PMIP 2 Variables

Variables' lists and definitions

How to read the tables

 Name(s)

There are two lines, for the tables that have been updated (if you have doubts or questions, get in touch with the webmaster and the coordinator of the current group of variables):

• The first line is the name of the output variable as it must appear in the NetCDF file, and in the file name (since we store only one output variable per file).
  
  
• The second line is the CF convention standard name of the variable.
  Note that this standard name identifies a physical quantity, regardless of the way the variable is sampled or averaged. Therefore more than one output variable (as defined above) can be associated with the same standard name.

Example: tos (output name) and sea_surface_temperature (standard name)

Note that when the name or the standard name of a PMIP 2 variable are not already defined in the IPCC and/or the CF tables, they are surrounded by braces ([new_var] or [new_standard_name]).

Example: [sos] in the case of ocean surface salinity

The variable names have been chosen to be the same as the IPCC variable names, or as close as possible. They were chosen in a consistent way (following the AMIP naming convention), so that related variables are grouped together when sorted alphabetically.

Units 

Units of the variable.

Units should be written as a product of IS units, where each sub-unit is immediately followed by its exponent (when different from 1). Individual terms (unit followed by its exponent) should be separated by spaces (no '.', '*', 'x' or 'X' multiply sign!). Dimensionless variables should be specified as having unit 1 (integer number one) or the multiplying factor that has been applied to the variable before storing it.

Example: use K s-1, not C/s or °C.s-1.

Note: sign conventions are specified in the Description field below.

Description 

Description of the variable, including the sign convention, when required.

Example: Vertical current velocity (+ up)

Note: we will probably provide somewhere a list of accepted values' range for testing purpose (basic units and sign testing).

Axes 

The axes or dimensions over which the variable is defined.

Example: XYT

• X: Longitude (degrees East)
• Y: Latitude (degrees North)
• P/Z/S: Level
  • Atmosphere: all pressure level diagnostics should be either on the standard 17 WMO pressure levels to allow comparison with reanalysis products (P17 = [1000, 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20, 10] hPa), or on a 3-level subset (P3 = [850, 500, 200] hPa), or on a 2-level subset (Pbt = [850, 200] hPa, and Pbm = [850, 500] hPa), or on a 1-level subset (Pb = 850 hPa and Pm = 500 hPa, used for some Daily Average).
  • Ocean: all diagnostics should be provided at model depths (Z coordinates) or on the 33 standard levels of Levitus observations (Z33 = [0, 10, 20, 30, 50, 75, 100, 125, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1750, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500] m). Please document these depths!
  • Soil: all diagnostics should be provided at model soil depth levels (S coordinates). Please document these depths!
• V: Vegetation Type or Plant Functional Type. Since there is no standard here, people should provide the full details of their vegetation index (V coordinates)!
• R: Geographic region for the variables that are stored by basin (atlantic_ocean, indian_ocean, pacific_ocean, global_ocean)
• T: Time
• Special cases:
  • 2HT: we only store the average over the Northern hemisphere, and the average over the Southern hemisphere.
  • 1T: we store only 1 value

Frequency 

Frequency chosen to save the variable. The frequencies are listed in expected decreasing storage space required in the database (though this also depends on the actual number of years saved).

A circle (O) or some other more appropriate symbol (for 3D variables and zonal means) in a frequency column means that a given variable is required at this frequency.

• DA: daily means (1 day x N days x N_da years)
  
  Note: Sandy Harrison has requested that some atmosphere variables be saved at a higher frequency, in order to use them in the Dust Model!
  
  Note: Noah Diffenbaugh has also requested some higher frequency daily variables, for the NCAR RegCM regional climate model.
  
  
  • O : daily frequency (daily average, unless specified otherwise).
  • ! : 12-hourly (O! or P₁₇!).
  • !!: 6-hourly (O!!).
• MO: monthly means (12 months x N_mo years)
  • 1: fixed geographical field
• SE: mean seasonal cycle (12 months)
• AN: yearly average (1 year x N_an years)

Note: for obvious storing space problems reasons, most variables will only be stored at the SE frequency! You can read the note about estimated storage space below for more details.

Symbols used in the Frequency columns

A blank space in a given frequency column means that the current variable will not be stored in the PMIP 2 database.

If a variable has to be stored in the database, we use a symbol that depends on the axes (longitude, latitude and level) on which the variable is defined:

• 1V : 0D variable (1 type of axis) where only one value is saved.
• 2H : 0D variable (2H type of axis) where only an average over the Northern and an average over the Southern hemispheres are saved.
• Y  : 1D zonal variable (Y).
• Y_R : 1D zonal variable, by basin (atlantic_ocean, indian_ocean, pacific_ocean, global_ocean) (YR).
• O  : 2D variable (XY).
• Z_on: 2D zonal ocean variable (YZ).
• Z_onR: 2D zonal ocean variable, by basin (atlantic_ocean, indian_ocean, pacific_ocean, global_ocean) (YZR).
• P_b : 3D atmosphere variable (XYP) defined only on the 850 hPa (bottom) pressure level.
• P_m : 3D atmosphere variable (XYP) defined only on the 500 hPa (middle) pressure level.
• P_t : 3D atmosphere variable (XYP) defined only on the 200 hPa (top) pressure level.
• P_bt : 3D atmosphere variable (XYP) defined on a subset of the WMO pressure levels ([850, 200] hPa).
• P_bm : 3D atmosphere variable (XYP) defined on a subset of the WMO pressure levels ([850, 500] hPa).
• P₃ : 3D atmosphere variable (XYP) defined on a subset of the WMO pressure levels ([850, 500, 200] hPa).
• P₁₇: 3D atmosphere variable (XYP) defined on all the WMO pressure levels ([1000, 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50,30, 20, 10] hPa).
• Z_n : 3D ocean variable (XYZ).
• V_n : 3D vegetation variable (XYV).
• S_n : 3D soil variable (XYS).

DB 

International project (or database) where this variable has already been defined and studied. When possible, we will try to use the names and conventions that have already been defined in the projects listed below.

In the case of IPCC, we give the name of the table where the variable can be found (and the number of the variable in the table), in the IPCC Standard Output from Coupled Ocean-Atmosphere GCMs document.

Example: O1e2 is thetao, the 2^nd variable of table 01e

Estimated storage space

The tables in the variables' lists give a rough estimation of the storage space that will be required per model and per run. The estimation is based on a T42 (128*64) horizontal grid for the atmosphere (with the 17 WMO pressure levels, or a subset of WMO), vegetation and land-surface variables (with 20 vegetation levels and 5 soil depth levels) and a 240*120 horizontal grid for the ocean variables (with 25 depth levels) and the ice variables. Each data point is stored in a 4-byte real, and we don't count the extra space required by the metadata (names, units, axes, ...) in the netCDF files.

Requirements for the daily variables are based on 360-day years.

The expected size of the database, for 15 models and 6 runs per model, and 100-200 years of run (50-100 for daily values) is 1.5 Tb (yes, that is indeed Tb, and 1 Terabyte = 1024 Gigabytes...).