspot minimum and 2002 is a sunspot maximum. (author) (author)