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Use of ERA40 data for chemistry-transport modeling

Use of ERA40 data for chemistry-transport modeling. Peter van Velthoven with contributions from: T. van Noije, D. Olivi é, and R. Scheele Royal Netherlands Meteorological Institute (KNMI). Overview. Convective transport Archived versus diagnosed fluxes Assessment of fluxes with radon

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Use of ERA40 data for chemistry-transport modeling

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  1. Use of ERA40 data for chemistry-transport modeling Peter van Velthoven with contributions from: T. van Noije, D. Olivié, and R. Scheele Royal Netherlands Meteorological Institute (KNMI)

  2. Overview • Convective transport • Archived versus diagnosed fluxes • Assessment of fluxes with radon • Impact on tropospheric ozone • Transport by turbulent diffusion • Archived versus diagnosed diffusion • Boundary layer height, diurnal cycle • Assessment with radon • Brewer-Dobson circulation • Problem + 3 remedies • Age of air sensitivity studies: update frequency, type of data, trajectory-CTM comparison

  3. Convective transport Large scale subsidence Downdraft Updraft Archived in ERA40: entrainments & detrainments

  4. Global mean convective mass fluxes

  5. Effect of convective mass fluxes on Rn222

  6. Evaluation with Rn222: STEP 1987

  7. Effect of convective mass fluxes on ozone Effect of convection Effect of convection treatment Differences up to ~20% !

  8. Conclusions convective transport • Off-line diagnosed and archived convective updraft mass fluxes have similar distributions, but • archived ones extend higher up • diagnosed ones are more intense in mid-troposphere • Comparison to radon observations slightly favours archived over diagnosed fluxes. Both are much better than simulation without convective transport. • The sensitivity of tropospheric ozone to convective transport scheme is a major modelling uncertainty. • Further evaluation against observations in other regions needed !

  9. Evaluation of diffusion coefficients, Kz Dirk Olivié and Peter van Velthoven

  10. E3/E6 : archived during ERA-40 0h00 3h00 6h00 9h00 12h • time averaged : 3h00 or 6h00 • non-local scheme • [Beljaars and Viterbo, 1999] • entrainment formulation • ABL height : via parcel ascent method • [Troen and Mahrt, 1986] • mixing length : intermediate • different temperature excess of thermals • different stability functions : Fh(Ri) E3 E6 E3/E6 H3 : off-line diagnosed • instantaneous : 3h00 • non-local scheme : similar to E3/E6 • [Holtslag and Boville, 1993] • no entrainment formulation at top ABL • ABL height : bulk Ri-criterium • [Vogelezang and Holtslag, 1996] • mixing length : small L6 H3 L6 : off-line diagnosed H3 • instantaneous : 6h00 • local scheme : [Louis, 1979; Louis et al., 1982] • mixing length : large 0h00 3h00 6h00 9h00 12h L6

  11. zonal mean July 1993 Comparison of Kz profiles L6 L6 E3/E6 E3/E6 H3 H3 E3/E6 : archived during ERA-40 H3 : off-line diagnosed (similar to E3/E6, “Holtslag”) L6 : off-line diagnosed (local scheme, “Louis”)

  12. Boundary layer height Cabauw, The Netherlands, June-July 1996 Radar-sodar E6 (archived) H3 (diagnosed)

  13. Boundary layer height Schemes: E6 (archived) H3 (diagnosed)

  14. Diurnal cycle Radon222 xxx Freiburg Observations E3 (archived) E6 (archived) H3 (diagnosed, Holtslag) L6 (diagnosed, Louis)

  15. Time shifts in Radon222 simulation 0-12 h E3 (archived) E6 (archived) H3 (diagnosed, Holtslag) L6 (diagnosed, Louis)

  16. Findings • BL height : H3, E6 (E3) correspond well with observations • L6 : largest (unrealistic) daily cycle • E3, H3 better than E6, L6 • E3, H3 : +/- same quality • E3, E6 : more transport to free troposphere than H3 and L6 (entrainment formulation, extended daytime regime, larger mixing length) Note: Archived Kz is not available for operational forecasts E3/E6 : archived during ERA-40 H3 : off-line diagnosed (similar to E3/E6) L6 : off-line diagnosed (local scheme)

  17. How to obtain better vertical ozone transport in CTMs driven by ERA40? • Introduction of the problem • Implications for the downward transport of ozone • Possible remedies : Synoz, relaxation, use forecasts

  18. Ozone flux from the stratosphere in TM4

  19. Estimate of air mass transport ERA-40 overestimates fluxes by a factor 1.6–1.7 (Appenzeller et al. method)

  20. A parameterised stratospheric chemistry model (Cariolle and Déqué, 1986; McLinden et al., 2000) Testing ozone transport with Linoz-”chemistry” Dec 1997 ERA40 ozone TM-Linoz ozone (using ERA40)

  21. Ozone vertical fluxes in free Linoz-run with ERA40 • 100-hPa flux (1480/1620 Tg/yr at 6o x 4o/3o x 2o) exceeds estimated range (450–590 Tg/yr) by a factor 2–3 • ‘cross-tropopause’ flux (1260/1380 Tg/yr) exceeds values obtained by McLinden et al. (421/458 Tg/yr) using the same setup

  22. Remedies? • Synthetic ozone (Synoz) • Relaxation to climatological concentrations in the stratospheric ‘overworld’ • Use wind fields from ERA40 forecasts (suggested by A. Simmons, ECMWF)

  23. Synthetic ozone (Synoz) Set ozone production between 30oS–30oN/70–10 hPa to desired rate of 550 ( 140) Tg/yr

  24. Synoz: ozone concentrations ERA-40 Dec 1997 Spuriously low ozone concentrations in the UTLS !

  25. Relaxation towards zonal mean ozone climatology of Fortuin and Kelder in the stratospheric over-world (time constant 2.5 days) Relaxation to climatological ozone Linoz relaxation Synoz Concentration drop due to relaxation Mixing ratio at 100 hPa

  26. Relaxation: vertical ozone flux • 100-hPa flux drops to 716/761 Tg/yr (6o x 4o/3o x 2o) • ‘cross-tropopause’ flux to 629/663 Tg/yr

  27. Use of forecasts: air mass fluxes ERA-40 (1997) Appenzeller et al. (1992/1993) Compared to the results of Appenzeller et al., the ERA-40 forecasts give reasonable annual means, but enhanced seasonal cycles

  28. Conclusions stratospheric ozone flux • ERA40 Brewer-Dobson circulation is 1.6–1.7 too strong  CTM vertical ozone fluxes factor 2–3 too large • Three possible remedies in CTMs: 1) Synthetic ozone (Synoz)  anomalous LS ozone mixing ratios 2) Relaxation in stratospheric overworld 3) Use of forecasts Our choice for ERA40: 2 and 3 (FC steps +12..+30) • Need for further studies on the effect of meteorological analysis on the Brewer-Dobson circulation

  29. New study of the ERA40 Brewer-Dobson circulation with trajectories Sensitivity studies 50-day back-trajectories ending just above the tropical tropopause (460 K), 10°S-10°N, resolution 1° in longitude and latitude, 9 days in February, 12 UTC 9720 traj.) Determine when these trajectories cross the tropopause Age-of-air calculations 5 year back-trajectories ending at 20 km, resolution 3° in longitude and 2° in latitude, 1 January 2001, 0 UTC  10680 traj. Estimate of asymptotic behaviour (exponential) of age of air distribution

  30. Fraction of 50-day back-trajectoriesin the troposphere for ERA40 3D-Var data

  31. Fraction of 50-day back-trajectoriesin the troposphere for operational 4D-Var data 2000

  32. Comparison trajectory age-of-airfrom OD analysis& 3 day forecast to observations

  33. Comparison age-of-airCTM-trajectories-observations

  34. Age of air is quite sensitive to frequent updates of the forecast • Best result for simulated age-of-air: • ERA40 (3D-Var) – use 1 day update frequency (of forecasts) • Operational (4D-Var) – use 3 up to 9 day update frequency (still underestimate of 0.5-1.5 years, but better than ERA40) • Trajectory and CTM ages of air similar for same input • Scheele et al., to be submitted to ACP (June 2004) Conclusions trajectory studies

  35. Thanks/acknowledgements • ECMWF for adapting ERA40 archival to CTM needs • Anton Beljaars (ECMWF) for discussions • EU RETRO for funding ??? Questions ???

  36. Spare slides follow hereafter

  37. Diagnosed in TM Archived in ERA40 Convective upward mass fluxes Difference at 200 hPa:

  38. Convective downdraft mass fluxes Diagnosed in TM Archived in ERA40

  39. Convective mass fluxes • Updraft mass fluxes : • Archived similar to diagnosed case • Archived fluxes extend higher up • Archived fluxes smaller in lower troposphere • Downdraft mass fluxes: • Much smaller than updrafts • Large differences between diagnosed and archived fluxes • Diagnosed: downdraft and updraft mass fluxes have similar distributions

  40. Effect of convective mass fluxes on Rn222

  41. blue stars=observations TROPOZ II green squares=no convection red triangles=diagnosed convection black diamonds=archived convection Evaluation with Rn222: TROPOZ

  42. Evaluation with Rn222: STEP 1987

  43. Effect of convective mass fluxes on ozone JJA ozone Diagnosed convection Ozone difference (%) Diagnosed-Archived convection Differences up to ~20% !

  44. How well do models simulate UTLS ozone? X dfd (Bregman et al., 2001) TOPOZ II project

  45. Wind interpolation errors need to be minimized MOZAIC new winds old winds (Segers et al., 2002; Bregman et al., , 2003)

  46. Age of air in TM from ERA15 (old/new numerics), OD and ERA40

  47. Exp. Year Source Forecast hrs Update Grid F(50) 1 1997 3D-Var 6 6h 1x1 46% 2 1997 3D-Var 24, 30 12h 1x1 22% 3 1997 3D-Var 12,18,24,30 24h 1x1 15% 4 1997 3D-Var 12,18,24,30 24h 2.5x2.5 14% 5 2000 3D-Var 12,18,24,30 24h 3x2 16% 6 2000 4D-Var 0 6h 3x2 12% 7 2000 4D-Var 12,18,24,30 24h 3x2 7% 8 2000 4D-Var 12,18,…,78 3day 3x2 3% 9 2000 4D-Var 18,24,30,…,234 9day 3x2 3% Summary of sensitivity studies

  48. 5-year back-trajectories

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