Egroup FMS -> v197
GCM Development Effort

Primary Objective:

Identify and eliminate as many differences as possible between an FMS GCM and the v197 GCM.
1) FMS GCM is re-configured to look like v197
2) Some simple changes were made to v197 when it was not possible to change the FMS GCM
3) Documentation of remaining differences.


Experiments:

Primary
Control - T42 v197 (very close to AMIP2 experiment)
FMS T42 "v197 like"

Sensitivity
Prognostic clouds
Lin-Rood
AM1 T42
AM1 N45


Differences in Model Structures:

Overview of key features

Overview of differences


Results/Validation:

Primary Experiments

Sensitivity Experiments


 
Key Model Features

T42 v197


(atm1.v197)


T42 
FMS-v197
(atm2b.FMS)

AM1.T42L18

AM1.N45L30(L18)

Convection

RAS (v197)

RAS (v197)

RAS (FMS)

RAS (FMS)

Radiation

FS81-CO2=348


2hr Diurnal

FS90-CO2=330


2hr Diurnal

FS90-CO2=330
3hr Diurnal

FS90-CO2=330
3hr Diurnal

Clouds

Diagnostic

Diagnostic

Prognostic

Prognostic

Bndy Layer

MY, akmin_land=5

MY, akmin_land =5

MY, akmin_land =0

MY, akmin_land =0

Sfc. Layer

MO

MO 


> stable mix

MO


> stable mix

MO


> stable mix

Ocn Rough

Beljaars (v197)

Beljaars (v197)

Beljaars (FMS)

Beljaars (FMS)

Land Model

Simple 3Lyr


Matth Sfc Alb

Simple 3Lyr


CLIMAP Sfc Alb

LAD

LAD

GWD

v197 subgrid


gmax,a=2,1

v197 subgrid


gmax,a=2,1

v197 subgrid


gmax,a=2,1

FMS subgrid


gmax,a=2,1

Other

Bgrid


 
Parameterization/Model Feature Differences


FMS vs. v197

Description

Status

Vertical structure - sigma half & full levels specified in v197, full levels are computed in FMS. Bgrid uses hybrid coord.

1

Radiation - FS ~1981, CO2=348 ppm (v197) vs FS ~1990, CO2=330 ppm (FMS), Solar Consts agree within 0.5W/M**2

1

Surface Layer - Monin-Obukhov(MO) v197 stable mix coef ~ 1/15 of FMS

1

Sea Ice and Snow Melt - v197 allows snow on sea ice and melts the snow at 273.16 but allows sea ice to "melt" at 271.5. FMS does not allow snow to accumulate on sea ice but "melts" the ice at 273.16. Freezing temp is very close

1

Land Model - 3 layer Simple land implemented similarly in both v197 and FMS except background sfc albedos in v197 based on Matthews while FMS uses CLIMAP. LAD is only implemented in FMS (sfc albedos used Matthews vegetative type but linked these types to values from Moran and Sellers?)

1

Convection - RAS with 100% precip Eff. (v197)- with diagnostic clouds vs 97% (FMS) - with prognostic clouds

2

Diurnal frequency - 2 hours (v197) vs. 3 hours (FMS)

2

Boundary Layer - MY akmin_land=5 (v197) vs. akmin=0 (FMS) + other less significant changes

2

Beljaars Ocean Roughness - different strong wind limit from v197 to FMS

2

Gustiness - implemented in FMS; lower limit to wind speed imposed instead in v197

2

SSTs - AMIP1 used here, FMS generally used Reynolds

2

Land-Sea Mask - v197 mask differs from FMS

2

Time Smoothing - Robert filter value in v197 = .03, in FMS = .04

2

Sea Ice - S.H sea ice in v197 = 1.5m vs. 2m in FMS

3

Land Roughness - variable in v197; constant in FMS with Simple Land Model

3

Land Deep Soil Temp - v197 used Ann mean, FMS used 280K

3

Clouds - Diag clouds in v197 included marine stratus, FMS does not. (Fully prognostic clouds not implemented in v197.)

3

Constants - "Universal" constants differ between v197 and FMS

3

Status Codes: 1 -> Unresolved difference, 2 -> Difference (totally or mostly) resolved by changing FMS, 3 -> Difference resolved by changing v197

Summary

 

Impact of eliminating differences between FMS & v197:

Improved features (relative to AM1)

1) DJF - Meridional SLP gradient stronger, trough much deeper and shifted more poleward in S.Hem mid-high latitudes ->Fig.1

2) JJA - S.Hem SLP trough moderately deeper

3) DJF - S.Hem extratropical jet position more poleward->Fig.2

4) Reduction of tendency for surface warm bias over continents in the summer->Fig.3

[Note: differences in sfc albedos may be a contributing factor to the warm bias(see table of "Key Model Features")]

Degraded features (relative to AM1)

1) Zon. Mean TOA Radiative balance ->Fig.4

/ tropical cloud forcing->Fig.5 / strength of upper tropospheric tropical westerlies in DJF->(see Fig.2)

2) Relative humidity (drier, especially in boundary layer) <- relative to v197->Fig.6

3) DJF - Precip (excessive) over S. Africa and the Amazon->Fig.7

 

Sensitivities to advection scheme:

Spectral vs. Lin-Rood for water vapor
[Compare: atm2b vs. atm3b.L-R ; atm3B.sakcld.spkadv vs. atm3B.sakcld]

1) DJF - S. Hem SLP trough deeper and shifted slightly poleward (with spectral)->Fig.8

2) DJF - S.Hem jet position more poleward ->Fig.9

3) DJF - Tropical upper tropospheric winds more westerly ->(see Fig.9)

 

Sensitivities to cloud parameterization:

Diagnostic (atm2b, atm3b.L-R) vs. Prognostic Clouds (atm3B.sakcld, atm3B.sakcld.spkadv)

1) DJF - N. Hem SLP trough deeper and shifted poleward with diagnostic clouds->( see Fig.8)

2) DJF - Tropical upper tropospheric winds more westerly with prognostic clouds->( see Fig.9

 

Sensitivities to dynamical core:

T42L18 AM1 vs. N45L30 (or L18) AM1

JJA - More precip extending over continental India during the monsoon and less spurious precip extending off the coast of east Asia over the western Pacific (AM1.T42L18)->Fig.10

(AM1.N45L18)-> Fig.11