title: Fluctuations of temperature gradients in turbulent thermal convection.
abstract: Broad theoretical arguments are proposed to show, formally, that the magnitude G of the temperature gradients in turbulent thermal convection at high Rayleigh numbers obeys the same advection-diffusion equation that governs the temperature fluctuation T , except that the velocity field in the new equation is substantially smoothed. This smoothed field leads to a -1 scaling of the spectrum of G in the same range of scales for which the spectral exponent of T lies between -7/5 and -5/3 . This result is confirmed by measurements in a confined container with cryogenic helium gas as the working fluid for Rayleigh number Ra=1.5x 10(11) . Also confirmed is the logarithmic form of the autocorrelation function of G . The anomalous scaling of dissipation-like quantities of T and G are identical in the inertial range, showing that the analogy between the two fields is quite deep.
authors.affiliation: International Center for Theoretical Physics, Strada Costiera 11, I-34100 Trieste, Italy.
authors.forename: K R
authors.initials: KR
authors.lastname: Sreenivasan
authors.forename: A
authors.initials: A
authors.lastname: Bershadskii
authors.forename: J J
authors.initials: JJ
authors.lastname: Niemela