WCRP/SCOR WORKING GROUP ON AIR-SEA FLUXES
AIR-SEA FLUX CATALOGUE 

Title:

NCEP-1 Reanalysis

Submitted by:

Glenn White

Geographical area:

global

Time period:

1948 to present

Resolution:

192 by 94 Gaussian grid (approx. 2o)

Variables:

near surface meteorological fields (2-meter temperature and specific humidity, 10-m winds), surface fluxes

Data source:

NCEP-1 reanalysis data assimilation/forecast system

Data availability:

Sites for Internet access to the NCEP/NCAR reanalysis and ongoing CDAS data are: http://wesley.wwb.noaa.gov/ncep_data/index.html and http://wesley.wwb. noaa.gov/ cdas_data.html. (The NCEP-1 reanalysis is currently being run on current data as the Climate Data Assimilation System (CDAS). The Climate Prediction Center at NCEP is currently considering whether to run NCEP-1 or NCEP-2 or both as the operational CDAS.) These sites give on-line access to monthly and daily averages of selected fields. CDAS data sets are normally updated by the 5th of the month for the previous month. (This was interrupted for a month or two in late 1999 because of a computer fire at NCEP.) Most of the reanalysis output is in GRIB, a standard format for NWP output. A guide to GRIB can be found at http://wesley.wwb.noaa.gov/reading_grib.html.

NCAR (http://www.scd.ucar.edu/dss/pub/reanalysis) has the complete output of the NCEP-1 reanalysis and will provide tapes for outside users for a fee. Some data sets are freely available over the Internet. Annual CD-ROMs for each year of the reanalysis are also available from NCAR (http://www.scd.ucar.edu/dss/pub/reanalysis/ rean_cdroms.html) as is an 18-year CD-ROM of daily synoptic fields.

A CD-ROM of reanalysis fields for 1982-94 was included in an article in the Bulletin of the American Meteorological Society in March 1996: Kalnay, E., et al., 1996: The NCEP/NCAR 40-year reanalysis project. Bulletin of the American Meteorological Society, 77, 437-471. The contents of the BAMS CD-ROM are available on-line at http://sgi62.wwb.noaa.gov:8080 /reanlm//. A CD-ROM of monthly means for 1958-98 and selected monthly means for 1948-57 has been prepared for a closure article submitted to the Bulletin. A few preliminary copies of the CD-ROM are available at NCAR and from Glenn White at NCEP (email Glenn.White@NOAA.GOV).

The NOAA-CIRES Climate Diagnostics Center in Boulder, Colorado, USA, also has the NCEP/NCAR reanalysis data available (http://www.cdc.noaa.gov/cdc/reanalysis/reanalysis. shtml). It can provide data in GRIB and NetCDF format on Exabyte tapes and has a large subset online.

Documentation:

The official web sites for the NCEP/NCAR reanalysis are: http://wesley.wwb.noaa.gov/reanlysis.html and http://wesley.wwb.noaa.gov/reanalysis.html. Kalnay et al. (1996) and Kistler et al. (2000) document the NCEP1 reanalysis. (A preliminary version of Kistler et al. (2000) is available at http://sgi62.wwb.noaa.gov:8080/DISTRIBUTION/ wd23gw/close /reanl2.htm.) The 1st International Conference on Reanalyses was help in Silver Spring, Maryland in 1997. Proceedings of the conference are available as WCRP Report 104. The 2nd International Conference on Reanalyses was held in Aug. 1999 and the proceedings are being printed. Abstracts and extended abstracts of the presentations are available on-line at http://www.ecmwf.int/pressroom/conf/sicra/abstracts/programme.html. Problems in the NCEP/NCAR reanalysis can be found at http://wesley.wwb.noaa.gov/ reanalysis.html#problem and http://www.cdc.noaa.gov/cdc/reanalysis/problems.shtml. Reanalysis studies and problem reports by Robert Kistler, the technical manager of the NCEP/NCAR reanalysis, can be found at http://lnx21.wwb.noaa.gov/. The site includes examples of the observation (http://lnx21.wwb.noaa.gov/oberr/reanl-obs.html) and forecast (http://lnx21.wwb.noaa.gov/oberr/fcsterr.html) errors used in the reanalysis.

  1. System formulation

  1. NCEP/NCAR-1

The NCEP/NCAR reanalysis analysis/forecast system was identical to the NCEP global operational model implemented in Jan. 1995, except that it had a horizontal resolution of T62 (about 210 km). The vertical resolution is the same as the current operational model. The physical parameterizations are done on a Gaussian grid of 192x94, roughly 2x2 degree latitude. The radiation grid is a Gaussian grid of 128x62. A time step of 20 minutes is used for computing dynamics and physics, except that the full atmospheric radiation is calculated every 3 hours with corrections every time step for diurnal variations in short wave fluxes and in surface upward long wave flux. Mean orographic heights are used. The radiation used in reanalysis is an older short wave radiation (Lacis and Hansen, 1974) than that used in operations. An incorrect, too high surface albedo was used over the oceans. An older boundary layer than that currently in operations was used. The equation for roughness length for heat in the NCEP bulk flux algorithm used in the reanalysis has been found to be inappropriate under strong wind conditions and to overestimate latent heat flux (Zeng et al., 1998). It has been changed in the operational model.

The following data was used by the NCEP/NCAR-1 reanalysis (Ebisuzaki et al., 1998):

    1. radiosondes, dropsondes, pibals

    2. conventional aircraft winds

    3. ACARS aircraft winds and temperatures

    4. Marine winds, temperature, specific humidity in surface layer

    5. Land surface pressure

    6. Cloud-track winds

    7. NESDIS temperature retrievals

    8. PAOBS

    9. SST and snow-cover analyses

The following data was not used:

    1. precipitation

    2. radar, profilers

    3. SSM/I winds and precipitable water

    4. Land winds, temperature specific humidity in surface layer

    5. Most cloud information

    6. Radiances from satellite

    7. Satellite humidity estimates

    8. Soil/albedo/snow depth.

The analysis system used was the spectral statistical interpolation (SSI or 3D variational) analysis (Parrish and Derber, 1992; Derber et al., 1991). Nonlinear normal-mode initialization is not needed. Additional details can be found in Kalnay et al., 1996.

Several problems have been found in the reanalysis. Among them are:

    1. Bogus sea-level pressure observations generated by Australian analysts over the Southern Hemisphere oceans during 1979-92 were misplaced by 180 degrees. (Reruns of 1979 and Nov.-Dec, 1992 corrected this.) The problem has little effect north of 40S and little effects on monthly means. The error is comparable to the difference between ECMWF and NCEP analyses.

    2. The initial attempt to use high-density vertical soundings over the TOGA COARE region from Nov. 92 to Feb. 93 included a failure to convert temperature to virtual temperature and resulted in a cold bias over the TOGA COARE region. The problem has been corrected, the period rerun, and the archives corrected, but the annual CD-ROMS for 1992 and 1993 include this error for the 4 months. The effects are limited to the TOGA COARE region and are strongest near the surface.

    3. The snow cover for 1973 was used for 1974-94 as well.

    4. Due to an incomplete parameterization of the horizontal diffusion of moisture, snow over land tended to fall in valleys.

    5. Discontinuities in radiation fluxes at the International Date Line due to cloud tuning were discovered.

In other instances, not all appropriate data made it into the NCEP/NCAR reanalysis, such as poorly encoded surface observations between 1848 and 1967 and radiosondes in particular areas in particular periods (http://lnx21.wwb.noaa.gov/). A comparison of ERA and NCEP/NCAR reanalyses for a few months revealed that each contained observations not in the other.

Comments: In reanalysis a frozen NWP analysis forecast system is used to process data over several years of past data. The advantages of a reanalysis over operational NWP data assimilation is that it offers several years of fields from an unchanging system and that the fields can be more easily obtained. The disadvantage is that by the time the complete reanalysis record is available the system used is lower resolution and uses older, less developed physical parameterizations than the operational NWP systems.

While the data assimilation system was not changed during the reanalysis (except for some very minor modifications after 1986-89 were processed), the data did change

dramatically during the 50 years. Satellite temperature soundings became available in significant numbers in 1979, the major change in the data record in the last 50 years, and had a noticeable effect on atmospheric temperatures (Fiorino, 1999). An increase in data in the late 1960s is also evident, as is an increase in the last few years, reflecting an increase in satellite winds. In recent years conventional observations have declined. White (1999) examined global trends in precipitation and air-sea temperature contrast that could be related to changes in the observational network. It should be noted, however, that the four-dimensional data assimilation systems used in reanalysis can transport information from data rich to data sparse regions. Ebisuzaki and Kistler (1999) examined the effect of changes in data on reanalysis by comparing fields from NCEP and NCEP-2 to a rerun of 1998 without PAOBS, aircraft or satellite data.

References

Derber, J. C., D. F. Parrish and S. J. Lord, 1991: The new global operational analysis system at the National Meteorological Center. Wea. and Forecasting, 6, 538-547.

Ebisuzaki, W., M. Chelliah, and R. Kistler, 1998: NCEP/NCAR Reanalysis: Caveats.

Proceedings of the 1st WCRP Intl. Conf. on Reanalyses. 27-31 Oct. 1997, Silver Spring, MD, USA, WCRP-104, WMO/TD-876. World Meteorological Organization, Geneva, Switzerland, 81-84.

--- and R. Kistler, 1999: An examination of a data-constrained assimilation. 2nd Intl. Conf. of Reanalyses, Reading, England, 23-27 Aug. 1999. World Meteorological Organization, Geneva, Switzerland, in press.

Fiorino, M., 1999: The impact of observing system changes on the climate-scale variability and temperature in the ECMWF and NCEP reanalyses. 2nd Intl. Conf. of Reanalyses, Reading, England, 23-27 Aug. 1999. World Meteorological Organization, Geneva, Switzerland, in press.

Kalnay, E., M. Kanamitsu, R. Kistler, W. Collins, D. Deaven, L. Gandin, M. Iredell, S. Saha, G. White, J. Woolen, Y. Zhu, M. Chelliah, W. Ebisuzaki, W. Higgins, J. Janowiak, K. C. Mo, C. Ropelewski, J. Wang, A. Leetma, R. Reynolds, R. Jenne, and D. Joseph, 1996: The NCEP/NCAR 40-year reanalysis project. Bullet. Amer. Meteorol. Soc., 77, 437-471.

Kanamitsu, M., 1989: Description of the NMC global data assimilation and forecasting system. Wea. and Forecasting, 4, 335-42.

Kistler, R., E. Kalnay, W. Collins, S. Saha, G. White, J. Woollen, M. Chelliah, W. Ebisuzaki, M. Kanamitsu, V. Kousky, H. v. d. Dool, R. Jenne, and M. Fiorino, 1999: The NCEP/NCAR 50-year reanalysis. Submitted to Bullet. Amer. Meteorol. Soc.

Lacis, A. A., and J. E. Hansen, 1974: A parameterization for the absorption of solar radiation in the Earth’s atmosphere. J. Atmos. Sci., 31, 118-133.

Miyakoda, K., and J. Sirutis, 1996: Manual of the E-physics. Available from Geophysical Fluid Dynamics Laboratory, Princeton University, P. O. Box 308, Princeton, NJ 08542.

Pan, H. -L., 1999: Parameterization of subgrid-scale processes. Global Energy and Water Cycles, K.A. Browning and R. J. Gurney, ed., Cambridge University Press, Cambridge, England, 44-47.

--- and W. -S. Wu, 1995: Implementing a mass flux convection parameterization package for the NMC medium-range forecast model. NMC Office Note 409, 40 pp. Available from NCEP, 5200 Auth Road, Washington, DC 20233.

Parrish, D. F., and J. C. Derber, 1992: The National Meteorological Center’s spectral statistical interpolation analysis system. Mon. Wea. Rev., 120, 1747-1763.

Reynolds, W. R., 1988: A real time global sea surface temperature analysis. J. Climate, 1, 75-86.

--- and D. S. Marsico, 1993: An improved real time global sea surface temperature analysis. J. Climate, 6, 114-119.

--- and T.M. Smith, 1994: Improved global sea surface temperature analyses using optimal interpolation. J. Climate, 7, 929-948.

White, G., 1999: Long-term trends in the NCEP/NCAR reanalysis. 2nd Intl. Conf. of Reanalyses, Reading, England, 23-27 Aug. 1999. World Meteorological Organization, Geneva, Switzerland, in press.

Zeng, X., M. Zhao and R. E. Dickinson, 1998: Intercomparison of bulk aerodynamic algorithms for the computation of sea surface fluxes using TOGA COARE and TAO data. J. Climate, 11, 2628-2644.  

 

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