1 / 31

9 de setembro de 2010 LNCC From observation to modeling:

9 de setembro de 2010 LNCC From observation to modeling: Lessons and regrets from 36 years in the field. David Fitzjarrald Atmospheric Sciences Research Center University at Albany, SUNY Albany, New York USA. 1989. Experimentos do campo faz-se envelhecer. Observações .

darius
Download Presentation

9 de setembro de 2010 LNCC From observation to modeling:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 9 de setembro de 2010 LNCC From observation to modeling: Lessons and regrets from 36 years in the field. David Fitzjarrald Atmospheric Sciences Research Center University at Albany, SUNY Albany, New York USA

  2. 1989 Experimentos do campo faz-se envelhecer

  3. Observações Teoria/modelos simples Modelos mais complexos (DNS, LES, meso) Resultados: C = <C> + C’ conhecimento Ya conheciamos (o ‘obvio’) Inovação (merece publicar)

  4. A região de Xalapa, Veracruz, México 97°W 96°W 20°N Um projeto simple, 1980-81. 19°N a cidade de Xalapa fica alredor de un volcán

  5. Experimento do campo julho 1980 & fevereiro 1981 Balão cativo

  6. Julho 1980 Los alisios uphill downhill Vento catabático na presença no fluxo em oposição

  7. Fevereiro 1981 sem alisios, vento descendente depois a inversão pasa abaixo

  8. Vento catabático sem oposição

  9. h x3 x1 First simplification: 1D momentum equation along a slope: [1] [2] [3] [4] [5] [1] acceleration [3] stress divergence [2] advection of momentum [4] buoyant forcing [5] pressure forcing

  10. The Prandtl katabatic wind solution (1940’s) Prandtl assumed that the steady downslope momentum balance is made between “vertical” (perpendicular to the slope, called z here) turbulent flux of momentum (Fm ) and the “buoyancy force” (Archimedean acceleration): Turbulent flux divergence buoyancy force along slope Momentum (steady) : 0 = -∂Fm/∂z + [b q’ sin a] a [Here q’ is the deviation of the potential temperature from a base state and b is the buoyancy parameter g/Qv.] The whole analysis works because the base state is assumed to have a Theta(z’) that changes only in the true vertical, not perpendicular to the slope (n). The thermal balance is assumed to be between along-slope (labeled s) heat advection and turbulent flux divergence: horizontal thermal advection vertical turbulent heat flux divergence: U∂Q/∂s    ≈ U[g sin a] = -∂FQ/∂n , [ where gis the base state potential temperature gradient, ∂Q/∂z’ , where z’ is the true vertical. ]

  11. Prandtl (1953)

  12. Prandtl’s analytic solution Maximum wind speed independent of slope angle

  13. notes from USP IAG June1984 Most results can be obtained through dimensional analysis alone! (Comes from the simplification.)

  14. July 1980 Xalapa data revisited, scaled by height of wind speed maximum Effects of entrainment larger than Prandtl can predict Prandtl February 1981

  15. Redoing this problem using DNS & (inevitably) LES Fedorovich & Shapiro (2009)

  16. DNS simulation: confirms that maximum wind ≠ f(slope) Fedorovich & Shapiro (2009)

  17. A 2nd simple model approach: By integrating equations in the vertical, we form an analogy with open channel hydraulics

  18. The hydraulic jump Subcritical “tranquil” Supercritical “shooting”

  19. Modelo integrado no vertical Manins & Sawford (1979)

  20. Uh = integral mass transport Manins & Sawford (1979)

  21. ‘shooting’ (supercritical) flows vs. ‘tranquil’ (subcritical) Manins & Sawford (1979)

  22. Entrainment assumptions Manins & Sawford (1979)

  23. Uh UDQ U Ri Manins & Sawford (1979)

  24. Conditions on Ri for steady state

  25. Fitzjarrald (1984)

  26. Dimensionless equation set; uais the ambient wind.

  27. Changes in time

  28. Solutions in time Stability of models

  29. Steady solutions

  30. uphill downhill shooting tranquil shooting Fitzjarrald, 1984

  31. Some thoughts in 2010: Prandtl solution gave good insight. When do we know that we are publishing new information? Question of shooting vs tranquil flows (from the bulk models) observationally unresolved. Oscillations simulated with DNS, but no observations yet

More Related