NCAR Global Climate Four-Dimensional Data Assimilation (CFDDA) Hourly 40 km Reanalysis User Documentation Prepared by: National Center for Atmospheric Research (NCAR) Research Applications Laboratory PO Box 3000 Boulder, CO 80307-3000 Revision 3 (07/30/2014)
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GENERAL DESCRIPTION ................................................................................................................................ 2 CLIMATE MODEL .............................................................................................................................................. 2 VERTICAL COORDINATE .................................................................................................................................... 2 HORIZONTAL COORDINATE ............................................................................................................................... 3 TIME COORDINATE ........................................................................................................................................... 3
DATA ORGANIZATION AND FILE NAMING CONVENTION ........................................................................... 4
FILE FORMAT AND STRUCTURE ................................................................................................................... 4 NETCDF DATA MODEL ...................................................................................................................................... 4 DATA COMPRESSION…………………………………………………………………………………...........................5 CLIMATE FORECAST (CF) CONVENTION ............................................................................................................ 5 DIMENSIONS ................................................................................................................................................... 5 VARIABLES ...................................................................................................................................................... 7
Instantaneous fields for 1985-2005 ............................................................................................................ 7 Terrain fields ............................................................................................................................................ 14
FIELD ATTRIBUTES ......................................................................................................................................... 15 GLOBAL ATTRIBUTES ..................................................................................................................................... 16
1) The following attributes associated with MDV functionality can be safely ignored by netCDF users without
impacting the usability of the data files: mdv_master_header, forecast_reference_time, forecast_period, start_time,
stop_time, grid_mapping_0, and grid_mapping_1.
2) Please note that some data files from the earlier time periods also have “z” (geopotential height) variable, but this
parameter is an excess variable, i.e. one can compute geopotential height with available variables: pressure,
temperature, humidity, and terrain height.
Instantaneous fields for 1985-2005
Table 2. Variables contained within the CFDDA hourly files.
Field name
Current Data File Standard
Name Description
Current Data File Long Name Description
- same as Variable
Names shown under NCAR CISL RDA's Document tab for the dataset
(alternate
descriptions)
CF Standard Name
Additional Descriptions
Units
(CF Standard Units)
Type Dimensions
Time time Data time time Time.
seconds since 1970-01-01T00:00:00Z (s) float64
Time 1
z0 atmosphere_sigma_coordinate
sigma p levels atmosphere_sigma_coordinate Atmospheric sigma coordinate.
sigma_level (1) float32
z0 28
z1 surface surface N/A Surface layer.
Layer (N/A) float32
z1 1
U10 U10 10-meter U Component (10-meter U Wind Component)
eastward_wind Instantaneous eastward wind. "Eastward" indicates a vector component which is positive when directed eastward (negative westward). Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.)
Instantaneous northward wind. "Northward" indicates a vector component which is positive when directed northward (negative southward). Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.)
(m s-1
)
int16
(1 1 450 900)
T2C surface_air_temperature
2-meter Temperature in C
air_temperature Instantaneous air temperature is the bulk temperature of the air, not the surface (skin) temperature. “Surface” means at 2 m AGL. Note the units (C) are different from the CF norm (K).
C (K) int16
(time, z1, y0, x0)
(1 1 450 900)
pressure air_pressure Absolute pressure air_pressure Instantaneous air pressure. Note the units (hPa) are different from the CF norm (Pa).
hPa (Pa) int16
(time, z0, y0, x0)
(1 28 450 900)
ground_t ground_t Ground temperature (Temperature at interface of atmosphere and surface)
surface_temperature The surface called "surface" means the lower boundary of the atmosphere. The surface temperature is the temperature at the interface, not the bulk temperature of the medium above or below.
K (K) int16
(time, z1, y0, x0)
(1 1 450 900)
hrain_total total_precipitation_rate
Hourly rain total - con + non ( Hourly rain total: con + non (convective + large scale))
lwe_precipitation_rate "lwe" means liquid water equivalent. Instantaneous depth or thickness of the layer formed by precipitation per unit time. “Total” is convective plus explicit precipitation. “Convective” precipitation is that produced by the convection schemes in an atmosphere model. Note the units (mm hr
-1) are different from
the CF norm (m s-1
).
mm hr-1
(m s-1
)
int8
(time, z1, y0, x0)
(1 1 450 900)
hraincon convective_precipitation_rate
Hourly Rain total, Convective (Hourly total precipitation (convective + stratiform))
lwe_convective_precipitation_rate "lwe" means liquid water equivalent. Instantaneous depth or thickness of the layer formed by precipitation per unit time. “Convective” precipitation is that produced by the convection schemes in an atmosphere model. Note the units (cm hr
surface_upward_latent_heat_flux The surface called "surface" means the lower boundary of the atmosphere. "Upward" indicates a vector component which is positive when directed upward (negative downward). The surface latent heat flux is the exchange of heat between the surface and the air on account of evaporation (including sublimation). In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.
W m-2
(W m-2
) int8
(time, z1, y0, x0)
(1 1 450 900)
pressure2 surface_air_pressure
Mean sea level pressure at 2 meters (Mean sea level pressure)
air_pressure_at_sea_level sea_level means mean sea level, which is close to the geoid in sea areas. Air pressure at sea level is the quantity often abbreviated as MSLP or PMSL. Note the units (hPa) are different from the CF norm (Pa).
hPa (Pa) int8
(time, z1, y0, x0)
(1 1 450 900)
pbl_hgt atmosphere_boundary_layer_thickness
Pbl height (Atmospheric Boundary Layer Height)
atmosphere_boundary_layer_thickness The atmosphere boundary layer thickness is the "depth" or "height" of the (atmosphere) planetary boundary layer.
m (m) int8
(time, z1, y0, x0)
(1 1 450 900)
rwp
rwp Rain Water Path (Liquid Water Path)
atmosphere_mass_content_of_water "Content" indicates a quantity per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. "Water" typically means water in all phases for this variable. However, for CFDDA’s data files, we mean liquid water only (not the ice or vapor phases). This variable includes liquid phase water both within clouds and falling as precipitation. Note the units (g m
relative_humidity Instantaneous relative humidity with respect to water at 2m AGL.
% (%) int8
(time, z1, y0, x0)
(1 1 450 900)
shflux surface_upward_sensible_heat_flux
Sensible heat flux (Sensible heat flux at surface)
surface_upward_sensible_heat_flux The surface called "surface" means the lower boundary of the atmosphere. "Upward" indicates a vector component which is positive when directed upward (negative downward). The surface sensible heat flux, also called "turbulent" heat flux, is the exchange of heat between the surface and the air by motion of air. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.
W m-2
(W m-2
)
int8
(time, z1, y0, x0)
(1 1 450 900)
soil_m_1 soil_m_1
Soil moisture in layer 1 (Volumetric moisture content in the upper 10cm soil layer)
moisture_content_of_soil_layer "moisture" means water in all phases contained in soil. "Content" indicates a quantity per unit area. Note however that here, the soil moisture is not expressed in quantity per unit area; it is the volumetric soil moisture, but there is no CF-compliant standard name for volumetric soil moisture. “Layer” means topmost 10 cm soil layer.
m3 m
-3
(kg m
-2)
int16
(time, z1, y0, x0)
(1 1 450 900)
soil_t_1 soil_t_1 Soil temperature in layer 1 (Temperature in upper 10cm soil layer)
soil_temperature Soil temperature is the bulk temperature of the soil, not the surface (skin) temperature. “Layer” means topmost 10 cm soil layer.
K (K) int16
(time, z1, y0, x0)
(1 1 450 900)
tot_cld_con
tot_cld_con Sum of CLW and ICE (Mass of liquid and ice phase hydrometeors in layer in clouds)
mass_content_of_cloud_condensed_water_in_atmosphere_layer alias: cloud_condensed_water_content_of_atmosphere_layer "condensed_water" means liquid and ice. "Content" indicates a quantity per unit area. "Layer" means any layer with upper and lower boundaries that have constant values in some vertical coordinate. This variable includes liquid and ice phase water within clouds. Note the
surface_downwelling_longwave_flux_in_air alias: surface_downwelling_longwave_flux The surface called "surface" means the lower boundary of the atmosphere. "longwave" means longwave radiation. Downwelling radiation is radiation from above. It does not mean "net downward". When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.
surface_downwelling_shortwave_flux_in_air alias: surface_downwelling_shortwave_flux The surface called "surface" means the lower boundary of the atmosphere. "shortwave" means shortwave radiation. Downwelling radiation is radiation from above. It does not mean "net downward". Surface downwelling shortwave is the sum of direct and diffuse solar radiation incident on the surface, and is sometimes called "global radiation". When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.
Instantaneous air temperature is the bulk temperature of the air, not the surface (skin) temperature. Note the units (C) are different from the CF norm (K).
(K) int16
(1 28 450 900)
twp
twp Total Water Path atmosphere_mass_content_of_water "Content" indicates a quantity per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. "Water" typically means water in all phases for this variable. However, for CFDDA’s data files, we mean liquid and ice phases only (not the vapor phase). This variable includes liquid and ice phase water both within clouds and falling as precipitation. Note the units (g m
-2) are different from
the CF norm (kg m-2
).
g m-2
(kg m
-2)
int16
(time, z1, y0, x0)
(1 1 450 900)
U eastward_wind
u-component of wind
eastward_wind Instantaneous eastward wind. "Eastward" indicates a vector component which is positive when directed eastward (negative westward). Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.)
m s-1
(m s-1
)
int16
(time, z0, y0, x0)
(1 28 450 900)
V northward_wind
v-component of wind eastward_wind Instantaneous eastward wind. "Eastward" indicates a vector component which is positive when directed eastward (negative westward). Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.)
m s-1
(m s-1
)
Int8
(time, z0, y0, x0)
(1 28 450 900)
clwp
clwp Vertically Integrated CLW (Vertical Column Integral of Liquid Hydrometeors in clouds)
atmosphere_mass_content_of_cloud_liquid_water alias: atmosphere_cloud_liquid_water_content "Content" indicates a quantity
per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. This variable includes liquid phase water within clouds. Note the units (g m
-2) are different from the CF
norm (kg m-2
).
tot_cld_conp
tot_cld_conp
Vetrically Integrated TOT_CLD_CON (Vertical Column Integral of Liquid and Ice Hydrometeors in clouds)
atmosphere_mass_content_of_cloud_condensed_water alias: atmosphere_cloud_condensed_water_content "condensed_water" means liquid and ice. "Content" indicates a quantity per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. This variable includes liquid and ice phase water within clouds. Note the units (g m
-2) are different
from the CF norm (kg m-2
).
g m-2
(kg m
-2)
int16
(time, z1, y0, x0)
(1 1 450 900)
W upward_air_velocity
w-component of wind
upward_air_velocity Instantaneous vertical velocity. A velocity is a vector quantity. "Upward" indicates a vector component which is positive when directed upward (negative downward). Upward air velocity is the vertical component of the 3D air velocity vector.
m s-1
(m s-1
) int8
(time, z0, y0, x0)
(1 28 450 900)
weasd weasd Water equivalent snow depth
lwe_thickness_of_surface_snow_amount The surface called "surface" means the lower boundary of the atmosphere. "lwe" means liquid water equivalent. "Amount" means mass per unit area. The construction lwe_thickness_of_X_amount or _content means the vertical extent of a layer of liquid water having the same mass per unit area. Surface amount refers to the amount on the ground, excluding that on the plant or vegetation canopy. Note the units (mm) are different from the CF norm (m).
Table 3. Variables contained within the TERRAIN files.
Field name Description
Units
Type Dimensions
x0 longitude Longitude is positive eastward; its units of degree_east (or equivalent) indicate this explicitly.
degrees_east float32
x0 900
y0 latitude Latitude is positive northward; its units of degree_north (or equivalent) indicate this explicitly.
degrees_north float32
y0 450
z0 surface Level float32
z0 1
time time Time.
seconds since 1970-01-01T00:00:00Z float64
time 1
terrain surface_altitude The surface called “surface” means the lower boundary of the atmosphere. Altitude is the (geometric) height above the geoid, which is the reference geopotential surface. The geoid is similar to mean sea level.
m float32
(time, z0, y0, x0) (1 x 1 x 450 x 900)
land_use land_use Land cover category (see http://www.mmm.ucar.edu/mm5/mm5v2/landuse-usgs-tbl.html).
Each variable will have several useful metadata attributes, all of which are required by the CF conventions as listed in
Table 4.
Table 4. Attributes for all fields in the CFDDA reanlaysis dataset.
Attribute name Type Description
_FillValue float32 Floating-point value used to identify missing data.
valid_min float32 Smallest valid value of a variable. Required by CF when data are stored using packing.
valid_max float32
Largest valid value of a variable. Required by CF when data are stored using packing.
long_name string Ad hoc description of the variable.
standard_name string Standard description of the variable as defined in CF conventions.
units string The units of the variable. String is recognized by the Unidata Udunits package.
scale_factor float32 If variable is packed as 16-bit or 8-bit integers, they are to be multiplied by the scale_factor when the data are read, to recover floating point values.
add_offset float32 If variable is packed as 16-bit or 8-bit integers, they first must be multiplied by the scale_factor, and then have the add_offset added to them to recover floating point values.
In addition to metadata provided for each field, global metadata is also stored in the CFDDA reanlaysis files. Most of the
global metadata are required by the CF conventions, while others are included as a matter of record. A summary of global
attributes present in all CFDDA reanlaysis files is shown in Table 5.
Table 5. Global attributes for all CFDDA reanlaysis files.
Attribute name Type Description
Conventions string Identification of the file convention used, currently “CF-1.0”.
history string Software library used to create file.
source string Where data originated.
title string Name of dataset.
ref_sea_level_pressure string Reference sea level pressure for calculating model base state atmosphere. Provides a time invariant height for each sigma-p surface.
pressure_at_model_top string Reference pressure at model top for calculating model base state atmosphere. Provides a time invariant height for each sigma-p surface.
ref_sea_level_temperature string Reference sea level temperature for calculating model base state atmosphere. Provides a time invariant height for each sigma-p surface.
ref_temperature_lapse_rate string Reference tempeature lapse rate for calculating model base state atmosphere. Provides a time invariant height for each sigma-p surface.
TISO string Temperature at which the reference temperature becomes constant, for those vertical levels that extend into the stratosphere.
gravitational_constant string Value used for gravitational constant in analyses.
Universal_gas_constant string Value used for universal gas constant in analyses.
Version string Database version; currently “1.3”.
release_date string Date of release.
_Format string File format and structure. “netCDF-4 classic model”