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Implementation of RAS in NCAR CAM3:Preliminary Results

Implementation of RAS in NCAR CAM3:Preliminary Results. Eric D. Maloney College of Oceanic and Atmospheric Sciences Oregon State University AMWG Meeting, March 21, 2006. CAM3 Experiments. Relaxed Arakawa-Schubert convection parameterization is implemented in NCAR CAM3 (T42)

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Implementation of RAS in NCAR CAM3:Preliminary Results

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  1. Implementation of RAS in NCAR CAM3:Preliminary Results Eric D. Maloney College of Oceanic and Atmospheric Sciences Oregon State University AMWG Meeting, March 21, 2006

  2. CAM3 Experiments • Relaxed Arakawa-Schubert convection parameterization is implemented in NCAR CAM3 (T42) • Fraction of convective rainfall exposed to unsaturated grid-scale environmental air and allowed to evaporate is varied among three 15-year experiments: • Frac=0.3 (Strong evap.) • Frac=0.15 (Moderate evap.) • Frac=0.05 (Weak evap.) • Related to recent experiments conducted by Bacmeister et al (2006) with the NSIPP AGCM. • We will examine characteristics of the variability and basic climate (AMWG Diagnostics package) among these simulations.

  3. Lag-Regression onto 155oE (Dec-May) CAM3/RAS NCEP Reanalysis f=0.3 Lag (Days) Lag (Days) f=0.15 Lag (Days) 30-90 Day 850 hPa Zonal Wind f=0.05 Contour 0.1 m s-1 Lag (Days)

  4. Space-Time Spectra CAM3/RAS f=0.3 NCEP Reanalysis Zonal Wavenumber f=0.15 80 80 27 40 40 27 Period Westward Eastward f=0.05 Contour=0.006 m2s-2, >0.028 shaded. 80 80 40 27 27 40

  5. 2.5-12 Day Vorticity Variance (June-Sept) f=0.3 NCEP Reanalysis f=0.15 850 hPa Contours=1011 s-2 Associated with Tropical Depression-type disturbances of the west Pacific f=0.05

  6. Lag-Regression on Synoptic-Timescales (Wind and Vorticity) f=0.3 NCEP Reanalysis f=0.15 850 hPa Vorticity units 105 s-1. f=0.05

  7. The Sensitivity of Model Variability to Re-Evaporation is Consistent with Previous Experiments Perpetual March CCM3 simulations using a variant of RAS show a strong sensitivity to downdrafts/rain reevaporation. Maloney and Hartmann 2001

  8. Reevaporation/Downdraft Profiles in the Control Experiments Perpetual March experiments produce moisture and temperature profiles associated with rain evaporation (and downdrafts) that look something like this. An experiment was then conducted with these time-invariant profiles applied to determine whether model intraseasonal variability could be reproduced.

  9. Simulation with Time-Invariant Rain Re-evaporation Can Reproduce Much of the Intraseasonal Variability Maloney and Hartmann 2001

  10. Difference between time-invariant rain re-evaporation and no rain re-evaporation simulations Pressure 102 hPa Eq 10S 20S 10N 20N Robust intraseasonal variability appears to be associated with a moist time-mean tropical troposphere. Contour= 0.6 g kg-1, starting at 0.3 g kg-1

  11. Basic State in CAM3/RAS • Very brief overview

  12. CAM3/RAS Comparison with NVAP Column Precipitable Water f=0.05 f=0.3 f=0.15 The simulation with robust tropical variability is too moist.

  13. Soundings at Truk Island (7.5oN, 151oE) f=0.05 f=0.3 f=0.15 CAM Obs. Moist Static Energy f=0.05:

  14. DJF Precipitation CAM3/RAS Observations f=0.3 Xie-Arkin f=0.05

  15. JJA Precipitation Observations CAM3/RAS Xie-Arkin f=0.30 f=0.05

  16. JJA Surface Stress Relative to ERS f=0.30 f=0.05

  17. Wrap-Up • I have a full set of basic state diagnostics on CD and on my laptop. • Let me know if you are interested in seeing any of these results. • Further experiments: Autoconversion parameter, cumulus momentum transport • Thanks!

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