home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
NASA Global Data Sets for…phere Models 1987 - 1988
/
NASA Global Data Sets for Land-Atmosphere Models 1987 - 1988 - Disc 5.iso
/
document
/
ecmwf.doc
next >
Wrap
Text File
|
1995-04-05
|
91KB
|
1,791 lines
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.
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
