Is sub-grid scale topography represented in 'HB' PBL scheme?

[Jun]

Hi, forum:

I'm using cam4 and cesm1.2.1. I'm looking at how the model represents the vertical diffusions. One question is about if the default PBL scheme (HB scheme) in cam4 includes the parameterization of the effect from sub-grid scale topography (SCT)? My current understanding is that SCT has not been considered in this scheme. And the turbulence mountain stress (TMS) module introduced in cam5 was a specific update for this. However, I'm not quite sure about my current understanding. Does anybody have any insights into this question? Any advice would be appreciated.

Thanks

Jun

 

[juliob]

Hello Jun,
You are correct that no subgrid topographic PBL form drag is represented in the HB scheme. TMS needs to be included to represent this drag. Note though that orographic drag from gravity waves is included in CAM4.
Julio Bacmeister

 

[Jun]

Hello Jun,
You are correct that no subgrid topographic PBL form drag is represented in the HB scheme. TMS needs to be included to represent this drag. Note though that orographic drag from gravity waves is included in CAM4.
Julio Bacmeister

Thank you, Julio!

Does that mean that the orographic drag from gravity waves (CAM4) is equivalent to the drag from TMS (CAM5) in terms of characterizing the effect of sub-grid topography, even though the magnitude might be different?

Jun