Numerical simulations of the effects of coastlines on the evolution of strong, long lived squall lines

These three simulations provide a control for later simulations. Finally, the remaining two simulation sets examine squall-line interaction with a relatively cool or warm land surface. The simulations document the thermodynamic and shear characteristics of squall lines interacting with the coastline.

Results show that the inclusion of a land surface did not sufficiently affect the thermodynamic properties ahead of the squall line to change its overall structure. Investigation of ambient shear ahead of the squall line revealed that the addition of either warm or cool land reduced the strength of the net circulation in the inflow layer as measured by ambient shear. The amount of reduction in shear was found to be directly proportional to the depth and strength of the original shear layer.

For stronger and deeper shears, the reduction in shear is sufficiently great that the buoyancy gradient circulation at the leading edge of the cold pool is no longer in balance with the shear circulation leading to changes in squall-line updraft structure. The authors hypothesize two ways by which a squall line might respond to passing from water to land. The weaker and more shallow the ambient shear, the greater likelihood that the squall-line structure remains unaffected by this transition.

Conversely, the stronger and deeper the shear, the greater likelihood that the squall line changes updraft structure from upright/downshear to upshear tilted.