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

Experiments Using CORE Forcing ConfigurationForcingYearsCase Ocean aloneNYF129gx1v3.302 Ocean-IceNYF400 (running out to 500) gx1v3.411 Ocean aloneIVF4x43gx1v3.210 Ice aloneIVF1x43M_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 Ocean Only 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 Ocean Only 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 m depth, 180E Boundary layer not penetrating deep enough - related to sfc buoyancy forcing OBS Ocean Only Minus OBS Coupled-OBS

Ice-Only Experiments CORE-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 Forced Ice Only Experiments

Arctic Ice Variability Winter Variability Very Similar Summer Variability Quite Different. Associated with Mean Differences.

Antarctic Sept Averaged Sea Ice NCEP Large-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 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/m 2 ) but there are some large flux values changes (> 100 W/m 2 ) 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 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 , , , ? 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/m 2, compared to -1 W/m 2 for the IVF ( ). –Is this a problem? –Will be looking into in any case. NYF +5 W/m W/m 2

Dataset Issues - Others?

Antarctic Winter Ice Variability Nearly identical for the different forcing runs