NASA Global Data Sets for Land-Atmosphere Models 1987

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1. TITLE 1.1 Data Set Identification. Near-surface meteorological analyses and hybrid products. (fixed, monthly, monthly 6-hourly, 6-hourly ; ECMWF, NASA/LaRC) 1.2 Data Base Table Name. Not applicable. 1.3 CD-ROM File Name. The ECMWF, & ECMWF, NASA/LaRC hybrid data are on Volumes 2-5 of the 5 Volume ISLSCP Initiative I CD-ROM set. Volume 2 of this set contains fixed (time-invariant) data, instantaneous data (data for the first time period on the first day of each month), monthly data and monthly 6-hourly data, while Volumes 3-5 contain 6-hourly data. Volumes 3 & 4 have four ECMWF 6-hourly parameters and volume 5 has the ECMWF, NASA/LaRC hybrids for shortwave and longwave radiation and the NOAA/NMC, GPCP hybrids for total and convective precipitation. Below is a listing of the CD-ROMs and directories that contain these data: CD-ROM2: \DATA\ECMTH6HR\YyyMmm\nnnnnnnn\nnsymmhh.Z and \DATA\ECMTH6HR\YyyMmm\nnnnnnnn\nsymmhh.Z CD-ROM2: \DATA\EC_MTHIN\YyyMmm\nnnsymm.Z and \DATA\EC_MTHIN\YyyMmm\nnnymmdh.Z CD-ROM2: \DATA\ECINVRNT\nnnnnnnn.Z CD-ROM3: \DATA\YyyMmm\nnnnnnnn\nnnnnnnn\nymmddhh.Z CD-ROM4, and CD-ROM5: \DATA\YyyMmm\nnnnnnnn\nymmddhh.Z Where ECINVRNT = ECMWF fixed (time-invariant) data. EC_MTHIN = ECMWF Monthly data and instantaneous values from the first day of each month, ECMTH6HR = ECMWF monthly, 6-hourly data, and yy is the last two digits of the year (e.g., Y87=1987), mm is the month of the year (e.g., M12=December), and nnnnnnnn is the parameter name (see table below for parameter directory names). Note: capital letters indicate fixed values that appear on the CD-ROM exactly as shown here, lower case indicates characters (values) that change for each path and file. There are six types of filename formats used for these data; nnnnnnnn.Z (for the fixed (ECINVRNT) data), nnnymmdh.Z (for the instantaneous (EC_MTHIN) data), nnnsymm.Z (for monthly (EC_MTHIN) data), nnsymmhh.Z and nsymmhh.Z (for the monthly, 6-hourly (ECMTH6HR) data) nymmddhh.Z (for the 6-hourly daily data). Where: nnnnnnnn, nnn, nn, n are parameter descriptors (see table below), s is the statistical method used to derive the data (i.e., S=standard deviation, E=mean, A=maximum of range, and I=minimum of range), y is the last digit in a year (e.g. 7=1987), mm is the month (e.g., 12=December), dd is the day (i.e., 01 to 31), and hh is the first two digits in the hour (e.g., 12=1200 Greenwich Mean Time (GMT)). The instantaneous files have a 10 (dh) at the end of their prefix file name. The 1 identifies the first day of the month and the 0 identifies the first time period of the day. The filename extension (.Z), indicates that the files are compressed and must be decompressed before use (see section 8.4). I. Prescribed/Diagnostic Fields (fixed and monthly) Parameter CD-ROM Directory Descriptor Description Volume # Name ------------------------------------------------------------------------ Fixed Surface Roughness Length 2 NOT APPLICABLE ROUGHNSS Albedo 2 NOT APPLICABLE ALBEDO Monthly Surface Soil Wetness 2 NOT APPLICABLE SSM Deep Soil Temperature 2 NOT APPLICABLE DST Deep Soil Wetness 2 NOT APPLICABLE DSM Climate Deep-Soil Temperature 2 NOT APPLICABLE CST Climate Deep-Soil Wetness 2 NOT APPLICABLE CSM Snow Depth 2 NOT APPLICABLE SDP II. Monthly, 6-hourly Forcing Fields Parameter CD-ROM Directory Descriptor Description Volume # Name ------------------------------------------------------------------------ Temperature at 2m 2 TEMP_2M T Dewpoint Temperature at 2m 2 DWPNT_2M D Surface Pressure 2 SUR_PRSR P U-wind at 10 meters 2 UWND_10M UW V-wind at 10 meters 2 VWND_10M VW U-wind Stress 2 UWND_STR US V_wind Stress 2 VWND_STR VS Surface Temperature 2 SUR_TEMP ST Mean Sea Level Pressure 2 MSL_PRSR SP Surface Net Shortwave Radiation 2 SUR_SWR SS Surface Net Longwave Radiation 2 SUR_LWR SL TOA Net Shortwave Radiation 2 TOA_SWR TS TOA Net Longwave Radiation 2 TOA_LWR TL Surface Sensible Heat Flux 2 SUR_SBHT SH Surface Latent Heat Flux 2 SUR_LTHT LH III. Diurnally-resolved (6-hourly) Forcing Fields Parameter CD-ROM Directory Descriptor Description Volume # Name ------------------------------------------------------------------------ Temperature at 2m 3 TEMP_2M T Dewpoint Temperature at 2m 3 DWPNT_2M D Wind magnitude at 10 meters 4 MWND_10M W Surface Pressure 4 SUR_PRSR P Surface Shortwave Down Radiation 5 ECM_LANG\HSUR_SWR S NASA/LaRC, ECMWF Hybrid Surface Longwave Down Radiation 5 ECM_LANG\HSUR_LWR L NASA/LaRC, ECMWF Hybrid Total Precipitation 5 NMC_GPCP\TOTL_PRC O NOAA/NMC, GPCP, Hybrid Convective Precipitation 5 NMC_GPCP\TOTL_PRC C NOAA/NMC, GPCP, Hybrid 1.4 Revision Date Of This Document. April 5, 1995. 2. INVESTIGATOR(S) 2.1 Investigator(s) Name And Title. All products except hybrid products. Dr. Anthony Hollingsworth European Center for Medium-Range Weather Forecasts Dr. Horst Bottger European Center for Medium-Range Weather Forecasts Hybrid radiation products. ECMWF, NASA/LaRC, GSFC/DAAC and Code 923, NASA/GSFC Hybrid precipitation products. NOAA/NMC and GPCP/GPCC See the NMC_GPCP.DOC document for addtional information on the Hybrid precipitation data. 2.2 Title Of Investigation. Regridded ECMWF Level III-A data and hybrid products. 2.3 Contacts (For ECMWF Data Production Information). __________________________________________________________________ | Contact 1 | Contact 2 | ______________|________________________|__________________________| 2.3.1 Name |Kathy Rider |John T. Hennessy | 2.3.2 Address |ECMWF |Operations Department | | |ECMWF Forecasts | |Shinfield Park |Shinfield Park | City/St.|Reading/Berkshire |Reading/Berkshire | Zip Code|RG2 9AX |RG2 9AX, | |United Kingdom |United Kingdom | 2.3.3 Tel. |44 734 499453 |44 734 499400 | |FAX: 44 734 869450 |FAX: 44 734 869450 | 2.3.4 Email |rider@ecmwf.co.uk |john.hennessy@ecmwf.co.uk | ______________|________________________|__________________________| 2.4 Requested Form of Acknowledgment. The Technical Attachment to the Description of the ECMWF/WCRP Archive should be cited by users in publications (see reference section). The European Center for Medium-Range Weather Forecasts provided data for the ISLSCP Initiative 1 CD-ROM from the ECMWF/WCRP Level III-A Global Atmospheric Data Archive. ECMWF data are supplied on the CD-ROM subject to the following conditions: 1. The supplied data will not be transmitted in whole or in part to any third party without the authorization of ECMWF. 2. Articles, papers, or written scientific works of any form, based in whole or in part on data supplied by ECMWF, will contain an acknowledgment concerning the supplied data. 3. Access to the data is restricted to the scientists within the organization of the data recipient working on the same computer installation. 4. The recipient of the data will accept responsibility for informing all data users of these conditions. 5. Data will not be provided to commercial organizations. 3. INTRODUCTION 3.1 Objective/Purpose. The purpose of ECMWF level III-A atmospheric data are to support projects associated with the World Climate Research Program (WCRP). The hybrid radiation (and precipitation) products were generated to provide high temporal resolution forcing fields for land-atmosphere models. 3.2 Summary of Parameters. The ECMWF products include: Surface pressure, temperature, dew point temperature, wind speed, shortwave and longwave net radiation fluxes, sea level pressure, sensible and latent heat flux, wind stress, soil moisture, soil temperature, snow depth, albedo, and surface roughness. The hybrid products consist of incident longwave and shortwave radiation fluxes and total and convective precipitation. (The precipitation products are discussed in the NMC_GPCP.DOC document). 3.3 Discussion. The ECMWF, and ECMWF, NASA/LaRC data on the ISLSCP Initiative I CD-ROM are comprised of the ECMWF/TOGA Advanced Operational Analysis Data the ECMWF/TOGA Supplementary Fields data and a hybrid dataset using the radiation fields within the ECMWF/TOGA Supplementary Fields and the NASA/LaRC Surface Shortwave and Longwave Radiation Fluxes data set. ECMWF/TOGA Advanced Operational Analysis Data Sets: This data set contains uninitialized analysis values at the resolution of the data assimilation system in operational use at ECMWF. The Advanced Operational Analysis Data Set, on the ISLSCP Initiative 1 CD-ROM, are comprised only of the Surface and Diagnostic Fields. The original ECMWF Surface and Diagnostic Fields data set was represented on a 320 x 160 grid, with a regular spacing of 1.125 degrees (lat/long) between points along each row for the period January 1, 1987 - December 31, 1988. Grid point values were stored in latitude rows starting at the north and working southwards; within each row values ran from west to east, starting at the 0 degree longitude. All of the ECMWF Surface and Diagnostic Fields Data sets, on the ISLSCP CD-ROM, have been converted, by the Goddard DAAC, to a 1 X 1 degree equal angle lat/long grid, starting at 90 degrees latitude North and 180 degrees longitude West (see section 9.3.1). The Parameters from the Surface and Diagnostic Fields data set, on the ISLSCP Initiative I CD-ROM set, are: Surface Fields surface pressure, surface temperature, soil moisture, snow depth, mean sea level pressure, u- and v-components of wind at 10m, temperature at 2m, dew point temperature at 2m, deep-soil wetness, deep-soil temperature. Diagnostic Fields surface roughness, albedo, climate deep-soil wetness, climate deep-soil temperature. ECMWF/TOGA Supplementary Fields Data Set: The Supplementary Fields Data Set contains surface heat fluxes, net radiation and u- v-stress derived from 6-hour forecasts used as "first- guess" for analyses within ECMWF's data assimilation system. The Supplementary Fields Data Set acquired from ECMWF were represented in the same format, as the Surface and Diagnostic Fields Data set, described above. All ECMWF Supplementary Fields Data Sets, on the ISLSCP CD-ROM, have been converted, by the Goddard DAAC, to a 1 X 1 degree equal angle lat/long grid, starting at 90 degrees latitude North and 180 degrees longitude West (see section 9.3.1). The Parameters from the Supplementary Fields data set, on the ISLSCP Initiative I CD-ROM set, are: surface flux of sensible heat, surface flux of latent heat, surface shortwave radiation, surface longwave radiation, top of the atmosphere shortwave radiation, top of the atmosphere longwave radiation, and the zonal and meridional components of the surface wind stress. Most of the near-surface meteorological data are taken directly from forecast products generated by the ECMWF operational numerical weather prediction model. ECMWF requested that the following information be provided to users of the ECMWF data: The ECMWF data sets are adapted to a specific model orography; the data sets have biases which are only partially documented (reference list). No surface observations of T, q, precipitation, nor surface wind observations over land were used in the analysis. Model spin up can seriously affect the flux data. All flux fields, including total cloud cover, are first-guess fields (i.e. 6 hour forecasts). All the time-evolving fields on this CD-ROM, such as soil moisture, snow depth and deep soil parameters include no direct observations, but evolve during the data assimilation cycle. The Technical Attachment to the Description of the ECMWF/WCRP Archive should be cited by users in publications (see reference section). In addition to the routine products extracted from the ECMWF archive for this data set, NASA/GSFC generated synthetic 'hybrid' 6-hourly incident surface shortwave and longwave radiation fluxes, and NOAA/NMC generated 'hybrid' 6-hourly total and convective precipitation rates. As presented on the CD-ROMs the data sets include: I. Prescribed/Diagnostic Fields (see table in section 1.3), II. Monthly (6-hourly) Forcing Fields (see table in section 1.3), III. Diurnally-resolved (6-hourly) Forcing Fields (see table in section 1.3). (These include the hybrid products). The data in I are intended for reference rather than direct use by modelers. The data sets in II are suitable for forcing long time-step models. The data sets in III have been put together for the express purpose of forcing energy-water-carbon land models. 4. THEORY OF MEASUREMENTS The ECMWF level III-A global atmospheric data, are assimilated data resulting from the combination of atmospheric observations and model calculations. No surface observations are used, so that the surface data provided on these CD- ROM comes from the model simulations of surface processes, strongly constrained by observed atmospheric information and "a priori" surface climatological information. These data sets are based on quantities analyzed or computed within the ECMWF data assimilation scheme. The ECMWF data assimilation system in use in 1987 consisted of a multivariate optimal interpolation analysis, a non-linear normal model initialization and a high resolution spectral model which produced a first guess forecast for the subsequent analysis. Data were assimilated every 6 hours. There were frequent changes in the model (see section 9.2.2 for details), many involving surface processes, over the temporal period of the data on this CD- ROM. Since the data on this CD-ROM is inferred from model calculations constrained by atmospheric data, artificial discontinuities in the data would be expected at the dates of model changes. 5. EQUIPMENT 5.1 Instrument Description. 5.1.1 Platform. Not applicable. 5.1.2 Mission Objectives. Not applicable. 5.1.3 Key Variables. Not applicable. 5.1.4 Principles of Operation. Not applicable. 5.1.5 Instrument Measurement Geometry . Not applicable. 5.1.6 Manufacturer of Instrument. Not applicable. 5.2 Calibration. 5.2.1 Specifications. Not applicable. 5.2.1.1 Tolerance. Not applicable. 5.2.2 Frequency of Calibration. Not applicable. 5.2.3 Other Calibration Information. Not applicable. 6. PROCEDURE 6.1 Data Acquisition Methods. The data sets described in this document were acquired by the Goddard Distributed Active Archive Center (GDAAC) from the European Center for Medium-Range Weather Forecasting (ECMWF). 6.2 Spatial Characteristics. The original data was given on a regular lat/long grid that had a spatial resolution of on a 1.125 X 1.125, with an origin point at the Greenwich meridian (90 degrees latitude, 0 degrees longitude). The Goddard DAAC converted this data to a 1 X 1 degree lat/long grid with an origin point at the international date line (90 degrees latitude North, 180 degree longitude West), see section 9.3.1 for additional information. 6.2.1 Spatial Coverage. The coverage is global. Data in each file are ordered from north to south and from west to east beginning at 180 degrees west and 90 degrees north. Point (1,1) represents the grid cell centered at 89.5 N and 179.5 W (see section 8.4). 6.2.2 Spatial Resolution. The data are given in an equal-angle lat/long grid that has a spatial resolution of 1 X 1 degree lat/long. 6.3 Temporal Characteristics. 6.3.1 Temporal Coverage. January 1987 through December 1988. The time period of 0000 GMT January 1, 1989 are included for the following parameters: Temperature at 2 meters (T) Dew-point temperature at 2 meters (Tw) Wind magnitude at 10 meters (U) Surface Pressure (Ps) 6.3.2 Temporal Resolution. ECMWF produces routine global analyses for the four main synoptic hours 0000, 0600, 1200 and 1800 GMT and global 10 day forecast based on 1200 GMT data. The Hybrids were produced at the same 4 synoptic hours. The data correspond to four temporal resolutions. Time-invariant (fixed): Surface Roughness Albedo Monthly data, produced, by the Goddard DAAC, from the 6 hourly daily data (see section 9.3.1): Surface soil wetness Deep soil temperature Deep soil wetness Climate deep-soil temperature Climate deep-soil wetness Snow depth The Monthly data also includes instantaneous values from the first day of each month, at GMT 0000. Monthly 6-hourly data, produced, by the Goddard DAAC, from the 6-hourly data (see section 9.3.1): Temperature at 2 meters Dew-point temperature at 2 meters Surface pressure u-wind at 10 meters v-wind at 10 meters u-wind stress v-wind stress Surface temperature Mean sea level pressure Surface Net SW radiation* Surface Net LW radiation* TOA Net SW radiation* TOA Net LW radiation* Surface sensible heat flux* Surface latent heat flux* 6-hourly daily data: Temperature at 2 meters (T) Dew-point temperature at 2 meters (Tw) Wind magnitude at 10 meters (U) Surface Pressure (Ps) NASA/LaRC, ECMWF Hybrid Surface Shortwave down Radiation* NASA/LaRC, ECMWF Hybrid Surface Longwave down Radiation* NOAA/NMC, GPCP Hybrid Total Precipitation NOAA/NMC, GPCP, Hybrid Convective Precipitation These data are intended to be used as forcing data for Energy- Water-Carbon models. In addition to the ECMWF products of Ps, T, Tw and U, we have added synthesized hybrid products for downward shortwave and longwave radiation, and total and connective precipitation, generated by NOAA/NMC. Documentation (NMC_GPCP.DOC) on the precipitation hybrid products is provided in a separate document. * denotes fields accumulated over 6 hours since start of each ECMWF forcast. The Goddard DAAC converted these fields to [W] [m^-2] [s^-1]. The Hybrid radiation data sets also use monthly mean radiation data from LaRC in their derivation (see section 9.1.1). 7. OBSERVATIONS 7.1 Field Notes. Not applicable. 8. DATA DESCRIPTION 8.1 Table Definition With Comments. Not applicable. 8.2 Type of Data. ------------------------------------------------------------------------------ | 8.2.1 | | | | |Parameter/Variable Name | | | | ------------------------------------------------------------------------------ | | 8.2.2 | 8.2.3 | 8.2.4 | 8.2.5 | | |Parameter/Variable Description |Range |Units |Source | ------------------------------------------------------------------------------ | I. Prescribed/Diagnostic Fields | ------------------------------------------------------------------------------ | Fixed (Time Invariant) | ------------------------------------------------------------------------------ |ALBEDO (ALBEDO) | |[unitless]|ECMWF | | |The albedo calculated as the |min = 0 |fraction | | | |percent of reflected to |max = 0.8 |between 0 | | | |downwelling shortwave radiation. |Ice |and 1 | | | | |Sahara=0.4 | | | ------------------------------------------------------------------------------ |SURFACE ROUGHNESS LENGTH (ROUGHMSS) | |[m] |ECMWF | | |The total roughness length is a |min = 0 | | | | |combination of the roughness, at |max = 18 | | | | |the surface, due to vegetation and | | | | | |the roughness length derived from | | | | | |orography. (Max value = 18m) | | | | ------------------------------------------------------------------------------ | Monthly | ------------------------------------------------------------------------------ |SURFACE SOIL WETNESS (SSM) | |[m (of |ECMWF | | |The water content (Moisture) of the |min = 0.0 |water)] | | | |soil above 7 cm. This amount cannot |max = 0.02 | | | | |exceed 2 cm of water. | | | | ------------------------------------------------------------------------------ |DEEP SOIL TEMPERATURE (DST) | |[K] |ECMWF | | |The temperature of the ground |min = 200 | | | | |below 50 cm depth. |max = 316 | | | ------------------------------------------------------------------------------ |DEEP SOIL WETNESS (DSM) | |[m (of |ECMWF | | |The deep-layer water (Moisture) |min = 0.0 |water)] | | | |content of the soil. The deep-layer |max = 0.02 | | | | |wetness overlaps with the mid-layer | | | | | |wetness. The mid-layer begins at | | | | | |7 cm. Both Layers are 42 cm in | | | | | |depth and the total water content | | | | | |that each layer can hold cannot | | | | | |exceed 12 cm. | | | | ------------------------------------------------------------------------------ |CLIMATE DEEP SOIL TEMP. (CST) | |[K] |ECMWF | | |The climate temperature of the |min = 200 | | | | |ground below 50 cm depth. |max = 310 | | | ------------------------------------------------------------------------------ |CLIMATE DEEP SOIL WETNESS (CSM) | |[m (of |ECMWF | | |The climate deep-layer water |min = 0.0 |water)] | | | |(Moisture) content of the soil. |max = 0.02 | | | ------------------------------------------------------------------------------ |SNOW DEPTH (SDP) | |[m] |ECMWF | | |The snow depth measured in meters |min = 0 | | | | |of equivalent liquid water. |max = 10.1 | | | | | |Ice caps | | | ------------------------------------------------------------------------------ | II. Monthly, 6-hourly Forcing Fields | ------------------------------------------------------------------------------ |2-METER TEMPERATURE (T) | |[K] |ECMWF | | |The air temperature at 2 m above |min = 220 | | | | |the ground. |max = 330 | | | ------------------------------------------------------------------------------ |2-METER DEW POINT TEMPERATURE (D) | |[K] |ECMWF | | |The dew point temperature at 2 m |min = 215 | | | | |above the ground. |max = 306 | | | ------------------------------------------------------------------------------ |SURFACE PRESSURE (P) | |[Pa] |ECMWF | | |The atmospheric pressure at the |min = 50000 | | | | |surface. |max = 106000| | | ------------------------------------------------------------------------------ |10-METER U WIND VELOCITY (UW) | |[m] [s^-1]|ECMWF | | |The U (Zonal) component of wind |min = -35 | | | | |velocity, at 10 meter above the |max = 35 | | | | |ground. | | | | ------------------------------------------------------------------------------ |10-METER V WIND VELOCITY (VW) | |[m] [s^-1]|ECMWF | | |The V (Meridional) component of |min = -35 | | | | |wind velocity, at 10 meter above |max = 35 | | | | |the ground. | | | | ------------------------------------------------------------------------------ |U-STRESS (US) | |[N] [m^-2]|ECMWF | | |The U (Zonal) component of surface |min = -3 | | | | |wind stress. |max = 3 | | | ------------------------------------------------------------------------------ |V-STRESS (VS) | |[N] [m^-2]|ECMWF | | |The V (Meridional) component of |min = -3 | | | | |surface wind stress. |max = 3 | | | ------------------------------------------------------------------------------ |SURFACE TEMPERATURE (ST) | |[K] |ECMWF | | |The temperature of the soil above |min = 340 | | | | |7 cm depth. |max = 190 | | | ------------------------------------------------------------------------------ |MEAN SEA LEVEL PRESSURE (SP) | |[Pa] |ECMWF | | |The mean atmospheric pressure at |min = 95000 | | | | |sea level. |max = 106000| | | ------------------------------------------------------------------------------ |SURFACE NET SHORTWAVE RADIATION (SS) | |[W] [m^-2]|ECMWF | | |Net shortwave radiation absorbed |min = 0 | | | | |at the surface. |max = 950 | | | ------------------------------------------------------------------------------ |SURFACE NET LONGWAVE RADIATION (SL) | |[W] [m^-2]|ECMWF | | |Net longwave radiation absorbed at |min = -300 | | | | |the surface. |max = 60 | | | ------------------------------------------------------------------------------ |TOA NET SHORTWAVE RADIATION (TS) | |[W] [m^-2]|ECMWF | | |Net shortwave radiation at the top |min = 0 | | | | |of the atmosphere. |max = 1200 | | | ------------------------------------------------------------------------------ |TOA NET LONGWAVE RADIATION (TL) | |[W] [m^-2]|ECMWF | | |Net longwave radiation at the top |min = -350 | | | | |of the atmosphere. |max = -80 | | | ------------------------------------------------------------------------------ |SURFACE SENSIBLE HEAT FLUX (SH) | |[W] [m^-2]|ECMWF | | |The energy flux, at the surface, |min = -700 | | | | |due to temperature gradient |max = 400 | | | | |between surface and air. | | | | ------------------------------------------------------------------------------ |SURFACE LATENT HEAT FLUX (LH) | |[W] [m^-2]|ECMWF | | |The energy flux at the surface, |min = -700 | | | | |due to evaporation of water. |max = 200 | | | ------------------------------------------------------------------------------ | III. Diurnally Resolved 6-hourly Forcing Fields | ------------------------------------------------------------------------------ |2-METER TEMPERATURE (T) | |[K] |ECMWF | | |The air temperature at 2 m above |min = 220 | | | | |the ground. |max = 330 | | | ------------------------------------------------------------------------------ |2-METER DEW POINT TEMPERATURE (D) | |[K] |ECMWF | | |The dew point temperature at 2 m |min = 215 | | | | |above the ground. |max = 306 | | | ------------------------------------------------------------------------------ |10-METER WIND MAGNITUDE (W) | |[m] [s^-1]|ECMWF | | |The total wind magnitude (speed) |min = 0 | | | | |given by the square root of U^2 + |max = 35 | | | | |V^2. Where U and V are eastward | | | | | |northward wind components, | | | | | |respectively. | | | | ------------------------------------------------------------------------------ |SURFACE PRESSURE (P) | |[Pa] |ECMWF | | |The atmospheric pressure at the |min = 50000 | | | | |surface. |max = 106000| | | ------------------------------------------------------------------------------ |HYBRID SURFACE SHORTWAVE DOWN RADIATION (S)| |[W] [m^-2]|NASA/ | | |Shortwave down radiation at the |min = 0 | |LaRC, | | |surface. |max = 1200 | |ECMWF | ------------------------------------------------------------------------------ |HYBRID SURFACE LONGWAVE DOWN RADIATION (L)| |[W] [m^-2]|NASA/ | | |Longwave down radiation at the |min = 0 | |LaRC, | | |surface. |max = 600 | |ECMWF | ------------------------------------------------------------------------------ |HYBRID TOTAL PRECIPITATION (O) | |[W] [m^-2]|NOAA/NMC| | |Total precipitation |min = 0 | |GPCP | | | |max = 1200 | | | ------------------------------------------------------------------------------ |HYBRID CONVECTIVE PRECIPITATION (C) | |[W] [m^-2]|NOAA/NMC| | |Convective precipitation |min = 0 | |GPCP | | | |max = 600 | | | ------------------------------------------------------------------------------ 8.3 Sample Data Base Data Record. Not applicable. 8.4 Data Format. Compressed format: The ECMWF data has been compressed using Unix Compress. Compress uses the modified Lempel-Ziv algorithm popularized in "A Technique for High Performance Data Compression", Terry A. Welch, IEEE Computer, vol. 17, no. 6 (June 1984), pp. 8-19. Common substrings in the file are first replaced by 9-bit codes 257 and up. When code 512 is reached, the algorithm switches to 10-bit codes and continues to use more bits until the limit specified by the -b flag is reached (default 16). Bits must be between 9 and 16. The default can be changed in the source to allow compress to be run on a smaller machine. The amount of compression obtained depends on the size of the input, the number of bits per code, and the distribution of common substrings. The ECMWF data has been reduced by approximately 85%. So watch out!!! The data described here can be de-compressed using the platform specific programs listed below. DOS MAC UNIX VMS ---------------------------------------------------- u16.zip MacGzip0.3b2 gzip1-2-3 gzip-1-2-3 These programs are located in the SOFTWARE directory on this CD-ROM. The programs are also available via FTP from many archival data bases on the Internet. Information on anonymous FTP sites which supply these software can be obtained via anonymous FTP at ftp.cso.uiuc.edu in the directory /doc/pcnet in the file compression. Uncompressed format: The CD-ROM file format is ASCII, and consists of numerical fields of varying length, which are space delimited and arranged in columns and rows. Each column contains 180 numerical values and each row contain 360 numerical values. Grid arrangement ARRAY(I,J) I = 1 IS CENTERED AT 179.5W I INCREASES EASTWARD BY 1 DEGREE J = 1 IS CENTERED AT 89.5N J INCREASES SOUTHWARD BY 1 DEGREE 90N - | - - - | - - - | - - - | - - | (1,1) | (2,1) | (3,1) | 89N - | - - - | - - - | - - - | - - | (1,2) | (2,2) | (3,2) | 88N - | - - - | - - - | - - - | - - | (1,3) | (2,3) | (3,3) | 87N - | - - - | - - - | - - - | 180W 179W 178W 177W ARRAY(360,180) 8.5 Related Data Sets. NOAA/NMC, GPCP precipitation data available on ISLSCP Initiative I Volume 5 (see NMC_CPCP.DOC). 9. DATA MANIPULATIONS 9.1 Formulas. 9.1.1 Derivation Techniques/Algorithms. OROGRAPHY (SURFACE GEOPOTENTIAL HEIGHT) Although ECMWF Orography (Surface Geopotential Height) is not included on this CD-ROM, it is undoubtedly one of the most important surface fields. Once defined it determines directly or indirectly some other surface fields (temperatures for example) and it has an important role in the analysis and forecast. Therefore, a description on how it is derived is presented below. The model orography can be represented in terms of an area mean or an envelope orography. It is calculated according to the orography expression phi(s) = g [H(m) + [alpha][sigma]] where g = 9.80665 is the mean acceleration of the Earth's gravity, H(m) is the mean height on the user-defined grid retrieved from the US Navy summary data set (Tibaldi and Geleyn, 1981), alpha is the proportion of standard deviation to be added to the mean height over land points (alpha is not equal to 0 for an envelope orography), and sigma is the standard deviation of mean height defined for the same grid as H(m). I. Prescribed/Diagnostic Fields ALBEDO The background land albedo is interpolated to the model grid from the mean annual values of the climatology by Dorman and Sellers (1989). The original albedo climate data is a yearly averaged climate field, with a resolution of 1.875 degrees on a regular lat/long grid (Preuss and Geleyn, 1980; Geleyn and Preuss, 1983). The interpolated field is then filtered by the same Gaussian filter as is used in the orography filtering. Since sea ice has an important role in defining the global albedo it was necessary to derive an annual mean sea ice pattern. The following constraints are then imposed on the albedo field: over sea ice values are reset to 0.55; over open sea (water points) the albedo is 0.07; over land points the minimum albedo must not be below 0.07 and the overall maximum cannot exceed 0.80 (usually over snow-covered areas). In snow covered areas this background albedo, is modified taking into account the snow depth and temperature, masking by the vegetation and the presence of ice dew. The albedo of the snow covered part is set to vary between a minimum (0.4) at melting point, and a maximum (0.8) at temperature T(o) - C(ST), {C(ST) = 5C}. Where T(o) is the ice melting temperature and C(ST) is the temperature for the snow albedo. Finally, the albedo is modified for the parallel solar radiation depending on the cosine of the solar zenith angle. The thermal emissivity of the surface is assumed to be 0.996 everywhere, giving a thermal albedo of 0.004. The albedo, values provided on the Volume 2 CD-ROM are a yearly background climate field. The ECMWF model alters this field during the run according to the snow cover. SURFACE ROUGHNESS LENGTH The roughness length due to vegetation is an original climate data set, defined on a regular 5 degree lat/long grid all over the globe (Baumgartner et al., 1977), and therefore it must be interpolated from the original to the user-defined resolution. The total roughness length is calculated from a simple expression Z(o) = [Z(V)^2 + Z(H)^2]^0.5 Where Z(V) is the roughness length due to vegetation on the user defined grid and Z(H) is the roughness length derived from orography parameters and is part of the US Navy summary data set. The information about urbanization has already been built in to Z(H), in such a way that for 100% urban area a value of 2.5 meters is assumed. SURFACE SOIL WETNESS (MOISTURE) This surface field is derived in a straightforward way from the surface soil moisture climate data set. The surface soil moisture climate data set is defined on a global 4 x 5 degree lat/long grid and is available for the 1st and 16th day of each month (Mintz and Serafini, 1981). The surface soil moisture climate data are interpolated to a user-defined grid. The original maximum value of the moisture that the soil can hold is set to 15 cm of water. Since, the first ground layer reaches only 7.2 cm in depth, it is assumed that the maximum water content for this layer cannot exceed 2 cm, and therefore all original values are scaled accordingly. The field is of no relevance over the model water points, where it is set to zero. DEEP-LAYER SOIL TEMPERATURE This field was derived from surface temperature which has been obtained by the procedure described above. From the surface temperature, deep-layer temperature is calculated using the expression T(d)^n = [1-c]T(o) + c[aT(s)^n + bT(s)^n-1] Where T(o) denotes the mean annual surface temperature, T(s)^n and T(s)^n-1 are the surface temperature for month n and previous month n-1, a and b are constants defining the temperature phase lag and c is a constant describing the amplitude damping. Currently a = b = 0.5 and c = 0.77. The above formula applies only over land points. DEEP-LAYER SOIL WETNESS (MOISTURE) This climate field is derived from the original data of Mintz and Serafini (1981). The original soil moisture is first interpolated to the operational Gaussian grid. The depth of the model's deep (third) ground layer is 42 cm and the maximum water content in this layer is assumed to be 12 cm. The deep ground layer overlaps the middle layer, which begins at 7 cm and also has a depth of 42 cm. It is assumed that the soil moisture between these two layers is in balance, since values used in the forecast model are scaled to the depth of the first ground layer (which is 7 cm deep). CLIMATE DEEP SOIL TEMPERATURE Not available at this revision. CLIMATE DEEP SOIL WETNESS Not available at this revision. SNOW DEPTH There are a variety of meteorological phenomena which have various degrees of impact on snow creation and snow destruction. Eventually, it was decided that only the combination of precipitation and surface soil temperature over land points would be considered when creating the snow climate. The Snow Depth is not calculated as a prognostic variable as in most GCMs but is prescribed climatologically. The archived climatological snow is not derived from snow measurements but is derived according to some complicated semi-empirical modeling from climatological monthly precipitation and temperatures. Since there are now available, global climatologies of snow based on direct observations, it is suggested that the user be cautious in use of this unvalidated and indirectly derived climatology except to understand how the archived albedos are derived. II. Monthly, 6-hourly Forcing Fields 2-METER TEMPERATURE Not available at this revision. 2-METER DEW POINT TEMPERATURE Not available at this revision. SURFACE PRESSURE Not available at this revision. 10-METER U VELOCITY For information on how u-wind velocity is derived see Janssen et al. (1992). 10-METER V VELOCITY For information on how v-wind velocity is derived see Janssen et al. (1992). U-STRESS For information on how u-wind stress is derived see Janssen et al. (1992). V-STRESS For information on how v-wind stress is derived see Janssen et al. (1992). SURFACE TEMPERATURE A climatological surface temperature is derived according to the procedure described by Brankovic and Van Maanen (1985). The procedure described below was taken from Brankovic and Van Maanen (1985). A rather lengthy procedure is used to derive surface temperature from the ECMWF model output. The data has been interpolated to the model resolution, used with corrections for model elevation, and blended with the sea surface temperatures and sea-ice of Alexander and Mobley (Tibaldi and Geleyn, 1971). Since this data is based on early climatological information no longer in general use and has been highly manipulated to meet modeling requirements, it should be used with caution except for understanding its role in derivation of the time-dependent model surface fields. MEAN SEA LEVEL PRESSURE Not available at this revision. SURFACE NET SHORTWAVE RADIATION Surface shortwave radiation is derived from top of the atmosphere radiation and model atmospheric structure including clouds, according to the scheme of Foquart and Bonnel (1980) as given in detail in Research manual 3, ECMWF forecast model physical parameterization. SURFACE NET LONGWAVE RADIATION Surface longwave fluxes are calculated from model atmospheric structure using clouds according to a parameterization which includs a diffusivity factor. For further explanation, see Research manual 3, ECMWF forecast model physical parameterization. TOA NET SHORTWAVE RADIATION For information of on how top of the atmosphere shortwave radiation is derived, see Geleyn and Hollingsworth (1979), Morcrette (1990) and Morcrette (1991). TOA NET LONGWAVE RADIATION For information of on how top of the atmosphere longwave radiation is derived, see Geleyn and Hollingsworth (1979), Morcrette (1990), and Morcrette (1991). SURFACE FLUX OF SENSIBLE HEAT For information on how surface sensible heat flux is derived see Louis (1979) and Morcrette (1990). SURFACE LATENT HEAT FLUX For information on how surface latent heat flux is derived see Louis (1979) and Morcrette (1990). III. Diurnally-resolved (6-hourly) Forcing Fields 2-METER TEMPERATURE Not available at this revision. 2-METER DEW POINT TEMPERATURE Not available at this revision. WIND MAGNITUDE AT 10M Wind Magnitude was derived from the u and v components of wind at 10m. Wind magnitude is equal to the square root of U^2 + V^2. Where U and V are eastward & northward wind components, respectively. SURFACE PRESSURE Not available at this revision. NASA/LaRC, ECMWF HYBRID SURFACE SHORTWAVE DOWN RADIATION This parameter was derived from the NASA/LaRC (monthly mean radiation, on ISLSCP Initiative I CD-ROM Volume 1) surface shortwave down radiation, ECMWF surface net shortwave radiation, and ECMWF albedo. The following equation was used: S(EH) = S(L)/SUM[S(NE)/[1 - A(E)]] * S(NE)/[1 - A(E)] where S(EH) = Hybrid surface shortwave down radiation (6 hourly), SUM = Summation, S(L) = LaRC surface shortwave down radiation (monthly mean), S(NE) = ECMWF surface 6-hourly shortwave net radiation, A(E) = ECMWF Albedo (monthly mean). HYBRID SURFACE LONGWAVE DOWN RADIATION This parameter was derived from the NASA/LaRC (monthly mean radiation, on ISLSCP Initiative I CD-ROM Volume 1) surface longwave net radiation, ECMWF surface net longwave radiation, and ECMWF surface temperature data. The following equation was used: L(EH) = L(NL)/SUM[L(NE)] * L(NE) + 0.996[b] * [T(SE(t)) + T(SE(t-1))/2]^4 where L(EH) = Hybrid surface longwave down radiation (6-hourly), L(NL) = LaRC surface longwave net radiation (monthly mean), SUM = Summation, L(NE) = ECMWF surface longwave net radiation (6-hourly), T(SE(t)) = ECMWF surface temperature (at time = t), T(SE(t-1)) = ECMWF surface temperature (at time = t-1) 0.996 = Emissivity (used in ECMWF model for all land surfaces). b = Stefan-Boltzman constant (5.67051 x 10^-8 [W] [m^-2] [K^-4] HYBRID TOTAL AND CONVECTIVE PRECIPITATION These products were created by NOAA/NMC using four input data sets which are listed below: 1) The GPCP global 1-degree gauge-based monthly precipitation analyses for 1987/88 (available and documented on CD-ROM Volume of this set). 2) The NMC Reanalysis global 1.875-degree 4DDA-based 6-hourly total precipitation analyses for 1987/88, available from NMC, (Kalnay et al., 1993; Kalnay et al., 1995). 3) The NMC Reanalysis global 1.875-degree 4DDA-based 6-hourly convective precipitation analyses for 1987/88, available from NMC, (Kalnay et al., 1993; Kalnay et al., 1995). 4) The NASA/GSFC global 4x5 degree gauge-based daily precipitation analyses for Dec 1978 through Nov 1979, available from NASA/GSFC, (G. Walker, private communication, NASA/GSFC, greg@rootboy.gsfc.nasa.gov; see also Liston et al., 1993, specifically Sec. 2.c, page 13). A detailed explanation of methods used to derive these data are described in the file NMC_GPCP.DOC on ISLSCP Initiative I CD-ROM Volume 1 & 5. 9.2 Data Processing Sequence. 9.2.1 Processing Steps and Data Sets. The ECMWF data assimilation system in 1987 consisted of a multivariate optimal interpolation analysis, a non-linear normal model initialization and a high resolution spectral model which produced a first-guess forecast for the subsequent analysis. Data were assimilated every 6 hours. The forecast model in 1987 used a spectral formulation in the horizontal, with triangular truncation at total wavenumber 106, a vertical coordinate with 19-level resolution which was terrain- following at low levels. The comprehensive physical parametrization schemes included shallow and deep (Kuo) convection, a radiation scheme which allowed interaction with model generated clouds and the diurnal radiative cycle. ECMWF produces routine global analyses for the four main synoptic hours 0000, 0600, 1200 and 1800 GMT and global 10 day forecast based on 1200 GMT data. The operational schedule with the approximate running times of the analysis and forecast suite is shown in the figure below. As a forecasting center with the emphasis on the medium-range, ECMWF operates with long data collection times of between 18 hours for the 1800 GMT analysis and 8 hours for the 1200 GMT final analysis. This schedule ensures the most comprehensive global data coverage including the Southern Hemisphere surface data and global satellite sounding data. ________________________________________________________________ |DATA OBSERVATION| | | | | |TIME | 1501-2100 | 2101-0300 | 0301-0900 | 0901-1500 | |________________|___________|___________|___________|___________| || || || || _______________ || || || || |APPOXIMATE TIME| \/ \/ \/ \/ |OF DATA CUT-OFF|->(1100) (1630) (1730) (2000) |_______________| || || || || ___||___ ___||___ __||____ __||____ ->|ANALYSIS| ->|ANALYSIS| ->|ANALYSIS| ->|ANALYSIS| | |VT 1800 | | |VT 1000 | | |VT 0600 | | |VT 1200 | | |________| | |________| | |________| | |________| | || | || | || | || | ___\/___ | ___\/___ | __\/____ | __\/____ | |INITIAL.| | |INITIAL.| | |INITIAL.| | |INITIAL.| | |________| | |________| | |________| | |________| | || | || | || | || ^ || ^ || ^ || ^ \/ | \/ | \/ | \/ | (1200-0030) ________ | ___||___ | ___||___ | __||____ | ___||___ |FORECAST| | |FORECAST| | |FORECAST| | |FORECAST| | |FORECAST| |1200+6H |___| |VT 0000 |_| |VT 0600 |_| |VT 1200 |_| | TO | |VT 1800 | |________| |________| |________| |TEN DAYS| |________| |________| The ECMWF operational schedule in late 1987, all times shown in GMT. 9.2.2 Processing Changes. The section below summarizes the modifications to the ECMWF operational data production system from January 1987 through December 1988. This is the time period for the data in this ISLSCP Initiative I data set collection. For information on modifications made before and after these dates see "ECMWF, The Description of the ECMWF/WCRP Level III-A Global Atmospheric Data Archive." 3 February 1987 The humidity pre-processing was modified. 10 February 1987 SATEM precipitable water content was included to analysis. 7 April 1987 Forecast model cycle 29. The surface and subsurface parameterization scheme has been revised. Each grid box is now divided into vegetated and bare ground parts which concerns the evaporation over land surfaces. The time evolution of the soil water content takes root uptake, interruption of precipitation and collusion of dew by a skin reservoir, surface run off due to sloping terrain and gravitational drainage into account. The use of specific thermal properties of snow modifies the surface temperature evolution over snow covered ground. The convective Kuo scheme was modified. The accumulated convective precipitation now includes convective snowfall. Over sea surface convective precipitation is allowed to fall as snow when the sea surface temperature is above 0 degree C. For both land and sea points the air temperature at the first model level is required to be colder than minus 3 degree C for snowfall. The post-processing method to compute the 10 m winds, 2m temperature and dew point has been reformulated. The calculations of 10m wind components and the 2m temperature base on realistic profiles of wind speed and temperature gradients within the atmospheric boundary layer which is assumed to be a Constant Flux Layer (CFL). The variables (at any height) are obtained by integrating their vertical derivatives. The 2m dew point depression is computed by assuming that the relative humidity is constant in the CFL. The modifications of the near surface temperature give a more realistic simulation of the diurnal temperature variation under clear sky conditions. The old 2m dew point calculation suffered from a surface layer which was too moist which results in a too narrow dew point spread. The new scheme corrects this deficiency to a large extent. In stable conditions the new post-processing give lower wind speeds u-wind and v-wind at 10m height. The reduction which is of the order 1 - 3 ms^-1 is in better agreement with locally observed winds. Over sea the Charnock constant of 0.032 was replaced by the lower value of 0.018. Soil moisture analysis is not being done any more. The initial soil temperature and moisture content are taken from the first-guess. 13 April 1987 An error in the computation of 10m wind and 2m temperature and dew-point temperature was fixed. The data of u-wind 10m, v-wind 10m, 2m temperature and 2m dew-point temperature are incorrect within the time period from 7-13 April 1987. 16 June 1987 Land wind data in the Tropics were used and the wind direction check was tightened up. 7 July 1987 An error in post-processing of low cloud and total cloud amount was fixed. The total cloud cover is incorrect from 15 July 1986 to 6 July 1987 as a result. 21 July 1987 A number of changes relating mainly to the use of SATEMs was implemented. Now 7 SATEM layers are used in the vertical instead of 11, i.e. 1000/700 hPa, 700/500 hPa, 500/300 hPa, 300/100 hPa, 50/30 hPa, 30/10 hPa. The modifications allow better use to be made of satellite sounding data in agreement with the vertical resolution given by the satellite instruments. The satellite observation statistics and quality control were revised. 11 August 1987 A problem with the stratospheric SATEMs during early August caused the analysis to develop an erroneous warm dome in the 50-30 hPa thickness field over the Antarctic which was fixed on 11 August. 27 October 1987 Observations at North Pole were included in data selection. The humidity analysis data selection criteria were made consistent with mass and wind analysis. 8 December 1987 The first-guess rejection limit for winds was tightened and an asymmetric first-guess check on extra-tropical cloud track winds was introduced. 5 January 1988 Forecast model cycle 30. A revised vertical diffusion scheme was implemented. The turbulent diffusion is now limited to below the top of the boundary layer except when static instability is generated. This modification restricts the vertical mixing to the boundary layer. The reduction of dissipation and momentum and heat mixing in the free atmosphere has a positive impact on zonal mean temperatures and reduces the zonal wind errors. The eddy activity becomes stronger. Modest modifications in the parameterization of the surface processes were included. The revision of the numerical scheme affects the partitioning of the surface moisture flux in terms of water extraction from the various contributing reservoirs. The interaction between convective precipitation and surface hydrology was revised as well as the interaction between the radiation and both the canopy layer and the snow. The new surface parameters are only marginally influenced by these changes except in the case when snow is melting. Now the surface temperatures are allowed to be positive even with snow on the ground. 26 January 1988 Divergent structure functions were included in wind correlation's of the analysis. The divergent structure functions improved the analysis significantly especially in the Tropics but the improvements were found short-lived during the assimilation cycle. 1 March 1988 The revision of the MARS interpolation software affects especially the surface orographic field of the ECMWF/TOGA Level III Basic Data Set. 12 July 1988 To minimize the impact of bad data in the data assimilation system the quality control algorithm have been modified which includes a more efficient OI check of SATEMs in areas with sufficient non-SATEM data and a general tightening of first-guess and OI rejection limits. The structure functions were modified, resulting in an increased effective horizontal and vertical analysis resolution. 22 November 1988 Forecast model cycle 31. A modification of the surface scheme was implemented in order to correct some of the deficiencies of 2 m temperature forecast. 1. The root profile was adjusted. The values of the root percentage in each of the 2 soil layers are now 50% (70%) intermediate layer and a 0% (15%) in the climate layer (percentage values within the brackets are valid for the old scheme). In the absence of precipitation no root extraction is allowed from the climate reservoir. 2. The background vegetation cover in dry situations was changed. No plant transpiration is allowed if the soil wetness in the root zone is lower than a threshold value. The background vegetation cover is not decreased linearly to 0 when the root soil wetness decreases to 0. 14 December 1988 A change was made to the analysis, to prevent uncontrolled growth of spurious vortices at the top level of the model. 9.3 Calculations. 9.3.1 Special Corrections/Adjustments. Below is a description of the regridding procedures, performed by the NASA Goddard DAAC, used on the ECMWF data: 1) Converted the original ECMWF (1.125 x 1.125 degree) grid point to (1.125 x 1.125 degree) grid area. This was done by averaging the four grid point corners for each grid area. 2) The grid area data values were then replicated along a latitude by the factor that would result in a common multiple. Since the target grid count for the gridded ISLSCP data sets is 360 latitude grids by 180 longitude grids, the factors 360 and 180 were used for replication. Each original grid value along a latitude was then replicated a total of 360 times. Once a latitude band has been replicated, a set of replicated grid values starting at the beginning of the latitude band are summed, averaged and assigned to a grid cell in the target grid. This set of replicated grid cells for determining the target grid parameter value is equal to the number of total original grid cells along a latitude band. For example, if the original grids cell count for a latitude was 144, and the target count was 360, then the number of replicated cells is 51840. From these 51840 cells, consecutive sets of 144 values are summed, averaged and assigned to each of the target grid cells. This method is then repeated for each latitude band. 3) The results of the above steps are then taken, and each data value along a longitude band is replicated using a factor of 180, and then summed, averaged, and assigned to the target grid in much the same manner as before, then repeated for each longitude band. 4) The regridded (1 x 1 degree) ECMWF data were then used to produce monthly 6-hourly means, monthly means, monthly maximum, monthly minimum, and monthly Standard Deviation data files for the appropriate data sets (see section 6.3.2). The monthly 6 hourly mean data were produced by adding a months period of data for each of the four synoptic hours and dividing by the number of days for that particular month. The monthly mean data were then produced from the monthly 6-hourly mean data. 9.4 Graphs and Plots. See "ECMWF, The Description of the ECMWF/WCRP Level III-A Global Atmospheric Data Archive." 10. ERRORS 10.1 Sources of Error. The ECMWF data sets have biases which are only partially documented. Many of the surface and diagnostic field data sets are adapted to a specific model orography. For additional information on orography, see Jarraud et al. (1988), and Miller et al. (1989). See Janssen et al. (1992), for information on sources of error, for the following parameters: 10 meter u-wind velocity 10 meter v-wind velocity u-wind stress v-wind stress See Louis (1979) and Morcrette (1990), for information on sources of error, for the following parameters: surface sensible heat flux surface latent heat flux See Geleyn and Hollingsworth (1979), Morcrette (1990) and Morcrette (1991), for information on sources of error, for the following parameters: surface shortwave radiation surface longwave radiation TOA shortwave radiation TOA longwave radiation 10.2 Quality Assessment. 10.2.1 Data Validation by Source. See sections 9.2.2 and 10.1. 10.2.2 Confidence Level/Accuracy Judgment. See section 10.1. 10.2.3 Measurement Error for Parameters and Variables. See section 10.1. 10.2.4 Additional Quality Assessment Applied. A comparison between 48-hour forecasts from the ECMWF model and area averaged time series for the FIFE 1987 surface data was made by Betts et al. (1993). The comparison of the October 1987 data showed a consistent picture, reflecting five systematic errors in the model. 1) The incoming short-wave radiation is too high in clear-sky conditions, perhaps by as much as 10%. The fixed model albedo is lower than the data in October (the difference was less in August), but this may be unique to this grid point. 2) The ground-surface model, which has a 7 cm thick first surface layer, is too slow to respond to the net radiation after sunrise, and cools too slowly at night. Since this layer must warm before the Sensible Heat transfer to the atmosphere can become upward, the model needs a very large downward ground heat flux after sunrise, as large as 200 [W] [m^-2]. (The error is amplified by a time-truncation problem in the model.) This introduces a day-time phase lag into the upward Sensible Heat flux, and appears also to result in a net heat flux into the ground, even as late in the year as October. 3) The difference between surface temperature and air temperature is too small in the model. This is associated in part with having the same roughness lengths for heat and momentum in the model. 4) The model Latent Heat flux is near zero in October. This results from ground-moisture values below the model threshold for evaporation (set at 30% of the soil field capacity). These are kept low by the soil moisture specified in the climate layer for October. 5) The model Boundary Layer dries out as a result of having no surface Latent Heat flux. The Betts et al. (1993) analysis identified three possible small biases in the 1987 model: they were each about 1-2% and were all additive. 1) The parameterized version of the short-wave radiative code has an incoming flux 1-2% higher than a more exact narrow model. 2) The 1987 code did not include absorption in the shortwave by either the water-vapor continuum or aerosols; each of which might account for another 1-2% reduction in the incoming clear-sky shortwave at the surface. 3) The model's sensible- and latent-heat fluxes lag by about 2 hours because of the slow thermal response of the 7 cm soil layer. This is a result of the model's ground heat flux which is too high during the day-time heating cycle, reaching values in the morning of over 200 [W] [m^-2]. Dr. Robert Dickinson, of the University of Arizona's Department of Atmospheric Sciences, supplied the following quality assessment of the ECMWF parameters. Assessment Parameter ------------ --------------------------------- I. Prescribed/Diagnostic Fields Questionable Albedo Questionable Surface Roughness Length Unreliable Surface Soil Wetness Questionable Deep Soil Temperature Unreliable Deep Soil Wetness Unreliable Climate Deep-Soil Wetness Questionable Climate Deep-Soil Temperature Unreliable Snow Depth II. Monthly 6-hourly Forcing Fields Reliable Temperature at 2m Questionable Dew point Temperature at 2m Reliable Surface Pressure Reliable U-wind at 10 meters Reliable V-wind at 10 meters Questionable U-wind stress Questionable V-wind stress Questionable Surface Temperature Reliable Mean Sea Level Pressure Unreliable Surface Net Shortwave Radiation Questionable Surface Net Longwave Radiation Unreliable TOA Net Shortwave Radiation Unreliable TOA Net Longwave Radiation Unreliable Surface Sensible Heat Flux Unreliable Surface Latent Heat Flux III. Diurnally-resolved (6-hourly) Forcing Fields Reliable Temperature at 2m Questionable Dew point Temperature at 2m Reliable Wind magnitude at 10 meters Reliable Surface Pressure Not available NASA/LaRC, ECMWF hybrid incident SW and LW radiation. Not available NOAA/NMC, GPCP hybrid Total and convective Precipitation. 11. NOTES 11.1 Known Problems With The Data U- and V-Wind Components at the Poles ------------------------------------- In 1991 it was discovered that, on a regular latitude/longitude grid, the ECMWF u- and v- components of wind were incorrect at the poles. The problem was that the horizontal components of wind gave inconsistent polar values of wind magnitude and direction. Changes have been made to the interpolation routines used to create the ECMWF/TOGA Basic Data sets and to extract data from the ECMWF/TOGA Advanced Data Sets and the Supplementary Fields Data Set. These changes have had the following effects on u- and v-wind fields at the poles: Surface data. The grid points at each of the poles will contain horizontal wind components from the nearest neighboring Gaussian latitude circle interpolated to the required resolution. For the 0.5625 degree lat/lon grid (current ECMWF model, 17 September 1991 onwards) model the nearest latitude circle is + or - 89.578132. 11.2 Usage Guidance. No surface observations are used, so that the surface data provided via ECMWF comes from the model simulations of surface processes, strongly constrained by observed atmospheric information and a priori surface climatological information. There were frequent changes in the model (see section 9.2.2 for details), many involving surface processes, over the temporal period of these ECMWF data. Since the surface data are inferred from model calculations constrained by atmospheric data, artificial discontinuities in the data would be expected at the dates of model changes. Users of the Supplementary Fields Data Set should note the following statement which was issued by the Research Department at ECMWF in April 1990. Users of the ECMWF low level wind data, in particular over the oceans, should be aware of an inconsistency that exists between the archived surface stress values and the stresses calculated diagnostically from archived low level wind fields and temperatures. Using the ECMWF parametrization diagnostically for example, produces stresses that are higher than archived model values because of the impact of the time algorithms used for the model's boundary layer scheme. 11.3 Other Relevant Information. The data sets are adapted to a specific model orography; the data sets have biases which are only partially documented (reference list). No surface observations of temperature, specific humidity, precipitation, nor surface wind observations over land were used in the analysis. Model spin-up can seriously affect the flux data. All flux fields, including total cloud cover, are first-guess fields (i.e., 6-hour forecasts). Several fields such as soil moisture, snow depth, deep soil parameters, although included in the analysis data set, are not analyzed but evolve during the data assimilation cycle. The Technical Attachment to the Description of the ECMWF/WCRP Archive should be cited by users in publications (see reference section). 12. REFERENCES 12.1 Satellite/Instrument/Data Processing Documentation. Brankovic, C., and J. Van Maanen, 1985. The ECMWF Climate system. ECMWF Rech. Memo. No 109 51 pp + figs. ECMWF Manual 3: ECMWF forecast model physical parametrization, 3rd Edition. ECMWF Research Department, Shinfield Park, Reading, Berkshire RGE 9AX, England. ECMWF, The Description of the ECMWF/WCRP Level III-A Global Atmospheric Data Archive. ECMWF Operations Department Shinfield Park, Reading, Berkshire RGE 9AX, England. 12.2 Journal Articles and Study Reports. Alexander, R. C. and R. L. Mobley, 1974. Monthly average sea-surface temperatures and ice-pack limits for 1 degree global grid. RAND Rep. R01310-ARPA, 30 pp. Baumgartner, A., H. Mayer and W. Metz, 1977. Weltweite Verteilung des Rauhigkeitsparameters z(o) mit Anwendung auf die Energiedissipation and der Erdoberflache. Meteor. Rundschau., 30:43-48. Betts, A.K., J.H. Ball, and A.C.M. Beljaars, 1993. Comparison between the land surface response of the ECMWF model and the FIFE-1987 data. Q.J.R. Meteorol. Soc., 119:975-1001. Dewey, K. F. and R. Heim, Jr., 1982. Variations in Northern Hemisphere snow cover utilizing digitized weekly charts from satellite imagery, 1967-1980. Proceedings of the 6th Annual Climate Diagnostics Workshop, Palisades, N.Y., 157-165. Dorman, J.L. and P.J. Sellers, 1989. A global climatology of albedo, roughness length and stomatal resistance for atmospheric general circulation models as represented by the simple biosphere model (SiB). J.A.M., 28(9):833-855. Elsaser, W. M., 1942. Heat transfer by infrared radiation in the atmosphere. Harvard Meteorological Studies No. 6, 107 pp. Fouqart, Y., and B. Bonnel, 1980. Computations of solar heating of the earth's atmosphere: a new parameterization. Beitr. Phys. Atmos., 53:35-62 Geleyn, J. F., A. Hollingsworth, 1979. An economical analytical method for the computation of the interaction between scattering and line absorption of radiation. Beitr. Phys. Atmos., 52:1-16. Geleyn, J. F. and H. J. Preuss, 1983. A new data set of satellite- derived surface albedo values for operational use at ECMWF. Arch. Meteor. Geophys. Bioclim., Ser. A, 32:353-359. Janssen, P. A. E. M., A. C. M. Beljaar, A. Simmons, and P. Viterbo, 1992. The determination of the surface stress in an atmospheric model. Mon. Wea. Rev., 120:2977-2985. Jarraud, M., A. J. Simmons, and M. Kanamitsu, 1988. Sensitivity of medium-range weather forecast to the use of an envelope orography. Q. J. Royal Meteorol. Soc., 114:989-1025. Louis, J. F., 1979. A parametric model of vertical eddy fluxes in the atmosphere. Boundary Layer Meteorol., 17:187-202. Miller, M. J., T. N. Palmer, and R. Swinbank, 1989. Parametrization and influence of subgridscale orography in general circulation and numerical weather prediction models. Meteorol. Atmos. Phys., 40:84-109. Mintz, Y. and Y. Serafini, 1981. Global fields of soil moisture and land-surface evapotranspiration. NASA Goddard Space Flight Center Tech. Memo. 83907, Research review - 1980/81:178-180. Morcrette J. J., 1990. Impact of changes to the radiation transfer parameterizations plus cloud optical properties in the ECMWF model. Mon. Wea. Rev., 118:847-872. Morcrette J. J., 1991. Radiation and cloud radiative properties in the European Center for Medium Range Weather Forecasts forecasting system. J. Geophysical Res., 96(5)9121-9132. Preuss, J. H. and J. F. Geleyn, 1980. Surface albedos derived from satellite data and their impact of forecast models. Arch Meteor. Geophys. Biocl., Ser. A, 29:345-356. Rogers, C. D., and C. D. Walshaw, 1966. The computation of the infrared cooling rate in planetary atmospheres. Quart. J. Royal. Meteor. Soc., 92:67-92. Taljaard, J. J., H. van Loon, H. L. Crutcher, and R. L. Jenne, 1969. Climate of the upper air, Part 1 - Southern Hemisphere; Temperatures, dew points and heights at selected pressure levels. NAVAIR Atlas 50-1C-55, 135 pp. [Government Printing Office, Washington, D.C.] Tibaldi, S. and J. F. Geleyn, 1981. The production of a new orography land-sea mask and associated climatological surface fields for operational purposes. ECMWF Tech. Memo. No. 40, 13 pp. Welch, T.A., 1984. A Technique for High Performance Data Compression. IEEE Computer, 17(6):8-19. 12.3 Archive/DBMS Usage Documentation. GSFC DAAC User Services NASA/Goddard Space Flight Center Code 902.2 Greenbelt, MD 20771 Phone: (301) 286-3209 Fax: (301) 286-1775 Internet: daacuso@eosdata.gsfc.nasa.gov 13.2 Archive Identification. Goddard Distributed Active Archive Center NASA Goddard Space Flight Center Code 902.2 Greenbelt, MD 20771 Telephone: (301) 286-3209 FAX: (301) 286-1775 Internet: daacuso@eosdata.gsfc.nasa.gov 13.3 Procedures for Obtaining Data. Users may place requests by accessing the on-line system, by sending letters, electronic mail, FAX, telephone, or personal visit. Accessing the GSFC DAAC Online System: The GSFC DAAC Information Management System (IMS) allows users to ordering data sets stored on-line. The system is open to the public. Access Instructions: Node name: daac.gsfc.nasa.gov Node number: 192.107.190.139 Login example: telnet daac.gsfc.nasa.gov Username: daacims password: gsfcdaac You will be asked to register your name and address during your first session. Ordering CD-ROMs: To order CD-ROMs (available through the Goddard DAAC) users should contact the Goddard DAAC User Support Office (see section 13.2). 13.4 GSFC DAAC Status/Plans. The ISLSCP Initiative I CD-ROM is available from the Goddard DAAC. 14. OUTPUT PRODUCTS AND AVAILABILITY 14.1 Tape Products. The ECMWF Level III-A data can be obtained on tape from ECMWF. ECMWF Forecasts Shinfield Park Reading/Berkshire RG2 9AX, United Kingdom 14.2 Film Products. None. 14.3 Other Products. None. 15. GLOSSARY OF ACRONYMS CD-ROM Compact Disk (optical), Read Only Memory CFL Constant Flux Layer DAAC Distributed Active Archive Center ECMWF European Center for Medium-Range Weather Forecasts EOS Earth Observing System GMT Greenwich Mean Time GCM General Circulation Model of the atmosphere GPCP Global Precipitation Climatology Project GSFC Goddard Space Flight Center IDS Inter disciplinary Science ISLSCP International Satellite Land Surface Climatology Project LaRC Langley Research Center LW Longwave radiation NASA National Aeronautics and Space Administration NMC National Meteorological Center NOAA National Oceanic and Atmospheric Administration SiB Simple Biosphere Model SW Shortwave radiation TOA Top of the Atmosphere TOGA Tropical Ocean Global Atmosphere WCRP World Climate Research Project