CCSM Simulations w/CORE Forcing Some preliminary results and a discussion of dataset issues Marika Holland With much input from Bill Large Steve Yeager.

CCSM Simulations w/CORE ForcingSome preliminary results and a discussion of

dataset issues

Marika Holland

With much input from

Bill Large

Steve Yeager

Experiments Using CORE Forcing

Configuration Forcing Years Case

Ocean alone NYF 129 gx1v3.302

Ocean-Ice NYF 400 (running out to 500)

gx1v3.411

Ocean alone IVF 4x43 gx1v3.210

Ice alone IVF 1x43 M_controlYL

CORE I Results - Ocean-Ice Coupled Runs

Sea Ice equilibrates

rapidly

MOC

CORE-II Ocn-Only Experiments• Purpose of experiments

– Attribution of upper ocean biases in CCSM3 (Large and Danabasoglu, ‘05)

– Ocean variability and process studies (Yeager and Large, 2004; Capotondi et al., 2005)

• Protocol– Initialized with Levitus/PHC, no motion– 4x43 year cycles– Salinity Forcing

• Precipitation factor used• Weak restoring with piston velocity of 50m/4yrs globally• Specified ice-ocean flux from coupled run• Frazil ice formation salinity flux

Attribution of Upper Ocean Biases in CCSM3

Large and Danabasoglu, 2005

Equatorial Pacific Zonal Velocity

Coupled run biases

• upper ocean shear in west

• westward surface flow at 140E

Absent in Ocean-only runs

Associated with the lack of westerly wind bursts that are present in the observations

OBS

OceanOnly

Coupled

Attribution of Upper Ocean Biases in CCSM3

Large and Danabasoglu, 2005

Pacific Zonal Velocity at 140W

Coupled and Ocean-Only biases

• Westward SEC too weak

• Eastward NECC too weak

Coupled biases

• Too symmetric about equator

• Presence of a SECC

• Associated with symmetric atmospheric forcing

OBS

OceanOnly

Coupled

Attribution of Upper Ocean Biases in CCSM3

Large and Danabasoglu, 2005

Equatorial Pacific (2S-2N mean) Potential Temperature

Coupled and Ocean-only biases

• Warm bias indicative of a reduced temperature gradient

Coupled bias

• Cold bias at 100-200m depth, 180E

• Boundary layer not penetrating deep enough - related to sfc buoyancy forcing

OBS

Ocean OnlyMinus OBS

Coupled-OBS

Ice-Only ExperimentsCORE-II Forcing

• Purpose of Experiments– Examine issues/difficulties in validating sea ice models– Perform simulations with different forcing datasets, – Perform simulations with variations in parameter values – quantify uncertainty due to model forcing vs model

physics– Currently a single cycle of forcing performed with

NCEP and with Large-Yeager (43 years)

• Protocol– Initial ice conditions from a previous ice-only run– Ocean heat flux convergence specified (held fixed) from

a CCSM3 coupled integration

Average Sept Arctic Ice Concentration

CORE-II ForcedIce Only Experiments

Arctic Ice Variability

Winter Variability Very SimilarSummer Variability Quite Different. Associated with Mean Differences.

Antarctic Sept Averaged Sea Ice

NCEPLarge-Yeager

• NCEP forcing results in thicker ice cover

• SH variability very similar between runs

Discussion of Dataset Issues

Compiled by Bill Large with input from dataset users

New/Extended Data Available• IVF data through 2004 available at NCAR. • Should be checked out early in the new year. • Future CCSM IVF runs will run through 2004. • No intention of recomputing NYF (with data to 2004)

– Should the GFDL IVF data base be extended?

New/Extended Radiation Data• Radiation data has just arrived • Contains "replacements" for the previous data for

January ‘97 - June ‘01. • "replacements may have some minor effects in

terms of global means (up to a few tenths W/m2) but there are some large flux values changes (> 100 W/m2) for a few grid cells (primarily land areas) for a few flux components.”

– Should we use the "replacement" data?

Dataset Issues - Tropical Humidity• Comparison of TOA and NCEP humidity (Jiang et al., 2005 )

fundamentally different than earlier comparison (Wang and McPhaden, 2000) on which tropical corrections were based.

• In tropical E Pac, new study consistent with SOC (NOT in west). • New comparison and SOC suggest humidity corrections should NOT be

zonally uniform (as currently done). • Considering exploring an objective alternative SOC-based correction that

depends on both lat and lon. (ERA-40 consistency) – What should be done for CORE? Should we work with relative or

specific humidity ?

• Elizabeth Hunke (LANL) believes that the corrected humidity is still too high over Arctic Sea ice.

• She is trying to gather some data sets to quantify the possible problem, so that the correction could be improved.– Are there Arctic humidity data available?

Dataset Issues - Arctic Humidity

• Mean wind stress in NYF based on 1958-2000 • Southern ocean has trend in zonal wind stress to

increasing westerlies. • If ACC transport tuned to winds from later years, a

weaker ACC will result when forced with NYF.– Should mean NYF be based on 1958-2000, 1983-

2000, 1958-2004, 1983-2004 ?

Dataset Issues - Normal Year Winds

Dataset Issues - Wind Direction• NCEP wind direction has been compared to QSCAT. • There are 2 small regions of systematic bias; in the ITCZ

regions of central N Pacific, along the Pacific coast of S America.

• Possible correction being considered to adjust the mean and standard deviation of the wind direction

• N’=Q + (Q(N-N)• So N’ (corrected NCEP direction) is a function of the mean

QSCAT direction and the ratio of the standard deviations – Should corrections be applied? How? Globally?

• The 5% reduction made to the solar radiation is supported by measurements from TAO and PIRATA bouys in the tropical Pacific and Atlantic.– Has anyone else found a similar or different result?

Dataset Issues - Solar Radiation Corrections

Dataset Issues - Heat Imbalance

• Normal year forcing, when used with obs SST has a global ocean heat flux imbalance of -5 W/m2, compared to -1 W/m2 for the IVF (1958-2000).– Is this a problem?– Will be looking into in

any case.

NYF

+5 W/m2

+10 W/m2

Dataset Issues - Others?

Antarctic Winter Ice Variability

Nearly identical for the different forcing runs