Abstract
A laboratory experiment investigates the influence of salinity on the characteristics of bubble clouds in varying saline solutions. Bubble clouds were generated with a water jet. Salinity, surface tension, and water temperature were monitored. Measured bubble cloud parameters include the number of bubbles, the void fraction, the penetration depth, and the cloud shape. The number of large (above 0.5 mm diameter) bubbles within a cloud increases by a factor of three from fresh to saline water of 20 psu (practical salinity units), and attains a maximum value for salinity of 12–25 psu. The void fraction also has maximum value in the range 12–25 psu. The results thus show that both the number of bubbles and the void fraction vary nonmonotonically with increasing salinity. The lateral shape of the bubble cloud does not change with increasing salinity; however, the lowest point of the cloud penetrates deeper as smaller bubbles are generated.
Highlights
Bubble clouds arising from waves breaking at the ocean surface play an important role in the transport of momentum and scalars between the atmosphere and the ocean [1,2]
Less is known about the kinematics of bubble clouds, as it is a complex interaction of wave and buoyancy forcing, with salinity and surface tension playing influential roles
We present the results of a laboratory experiment designed to observe and quantify the effect of salinity S over the range of 1–38 psu on the characteristics of bubble clouds comprising large bubbles
Summary
Bubble clouds arising from waves breaking at the ocean surface play an important role in the transport of momentum and scalars between the atmosphere and the ocean [1,2]. Bubble size distribution N(r) (where r is the bubble radius) is the most representative quantity for bubble populations because it can be related to other bubble cloud characteristics. Both void fraction α (defined as the volume occupied by air in a volume of an air-water mixture) and penetration depth z can be evaluated from measurements of N(r) and its variations in the water column. Breaking waves at different scales yield bubble clouds with different z as varying bubble sizes stratify the entrainment of bubbles in water depth [13]. The universal use of N(r) to characterize bubble populations is the reason most experiments aim to measure the bubble size distribution
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