The diurnal variations of the galactic cosmic rays (GCRs) measured by ground-based detectors
represent an anisotropic flow of GCR at 1 AU, also known as solar diurnal anisotropy (SDA).
The GRAPES-3 muon telescope (G3MT) has been recording high statistics of muons at a rate
of ∼50000 per second for the past two decades allowing us to probe the tiny variations in the
muon flux caused by solar phenomena. We have examined the 22 years (2000-2021) of G3MT
data using the Fourier series technique to obtain the daily SDA amplitude and phase. We observe
that the yearly averages of SDA amplitudes have a period of one sunspot cycle (11 years), which
strongly correlates with the interplanetary magnetic field. The annual phase variation suggests
the presence of 22-year periodicity and shows a clear shift towards earlier hours with a decrease
in solar activity.