Dry Line Forcing

[Peter Wharton]

From my amateur knowledge of meteorology, I think I understand how a cold front or a warm front provides a forcing mechanism - the lift coming through the temperature differences/density and converging wind flows of the competing air masses. This might be a dumb question, but how does a dry-line provide the forcing mechanism? From my limited knowledge, there are no temperature differences, just a drop in relative humidity. What drives the lift of warm/moist air in front of the dry-line?

Thanks,
Peter

 

[Tony Laubach]

The main convergence in a dry line comes usually from the winds. On the dry side of the dryline, winds usually are blowing dry air from the southwest. On the moist side of the dryline, winds usually come from the southeast, bringing moist air with them. That convergence in the winds defines the dryline and acts as a focus to force air upward.

 

[Dennis Gulley]

Thats a good question so I looked it up and it all has to do with the differences between the weight of dry air as compared to humid air. Humid air is actually lighter than dry air. Water vapor molecules are lighter than the oxygen, nitrogen etc in the atmosphere. You can only put so many molecules into a given volume of air so the lighter water molecules take the place of the heavier molecules of the heavier gases. So the heavier, dry air forces the lighter moisture rich air upward.

Hope this helps

Dennis

 

[Peter Wharton]

Thanks - so a combination of wind convergence, and different densities in the two air masses - same as a cold front, warm front situation.

Cheers,
Peter