Implementation of RAS in NCAR CAM3:Preliminary Results

Eric D. MaloneyCollege 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)• 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.

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

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.

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

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

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

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.

Simulation with Time-Invariant Rain Re-evaporation Can Reproduce Much of the

Intraseasonal Variability

Maloney and Hartmann 2001

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

Basic State in CAM3/RAS

• Very brief overview

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.

Soundings at Truk Island (7.5oN, 151oE)

f=0.3 f=0.15 f=0.05

CAM

Obs.

Moist Static Energy f=0.05:

DJF Precipitation

f=0.3

f=0.05

Xie-Arkin

Observations CAM3/RAS

JJA Precipitation

Xie-Arkin f=0.30

f=0.05

Observations CAM3/RAS

JJA Surface Stress Relative to ERS

f=0.30

f=0.05

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!