1. 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.

2. 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

3. 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

4. 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 ： 1860-1957 de-trended ciaf-v2 x 2 1958-2006 ciaf-v2 period ： 1860-2006 (-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.

5. 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.

6. 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 2009 - 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

7. 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

8. 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)

9. MOC after 2000 yrs of CORE-II-moncl

10. 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

11. annual mean sea ice area 1979-2007 (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.

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

13. 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 (1958-2004) 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?)

14. 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

15. 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

16. 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

17. 11. Are there any un-spoken issues that may handicap the goal of producing a common benchmark simulation (besides the magnitude of the effort)? - 10. 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.

18. 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 2010. - 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.