Meteorological Research Institute: Model MRI MRI/JMA98 (T42 L30) 1998a 

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Experimental Implementation

Model Output Description

Model Characteristics

Contact Information

Modeling Group

AMIP Representative(s)

• Dr. Akio Kitoh
• Mail address: Climate Research Department, Meteorological Research Institute, Nagamine 1-1, Tsukuba, Ibaraki, 305-0052, JAPAN
• Phone number: +81-298-53-8594
• Fax number: +81-298-55-2552
• Internet e-mail address:  kitoh@mri-jma.go.jp
• Web Address: http://www.mri-jma.go.jp/

Experimental Implementation

Simulation Period

Earth Orbital Parameters

Calendar

Radiative Boundary Conditions

Ocean Surface Boundary Conditions

Orography/Land-Sea Mask

• The recommended raw orography data set (U.S. Navy 10' x 10' data set, Joseph, 1980) is used. These data are averaged over a 1x1-degree grid, then expanded to a series of spherical harmonics truncated at the spectral T42 horizontal resolution of the model (global-average atmospheric height is 237.193m).

• Filtering after Hoskins (1980) is applied in order to remove high frequency variations.

• The land/sea mask is determined, taking account of consistency between the orographic data and the 12 vegetation types of Dorman and Sellers (1989).  See also Surface Fluxes.

Atmospheric Mass

Spinup/Initialization

• The model was first run for 9 simulated years to attain quasi-equilibrium under prescribed monthly climatological boundary conditions: the SST climatology of Reynolds and Smith (1994) and the JMA sea-ice climatology derived from SMMR and SSM/I satellites.

• Initial conditions for the model atmosphere was obtained from the JMA global analysis for 00Z 1 January 1995.

• Initial soil moisture/temperatures and snow cover/depth for the spin-up were taken from the predictions of the operational JMA global model (GSM9603).

• After the 9-year spin-up, a 1-year integration was performed with boundary conditions for 1978 supplied by PCMDI, to minimize effects of the initial transient fluctuation on the AMIP II run.

Computer/Operating System

Computational Performance

Model Output Description

Calculation of Standard Output Variables

• Method for calculation of percentage time that a pressure surface is below ground: a one (1) is set when a pressure surface is below ground and a zero (0) is set when a pressure surface is above ground. The percentage time is calculated by accumulating this value at every time step.

• Method for calculation of monthly mean tendencies at 17 WMO standard pressure levels:

 
• The temperature tendency due to total diabatic heating includes the tendency due to radiation, moist convection, large-scale precipitation and vertical diffusion. The temperature tendency due to radiation is calculated from the short-wave and long-wave heating rates.  The temperature tendency due to moist convection icludes that obtained from a relaxed Arakawa-Schubert scheme with prognostic closure for penetrative convection and a mass flux scheme for mid-level convection. The temperature tendency due to precipitation includes that from condensation of supersaturated water vapor, as well as  evaporation and phase change of falling precipitation.

 
• The total moisture tendency includes that due to moist convection, large-scale precipitation and vertical diffusion.

• Method for calculation of cloud properties:  The sum of cloud water and ice is stored (see Cloud Formation), but the extinction coefficient (cloud optical thickness/layer depth) and cloud emittance are not.

• Method for calculation of surface variables:  When the specified height of canopy top, which depends on vegetation types, exceeds  the defined height of the surface variable (10 m for wind, 2 m for specific humidity and temperature), values in the canopy space are assigned to the surface quantities. Otherwise, on the assumption of a logarithmic distribution in neutral stability, the surface variables are interpolated between the values at the lowest atmospheric level (at 995 hPa for a surface pressure of 1000 hPa) and the canopy space values.

• The recommended method of Trenberth et al. (1993) is used for calculation of mean sea-level pressure.

• The recommended method of Potter et al.(1992) is used for calculation of clear-sky radiation and cloud radiative forcing.

• Potential vorticity is not calculated.

• The planetary boundary layer (PBL) height is not explicitly computed.

Sampling Procedures

Interpolation Procedures

• Variables are interpolated to constant pressure surfaces at every time step, (see Time Integration Scheme(s)) and then are time-averaged to obtain monthly mean data.

• Variables on pressure surfaces below ground are not calculated.

Output Data Structure/Format/Compression

Model Characteristics

AMIP II Model Designation

Model Lineage

• The horizontal resolution is reduced from spectral T63 to T42.

• There is a different treatment of radiation.

• Rayleigh friction is added to the gravity wave drag parameterization.

• The land-surface scheme is modified.

Model Documentation

Numerical/Computational Properties

Horizontal Representation

Horizontal Resolution

Vertical Domain

Vertical Resolution

Vertical Representation

Time Integration Scheme(s)

Smoothing/Filling

Dynamical/Physical Properties

Equations of State

Diffusion

• Fourth order linear (Del⁴) horizontal diffusion is applied to vorticity, divergence, temperature, and specific humidity on the hybrid vertical surfaces, but with a first-order correction of the temperature and moisture equations to approximate diffusion on constant-pressure surfaces (thereby reducing spurious mixing along steep mountain slopes).  Diffusion coefficients are chosen so that the enstrophy power spectrum coincides with that expected from two-dimensional turbulence theory.

• Stability-dependent vertical diffusion of momentum, heat, and moisture in the planetary boundary layer (PBL) as well as in the free atmosphere follows the Mellor and Yamada (1974) level-2 turbulence closure scheme. The eddy diffusion coefficient is diagnostically determined from a mixing length formulated after the method of Blackadar (1962). See also Planetary Boundary Layer and Surface Fluxes.

Gravity Wave Drag

• Orographic gravity wave drag is parameterized by two schemes that differ mainly in the vertical partitioning of the momentum drag, depending on the wavelength of the gravity waves (cf. Iwasaki et al.(1989a, 1989b) for further details).

• Longwaves (wavelengths >100 km) are assumed to exert drag mainly in the stratosphere (type A scheme), and shortwaves (wavelengths approximately 10 km) only in the troposphere (type B scheme). In both schemes,  gravity wave stress is a function of atmospheric density, wind, the Brunt-Vaisalla frequency and subgrid-scale orographic variance obtained from the 10'x10' U.S. Navy data set (see Orography/Land-Sea Mask). For the type B scheme, orographic variance is calculated as an average difference of maximum and minimum heights within each 10'x10' grid box.

• Since the momentum drag (stress) due to shortwave gravity waves decreases with height as a result of nonhydrostatic effects (cf. Wurtele et al. 1987), the type B scheme assumes the wave stress to be quadratic in pressure and to vanish near the tropopause.  In the type A scheme, the vertical structure of the momentum stress induced by gravity waves is simulated after a modified Palmer et al. (1986) amplitude saturation hypothesis.

• Rayleigh friction also operates as a non-orographic gravity wave drag. Its vertical profile is that of a a hyperbolic tangent function.

Chemistry

Radiation

• A delta-two-stream approximation is used to represent short wave radiation. Spectral intervals, the data for k-distribution and absorption cross section and optical parameters for  clouds are taken from Briegleb (1992). The absorption gases and bands are ozone (O₃) ultraviolet and visible region (8 intervals in the 0.2-0.7 micron band), water vapor near-infrared region (7 intervals in the 0.5-5.0 micron band), carbon dioxide (CO₂, 2.7 and 4.3 micron) and O₂ (A and B bands). Delta-two-stream calculation for transmission and reflection are implemented by the discrete ordinate method (Shibata and Uchiyama, 1992).

• The  multi-parameter random model (Shibata and Aoki, 1989) is used to represent long-wave radiation. Four spectral intervals (20-550, 550-800, 800-1200 and 1200-2200 cm^-1) and five gases are treated. Water vapor is treated in all the intervals with continuum absorption, while carbon dioxide (CO₂,15 micron) and ozone (O₃, 9.6 micron) absorption are included in the second and third spectral intervals, respectively. In addition nitrous oxide (N₂O, 7.8 micron) and methane (CH₄,7.6 micron) absorption are incorporated in the fourth spectral interval. Full- and half-level temperatures are calculated from the prognostic layer-mean temperature profile (cf. Shibata and Uchiyama, 1994) and a two-grid noise suppression scheme is included in the integration of transmission function (Shibata, 1989). In the longwave, cloud is treated as a gray body, with optical depth proportional to the cloud water path.

Convection

• The vertical profile of upward mass flux is assumed to be a linear function of height, as proposed by Moorthi and Suarez (1992). The mass flux at the cloud base (fixed near 950 hPa in the model) is determined by the prognostic equation of Randall and Pan (1993).

• The major contributions of the cumulus clouds are made through compensating downward motion, detrainment of mass, and reevaporation of the convective rainfall. See also Precipitation.

• The effects of an ensemble of multiple-type cumuli are considered. Each type is defined by the level of the cloud top, where the updraft cloud mass loses its buoyancy and detrainment occurs. During the upward movement of the cloud air mass, entrainment of environmental air is considered. The lower limit of the entrainment rate is proposed by Tokioka et al. (1988).

• The convective downdraft associated with the cumulus clouds affects the environment by decreasing the net upward mass flux, and by the detrainment of the downdraft in thesubcloud layer. The downdraft mass flux at the cloud base is specified so that the reevaporation of rainwater moistens the downward flux below the cloud base to saturation. In the extratropics, where moist convection is not always initiated at the surface, the mass flux is determined so that the large-scale moisture increase is spent by the convection. The effect of the cumulus convection on the large-scale tendency is calculated from a budget equation. See also Precipitation.

Cloud Formation

• There is no explicit determination of sub-gridscale convective cloud fraction.  Stratiform cloud fraction is diagnosed as a quadratic function of the excess of the layer relative humidity above a empirical threshold value that varies with height (cf. Saito and Baba 1988). Low-level (below 850 hPa) clouds associated with temperature inversions are treated.

 
• Cloud water content is parameterized as a function of temperature after Heymsfield (1977). All clouds form completely as liquid clouds if the temperature is higher than 273.15 K, and completely as ice clouds if the temperature is lower than 233.15 K. In between, the liquid/ice phase ratio of cloud water is linearly interpolated by temperature. The effective radius of a cloud liquid droplet is fixed at 15 microns, while the radius of an ice particle varies in the range 20-50 microns, according to the temperature. See also Radiation for the treatment of cloud-radiative interactions.

Precipitation

• Large-scale precipitation forms as a result of condensation when the predicted local specific humidity exceeds the saturation value at ambient temperature/pressure. Condensation is instantaneously converted into rain or snow (see Snow Cover).The precipitation amount depends on the new equilibrium specific humidity, so as to account for the associated latent heat release. Moisture and temperature are mutually adjusted in three iterations.

• For convective precipitation, all the condensed water in the updraft is assumed to be carried to the cloud top. Here part of the condensed water is converted from cloud droplets to raindrops, while the remainder is evaporated, moistening the environment through the detrainment process. See also Convection.

• Melting processes are considered when the mixed or ice phase precipitation encounters a model layer with temperature higher than 273.15 K. Subsequent evaporation of falling large-scale and convective precipitation is simulated following the formula proposed by Ogura and Takahashi (1971). The effect of the wind shear, which is responsible for the vertical tilting of the cumulus, is taken into account for reevaporation process using Fritsch and Chappel (1980) relationship of precipitation efficiency and shear. See also Cloud Formation.

Planetary Boundary Layer

Sea Ice

• The AMIP II monthly sea ice extents and concentrations are used as the model's sea ice, with intermediate daily values determined by linear interpolation (see Ocean Surface Boundary Conditions).  Because the model does not account for fractional sea ice, a threshold concentration of 50 % is used to determine whether a grid cell is covered by sea ice.

• Sea ice is assumed to have a constant depth of 2 m, and the ocean temperature below the ice is specified to be that for sea ice formation (about -2 degrees C). The surface temperature of the ice is prognostically determined by the force-restore method of Deardorff (1978). The forcing includes the net energy balance of surface heat fluxes as  well as the conduction heating from the ocean below.  Snow does not accumulate on sea ice.

Snow Cover

• Precipitation falls as snow if the temperature at the lowest atmospheric level (see Vertical Domain) is < 0 C. Snow may accumulate on land, but not on sea ice. The fractional coverage of a grid box is proportional to the water-equivalent snow depth up to 0.02 m; at greater depths, the proportionality constant varies with vegetation type. Snow cover alters the roughness and the albedo of bare and vegetated ground as well as the heat capacity and conductivity of soil, and sublimation from snow is included in the surface evaporative flux. Snow melts (and contributes to soil moisture) if the ground surface temperature is > 0 C. See also Surface Characteristics, Surface Fluxes, and Land Surface Processes.

• The fractional coverage of a grid box is proportional to the water-equivalent snow depth up to 0.004 m; at greater depths, the fractional coverage is unity.

Surface Characteristics

• Over land, the 12 vegetation/surface types of the Simple Biosphere (SiB) model of Sellers et al. (1986) are specified at monthly intervals.

 
• The local roughness length over land varies monthly according to vegetation type (cf. Dorman and Sellers 1989); it decreases with increasing snow depth, the minimum value being 5 percent of that without snow cover. The surface roughness of sea ice is a uniform 1 x 10^-3 m. Over oceans, the roughness length for momentum is a function of the surface wind stress after Charnock (1955), while the roughness length for surface heat and moisture fluxes is specified as a constant 1.52 x 10^-4 m (cf. Kondo 1975).

 
• Over land, surface albedos vary monthly according to seasonal changes in vegetation (cf. Dorman and Sellers 1989). The albedo is specified separately for visible (0.0-0.7 micron) and near-infrared (0.7-4.0 microns) spectral intervals, and is also a function of solar zenith angle. The surface albedo of ice is 0.95. Following Sellers et al. (1986), snow cover alters the surface albedo. Over oceans and sea ice, albedos are functions of solar zenith angle but are independent of spectral interval.

 
• Longwave emissivity is prescribed to be unity (blackbody emission) for all surfaces. See also Surface Fluxes and Land Surface Processes.

Surface Fluxes

• Solar absorption at the surface is determined from the albedo, and longwave emission from the Planck equation with prescribed emissivity of 1.0 (see Surface Characteristics).

• The representation of turbulent surface fluxes of momentum, heat, and moisture follows Monin-Obukhov similarity theory as expressed by bulk formulae. The wind, temperature, and humidity required for these formulae are taken to be the values at the lowest atmospheric level (at 995 hPa for a surface pressure of 1000 hPa). The associated drag/transfer coefficients are functions of the surface roughness (see Surface Characteristics) and vertical stability, following Louis et al. (1981).

• Over vegetated surfaces, the temperature and specific humidity of the vegetation canopy space of the SiB model of Sellers et al. (1986) are used as surface atmospheric values. Over land, the surface moisture flux includes evapotranspiration from dry vegetation (reflecting the presence of stomatal and canopy resistances) as well as direct evaporation from the wet canopy and from bare soil (see Land Surface Processes). Sublimation from snow contributes to the surface evaporative flux.

Land Surface Processes

• Vegetation in each grid box may consist both of ground cover and an upper-story canopy, with the spatial pattern of the ground cover varying monthly. Within the canopy, evaporative fluxes are computed by the Penman-Monteith method (cf. Monteith 1973). Evapotranspiration from dry leaves includes the detailed modeling of stomatal and canopy resistances. Direct evaporation from the wet canopy and from bare soil is also treated (see Surface Fluxes). Precipitation interception by the canopy (with large-scale and convective precipitation distinguished) is simulated, and infiltration of moisture into the ground is limited to less than the local hydraulic conductivity of the soil.

• At the surface, fluxes of radiation, sensible heat and latent heat (including evaporation and sublimation from snow) are implicitly computed. Soil temperatures are predicted by a heat conduction equation in three layers (instead of four, as in the Sato et al. 1989a, 1989b implementation) by the force-restore method of Deardorff (1978). The heat capacity and thermal conductivity for each layer are obtained from the arithmetic mean.

• The surface layer (0.02m thick) consists of ground cover and soil water/ice and ground water/snow. In the two deeper layers, soil water/ice are predicted.  This moisture is increased by infiltrated precipitation and snowmelt, and is depleted by evapotranspiration and direct evaporation. Both surface runoff and deep runoff from gravitational drainage are simulated. Soil water/ice phase change occurs in each layer when the corresponding soil temperature reaches the freezing/melting temperature. Coexistence of soil water and ice/snow is allowed and soil water can diffuse through frozen layers. Frozen water decreases the soil porosity and changes the soil matric potential and hydraulic conductivity.  A zero-flux condition applies for heat and moisture at the bottom of the soil column. See also Surface Characteristics and Surface Fluxes.

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