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Cloud Resolving Model Simulations of TTL Dehydration due to Overshooting Deep Convection.

Cloud Resolving Model Simulations of TTL Dehydration due to Overshooting Deep Convection. Daniel Grosvenor 1 , Tom Choularton 1 , Hugh Coe 1 & Gerhard Held 2 . The University of Manchester, U.K. IPMET, Bauru, Brazil.

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Cloud Resolving Model Simulations of TTL Dehydration due to Overshooting Deep Convection.

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  1. Cloud Resolving Model Simulations of TTL Dehydration due to Overshooting Deep Convection. • Daniel Grosvenor1, Tom Choularton1, Hugh Coe1 & Gerhard Held2. • The University of Manchester, U.K. • IPMET, Bauru, Brazil.

  2. How can deep convection can affect the vapour budget of the TTL and the stratosphere? Temp < environment Overshooting • Deep convection that overshoots its level of neutral buoyancy due to adiabatic uplift can detrain air into the TTL region that has been cooled to temperatures below the environmental cold point. If particle sedimentation can occur before the ice re-evaporates then dehydrated air will be left behind. (e.g. Danielsen, 1982, JGR, 9). • Deep convection can cause gravity/buoyancy waves producing low local ice saturation and subsequent ice sedimentation (e.g. Potter and Holton, 1995, JAS, 52). • Direct transport of vapour and ice. Temp > environment Environment curve Pseudoadiabatic curve (convection) Temp decreasing

  3. Approach • Cloud Resolving Model (CRM) studies to try and identify the quantitative effects of such processes on spatial and time scales relevant to a single cloud event and any to explore sensitivities to small scale processes within the cloud. • The Model:- • Large Eddy Model (LEM), UK Met Office (Brown, A. R., et al, 2002, QJRMS, 128). • Bulk microphysics:- number concentration and mixing ratio for ice, snow and graupel. Mixing ratio only for vapour, liquid and rain. • 1000km domain, 250m horizontal resolution, 2-D. • Periodic boundary conditions. • 30 km high domain, 250 points in vertical. Resolution of 75m in boundary layer, 127m elsewhere. • Damping layer from domain top down to 22km to prevent reflection of gravity waves. • Warm bubble used to initiate convection – fairly vigorous storms simulated.

  4. 24th Feb – Initial Model Profiles Cold point Approx QR=0 level in tropics

  5. Deep Convection on 24th Feb, 2004 10 dbZ echo tops • Bauru, Brazil (centre of radar image) : 22.36 S, 49.03 W. • 240km radius • Large squall line moving from north passes over Bauru. • Initiated by South Atlantic convergence zone • 10 dbZ echo tops of up to ~17-18km.

  6. 24th Feb – Max Updraught High updraughts – up to 44 m/s

  7. Possible gravity wave breaking at 16 – 18 km

  8. Water Vapour in Overshoot

  9. Water Vapour in Overshoot

  10. Water Vapour in Overshoot Vapour values as low as 0.33 ppmv.

  11. Water Vapour in Overshoot

  12. Water Vapour in Overshoot

  13. Water Vapour in Overshoot

  14. Water Vapour in Overshoot

  15. Water Vapour in Overshoot

  16. Water Vapour in Overshoot

  17. Water Vapour in Overshoot

  18. Water Vapour in Overshoot

  19. Water Vapour in Overshoot

  20. Water Vapour in Overshoot

  21. Water Vapour in Overshoot

  22. Total Water in Overshoot

  23. Total Water in Overshoot

  24. Total Water in Overshoot

  25. Total Water in Overshoot

  26. Total Water in Overshoot

  27. Total Water in Overshoot Low total water points forming as ice falls away from dry air

  28. Total Water in Overshoot

  29. Total Water in Overshoot

  30. Total Water in Overshoot

  31. Total Water in Overshoot Dehydrated air starts to sink due to negative buoyancy

  32. Total Water in Overshoot

  33. Total Water in Overshoot

  34. Total Water in Overshoot

  35. Total Water in Overshoot

  36. Total Water in Overshoot

  37. Total Water in Overshoot

  38. Total Water in Overshoot

  39. Total Water in Overshoot

  40. Total Water in Overshoot

  41. Total Water in Overshoot

  42. Total Water in Overshoot

  43. Total Water in Overshoot

  44. Total Water in Overshoot

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