Implementation of RAS in NCAR CAM3:Preliminary Results
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Transcript of Implementation of RAS in NCAR CAM3:Preliminary Results
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Implementation of RAS in NCAR CAM3:Preliminary Results
Eric D. MaloneyCollege of Oceanic and Atmospheric Sciences
Oregon State University
AMWG Meeting, March 21, 2006
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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:
1) Frac=0.3 (Strong evap.)2) Frac=0.15 (Moderate evap.)3) 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.
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Lag-Regression onto 155oE (Dec-May)La
g (D
ays) La
g (D
ays)
Lag
(Day
s)La
g (D
ays)
NCEP Reanalysis f=0.3
f=0.15
f=0.0530-90 Day 850 hPa Zonal Wind
Contour 0.1 m s-1
CAM3/RAS
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Space-Time Spectra
804027
804027
80 40 27
80 40 27
Westward EastwardPeriod
Zona
l Wav
enum
ber
f=0.3
f=0.15
f=0.05
NCEP Reanalysis
CAM3/RAS
Contour=0.006 m2s-2, >0.028 shaded.
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2.5-12 Day Vorticity Variance (June-Sept)f=0.3
f=0.15
f=0.05
NCEP Reanalysis
Contours=1011 s-2
Associated with Tropical Depression-typedisturbances of the west Pacific
850 hPa
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Lag-Regression on Synoptic-Timescales (Wind and Vorticity)
f=0.3
f=0.15
f=0.05
NCEP Reanalysis
Vorticity units 105 s-1.
850 hPa
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The Sensitivity of Model Variability to Re-Evaporation is Consistent with Previous
Experiments
Perpetual March CCM3 simulations using a variant of RAS show a strongsensitivity to downdrafts/rain reevaporation.
Maloney and Hartmann 2001
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Reevaporation/Downdraft Profiles in the Control Experiments
Perpetual March experiments producemoisture and temperature profiles associated with rain evaporation (and downdrafts) thatlook something like this.
An experiment was then conducted with these time-invariant profiles applied todetermine whether model intraseasonal variability could be reproduced.
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Simulation with Time-Invariant Rain Re-evaporation Can Reproduce Much of the
Intraseasonal Variability
Maloney and Hartmann 2001
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Difference between time-invariant rain re-evaporationand no rain re-evaporation simulations
Robust intraseasonal variability appears to be associated with a moisttime-mean tropical troposphere.
Contour= 0.6 g kg-1, starting at 0.3 g kg-1
20N 10N 20SEq 10S
Pre
ssur
e 10
2 hP
a
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Basic State in CAM3/RAS
• Very brief overview
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CAM3/RAS Comparison with NVAP Column Precipitable Water
f=0.3 f=0.15 f=0.05
The simulation with robust tropical variability is too moist.
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Soundings at Truk Island (7.5oN, 151oE)
f=0.3 f=0.15 f=0.05
CAM
Obs.
Moist Static Energy f=0.05:
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DJF Precipitation
f=0.3
f=0.05
Xie-Arkin
Observations CAM3/RAS
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JJA Precipitation
Xie-Arkin f=0.30
f=0.05
Observations CAM3/RAS
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JJA Surface Stress Relative to ERS
f=0.30
f=0.05
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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!