Modeling of ship effluent transport and its sensitivity to boundary layer structure

The LES model is applied for studying ship track formation under various bo undary layer conditions observed during the Monterey Area Ship Track experi ment. Simulations in well-mixed and decoupled boundary layers show that shi p effluents are easily advected into the cloud layer in the well-mixed conv ective boundary layer, whereas their transport may be suppressed by the sub cloud transitional layer in the decoupled case. The clear difference betwee n the well-mixed and decoupled cases suggests the important role of diurnal variation of solar radiation and consequent changes in the boundary layer stability for ship track formation. The authors hypothesize that, all other conditions equal, ship track formation may be facilitated during the morni ng and evening hours when the effects of solar heating are minimal. In a series of experiments, the authors also studied the effects of additio nal buoyancy caused by the heat from the ship engine exhaust, the strength of the subcloud transitional layer, and the subcloud layer saturation condi tions. The authors conclude that additional heat from ship engine and the i ncrease in ship plume buoyancy may indeed increase the amount of the ship e ffluent penetrating into the cloud layer The result, however, depends on th e strength of the stable subcloud transitional layer. Another factor in the ship effluent transport is the temperature of the subcloud layer, its decr ease will result in lowering the lifting condensation level and increased s hip plume buoyancy. However, the more buoyant plumes in this case have to o vercome a larger potential barrier The relation between all these parameter s may be behind the fact that ship tracks sometimes do, and sometimes do no t, form in seemingly similar boundary layer conditions.