An interesting mixing-fog event was identified during the C-FOG field campaign, where a cold-frontal airmass arriving from the north-east collided with The Downs peninsula in Ferryland, Newfoundland, Canada, to produce misty/foggy conditions. A comprehensive set of field observations suggests that this collision caused turbulent mixing of nearly saturated ambient air with an almost saturated cold-frontal airmass, creating conditions for mixing fog. To delve into the physical processes underlying this phenomenon, laboratory experiments were performed on the interaction of lock-exchange-induced gravity currents with a rectangular obstacle. Instantaneous velocity and density fields were obtained using particle image velocimetry and planar laser-induced fluorescence. The observations suggest that the obstacle starts affecting the approaching gravity-current propagation at an upstream distance of 2H and, upon collision, the mixing occurs over a length of 0.83H, where H is the depth of the ambient fluid layer. The time for larger-scale turbulent stirring to permeate to the smallest scales of turbulence and activate the condensation nuclei is estimated as \(3t^*\), where \(t^*=\sqrt{H/g'}\) is the intrinsic time scale of the gravity current, and \(g'\) is the reduced gravity. Extrapolation of laboratory results to field conditions shows a good agreement with observations.

在 C-FOG 野外活动期间发现了一个有趣的混合雾事件，来自东北部的冷锋气团与加拿大纽芬兰费里兰的唐斯半岛相撞，产生薄雾/雾气。一组全面的实地观察表明，这次碰撞导致几乎饱和的环境空气与几乎饱和的冷锋气团发生湍流混合，为混合雾创造了条件。为了深入研究这种现象背后的物理过程，对锁交换引起的重力流与矩形障碍物的相互作用进行了实验室实验。使用粒子图像测速和平面激光诱导荧光获得瞬时速度和密度场。H和碰撞时，混合发生在 0.83 H的长度上，其中H是环境流体层的深度。大规模湍流搅拌渗透到最小湍流尺度并激活凝聚核的时间估计为\(3t^*\)，其中\(t^*=\sqrt{H/g'}\)是重力流的固有时间尺度，\(g'\)是减少的重力。将实验室结果外推到现场条件表明与观察结果非常吻合。