  Wavelet analysis of different solar activity indices, sunspot numbers,
sunspot areas, flare index, magnetic fields, etc., allows us to investigate the
time evolution of some specific features of the solar activity and the
underlying dynamo mechanism. The main aim of this work is the analysis of the
time-frequency behavior of some magnetic strengtht indices currently taken at
the Mt. Wilson Observatory 150-Foot Solar Tower. In particular, we analyzed
both the long time series (Jan 19, 1970 - Jan 22, 2013) of the Magnetic Plage
Strength Index (MPSI) values and of the Mt. Wilson Sunspot Index (MWSI) values,
covering the descending phase of cycle 20, the full solar cycles 21-23 and the
current part of the 24 solar cycle. This study is a further contribution to
detect the changes in the multiscale quasiperiodic variations in the integrated
magnetic solar activity with a comparison between past solar cycles and the
current one, which is one of the weaker recorded in the past 100 years. Indeed,
it is well known that an unusual and deep solar minimum occurred between solar
cycles 23 and 24 and the time-frequency behavior of some magnetic strengtht
indices can help to better interpret the responsible mechanisms.
