CLIVAR-WGOMD 8 th panel meeting UK Met Office Hadley Centre, Exeter, UK 30April – 01 May 2009 Current status of the Coordinate Ocean-ice Reference Experiments (COREs) in Japan Hiroyuki Tsujino Meteorological Research Institute / Japan Meteorological Agency collaboration with M. Hirabara, H. Nakano, G. Yamanaka, T. Motoi, H.Ishizaki (MRI/JMA) contributions from T. Suzuki, Y. Komuro, Y. Sasaki (JAMSTEC) Outline: 1.Some preliminary results from CORE-II related activities in MRI. 2.Solution / idea to deal with specific questions asked.

Requested issue 1: Summarize use of interannually forced simulations in Japan, and detail experimental design. Institutional efforts in Japan Meteorological Research Institute - CORE-II v2 for 1º x 1/2º global model (used in CMIP5) - status: on-going CCSR Univ. of Tokyo / JAMSTEC - CORE-II v1 for 1/4º x 1/6º global model (used in CMIP5) - status: done, CORE-II v2 planned JAMSTEC Earth Simulator Center - CORE-I for 1/30º x 1/30º North Pacific model, considering CORE-II - status: highly-likely, CORE-II v2 planned

Meteorological Research Institute CORE-II v2 for 1 x 0.5 CMIP-type global model Model settings global (tri-pole) 1º x 0.5º x (L50+BBL) oceanic component of MRI-CGCM used for CMIP5 Initialization and integration period (on-going) initial state: spun-up (accelerated 5000 years and synchronized 500 years) period: two cycles of de-trended CORE-II ver. 2 and one cycle of CORE-II ver.2 Objectives baseline hindcast simulation of the latter half of 20C to facilitate CMIP5 expt. to understand interannual variability and trend in the ocean under “true” atmospheric forcing

a. CORE-I-500yr initial: PHC3.0 (no ice) forcing: cnyf-v1 period: 500yrs purpose: check with Griffies et al. (2009) parameter sensitivity tests b. CORE-II-moncl-millennia initial: “a” or PHC3.0 (no ice) forcing : monthly climatology of ciaf-v2 period : 50 yrs (synchronous) ~ 5000 yrs (accelerated) ~ 500 yrs (synchronous) terminated when drift becomes small purpose: obtain balanced state to initialize “c” c. CORE-II-20C initial ： ”b” forcing ： de-trended ciaf-v2 x ciaf-v2 period ： (-2008) purpose ： reproduce oceanic state of the latter half of 20C Our experimental design and recommendation for CORE-II expt. Notes: - One of main targets should be long-term trends of the simulated field. - Off-line bio-geochemical model will be run using the flow fields. - There remain concerns regarding discrepancy between re-constructed (monthly climatology) and original forcing. Do they really yield similar mean simulated states? - Fresh water flux and salinity restoring adjustment would be needed during the long-term integration. - How should fresh water and salinity restoring adjustments be treated in the interannual run? (Fresh water adj. fixed during integration; salinity adj.) - This recommendation assumes use of eddy-less models. Requested issue 2: Provide recommendations for CORE-II experimental design.

A long-term spin-up is needed because - “drift” should desirably be removed from simulated fields to detect “trends” - deep circulation of the Pacific Ocean, which is of particular interest to Japanese modelers, needs more than a few thousand years to establish Why is monthly climatology used to force the model? - to take a long model time step (e.g., > 6hr; original forcing time interval) - short-time variability in forcing should be absent in a distorted physics How to make CORE-II-monthly climatology and how to calculate fluxes - monthy climatology for all items & scalar wind speed - we presently calculate fluxes in the same way as the 6-hourly data, except - scalar wind speed is based on absolute wind speed - wind stress is calculated using scalar wind speed and relative wind vector High resolution (eddy-permitting/resolving) models might be initialized by a spun-up state of a lower-resolution model and integrated using monthly climatology for 20 yrs, and then switched to CORE-II interannual expt.

Model Settings - Meteorological Research Institute Community Ocean Model (MRI.COM, Ishikawa et al. 2005) English document is almost completed and will be released by the end of tracer advection scheme ： Second Order Moment (Prather, 1986) for non-accelerated run UTOPIA and QUICKEST (Leonard 1979, 1993) for accelerated run - sea ice part: 5-categories, 1-layer ice, EVP dynamics, MPDATA advection - neutral physics: GM （ 250 m 2 s -1 / 100 km x gridsize ） and isopycnal diffusion (1000 m 2 s -1 ) - viscosity: Smagorinsky viscosity with scaling factor 4.0, anisotropic tensor (direction of the flow:1 / normal to the flow 0.2) - SSS restore ： 50m / 365day except for coastal gridpoints with sea ice - fresh water flux adjustment: global correction factor for P+R, adjusted annually - tidal mixing parameterization: Kuril Islands (St. Laurent and Simmons 2006) for the sake of North Pacific intermediate salinity minimum

Test 1. CORE-II-ciaf and CORE-II-moncl as a continuation of CORE-I (500yr) (Note: the model version is changed from the 500 th year) Atlantic MOC at 45N Southern Ocean MOC Pacific Deep MOC Drake Passage transports CORE-II-moncl: monthly climatology for all items & scalar wind speed CORE-II-ciaf and CORE-II-moncl might be expected to yield similar mean fields Black: CORE-I Red: CORE-II-moncl (non-accel.) Green: CORE-II-ciaf

Test 2. Long-term (2000yr) accelerated spin-up using CORE-II-moncl forcing Why monthly? … to take a long time step (8hr). Short-time variability in forcing should be absent in a distorted physics Atlantic MOC at 45N Southern Ocean MOC Pacific Deep MOC Drake Passage transports Grey: CORE-I Orange: CORE-II-moncl (non-accel.) Brown: CORE-II-moncl (accelerated)

MOC after 2000 yrs of CORE-II-moncl

OBS(COBE-SST) MODEL Tropical Indian Ocean SST Anomalies (Yamanaka 2008; GRL) Tropical Indo-Pacific Ocean SST ERA-40 JRA-25 CORE OBS CORE 8July2008 version CORE 5March2009 version Results from CORE-II-ciaf (1): Tropical SST CORE-II is superior to reanalyses

annual mean sea ice area (solid: CORE-II-ciaf simulation, dashed: HadISST) (blue: sea ice extent, red: actual area) correlation ： extent: 0.81, actual area: 0.90 Results from CORE-II-ciaf (2): Arctic sea ice Sea ice seems to have adjusted by 1979.

Shouldn’t CORE-II be extended to the year 2007? upper: HadISST, lower: CORE-II-ciaf simulation extended to 2007 using Japanese re-analysis

JAMSTEC / CCSR Univ. of Tokyo - CORE-II version 1 for 1/4 x 1/6 global model Model setting global (rotated pole) 1/4 x 1/6 x L50+BBL oceanic component for the decadal prediction expt. in the context of CMIP5 Initialization and integration period initial state: climatological temperature and salinity (WOA01) period : CORE-II version 1 ( ) 1-cycle Objective check reproducibility of the latter half of 20C provide physical fields to marine bio-geochemical models Known problems possibly related to forcing: low SST along the Equator (too weak radiation?) thin ice around North Pole (too strong short wave radiation?) divergent wind-driven ice drift around the Antarctica (too strong wind?)

1.What are the key scientific uses for interannually forced global ocean-ice simulations? - to understand ocean’s response (adjustment) to “true” atmospheric forcing - attribution of recent ocean-climate events to trends or natural variability 2. How does CORE-II fit into the spectrum of coupled climate modelling (e.g., IPCC “historical experiments”) and reanalysis projects such as those addressed in GSOP? - CORE-II could serve as a baseline simulation for 20C expt. of CMIP5 - MRI assimilation group plans a reanalysis expt. using CORE-II in the near future 3. Can we identify interesting scientific questions that will make a CORE-II project of scientific interest to the panel? - direct comparison with WOCE re-visit observations - detect of trends

5. What further metrics and diagnostics are of scientific interest for CORE-II simulations? - zonally averaged linear trends of temerature and salinity - some EOFs for SST, SSH, upper layer heat content 6. What observational datasets and reanalysis products should be used to evaluate the CORE-II simulations? - a carefully QC’ed upper layer temperature data by Ishii et al.(2006) would be available 4. What are the baseline metrics required to assess the simulation integrity? - to compare climatological state with WOCE and re-visited WOCE sections - SST, SSH, upper layer heat content

8. Would it be possible to construct key atmospheric forcing fields for the first half of the 20th century and merge this (constructed) forcing with CORE-II to generate a continuous, albeit not fully consistent, data set from year 1900 (or 1880)? - Can objective-analysis SST data by JMA (COBE SST, 1x1, 1890-present) be utilized? 7. Should Large and Yeager (2008), using NCAR bulk formula (as in CORE-I), form the basis of the CORE-II benchmark simulation? What are the problems with this dataset that make certain groups use reanalysis products, or alternative approaches? - “Yes” to the first question - radiation data before 1984 are replaced by satellite climatology - Arctic ice retreat event in 2007 could be a good test for the ocean-ice model

11. Are there any un-spoken issues that may handicap the goal of producing a common benchmark simulation (besides the magnitude of the effort)? How should the ocean and sea ice models be initialized? What about spin- up time prior to the focused analysis period? What portion of the simulation should be analyzed, and what should be ignored (due to initialization shock)? - simulations are desirably started from a quasi-steady state - if some repeated cycles are applied prior to the last cycle, the forcing for the cycles except for the last should be de-trended - about first 10 years of the last cycle would not be reliable - sea ice may be feasible after a short period even without careful initialization 9. What about the salinity boundary conditions? Should this remain a choice for each group, much as in CORE-I? Can we instead provide more specific guidance, and perhaps make another effort to unify the approaches? - This should remain a choice of each group to guarantee simulation integrity of each group’s model, i.e., to be usable for scientific analyses.

12. How can we make the CORE-II simulation output more accessible to the broader community? - making use of repository, like PCMDI, REOS would be useful - publish an inter-comparison paper to notify this project to broader community 13. Is it feasible, and of interest, to aim towards a comparison paper to be written during 2010? - Yes, our CORE-II expt. would be completed by early A new set of CORE-II expt. with some specific protocols would be possible. 14. How can we coordinate simulations leading up to a CORE-II paper (e.g., password protected Wiki page monitored by Anna)? - Wiki would be useful. More “on-the-spot” discussion would be needed.