Experimental study of rotating convection in the presence of bi-directional thermal gradients with localized heating

We conduct experiments on the convective dynamics of a rotating fluid in a novel configuration, which comprises of a cylindrical annulus with peripheral spot heating at the bottom on the outer edge and uniform cooling on the inner edge. This system naturally provides an additional vertical gradient on the outer edge of the annulus, along with a radial gradient, thereby mimicking the thermal gradient patterns encountered in a real atmosphere. Localized heating is carried out at the bottom using a thin annular metal strip of thickness, h=5 mm. Water is used as the working fluid. Once the system reaches a statistically steady state, localized temperature measurements are carried out at various radial locations along the vertical fluid height. We measure time series of the temperature at several locations and visualize the flow structures over a range of Taylor number Ta (spanning 6.5 x 10(8) - 2.7 x 10(9)) and Rayleigh number Ra (spanning 2.2 x 10(8) - 6.2 x 10(8)). Temperature time series data at different heights, z, near the outer edge, along with two point correlations of temperature data indicate that, in the presence of rotation, columnar convective plumes (CCP) exist above the heating zone that aid in the vertical transport of heat. Qualitative flow field and temperature measurements in the bulk fluid also indicate the existence of baroclinic waves, which aid in the horizontal transport of cold and hot fluids between the annuli. The two point temperature correlations show that these waves break into eddies as the value of Ta increases. Overall, it is speculated that heat transport in this new configuration is governed by the co-existence and interplay of convective plumes and baroclinic waves/eddies, which closely simulates the dynamics of geophysical motions. It is found that the heat transport near the outer edge and in the fluid bulk is a strong function of Ra and Ta. For the highest value of Ra=6.2 x 10(8), the radial heat transport was most effective at Ta=0. However, at lower values of Ra, the radial heat transport in the outer and bulk regions was highest at Ta=1.5 x 10(9). These results indicate that an optimum value of Ra and Ta exists at which the convection driven radial heat transport is most energetic through the interaction of CCP and baroclinic waves/eddies. (C) 2018 Author(s).