Convective circulation in littoral water due to surface cooling

Cooling of littoral waters of a lake under calm conditions creates a horizontal temperature gradient because surface heat loss is distributed over progressively larger depth by plunging sheets (thermals). Resulting convective circulation establishes an exchange flow between littoral and open waters. Numerical simulations illustrate the development of the flow from the formation of thermals to the establishment of a horizontal circulation. Circulation flow rate was found to be proportional to ℛ 1/ n , 2 < n < 3 ( ℛ is the Rayleigh number) for values in the range 10 4 –10 8 . A laboratory visualization experiment at ℛ ∼ 10 9 confirmed the main features of the simulation. To consider applications to vegetated littoral slopes, we interpreted the results with a formula accounting for the added resistance offered to the flow by the aquatic plants. An example showed that convective circulation can be a significant factor in renewing littoral waters.