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Why Not Look Only at Model Output?
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Comparison of Various Forms of the Q-G Omega Equation
Classic (Two terms: differential vorticity advection, Laplacian of the thermal wind)
• The result is the difference between two large terms resulting in large truncation error.
• Cannot estimate reliably from vorticity advection at a single level or from warm advection alone.
• Using at a single level, best done at 500 hPa for strong events. Really need a 3D solution for an accurate answer.
Trenberth/Sutcliffe formulation (advection of absolute vorticity by the thermal wind) is more accurate since no cancellation problem.
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Q-Vector approach is the best in many ways
• No cancellation problems• Includes deformation term• Provides insights into the lower branch of the ageostrophic circulation forced by the geostrophic forcing• Provides insights into frontogenesis•Allows rapid and intuitive graphical interpretation
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QG Diagnostics Online
Classic approach:http://www.mmm.ucar.edu/people/tomjr/files/realtime/qg_diag/Omeg700Tot-NorAmer/res.html
Sutcliffe-Trenberth:http://www.mmm.ucar.edu/people/tomjr/files/realtime/qg_diag/OmegSutTren700Tot-NorAmer/res.html
Q-vector http://www.mmm.ucar.edu/people/tomjr/files/realtime/qg_diag/OmegQvec700Tot-NorAmer/res.html
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Vertical Motion
• Can be as the complex sum of:• QG motions (relatively large scale and smooth)
• Orographic forcing
• Convective forcing
• Gravity waves and other small-scale stuff
• QG diagnostics helpful for seeing the big picture
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Jet Streak Vertical Motions
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For unusually straight jets, it might be reasonable
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But usually there is much more going on, so be VERY careful in application of simple jet streak
modelGarp example…