Published online by Cambridge University Press: 31 March 2021
We present experimentally obtained time-averaged vertical temperature profiles $\theta (z)$ in horizontal convection (HC) in water (Prandtl number
$Pr \simeq 6$), which were measured near the heating and cooling plates that are embedded in the bottom of HC samples. Three HC rectangular samples of different sizes but the same aspect ratio
$\varGamma \equiv L:W:H = 10:1:1$ (
$L$,
$W$ and
$H$ are the length, width and height of the sample, respectively) were used in the experiments, which allowed us to study HC in a Rayleigh-number range
$2 \times 10^{10} \lesssim {Ra} \lesssim 9 \times 10^{12}$. The measurements revealed that above the cooling plate, the mean temperature profiles have a universal scaling form
$\theta (z/\lambda _c)$ with
$\lambda _c$ being a
$Ra$-dependent thickness of the cold thermal boundary layer (BL). The
$\theta (z/\lambda _c)$-profiles agree well with solutions to a laminar BL equation in HC, which is derived under assumption that the large-scale horizontal velocity achieves its maximum near the plate and vanishes in the bulk. Above the heating plate, the mean temperature field has a double-layer structure: in the lower layer, the
$\theta$ profiles scale with the hot thermal BL thickness
$\lambda _h$, while in the upper layer, they again scale with
$\lambda _c$. Both scaling forms are in good agreement with the solutions to the BL equation with a proper parameter choice.