Implementation of RAS in NCAR CAM3:Preliminary Results

1
Implementation of RAS in NCAR CAM3Preliminary
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
• Frac0.3 (Strong evap.)
• Frac0.15 (Moderate evap.)
• Frac0.05 (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
f0.3
Lag (Days)
Lag (Days)
f0.15
Lag (Days)
30-90 Day 850 hPa Zonal Wind
f0.05
Contour 0.1 m s-1
Lag (Days)
4
Space-Time Spectra
CAM3/RAS
f0.3
NCEP Reanalysis
Zonal Wavenumber
f0.15
80
80
40
27
40
27
Period
Westward
Eastward
f0.05
Contour0.006 m2s-2, gt0.028 shaded.
80
80
40
27
40
27
5
2.5-12 Day Vorticity Variance (June-Sept)
f0.3
NCEP Reanalysis
f0.15
850 hPa
Contours1011 s-2
Associated with Tropical Depression-type disturban
ces of the west Pacific
f0.05
6
Lag-Regression on Synoptic-Timescales (Wind and
Vorticity)
f0.3
NCEP Reanalysis
f0.15
850 hPa
Vorticity units 105 s-1.
f0.05
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
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Basic State in CAM3/RAS

• Very brief overview

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CAM3/RAS Comparison with NVAP Column Precipitable
Water
f0.05
f0.3
f0.15
The simulation with robust tropical variability
is too moist.
13
Soundings at Truk Island (7.5oN, 151oE)
f0.05
f0.3
f0.15
CAM
Obs.
Moist Static Energy f0.05
14
DJF Precipitation
CAM3/RAS
Observations
f0.3
Xie-Arkin
f0.05
15
JJA Precipitation
Observations
CAM3/RAS
Xie-Arkin
f0.30
f0.05
16
JJA Surface Stress Relative to ERS
f0.30
f0.05
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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!