Variables from the NCEP/NCAR Reanalysis
The Analysis Archive
In this section we will list the variables that are in the
different data files from the NCEP/NCAR reanalysis. All of these
fields are output each six hours.
The model used for the NCEP/NCAR Reanalysis is a T62 sigma
coordinate system (resolution 208 Km). There are 28 levels. The
analyses are done directly in the sigma coordinate system (there is
no interpolating back and forth between pressure and sigma, as in
many previous methods).
1. Data volume each year from reanalysis.
The following table gives an approximate volume for selected main
files in the reanalysis output.
File Mbytes Type of data
per Year
pgb.f00 2533 Analysis stack, pressure coord., 2.50 resol.
grb2d 1989 Fluxes in synop sort, Gaussian grid
grbsanl 4909 Sigma analyses, Gaussian grid
ipvanl 1462 Analyses on theta, derived from sanl (synop sort)
- 2972 Forecast data, an 8-day forecast each 5-days
grib 269 Monthly means and variances
---Time sorts follow---
prs 2152 Analyses in time sort, pressure levels
2D 2606 Flux and surface fields in time sort (Gaussian, lat-lon)
theta 1971 Analyses on theta in time sort
2. Data in pressure coordinates, 17 levels, 2.50 resol. (140 fields).
All of these upper air and other fields are output at 2.5°
resolution in a global grid (144 x 73 points).
a. Data for each of 17 levels (1000-10mb), 105 fields
Height, Temperature, Relative Humidity (8 levels), U wind,
V wind, absolute vorticity, vertical velocity (12 levels).
b. Terms at the surface
Pressure at model sfc Lifted index
MSL pressure elevation (constant)
Precipitable water
c. Data for the lowest sigma level (about 40m height):
Temperature, Potential temperature, RH, U wind, V wind,
Vertical velocity.
d. Data in the lowest 30h Pa layer: Temperature, RH, U and
V winds
e. Tropopause data: Temperature, Pressure, U wind, V wind,
vertical speed shear
f. Maximum wind level: Temperature, Pressure, U wind, V
wind.
g. Humidity of layers
RH in three sigma layers (overlapping layers)
RH of total atmosphere
3. Time series file of the 2.50 pressure data (113 fields).
This dataset (prs file) is 15% smaller in volume than the synoptic
sort file (pgb.f00). This has the same data (but in time sort).
However, it includes only fields on pressure surfaces. For
example, it leaves out the tropopause data, the surface fields, and
some other data.
4. Output on Model Levels (sigma), 174 fields.
These data are output on the global Gaussian grid (192 x 94
points). The data on 28 model levels are:
Temperature Relative Vorticity
Sp. Humidity Divergence
U wind V wind
At the surface, there are 6 variables, including pressure and
elevation. The total number of fields in the file of model level
data are (28 x 6) plus 6.
5. Grb2d file: Two-dimensional diagnostic file ("flux fields"),
69 fields
The following variables are output from the model each 6-hours.
These are all on the Gaussian grid (192 x 94). These are all from
the forecast model. Fields such as temperature, pressure and wind
are instantaneous values at the end of the 6-hr forecast. Other
data such as precipitation, radiation, etc. are averages over a six
hour period. There are also specified fields (ice concentration,
land-sea mask, and surface roughness).
a. Surface terms:
Pressure at model sfc temp at 2m
Potential evap rate spec humidity 2m
Latent heat flux max, min temp 2m
Sensible heat flux u, v wind at 10m
Temp at sfc (skin temp)
b. Water terms:
Convective precip
Total precip rate
Runoff
Water equiv. of accumulated snow
c. Soil terms:
ground heat flux
soil moisture (2 lyrs)
temp of soil (3 lyrs)
d. Cloud Data (19 fields):
1) Cloud cover (%) for low, middle and high clouds
2) Temperature at top of low, middle, and high clouds
3) Pressure at top and base of low, middle and high clouds
4) Nearby model level of top and base of low, middle, and
high clouds
5) Cloud work function
Note: Item 4 isn't really necessary, because item 3 has more precise
information.
e. Radiation (11 fields)
up and down S Wave at sfc
up and down L Wave at sfc
up and down S Wave at top
up L Wave at top
Beam and diffuse down S Wave at sfc
Near IR, beam & diffuse at sfc
f. Radiation, for clouds and clear sky
Cloud forcing radiation
Clear sky radiation
net LW top down LW sfc
net LW sfc down SW sfc
net LW for columnup SW sfc
net SW top up SW top
net SW sfc up LW top
net SW for column
g. Miscellaneous
Momentum flux, 2 components
gravity wave stress, 2 components
Note: It would be desirable if fields such as 10m winds and 2m
temperature would also be derived from the analysis stack at time
equals zero so that they would be consistent with the output of
upper air analysis data (in sigma and pressure coordinates).
However, as it happened, this is not the case as yet; the only
version is now at the end of the 6-hour forecasts.
6. Isentropic coordinate output (89 fields).
These fields are derived from model coordinate data and output on
the global lat-lon (144 x 73) grid. Data are given for 11
isentropic surfaces. The variables on each of the 11 levels are
given below. The number of fields are 8 x 11 plus 1 for potential
temp at the model surface.
Temperature Potential vorticity
U and V wind Montgomery stream function
Relative humidity Brunt-Vaisala frequency
squared
Pressure vertical velocity
Note: the isentropic surfaces (K) are: 650, 550, 450, 400, 350,
330, 315, 300, 290, 280, 270.
7. The 2D file: flux and surface fields in time sort.
Note that this file has more volume than grb2d. The reason is that
this contains some of the other fields that might have gone into
the prs file. Most of these fields are on Gaussian grid. The ones
that could have been in the prs file are 2.5° lat-lon grids.
8. Data on the yearly CD-ROMs.
Please see Appendix C of the March 1996 BAMS paper for a list of
variables.
a. A brief summary follows:
Height, temp, U, V at 850, 500, 200, 100, 50 20 mb (2/day)
Heights at 1000, 850, 700, 500, 300 mb (2/day)
Also vertical motion, precipitable water, humidity
b. Once Daily fields:
Net short wave, long wave fluxes, down shortwave at sfc,
precip, snow, latent, sensible fluxes, etc.
c. Miscellaneous data:
Monthly cross section, monthly means variances, covariances,
observed OLR, display software, and documentation.
9. Output of monthly mean data, and statistics.
These data are described in the Mar 1996 BAMS paper.
10. The CD-ROM with Bull. AMS (Mar 1996).
This issue of BAMS had a major paper about the NCEP/NCAR Reanalysis
and it has a free Reanalysis CD-ROM. The CD had monthly data for
13 years (1982-1994). It also had selections of daily data for
1993. Note that the year 1985 had been rerun, and there had been
a trouble with winds near the pole on early versions of 2.5° data.
The CD has the latest (and correct) version of the data. Written
September 1996.
The Forecast Archive for Reanalysis
During reanalysis, an 8-day forecast is made each five days. The
first ones each year are made on January 1, 6, 11, etc. There is
output for each 12-hours during the forecast run. Data are given
in pressure coordinates (2.5° resolution), and the flux fields are
given (on Gaussian grid).
1. Data in pressure coordinates, 16 levels, 2.5 resolution, 128
fields.
All of these upper air and other fields are output at 2.5
resolution on a global grid (144 x 73 points).
a. Data for each of 16 levels (1000 - 10mb), 98 fields
Height, temperature, RH (7 levels), U wind, V wind, absolute
vorticity, vertical velocity (11 levels)
b. Terms at the surface
Pressure at model sfc lifted index
MSL pressure Best (4-lyr) lifted index
Precipitable water
Pressure tendency
c. Data in lowest 30 mb layer: Temperature, RH, U and V winds
d. Tropopause data: Pressure, temperature, U wind, V wind,
vertical speed shear
e. Maximum wind level: Pressure, temperature, U wind, V wind
f. Humidity of layers
RH of three sigma layers (overlapping layers)
RH of total atmosphere
Note: the 16 pressure levels are: 1000, 925, 850, 700, 500, 400,
300, 250, 200, 150, 100, 70, 50, 30, 20, 10 mb. Note that 600mb
is not included here.
2. Flux fields in the forecast model output, on Gaussian Grid,
43 fields.
These fields are output each 12-hours from the 8-day forecast.
These are on the Gaussian grid (192 x 94).
a. Surface terms (10 fields)
Pressure at model sfc temp at 2m
Potential evap rate spec. humidity 2m
Sensible heat flux max, min temp 2m
Latent heat flux U, V wind at 10m
b. Water terms
1) Convective precip
2) Total precip rate
3) Runoff
4) Water equiv. of accumulated snow
c. Soil terms
1) ground heat flux
2) Soil moisture content
d. Cloud Data (13 fields)
1) Cloud cover (%) for low, middle, and high clouds
2) Temperature at top of low, middle, and high clouds
3) Pressure at top and base of low, middle, and high clouds
4) Cloud work function (for column)
e. Radiation (7 fields)
1) Up and down, s-wave at surface
2) Up and down, long-wave at surface
3) Up, long-wave at top
4) Up, s-wave at top
5) Surface albedo
f. Misc.
Momentum flux, 2 components (neg of sfc stress)
Gravity wave stress, 2 components