THE EFFECT OF VORTICITY ADVECTION
ON HEIGHT CHANGE
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METEOROLOGIST JEFF HABY
As you well know, the two types of vorticity advection are PVA and NVA while the two types of height change are
height falls and height rises. PVA promotes upper level divergence and rising air. Rising air will cause the
average virtual temperature of air to decrease because rising air cools. Cooling through a deep layer of the
troposphere not only causes the average temperature of the air to decrease, it also increases the average density
of the air and subsequently lowers the thickness of the troposphere. If thicknesses decrease, the height change
tendency will be for height falls. Therefore, PVA IS ACCOMPANIED BY HEIGHT FALLS. Since NVA causes sinking air,
the air warms. The warming causes an increase of thickness. If thickness increases, the height change tendency
will be for height rises. Therefore, NVA IS ACCOMPANIED BY HEIGHT RISES. As a 500 mb shortwave approaches and
the dynamic forcing over the forecast region is only from vorticity advection, the PVA region will act to lower
heights and increase the likeliness of clouds and precipitation. As the shortwave leaves and heights rise, the
NVA pattern takes over and clouds and precipitation become less likely.
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