User:Cornellwx/sandbox

=Erosion= It is often more difficult to forecast the erosion of a CAD event than the development. Numerical models tend to underestimate the event's duration. The bulk Richardson number, Ri, calculates shear to help forecast erosion. The numerator corresponds to the strength of the inversion layer separating the CAD cold dome and the immediate atmosphere above. In the denominator, the square of the vertical wind shear across the inversion layer is expressed. Small values of the Richardson number result in turbulent mixing that can weaken the inversion layer and aid the deterioration of the cold dome.

One of the most effective erosion mechanisms is cold advection aloft. With cold advection maximized above the inversion layer, cooling aloft can weaken in the inversion layer, which allows for mixing and the demise of CAD. The Richardson number is reduced by the weakening inversion layer. Cold advection favors subsidence and drying, which supports solar heating beneath the inversion.

Solar heating has the ability to erode a CAD event by heating the surface in the absence of thick overcast. However, even a shallow stratus layer during the cold season can render solar heating ineffective. During breaks of overcast for the warm season, absorption of solar radiation at the surface warms the cold dome, once again lowering the Richardson number and promoting mixing.

In the United States, as a high pressure system moves eastward out to the Atlantic, northerly winds are reduced along the southeast coast. If northeasterly winds persist in the southern damming region, net divergence is implied. Near-surface divergence reduces the depth of the cold dome as well as aid the sinking of air, which can reduce cloud cover. The reduction of cloud cover permits solar heating to effectively warm the cold dome from the surface up.

The strong static stability of a CAD inversion layer usually inhibits turbulent mixing, even in the presence of shear. However, if the shear strengthens in addition to a weakening of the inversion, the cold dome becomes vulnerable to shear-induced mixing. Opposed to solar heating, this erosion of a CAD event is from the top down. This occurs when the depth of the northeasterly flow becomes increasingly shallow, and strong southerly flow makes a downward progression resulting in high shear.

Erosion of a cold dome will typically occur first near the fringes where the layer is relatively shallow. As mixing progresses and the cold dome erodes, the boundary of the cold air, often indicated as a coastal or warm front, will move inland, diminishing the width of the cold dome.

Numerical models tend to underestimate duration. Bulk Richards number 'Ri". Stability, strength of inversion layer, vertical wind shear. Cold advection aloft, solar heating, near-surface divergence, shear-induced mixing, frontal advance, synoptic settings.