The Hough analysis method was used through 1978Sep21. It forced a relationship
between heights and winds which causes the zonal mean meridional wind at every
level to be zero. This also caused other problems with winds in equatorial
areas. The Global Data Assimilation System (GDAS) was started on 1978Sep22,
using the optimal interpolation (OI) analysis method (9 layer). The quality
of stratospheric global analyses are then very poor until about mid-1980, but
better grids are in DS067.1.. On 1980May27, the GDAS was switched to a 12
layer (R24) model. Multivariate OI (R30) implemented 1982Aug14. On 1986May28,
GDAS started using the Medium Range Forecast (MRF) model, with 18 layers and
R40 resolution. On 1987Aug12, MRF87 implemented, raising resolution from R40
to T80. Throughout the period 1976-1987, and probably continuing, various
changes made: in applications of satellite and buoy data; and in first guess
fields and error-corrections.
Prior to 1981Feb22, the land temperature analyses were derived from the model
surface energy budget. Then they were extrapolated from the lowest model
layers. Surface temperatures over the oceans were at first derived from
climatologies, then from analyses. Boundary layer grids, including wind,
relative humidity, and potential temperature, start 1980Jun06.00Z. Sea level
pressure starts 1977Dec08. Surface pressure starts 1978Sep21.00Z. Sea surface
temperature starts 1979May16. Snow cover grids, about every 7 to 10 days,
begin 1979Jul. Vertical motion not available, but could be calculated from
the winds. No forecasts. See DS066.0. for forecasts, and vertical motion.
Additional information about the model is
here and a
change history here.
Also see these
references.
Correspondence received from NCEP in June 1992 indicates that the production
of the global analyses was given second priority. They considered it their
most expendable product. When they experienced hardware failures and the like,
they gave the MRF model priority, and sometimes (especially at 00Z) this meant
skipping the final run which produced the global analyses. The topographic
grids from NCEP, which correspond to the global grids, may be found in DS757.0..
Background information about the characteristics of this data may be
found in An Introduction to Atmospheric and Oceanographic Datasets.
There is general basic information in its Introduction .
More specific information may be found in these chapter(s) or section(s):
Analyzed and Model Data .
You may wish to refer to Other Sources of Data .
Note that NCEP also made the Aviation (AVN) Analyses using the same model, but DSS
did not not collect them.
For a 1987-1994 subset of this dataset, where gaps are filled with
ECMWF data and monthly means are available, see this NCAR Climate
Analysis (CAS) page.
TYPES:
Operational
Gridded analyses
Synoptic
Surface analyses
Upper air analyses
Sea analyses
Oceanographic
COVERAGE:
Global coverage
Latitude / longitude grid
Northern hemisphere and Southern hemisphere are in separate grids. Information
about the grid orientation is here.
UPDATES:
None
See DS081.0 for earlier analyses.
See DS083.0 for later analyses.
TIMES:
daily 12-hourly
at 00Z and 12Z
VARIABLES:
About 1991, NCEP acknowledged that the temperature is
actually virtual temperature. I.e., in the LIST O (ON84 formatted) files, Q=16 means
virtual temperature. In the LIST G (GRIB formatted) files, kpds=11 means virtual
temperature (which would normally be kpds=12).
A humidity field problem is described
here.
Some wind field problems are described
here.
Sea surface temperatures, based on Navy analyses, begin 1979May16. For earlier
analyses, see DS240.0.
Snow depth analyses begin 1979Jul25 and appear just once a week or so.
Surface elevation field from DS757.0.
LEVELS:
1000mb 850mb 700mb 500mb 400mb 300mb 250mb 200mb 150mb 100mb 70mb 50mb
surface upper air troposphere mandatory tropopause stratosphere sigma
A surface subset has been built by DSS in DS082.1.
A tropopause subset has been built by DSS in DS082.2.
For stratospheric levels (70 to 0.4mb) on a 65x65 grid, please see DS067.0.
VARIABLE / LEVEL TABLES:
(in 1993: 69 grids max per hemisphere per analysis time)
tpause p t
50 z t u v
70 z t u v
100 z t u v
150 z t u v
200 z t u v
250 z t u v
sigma(3) rh (0.33-1.00, 0.67-1.00, 0.33-0.67)
sigma(1) pwat (0.33-1.00)
300 z t u v rh
400 z t u v rh
500 z t u v rh
700 z t u v rh
850 z t u v rh
bound theta rh
1000 z t u v rh
msl slp
sfc sfcp sfct sst snow(weekly)
FORMAT:
Be aware of these processing issues.
MM5, WRF and RAMS users click here.
A little advice is available for: GRIB and GrADs (display) software
VOLUME:
Through 1997mar31:
DATA FORMAT AVERAGE TOTAL
LIST O ON84 2.7 MB/day 20.6 GB
LIST G GRIB 2.3 MB/day 17.7 GB
Through 1995Jan, about 18.3GB total. About 3MB/day or 43MB/15-day file.
Notice that comparing the ON84 and GRIB files shows that the dynamic packing of
the GRIB format reduces the volume by about 15%.
COST:
Users with NCAR computing accounts have free access from the NCAR MSS through clicking the 
tab in the navigation bar.
For all others, costs depend on the amount requested, and the DSS standard charging rate applies unless their order qualifies for a substantially reduced charging rate, aka "direct copy rate" as shown on the service charges page.
We can extract a limited variety of subsets from the NCAR MSS files, such as whole grids or whole observations. This may greatly reduce our output charges, but not our input charges. Please inquire, but note that internal logical record reformatting or subsetting is usually not supported.
To send a data request to a staff member, please use this form.
