NASA/GISS C-grid Atmospheric Model, A170 (5x4, L9), 2002

AMIP Representatives

• Gary L. Russell, E-mail: grussell@giss.nasa.gov
• James E. Glover, E-mail: jglover@giss.nasa.gov
• NASA/GISS, 2880 Broadway, New York, NY 10025
• Tel: 212-678-5547
• Fax: 212-678-5552
• World Wide Web Address: http://aom.giss.nasa.gov

Model Designation

• GISS C-grid A170 (5x4, L9), 2002

Model Lineage

• New C-grid Model. Only basic radiation is similar to prior GISS 1994 B-grid Model; aerosols are completely overhauled.

Model Documentation

• Unpublished programmer's description of Atmosphere-Ocean Model DOCUMENTATION from AOM web site
• Published description of 1995 Atmosphere-Ocean Model
• Both documents describe an earlier version of the C-grid Atmospheric Component of a coupled Model

General Model Description

AMIP Simulation Period

• Start: 1979/01/01/00Z
• Stop: 1996/03/01/00Z

Calendar

• Gregorian calendar including appropriate leap years.
• Tropical year = 365.2425 days
• Vernal Equinox in year 2000 AD = March 20, 7:30 GMT
• Vernal Equinoxes are separated by one Tropical Year
• Equinoxes and Solstaces are within minutes of actual time

Orbital Parameters

• Eccentricity = .016715
• Obliquity = 23.441°
• Longitude of Perihelion = 282.7° = 180 + 102.7

Insolation

• Solar constant = 1365 W/m²
• Diurnal cycle used
• Additional information about EARTH'S INSOLATION

Atmospheric Composition

• Dry atmospheric mass = 10016 kg/m² (98227 Pa)
• Mean annual water vapor mass = 26.871 kg/m² (263.52 Pa)
• Ozone concentration from McPeters with monthly, latitudinal and vertical distribution
• Greenhouse gases are uniform throughout the simulation from observed (and estimated) composition of 1987
• CO2 concentration = 347.92 ppm
• N2O concentration = 305.80 ppb
• CH4 concentration = 1642.0 ppb
• CFC-11 concentration = 234.80 ppt
• CFC-12 concentration = 427.29 ppt
• Concentration of other CFCs = 100.80 ppt

Spherical Earth

• Radius = 6371000 m

Gravity

• Earth's gravitational acceleration is uniform = 9.807 m/s²

Resolution

• Horizontal resolution = 5° longitude by 4° latitude
• Heat and water vapor have both mean and three prognostic gradients
• Moist convection and large scale condensation are performed on 2.5° x 2° resolution
• 9 atmospheric layers, sigma coordinate used

Orography and Surface Fractions

• Each surface grid cell is either all ocean or all continent
• Ocean grid cells have variable surface fractions of open ocean and sea ice
• Atmospheric topography of ocean cells is 0 m except for Caspian Sea where it is -30 m
• Continental grid cells have fixed surface fractions of ground, land ice, and lakes (including rivers)
• Lake fractions have Model predicted fractional lake ice cover
• Atmospheric topography of continental cells is derived from ETOPO5 averaging over only high resolution continental mask
• Global mean atmospheric topography = 238.21 m

Ocean Surface Boundary Conditions

• Monthly sea surface temperature and horizontal sea ice cover downloaded from AMIP II web site
• Interpolated to 5° x 4° using AMIP masks
• End of month values are evaluated from cubic polynomials as functions of time that fit monthly mean values for two months on each side
• Quadratic polynomials as functions of time are determined from end of month values and monthly mean
• Model's daily values evaluated from above quadratic polynomials
• Monthly mean value is preserved
• Sea ice thickness from Canadian Climate Centre downloaded from AMIP II web site

Spinup / Initialization

• Model initialized on 1976/12/01/00 from an observed atmospheric state and prior Model subsurface variables
• Model was spunup for 25 months to 1979/01/01/00 using AMIP II sea surface temperatures and sea ice cover
• Since the initial subsurface variables came from a Model with a different ground hydrology scheme, the deeper subsurface variables may not be in proper equilibrium, even after 25 months of integration

Computer System

• The Atmospheric Model was integrated on a single processor on an SGI Origin 2000 workstation under UNIX
• One simulated day takes about one minute of computer time

Model Output

Precision of Flux Output

• Fluxes of mass, energy and momentum are accumulated every step
• Water mass is conserved precisely by all processes
• Total static energy is conserved precisely by all processes except for dynamics.
• Kinetic energy that is destroyed by non dynamical processes is not conserved but is lost by the Model