  It is shown that helicity dynamics dominates spectral distribution of the
velocity fluctuations in turbulent thermal convection at moderate and large
values of the Rayleigh number (distributed chaos and scaling respectively). The
large-scale circulation (wind) in the turbulent Rayleigh-B\'{e}nard convection
is especially sensitive to the helicity dynamics and its chaotic reversals can
be associated with the reversals of the mean helicity sign (the ergodic
restoration of the reflectional symmetry in a long run). Results of the
laboratory experiments and measurements in the free atmospheric convection have
been used in order to support the theoretical considerations based on the
adiabatic invariance of the second order moment of the helicity distribution.
The geomagnetic field dipole variability and reversals have been also discussed
in this context and good agreement with results of numerical simulations and
observational data has been established.
