Ocean Data Assimilation System (MOVE/MRI.COM-G)

  1. Introduction

  2. Ocean General Circulation Model

  3. Observations and data assimilation

  4. Products

  1. Introduction

    The Japan Meteorological Agency (JMA) began operation of an ocean data assimilation system (ODAS) in 1995 to monitor El Niño and Southern Oscillation (ENSO) conditions. The details of the system are described in Kimoto et al. (1997). Subsequently, the analysis scheme of the ODAS was improved in July 2003 (Ishii et al., 2003).

    In March 2008, JMA introduced a new system developed at its Meteorological Research Institute (MRI). The system is composed of an ocean general circulation model (OGCM) and a variational analysis scheme. The OGCM is the MRI Community Ocean Model (MRI.COM) described in Ishikawa et al. (2005), and has higher horizontal and vertical resolutions. The analysis scheme is a multivariate ocean three-dimensional variational estimation (MOVE) type with vertical coupled temperature-salinity empirical orthogonal function (EOF) modes (Usui et al., 2006). In the scheme, the amplitudes of the coupled EOF modes are employed as control variables, and the analyzed temperature and salinity fields are represented by linear combination of the EOF modes. The new ODAS is a global system named MOVE/MRI.COM-G.

  2. Ocean General Circulation Model

    MRI.COM is an ocean primitive equation model with σ-z hybrid vertical coordinates to allow freely elevating surfaces. The horizontal resolution is 1.0º latitude and 1.0º longitude except for the 15ºS - 15ºN band, where the latitudinal grid spacing decreases to the minimum of 0.3º between 6ºS and 6ºN (Figure 1).

    The model has 50 vertical levels, 24 of which are placed above 200 meters (Figure 2). It features realistic bottom topography, and the maximum depth of the bottom is set to 5,000 meters. The computational domain is global from 75ºS to 75ºN, excluding the Arctic Oceans.

    Included in the physical schemes of the model are harmonic viscosity with the parameterization of Smagorinsky (1963) and vertical mixing of the turbulence closure scheme of Noh and Kim (1999). With regard to sea ice, daily climatological data are applied to MRI.COM. The values of wind stress, heat and freshwater fluxes to drive the model are produced with the routinely operated JMA Climate Data Assimilation System (JCDAS), which is almost the same system as the Japanese 25-year Re-Analysis (JRA-25; Onogi et al., 2007). Additionally, the deviation of the model sea surface temperature (SST) from the daily analyzed SST for climate (COBE-SST; Ishii et al., 2005) is referred to in calculating long-wave radiation to keep the model SST closer to the observation.

    Figure 1 The horizontal grids and land-sea distribution of the ocean general circulation model.

    Figure 2 OGCM vertical levels indicating depth in meters.

  3. Observations and data assimilation

    In the MOVE scheme of this data assimilation system, not only in-situ observations of subsurface temperature and salinity but also satellite altimeter data are assimilated into the model. These in-situ observations are reported from ships, profiling floats and moored or drifting buoys through the GTS and other communication systems. COBE-SST data, which are analyzed independently of the MOVE/MRI.COM-G system, are used as observation information to be fed into the assimilation system. Before the assimilation, subsurface temperatures and salinity fields are analyzed at a depth of less than 1,500 meters with the MOVE scheme using these observation data. The analyzed temperature and salinity data are then assimilated into the model with an incremental analysis update (IAU) scheme (Bloom et al., 1996). The heat and freshwater fluxes derived from the JCDAS are used as driving forces for the model of the system.

    The latest objective analysis data are obtained as outputs of the assimilation every 5 days, and the targeted term of the analysis is 3-7 days before the assimilation is implemented. The objective analysis data for the same term are updated every 5 days using additional delayed-mode observation data until the term reaches 39-43 days before the final assimilation implementation.

  4. Products

    The output of MOVE/MRI.COM-G is used in various forms for the monitoring of ENSO at JMA, and a number of products for the equatorial Pacific region are distributed in publications such as Report on Climate System and Monthly El Niño Monitoring Report. Figure 3 shows a MOVE/MRI.COM-G chart indicating depth-longitude sections of temperature and its anomalies. The charts in the reports are also made available through JMA's Distributed Database (http://ddb.kishou.go.jp) and the Tokyo Climate Center website (http://ds.data.jma.go.jp/tcc/tcc/index.html).

    Output from MOVE/MRI.COM-G



    Figure 3 Depth-longitude cross sections of monthly mean temperature (upper) and temperature anomalies (lower) along the equator in the Pacific Ocean for January 2008 by MOVE/MRI.COM-G. The base period for the normal is 1979-2004.

References

Bloom, S. C., L. L. Tacks, A. M. daSilva, and D. Ledvina, 1996: Data assimilation using incremental analysis updates. Mon. Wea. Rev., 124, 1256-1271.

Ishii, M, M. Kimoto, and M. Kachi, 2003: Historical Surface Temperature Analysis with Error Estimates. Mon. Wea. Rev., 131, 51-73.

Ishii, M., A. Shouji, S. Sugimoto, and T. Matsumoto, 2005: Objective Analyses of Sea-Surface Temperature and Marine Meteorological Variables for the 20th Century using ICOADS and the Kobe Collection. Int. J. Climatol., 25, 865-879.

Ishikawa, I., H. Tsujino, M. Hirabara, H. Nakano, T. Yasuda, and H. Ishizaki, 2005: Meteorological Research Institute Community Ocean Model (MRI.COM) manual. Technical Reports of the Meteorological Research Institute, 47, 189pp. (In Japanese)

Kimoto, M., I. Yoshikawa, and M. Ishii, 1997: An ocean data assimilation system for climate monitoring. J. Meteor. Soc. Japan, 75, 1-16.

Noh, Y., and H.-J. Kim, 1999: Simulation of temperature and turbulence closure model for geophysical fluid problems. Rev. Geophys. Space Phys., 20, 851-875.

Onogi, K., J. Tsutsui, H. Koide, M. Sakamoto, S. Kobayashi, H. Hatsushika, T. Matsumoto, N. Yamazaki, H. Kamahori, K. Takahashi, S. Kadokura, K. Wada, K. Kato, R. Oyama, T. Ose, N. Mannoji, and R. Taira, 2007: The JRA-25 Reanalysis. J. Meteor. Soc. Japan, 85, 369-432.

Smagorinsky, J., 1963: General circulation experiments with the primitive equations: I. The basic experiment. Mon. Weather Rev., 91, 99-164.

Usui N., S. Ishizaki, Y. Fujii, H. Tsujino, T. Yasuda, and M. Kamachi, 2006: Meteorological Research Institute multivariate ocean variational estimation (MOVE) system: Some early results. Advances in Space Res., 37, 806-822.

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