  We present a method of disentangling the anisotropies produced by the cliff
structures in turbulent velocity field and test it in the system of turbulent
Rayleigh-B\'{e}nard (RB) convection. It is found that in the RB system the
cliff structures in the velocity field are generated by thermal plumes. These
cliff structures induce asymmetry in the velocity increments, which leads us to
consider the plus and minus velocity structure functions (VSF). The plus
velocity increments exclude cliff structures, while the minus ones include
them. Our results show that the scaling exponents of the plus VSFs are in
excellent agreement with those predicted for homogeneous and isotropic
turbulence (HIT), whereas those of the minus VSFs exhibit significant
deviations from HIT expectations in places where thermal plumes abound. These
results demonstrate that plus and minus VSFs can be used to quantitatively
study the effect of cliff structures in the velocity field and to effectively
disentangle the associated anisotropies caused by these structures.
