We investigate sensible and latent heat exchange between evaporating saline droplets and carrier air by performing direct numerical simulation (DNS) of an idealized flow modelling the marine atmospheric boundary layer. Turbulent, droplet-laden Couette airflow over a waved water surface is considered in the DNS under two different sets of bulk air and water temperatures, $$ T_{a} = -\, 10\,^{\circ}{\hbox{C}} $$ T a = - 10 ∘ C , $$ T_{s} = 0\,^{\circ} {\hbox{C}} $$ T s = 0 ∘ C , and $$ T_{a} = 27\,^{\circ} {\hbox{C}} $$ T a = 27 ∘ C , $$ T_{s} = 28\,^{\circ} {\hbox{C}} $$ T s = 28 ∘ C , conditionally termed as “polar low” and “tropical cyclone” conditions, respectively. Coupled equations of the airflow and droplet transport are solved, and diffusive sensible and latent heat fluxes from droplets to the air are evaluated, and their distributions over droplet size are obtained. The DNS results show a qualitative difference in the droplet-mediated heat transfer of the two cases. Under polar low conditions, both the sensible heat, Q S , and the latent heat, Q L , fluxes are positive (directed upwards), and the Q L contribution is significantly reduced as compared to the Q S contribution. In this case, droplets mostly warm up the air. On the other hand, under tropical cyclone conditions, Q S is negative and Q L is positive, and thus droplets cool and moisturize the air. In both cases, the droplet-mediated enthalpy flux, Q S + Q L , is positive, vanishes for sufficiently small droplets (with diameters d ≤ 150 μm), and further increases with d . The net droplet-mediated enthalpy transfer is most pronounced in the buffer region and negligible in the logarithmic region of the boundary layer, and reduced with increasing surface-wave slope.

中文翻译：

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关于海洋大气边界层中液滴介导的感热和潜热传递：“极地低”与“热带气旋”条件

我们通过对海洋大气边界层进行建模的理想化流的直接数值模拟 (DNS) 来研究蒸发的盐滴和载气之间的显热和潜热交换。在 DNS 中，在两组不同的整体空气和水温下，考虑了波浪状水面上充满液滴的湍流 Couette 气流，$$ T_{a} = -\, 10\,^{\circ}{\hbox{ C}} $$ T a = - 10 ∘ C , $$ T_{s} = 0\,^{\circ} {\hbox{C}} $$ T s = 0 ∘ C , $$ T_{a } = 27\,^{\circ} {\hbox{C}} $$ T a = 27 ∘ C , $$ T_{s} = 28\,^{\circ} {\hbox{C}} $$ T s = 28 ∘ C ，分别有条件地称为“极地低压”和“热带气旋”条件。求解气流和液滴传输的耦合方程，并评估从液滴到空气的扩散感热和潜热通量，并获得它们在液滴尺寸上的分布。DNS 结果显示两种情况下液滴介导的热传递存在质的差异。在极地低温条件下，显热 QS 和潜热 QL 通量均为正（向上），与 QS 贡献相比，QL 贡献显着降低。在这种情况下，水滴主要是使空气升温。另一方面，在热带气旋条件下，QS 为负，QL 为正，因此水滴冷却和滋润空气。在这两种情况下，液滴介导的焓通量 QS + QL 为正值，对于足够小的液滴（直径 d ≤ 150 μm）消失，并随着 d 进一步增加。