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ono

CAA and negative omega with orographic influence

5 posts in this topic

so i'm trying to wrap my head around omega values and WAA/CAA with regard to uplsope/terrain forcing (terminology correct?). I'm no met, though have some science in me.  Basically, I understand that CAA and negative omega is a sinking airmass (without lift), while a positive omega would provide greater lift (without terrain in play). However, there's some sort of balance that is broken by terrain- that CAA with a negative omega value can still result in lifting due to the upslope nature of things.

 

I realize this is super simplified, just wondering what a very strong negative omega is during CAA while working against upslope terrain.  

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2 hours ago, ono said:

so i'm trying to wrap my head around omega values and WAA/CAA with regard to uplsope/terrain forcing (terminology correct?). I'm no met, though have some science in me.  Basically, I understand that CAA and negative omega is a sinking airmass (without lift), while a positive omega would provide greater lift (without terrain in play). However, there's some sort of balance that is broken by terrain- that CAA with a negative omega value can still result in lifting due to the upslope nature of things.

 

I realize this is super simplified, just wondering what a very strong negative omega is during CAA while working against upslope terrain.  

CAA and positive omega are sinking air, and no lift. WAA and negative omega are rising air and lift. Your question is answered by the orientation of the slope of the mountain range, and wind direction. 

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1 minute ago, Metsfan said:

CAA and positive omega are sinking air, and no lift. WAA and negative omega are rising air and lift. Your question is answered by the orientation and the slope, and wind direction. 

and the inverse would be true as well, correct?  

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1 minute ago, ono said:

and the inverse would be true as well, correct?  

If the wind flows down the slope of the mountain range would cause adiabatic warming and subsidence. 

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I think you're alluding to quasi-geostrophic theory in your question. This theory is only applicable for large-scale troughs and ridges, and the vertical motion induced by QG mechanisms is generally much weaker than vertical motion induced by mesoscale forcing such as upslope flow or convection. Therefore, significant upslope will usually be more important than QG effects for vertical motion.

As an example, lake-effect snow usually occurs in CAA regimes where synoptic-scale sinking motion is favored. However, lake-induced instability and upslope flow (i.e, like over the Tug Hill plateau) produce vertical motions at least an order of magnitude greater and thus outweigh the sinking motion induced by the large scale flow.

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