Why Not Look Only at Model Output? Comparison of Q-G Omega Equations

1. Why Not Look Only at Model Output?

5. 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.

6. 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

7. 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

8. 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

9. Jet Streak Vertical Motions

11. For unusually straight jets, it might be reasonable

12. But usually there is much more going on, so be VERY careful in application of simple jet streak model • Garp example…

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