GCSS Pacific Cross-Section Intercomparison (GPCI)

NCAR CAM3.0 simulation

 

 

Contact

Cecile Hannay (hannay@ucar.edu). Please contact me for further information 

 

Model

-       Model : NCAR atmospheric GCM

-       Version: Community Atmosphere Model (CAM3.0) 

-       Model dynamics: Spectral eulerian dynamical core.

-       Model physics: a short description of CAM physics is available in appendix.  A full description can be found at

http://www.ccsm.ucar.edu/models/atm-cam/docs/description/

 

Run specifications

-       Integration type: AMIP run, i.e. prescribed sea surface temperature (SST) and sea ice concentration.

-       Resolution: T42 (it is about 2.8 degree grid spacing)

-       Model timestep: 20 minutes

-       Vertical levels: 26 hybrid levels (it is NOT pressure levels).

 

Boundary condition forcing

In an AMIP run, the model is forced with observed monthly SST and sea ice concentration.

The SST and sea-ice concentration boundary conditions are specified such that the monthly means computed from the model output precisely agree with the observed monthly means.  It means we constructed an artificial mid-month values dataset that, upon linear time interpolation (e.g. as done in a model) reproduces the observed monthly means. The procedure is described in: http://www-pcmdi.llnl.gov/publications/ab60.html

 


Cross-section1: Vertical profiles as a function of pressure.

 

We provide vertical profiles every 3 hours for the variables described in table 1. We interpolated the data from the T42 grid to the specified locations using a bilinear interpolation.

 

 

Field name

Units

Short name

A/I

Pressure (hPa)

hPa

press

I

Potential temperature (K)

K

theta

I

Specific humidity (kg/kg)

kg/kg

q

I

Relative humidity (%)

%

rh

I

Zonal wind (m/s)

m/s

u

I

Meridional wind (m/s)

m/s

v

I

Vertical velocity (Pa/s)

Pa/s

w

I

Cloud cover (%)

%

cc

I

Liquid water content (kg/kg)

kg/kg

clwc

I

Ice water content (kg/kg)

kg/kg

ciwc

I

 

Table 1: Vertical profiles. The column A/I indicates whether the field is instantaneous (I) or averaged over the 3-hours prior the output time (A).

 

The format of the files is:

- Format: ASCII file, 1 file per parameter per month, line format: I8,13(1X,E14.6)

- Lines: levels from top to bottom; per period of 3 hours;

- Columns: 1 is the time stamp (YYMMDDHH); 2 to 14 are the points from 35 N, 125 W onwards

- Filename: cross_shortname_month.ascii  where month = [9806, .., 0308] and the short names are described in table 1.

 

 


Cross-section2: Single-level fields

 

We provide data for the variables described in table 2. We interpolated the data from the T42 grid to the specified locations using a bilinear interpolation.

 

Field name

Units

A/I

Sea surface temperature

K

I

Outgoing longwave radiation

W/m2

A

Surface downward longwave radiation

W/m2

A

Net shortwave radiation at the top of the atmosphere

W/m2

A

Surface net shortwave radiation

W/m2

A

Surface downward shortwave radiation

W/m2

A

Surface latent heat flux

W/m2

A

Surface sensible heat flux

W/m2

A

Total cloud cover

%

I

Total column water vapour

Kg/m2

I

Liquid water path

Kg/m2

I

Ice water path

Kg/m2

I

Convective precipitation

mm/day

I

Stratiform precipitation

mm/day

I

TOA net clear sky shortwave

W/m2

A

TOA clear sky longwave

W/m2

A

Surface net clear sky shortwave

W/m2

A

Surface net clear sky longwave

W/m2

A

 

Table 2: Single-level fields. The column A/I indicates whether the field is instantaneous (I) or averaged over the 3-hours prior the output time (A).

 

The format of the files is:

- Format: ASCII file, 1 file per parameter per month, line format: I8,13(1X,E14.6)

- Lines: 1  parameter per time, per line in the order of the table 2.

- Columns: 1 is the time stamp (YYMMDDHH); 2 to 14 are the points from 35 N, 125 W onwards

- File name: cross_singleLevel_month.ascii  where month = [9806, .., 0308] and the short names are described in table 2.

 


2D maps

 

We provide a 2D map for the variables described in table 3. We interpolated the data from the T42 grid to the specified grid (5 degrees x 5 degrees) using a bilinear interpolation. The variable names were not specified, and we used the CAM terminology

 

Field name

Units

Short name

AF

-Outgoing longwave radiation

W/m2

FLNT

A

-Precipitation (mm/day):

mm/day

PRECT

I

-Total cloud cover

%

CLDTOT

I

-Total column water vapour 

kg/m2

TMQ

I

-Liquid water path

kg/m2

TGCLDLWP

I

-Ice water path 

kg/m2

TGCLDIWP

I

-Relative humidity at 850 hPa

%

RELHUM850

I

-Relative humidity at 200 hPa

%

RELHUM200

I

-Vertical velocity at 300 hPa

Pa/s

OMEGA300

I

-Vertical velocity at 700 hPa

Pa/s

OMEGA700

I

 

Table 3: Single-level fields. The column A/I indicates whether the field is instantaneous (I) or averaged over the 3-hours prior the output time (A).

 

The files are in netcdf format and the file names are: eul64x128_GCSS-1998-2Dmap.nc and eul64x128_GCSS-2003-2Dmap.nc


 

Figure 1: Vertical profiles – Mean over JJA (1998)

'

 

Figure 2: Vertical profiles – Mean over JJA (2003)

 

Figure 3: 2D map  – Mean over JJA (1998)

 

 

Figure 4: 2D map  – Mean over JJA (2003)

APPENDIX CAM physics:

 

The Community Atmosphere Model (CAM3) represents the sixth generation of Atmospheric General Circulation Models (AGCMs) developed by th climate community in collaboration with the National Center for Atmospheric Research (NCAR).  Like its predecessors, CAM is designed to be a modular and versatile model suitable for climate studies by the general scientific community. CAM3 can be run either as a stand-alone AGCM (coupled to the CLM land model) or as a component of the Community Climate System Model (CCSM). When coupled to the CCSM it interacts with fully prognostic land, sea-ice, and ocean models. It is also being employed in biogeochemical and physical-chemistry studies in experimental configurations.

 

CAM3 includes prognostic equations for three water substances: vapor, small cloud water drops, and cloud ice particles, and diagnoses the production of rain and snow mixing ratios (and their fluxes) by assuming the sources terms balance the sinks.  The CAM3 employs an internally consistent formulation for the fractional condensation rate and a self-consistent treatment of the evolution of water vapor, heat, cloud fraction, and both cloud condensate quantities. Condensed water detrained from shallow and frontal convection can either form precipitation or additional stratiform cloud water.

 

Advection and sedimentation of cloud droplets and ice particles are included in the equations governing cloud condensate.  The ice effective radius used in the microphysics and radiation is a function of temperature.  The effective radius and the prescribed number density of liquid droplets transition from polluted values over land surface to pristine values over ocean.  This transition affects the radiative properties and microphysical evolution of these droplets.

 

The radiative parameterizations have been updated to include new treatments of the interactions of shortwave and longwave radiation with cloud geometry and with water vapor.  The new, generalized formulation for clouds can calculate the radiative fluxes and heating rates for any arbitrary combination of maximum and random overlap. The type of overlap assumptions are independent of the radiative parameterizations, and vary from one grid cell or time step to the next.  The parameterizations are mathematically equivalent to the independent column approximation.

 

The absorption and emission of longwave radiation by water vapor have been updated using modern spectral line data bases and empirical approximations for the water-vapor continuum.  The absorption of near-infrared radiation by water vapor has been updated using the same modern line data and approximation for the continuum.

 

In its default configuration, CAM3 includes the radiative effects of an aerosol climatology in its calculation of shortwave fluxes and heating rates. The CAM3 also includes an optional prognostic formulation for the evolution of natural and anthropogenic sulfate aerosol, and its interactions with clouds and radiation.

 

CAM3 can employ any of three different formulations for the numerical representation of the atmospheric equations of motion, and dynamical transport. The standard scheme uses a traditional spectral/finite difference formulation for the model dynamics and a semi-Lagrangian formulation for the tracer transport. A complete semi-Lagrangian, and a flux form semi-lagrangian formulation are available as options. Tuned configurations of each of these formulations are available at a variety of spatial resolutions.