Experimental observation of 1/f noise in quasi-bidimensionnal turbulent flows

We report the experimental observation of $1/f^{\alpha}$ noise in quasi-bidimensionnal turbulence of an electromagnetically forced flow. The large scale velocity $U_L$ exhibits this power-law spectrum with $\alpha \simeq 0.7$ over a range of frequencies smaller than both the characteristic turn-over frequency and the damping rate of the flow. By studying the statistical properties of sojourn time in each polarity of $U_L$, we demonstrate that the $1/f^{\alpha}$ noise is generated by a renewal process, defined by a two-state model given by the polarities of the large scale circulation. The statistical properties of this renewal process are shown to control the value of the exponent $\alpha$.