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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)

© 2014 University Corporation for Atmospheric Research. All rights reserved. 1

Table of Contents

INTRODUCTION ............................................................................................................................................... 2

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

REFERENCES ................................................................................................................................................ 17

APPENDIX A: SAMPLE HEADER FOR INSTANTANEOUS FIELDS FOR 1985-2005 .................................. 18

APPENDIX B: HEADER FOR TERRAIN FILE ................................................................................................ 23


Introduction

This document describes the global reanalysis dataset created by the National Center for Atmospheric Research (NCAR)

Research Applications Laboratory (RAL) under sponsorship from the Defense Threat Reduction Agency (DTRA). This

new dataset represents the global atmospheric state with unprecedented spatial and temporal detail. The dataset is formed

from a 21-year collection of hourly, global meso-beta scale reanalyses (0.4º grid increment) from 1985 to 2005; the era of

modern global satellite observations. Instantaneous hourly, three-dimensional analyses of the global atmospheric state for

the entire 21-year period are included in the dataset.

General Description

Climate Model

The global reanalysis was created using NCAR’s Climate Four-Dimensional Data Assimilation system (CFDDA)

(Hahmann et al. 2010). CFDDA is a state-of-the-art dynamical downscaling system for generating high-resolution

climatographic analyses for any part of the world. At the heart of CFDDA is NCAR’s Real Time Four-Dimensional Data

Assimilation (RTFDDA) system (Liu et al. 2008), a mesocale-model-based assimilation and forecasting system with

versions based upon both the Pennsylvania State University (PSU)/NCAR mesoscale model (MM5) and its sequel, the

Weather Research and Forecasting (WRF) Model (Skamarock et al. 2008). For the dataset described herein, we use the

MM5-based version (version 3.6) of CFDDA (Grell et al. 1994) to create global hourly analyses on a 40-km horizontal

grid, with 28 vertical levels covering the period 1985-2005. The result is a dataset of 21 years 365 days 24 hours,

three-dimensional analyses.

CFDDA continuously assimilates standard surface and upper-air observations. Observation data include both hourly and

6-hourly surface data reports that are primarily land based, but a few ship observations also exist. Upper-air

measurements are also used and consist primarily of standard rawinsonde measurements, typically at 12- and 24-hourly

intervals. Initial land surface conditions for the CFDDA analyses are based on the NASA Global Land Data Assimilation

System (GLDAS) (Rodell et al. 2004) on a 1° × 1° latitude-longitude grid, compiled using the Noah land surface model

(LSM) (Chen and Dudhia 2001a,b). GLDAS values of substrate soil moisture and temperature, ground skin temperature

and snow water equivalent are used. Daily sea-surface temperatures (SSTs) are specified by the National Centers for

Environmental Prediction (NCEP) Version 2.0 global, daily SST dataset (OISST) (Reynolds et al. 2002), defined on a

0.25 0.25 grid.

Full details for CFDDA’s global configuration can be found in Rife et al. (2010).

Vertical Coordinate

The CFDDA global reanlaysis uses the terrain-following sigma-p coordinate, with 28 levels extending from about 15 m

Above Ground Level (AGL) through approximately 19 km AGL, and ~15 vertical layers within the first 1.5 km AGL.

The model top is specified at 30 hPa. Table 1 lists the nominal pressure and height of each layer. Actual values at each

grid point and time vary.


Table 1. Vertical structure of the CFDDA renalysis files. Pressures and heights are nominal, and are based on a standard

sea level pressure of 1013.25 hPa.

Level Half sigma Reference

pressure (hPa) Reference height

(m AGL)

28 0.9981 1011.4 15.7 27 0.9930 1006.4 58.1 26 0.9861 999.6 115.1 25 0.9784 992.0 179.2 24 0.9699 983.7 250.9 23 0.9605 974.4 330.9 22 0.9500 964.1 420.2 21 0.9384 952.7 520.0 20 0.9256 940.1 631.5 19 0.9115 926.2 756.1 18 0.8959 910.9 895.3 17 0.8787 894.0 1050.9 16 0.8598 875.4 1225.0 15 0.8391 855.0 1419.6 14 0.8163 832.6 1637.4 13 0.7915 808.2 1881.3 12 0.7643 781.5 2153.8 11 0.7348 752.5 2459.3 10 0.7028 721.0 2801.6 9 0.6683 687.1 3185.5 8 0.6105 630.3 3863.1 7 0.5258 547.0 4952.8 6 0.4317 454.5 6332.3 5 0.3306 355.1 8091.7 4 0.2269 253.1 10359.1 3 0.1356 163.3 13040.9 2 0.0680 96.9 15875.6 1 0.0199 49.6 18920.2

Horizontal Coordinate

The CFDDA reanlaysis files are defined on a global equidistant latitude-longitude grid, whose increment is 0.4°. This

resolution was chosen to be similar to the nominal (~ 40 km) native MM5 grid on which the climate analysis was

performed. The dimensions of the global grid are (450 900) in latitude and longitude, respectively.

Time Coordinate

Each output file in the dataset contains the hourly instantaneous three-dimensional analysis of the global atmospheric state

for a given time. Specifically, there are output files for 0000 UTC, 0100 UTC, 0200 UTC, 0300 UTC, and so forth on

through to 2300 UTC. The output for each month, day, and hour are stored in separate files, for a total 24 hourly files

365 days 21 years for 1985-2005. Thus, the total dataset consists of 184,080 files (accounting for leap years).


Data Organization and File Naming Convention

The CFDDA hourly instantaneous fields for 1985-2005 are organized in separate directories, using an intuitive

hierarchical directory and file naming convention.

FS/DSS/DS604.0/YYYY/YYYYMMDD/CFDDA_YYYYMMDDhhmmss.mdv.nc

Where: YYYY is the four digit year, MM is the two digit month, DD is the two digit day, hh is the two digit hour, mm is

the two digit minute (UTC), and ss is the two digit second.

Given these rules, the directory containing the hourly fields for the 15th of July 2005 is named as follows:

FS |-- DSS | |-- DS604.0 | | |-- |2005 | | | |-- 20050715 | | | | |-- CFDDA_20050715000000.mdv.nc | | | | |-- CFDDA_20050715010000.mdv.nc | | | | |-- CFDDA_20050715020000.mdv.nc | | | | |-- CFDDA_20050715030000.mdv.nc | | | | |-- CFDDA_20050715040000.mdv.nc | | | | |-- CFDDA_20050715050000.mdv.nc | | | | |-- CFDDA_20050715060000.mdv.nc | | | | |-- CFDDA_20050715070000.mdv.nc | | | | |-- CFDDA_20050715080000.mdv.nc | | | | |-- CFDDA_20050715090000.mdv.nc | | | | |-- CFDDA_20050715100000.mdv.nc | | | | |-- CFDDA_20050715110000.mdv.nc | | | | |-- CFDDA_20050715120000.mdv.nc | | | | |-- CFDDA_20050715130000.mdv.nc | | | | |-- CFDDA_20050715140000.mdv.nc | | | | |-- CFDDA_20050715150000.mdv.nc | | | | |-- CFDDA_20050715160000.mdv.nc | | | | |-- CFDDA_20050715170000.mdv.nc | | | | |-- CFDDA_20050715180000.mdv.nc | | | | |-- CFDDA_20050715190000.mdv.nc | | | | |-- CFDDA_20050715200000.mdv.nc | | | | |-- CFDDA_20050715210000.mdv.nc | | | | |-- CFDDA_20050715220000.mdv.nc | | | | |-- CFDDA_20050715230000.mdv.nc File Format and Structure

netCDF4 Data Model

CFDDA reanalysis dataset files are stored in Network Common Data Form Version 4 (netCDF-4) format, which is an

extension of the Hierarchical Data Format Version 5 (HDF-5), developed jointly by the National Center for

Supercomputing Applications http://www.hdfgroup.org/HDF5 and the Unidata Program Center

http://www.unidata.ucar.edu/software/netcdf/. netCDF-4 is a freely-distributed collection of data access libraries for C,

Fortran, C++, Java, and other languages. The netCDF-4 libraries provide a machine-independent format for representing

scientific data. Together, the interfaces, libraries, and format support the creation, access, and sharing of scientific data.

Quoting from the Unidata Web site:

netCDF data is:

http://www.hdfgroup.org/HDF5

http://www.unidata.ucar.edu/software/netcdf/


Self-Describing. A netCDF file includes information about the data it contains.

Portable. Computers with different ways of storing integers, characters, and floating-point numbers can access a

netCDF file.

Scalable. A small subset of a large dataset may be accessed efficiently.

Appendable. Data may be appended to a properly structured netCDF file without copying the dataset or redefining

its structure.

Sharable. One writer and multiple readers may simultaneously access the same netCDF file.

Archivable. Access to all earlier forms of netCDF data will be supported by current and future versions of the

software.

Each CFDDA reanlaysis file contains atmospheric quantities for a single hourly output. These quantities are referred to as

“fields” or “variables.” The TERRAIN files contain 2-D variables on a longitude-latitude grid, while the remaining files

contain a mix of 2-D and 3-D variables on the same longitude-latitude grid, but with a vertical dimension applicable to all

the 3-D variables.

The files are created using the NCAR’s Met Data Volume infrastructure, which stores them as netCDF-4 classic model

(see the netCDF User’s Guide available from the Unidata Web site http://www.unidata.ucar.edu/software/netcdf/). Thus,

the files can be read with standard netCDF routines and utilities. There are many freely available utilities for reading and

plotting netCDF-4 data, as listed on the Unidata netCDF Web site.

In addition to the atmospheric variables, the files have arrays that define dimensions (or coordinate variables) of each field.

There are 4 distinct coordinate variables: time, latitude, longitude, and vertical level. This ensures that a wide variety of

libraries, utilities, and graphical display tools can interpret the data.

Data Compression

Due to the large size of the CFDDA reanlaysis dataset, all fields are compressed using packing and compression. Packing

reduces the data volume by decreasing the precision of the stored numbers. It is implemented by storing the original

floating point values as either 2-byte integers (short) or 1-byte integers (byte) with a scale and offset. Thus, when the data

are read, they are to be multiplied by the scale_factor, and then have the add_offset added to them according to:

floating_point_array = (file_array * scale_factor) + add_offset. The attributes for most variables will have the

scale_factor and add_offset specified, as described in the Attributes section below. Although the packing method

degrades the precision of the data, great care is taken to ensure that differences between the compressed output and the

original (uncompressed) data are not scientifically meaningful. Once the precision has been decreased, the files are

written using the standard gzip compression available in netCDF-4. gzip compression provides an additional level of

storage efficiency, results in no loss of precision, and is transparent to the user.

Climate Forecast (CF) Convention

The files conform to the netCDF Climate and Forecast (CF) Metadata Conventions (http://cf-pcmdi.llnl.gov). The

conventions define metadata that provide a definitive description of what the data in each variable represents, and of the

spatial and temporal properties of the data. Extensive metadata also provides a precise definition of each variable via

specification of a standard name. It also describes the vertical locations corresponding to dimensionless vertical

coordinate values, and provides the spatial coordinates for the gridded data.

Dimensions

CFDDA reanlaysis files contain dimension (or coordinate) information. Each coordinate variable has an attribute named

units and is set to an appropriate string defined by the CF convention.

http://www.unidata.ucar.edu/software/netcdf/

http://cf-pcmdi.llnl.gov/


Table 1. Dimension variables used for all fields in the CFDDA reanlaysis dataset.

Notes: Please note that some data files from the earlier time periods also have x1 and y1 dimension variables. Since these

are the longitude latitude coordinates that are identical to x0 and y0 respectively, x0 and x1 can be used interchangeably,

and likewise, with y0 and y1.

Name Description

Size

Type units attribute

x0 longitude 900

float32 degrees_east

y0 latitude 450

float32 degrees_north

z0 (3D only) layer index 28

float32 sigma_level

z1 (2D only) surface layer 1

float32 level

time seconds since 00:00:00Z on 01 January 1970 1

float64 Seconds since 1970-01-01T00:00:00Z


Variables

Notes:

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.)

m s-1

(m s-1

)

int16

(time, z1, y0, x0)

(1 1 450 900)

V10 V10 10-meter V Component

northward_wind

m s-1

(time, z1, y0, x0)


(10-meter V Wind Component)

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

-1)

are different from the CF norm

cm hr-1

(m s

-1)

int8

(time, z1, y0, x0)

(1 1 450 900)


(m s-1

), and from the total precipitation (mm hr

-1).

Lhflux surface_upward_latent_heat_flux

Latent heat flux (Latent heat flux at surface)

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

-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)

RH relative_humidity

Relative humidity relative_humidity Instantaneous relative humidity

% (%)

(time, z0, y0, x0)


with respect to water. int8

(1 28 450 900)

RH2 surface_relative_humidity

Relative humidity at 2 meters

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

g m-3

(kg m

-2)

int16

(time, z0, y0, x0)

(1 28 450 900)


units (g m-3

) are different from the CF norm (kg m

-2).

lwdown lwdown Surface downward longwave radiation

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.

W m-2

(W m-2

) int8

(time, z1, y0, x0)

(1 1 450 900)

swdown swdown Surface downward shortwave radiation

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.

W m-2

(W m-2

) int8

(time, z1, y0, x0)

(1 1 450 900)

Temp air_temperature

Temperature air_temperature

oC

(time, z0, y0, x0)


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

g m-2

(kg m

-2)

int16

(time, z1, y0, x0)

(1 1 450 900)


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).

mm (m) int16

(time, z1, y0, x0)

(1 1 450 900)


Terrain fields

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).

Category Float32

(time, z0, y0, x0) (1 x 1 x 450 x 900)


Field Attributes

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.


Global Attributes

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”


References

Chen, F., and J. Dudhia, 2001a: Coupling an advanced land-surface/hydrology model with the

Penn State/NCAR MM5 modeling system. Part I: Model implementation and sensitivity. Mon. Wea. Rev., 129, 4,

569–585, doi:http://dx.doi.org/10.1175/1520-0493(2001)129<0569:CAALSH>2.0.CO;2.

Chen, F., and J. Dudhia, 2001b: Coupling an advanced land-surface/hydrology model with the

Penn State/NCAR MM5 modeling system. Part II: Model validation. Mon. Wea. Rev., 129, 4, 587–604,

doi:http://dx.doi.org/10.1175/1520-0493(2001)129<0587:CAALSH>2.0.CO;2.

Grell, G. A., J. Dudhia, and D. R. Stauffer, 1994: A description of the fifth-generation Penn

State/NCAR mesoscale model (MM5). NCAR Technical Note, NCAR/TN-398+STR, doi:10.5065/D60Z716B.

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S. P. Swerdlin, 2010: A reanalysis system for the generation of mesoscale climatographies. J. Appl. Meteorol.

Climatol, 49, 5, 954-972, doi:http://dx.doi.org/10.1175/2009JAMC2351.1.

Liu, Y., and Coauthors, 2008: The operational mesogamma-scale analysis and forecast system

of the U.S. Army Test and Evaluation Command. Part 1: Overview of the modeling system, the forecast products,

and how the products are used. J. Appl. Meteor. Climatol., 47, 4, 1077–1092,

doi:http://dx.doi.org/10.1175/2007JAMC1653.1.

Reynolds, R. W., N. A. Rayner, T. M. Smith, D. C. Stokes, and W. Q. Wang, 2002: An improved

in situ and satellite SST analysis for climate. J. Climate, 15, 13, 1609-1625, doi:http://dx.doi.org/10.1175/1520-

0442(2002)015<1609:AIISAS>2.0.CO;2.

Rife, D. L., J. O. Pinto, A. J. Monaghan, C. A. Davis, and J. R. Hannan, 2010: Global distribution

and characteristics of diurnally varying low-level jets. J. Climate, 23, 19, 5041-5064, doi:

http://dx.doi.org/10.1175/2010JCLI3514.1.

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Soc., 85, 3, 381–394, doi: http://dx.doi.org/10.1175/BAMS-85-3-381.

Skamarock, W. C., J.B. Klemp, J. Dudhia, D.O. Gill, D. Barker, M.G. Duda, X.-Y. Huang, and W.

Wang, 2008: A description of the advanced research WRF Version 3. NCAR Technical Note, NCAR/TN475+STR,

doi:10.5065/D68S4MVH.


Appendix A: Sample header for instantaneous fields for 1985-2005

netcdf \120000.mdv {

dimensions:

time = 1 ;

bounds = 2 ;

x0 = 900 ;

y0 = 450 ;

z0 = 28 ;

z1 = 1 ;

variables:

double time(time) ;

time:standard_name = “time” ;

time:long_name = “Data time” ;

time:units = “seconds since 1970-01-01T00:00:00Z” ;

time:axis = “T” ;

time:bounds = “time_bounds” ;

time:comment = “2005-07-15T12:00:00Z” ;

double start_time(time) ;

start_time:units = “seconds since 1970-01-01T00:00:00Z” ;

start_time:comment = “2005-07-15T12:00:00Z” ;

double stop_time(time) ;

stop_time:units = “seconds since 1970-01-01T00:00:00Z” ;

stop_time:comment = “2005-07-15T12:00:00Z” ;

float x0(x0) ;

x0:standard_name = “longitude” ;

x0:long_name = “longitude” ;

x0:units = “degrees_east” ;

x0:axis = “X” ;

float y0(y0) ;

y0:standard_name = “latitude” ;

y0:long_name = “latitude” ;

y0:units = “degrees_north” ;

y0:axis = “Y” ;

float z0(z0) ;

z0:standard_name = “atmosphere_sigma_coordinate” ;

z0:long_name = “sigma p levels” ;

z0:units = “sigma_level” ;

z0:positive = “up” ;

z0:axis = “Z” ;

float z1(z1) ;

z1:long_name = “surface” ;

z1:units = “level” ;

z1:positive = “up” ;

z1:axis = “Z” ;

int grid_mapping_0 ;

grid_mapping_0:grid_mapping_name = “latitude_longitude” ;

short U(time, z0, y0, x0) ;

U:scale_factor = 0.001828242f ;

U:add_offset = 11.98899f ;

U:valid_min = -32767s ;

U:valid_max = 32767s ;

U:_FillValue = -32768s ;

U:standard_name = “eastward_wind” ;

U:long_name = “u-component of wind” ;

U:units = “m/s” ;

short V(time, z0, y0, x0) ;

V:scale_factor = 0.001329695f ;

V:add_offset = -2.152804f ;

V:valid_min = -32767s ;

V:valid_max = 32767s ;

V:_FillValue = -32768s ;

V:standard_name = “northward_wind” ;

V:long_name = “v-component of wind” ;


V:units = “m/s” ;

short W(time, z0, y0, x0) ;

W:scale_factor = 2.177236e-05f ;

W:add_offset = 0.354409f ;

W:valid_min = -32767s ;

W:valid_max = 32767s ;

W:_FillValue = -32768s ;

W:standard_name = “upward_air_velocity” ;

W:long_name = “w-component of wind” ;

W:units = “m/s” ;

short Temp(time, z0, y0, x0) ;

Temp:scale_factor = 0.002128154f ;

Temp:add_offset = -21.75333f ;

Temp:valid_min = -32767s ;

Temp:valid_max = 32767s ;

Temp:_FillValue = -32768s ;

Temp:standard_name = “air_temperature” ;

Temp:long_name = “Temperature” ;

Temp:units = “C” ;

short RH(time, z0, y0, x0) ;

RH:scale_factor = 0.001526718f ;

RH:add_offset = 49.99542f ;

RH:valid_min = -32767s ;

RH:valid_max = 32767s ;

RH:_FillValue = -32768s ;

RH:standard_name = “relative_humidity” ;

RH:long_name = “Relative humidity” ;

RH:units = “%” ;

float pressure(time, z0, y0, x0) ;

pressure:valid_min = 41.26792f ;

pressure:valid_max = 1034.076f ;

pressure:_FillValue = -9999.f ;

pressure:standard_name = “air_pressure” ;

pressure:long_name = “Absolute pressure” ;

pressure:units = “hPa” ;

short tot_cld_con(time, z0, y0, x0) ;

tot_cld_con:scale_factor = 1.533216e-07f ;

tot_cld_con:add_offset = 0.005020821f ;

tot_cld_con:valid_min = -32767s ;

tot_cld_con:valid_max = 32767s ;

tot_cld_con:_FillValue = -32768s ;

tot_cld_con:standard_name = “cloud_condensed_water_of_atmosphere_layer” ;

tot_cld_con:long_name = “ Sum of CLW and ICE “ ;

tot_cld_con:units = “g m{-3}” ;

short pressure2(time, z1, y0, x0) ;

pressure2:scale_factor = 0.00128017f ;

pressure2:add_offset = 993.9893f ;

pressure2:valid_min = -32767s ;

pressure2:valid_max = 32767s ;

pressure2:_FillValue = -32768s ;

pressure2:standard_name = “surface_air_pressure” ;

pressure2:long_name = “Mean sea level pressure at 2 meters” ;

pressure2:units = “hPa” ;

short weasd(time, z1, y0, x0) ;

weasd:scale_factor = 0.8406123f ;

weasd:add_offset = 27527.53f ;

weasd:valid_min = -32767s ;

weasd:valid_max = 32767s ;

weasd:_FillValue = -32768s ;

weasd:standard_name = “lwe_thickness_of_surface_snow_amount” ;

weasd:long_name = “Water equivalent snow depth” ;

weasd:units = “mm” ;

short hrain_total(time, z1, y0, x0) ;

hrain_total:scale_factor = 0.000573204f ;

hrain_total:add_offset = 18.77071f ;


hrain_total:valid_min = -32767s ;

hrain_total:valid_max = 32767s ;

hrain_total:_FillValue = -32768s ;

hrain_total:standard_name = “total_precipitation_rate” ;

hrain_total:long_name = “Hourly rain total - con + non” ;

hrain_total:units = “mm/hr” ;

short U10(time, z1, y0, x0) ;

U10:scale_factor = 0.0006784003f ;

U10:add_offset = 3.766783f ;

U10:valid_min = -32767s ;

U10:valid_max = 32767s ;

U10:_FillValue = -32768s ;

U10:standard_name = “eastward_wind_at_surface” ;

U10:long_name = “10-meter U Component” ;

U10:units = “m s{-1}” ;

short V10(time, z1, y0, x0) ;

V10:scale_factor = 0.000667928f ;

V10:add_offset = -4.16594f ;

V10:valid_min = -32767s ;

V10:valid_max = 32767s ;

V10:_FillValue = -32768s ;

V10:standard_name = “northward_wind_at_surface” ;

V10:long_name = “10-meter V Component” ;

V10:units = “m s{-1}” ;

V10:mdv_native_vlevel_type = 1 ;

V10:mdv_transform = “none” ;

short RH2(time, z1, y0, x0) ;

RH2:scale_factor = 0.001479879f ;

RH2:add_offset = 51.52953f ;

RH2:valid_min = -32767s ;

RH2:valid_max = 32767s ;

RH2:_FillValue = -32768s ;

RH2:standard_name = “relative_humidity_at_surface” ;

RH2:long_name = “Relative humidity at 2 meters” ;

RH2:units = “%” ;

short T2C(time, z1, y0, x0) ;

T2C:scale_factor = 0.001763607f ;

T2C:add_offset = -5.967218f ;

T2C:valid_min = -32767s ;

T2C:valid_max = 32767s ;

T2C:_FillValue = -32768s ;

T2C:standard_name = “air_temperature_at_surface” ;

T2C:long_name = “2-meter Temperature in C” ;

T2C:units = “C” ;

short shflux(time, z1, y0, x0) ;

shflux:scale_factor = 0.01518277f ;

shflux:add_offset = 371.1822f ;

shflux:valid_min = -32767s ;

shflux:valid_max = 32767s ;

shflux:_FillValue = -32768s ;

shflux:standard_name = “surface_upward_sensible_heat_flux” ;

shflux:long_name = “Sensible heat flux” ;

shflux:units = “W/m^2” ;

short lhflux(time, z1, y0, x0) ;

lhflux:scale_factor = 0.01487515f ;

lhflux:add_offset = 379.1235f ;

lhflux:valid_min = -32767s ;

lhflux:valid_max = 32767s ;

lhflux:_FillValue = -32768s ;

lhflux:standard_name = “surface_upward_latent_heat_flux” ;

lhflux:long_name = “Latent heat flux” ;

lhflux:units = “W/m^2” ;

short pbl_hgt(time, z1, y0, x0) ;

pbl_hgt:scale_factor = 0.0709324f ;

pbl_hgt:add_offset = 2336.878f ;


pbl_hgt:valid_min = -32767s ;

pbl_hgt:valid_max = 32767s ;

pbl_hgt:_FillValue = -32768s ;

pbl_hgt:standard_name = “atmosphere_boundary_layer_thickness” ;

pbl_hgt:long_name = “Pbl height” ;

pbl_hgt:units = “m” ;

short soil_t_1(time, z1, y0, x0) ;

soil_t_1:scale_factor = 0.0018755f ;

soil_t_1:add_offset = 261.5129f ;

soil_t_1:valid_min = -32767s ;

soil_t_1:valid_max = 32767s ;

soil_t_1:_FillValue = -32768s ;

soil_t_1:standard_name = “temperature_of_soil_layer” ;

soil_t_1:long_name = “Soil temperature in layer 1” ;

soil_t_1:units = “K” ;

short soil_m_1(time, z1, y0, x0) ;

soil_m_1:scale_factor = 1.476923e-05f ;

soil_m_1:add_offset = 0.5162632f ;

soil_m_1:valid_min = -32767s ;

soil_m_1:valid_max = 32767s ;

soil_m_1:_FillValue = -32768s ;

soil_m_1:standard_name = “moisture_content_of_soil_layer” ;

soil_m_1:long_name = “Soil moisture in layer 1” ;

soil_m_1:units = “m^3/m^3” ;

short twp(time, z1, y0, x0) ;

twp:scale_factor = 0.003672245f ;

twp:add_offset = 120.255f ;

twp:valid_min = -32767s ;

twp:valid_max = 32767s ;

twp:_FillValue = -32768s ;

twp:standard_name = “atmosphere_water_content” ;

twp:long_name = “Total Water Path” ;

twp:units = “g m{-2}” ;

short hraincon(time, z1, y0, x0) ;

hraincon:scale_factor = 1.34781e-05f ;

hraincon:add_offset = 0.4413674f ;

hraincon:valid_min = -32767s ;

hraincon:valid_max = 32767s ;

hraincon:_FillValue = -32768s ;

hraincon:standard_name = “convective_precipitation_rate” ;

hraincon:long_name = “Hourly Rain total, Convective” ;

hraincon:units = “cm/hr” ;

short ground_t(time, z1, y0, x0) ;

ground_t:scale_factor = 0.00187675f ;

ground_t:add_offset = 267.2289f ;

ground_t:valid_min = -32767s ;

ground_t:valid_max = 32767s ;

ground_t:_FillValue = -32768s ;

ground_t:standard_name = “temperature_at_ground_level” ;

ground_t:long_name = “Ground temperature” ;

ground_t:units = “K” ;

ground_t:mdv_field_code = 0 ;

short rwp(time, z1, y0, x0) ;

rwp:scale_factor = 0.003606715f ;

rwp:add_offset = 118.1091f ;

rwp:valid_min = -32767s ;

rwp:valid_max = 32767s ;

rwp:_FillValue = -32768s ;

rwp:standard_name = “stratiform_precipitation_amount” ;

rwp:long_name = “Rain Water Path” ;

rwp:units = “g m{-2}” ;

short tot_cld_conp(time, z1, y0, x0) ;

tot_cld_conp:scale_factor = 0.001536748f ;

tot_cld_conp:add_offset = 50.32387f ;

tot_cld_conp:valid_min = -32767s ;


tot_cld_conp:valid_max = 32767s ;

tot_cld_conp:_FillValue = -32768s ;

tot_cld_conp:standard_name = “atmosphere_mass_content_of_cloud_condensed_water” ;

tot_cld_conp:long_name = “ Vertically Integrated TOT_CLD_CON “ ;

tot_cld_conp:units = “g m{-2}” ;

short clwp(time, z1, y0, x0) ;

clwp:scale_factor = 0.0001477031f ;

clwp:add_offset = 4.836832f ;

clwp:valid_min = -32767s ;

clwp:valid_max = 32767s ;

clwp:_FillValue = -32768s ;

clwp:standard_name = “atmosphere_mass_content_of_cloud_liquid_water” ;

clwp:long_name = “ Vertically Integrated CLW” ;

clwp:units = “g m{-2}” ;

short swdown(time, z1, y0, x0) ;

swdown:scale_factor = 0.01637204f ;

swdown:add_offset = 536.1351f ;

swdown:valid_min = -32767s ;

swdown:valid_max = 32767s ;

swdown:_FillValue = -32768s ;

swdown:standard_name = “surface_net_downward_shortwave_flux” ;

swdown:long_name = “Surface downward shortwave radiation” ;

swdown:units = “W/m^2” ;

short lwdown(time, z1, y0, x0) ;

lwdown:scale_factor = 0.006836955f ;

lwdown:add_offset = 283.4802f ;

lwdown:valid_min = -32767s ;

lwdown:valid_max = 32767s ;

lwdown:_FillValue = -32768s ;

lwdown:standard_name = “surface_net_downward_longtwave_flux” ;

lwdown:long_name = “Surface downward longwave radiation” ;

lwdown:units = “W/m^2” ;

// global attributes:

:Conventions = “CF-1.0” ;

:history = “Data blended from the following files:\n”,

“/raid10/CFDDA/mdv/SH_LL/20050715/120000.mdv\n”,

“/raid10/CFDDA/mdv/NH_LL/20050715/120000.mdv\n”,

““ ;

:institution = “UCAR” ;

:source = “DTRA Project, RAL, NCAR. See document describing CFDDA runs used to produce

global climatography” ;

:title = “Blend NH and SH with new terrain using MdvBlend.” ;

:comment = “Converted by DsMdvServer” ;

}


Appendix B: Header for Terrain file netcdf terrain_nc3 {

dimensions:

x0 = 900 ;

y0 = 450 ;

z0 = 1 ;

time = UNLIMITED ; // (1 currently)

variables:

float x0(x0) ;

x0:standard_name = "longitude" ;

x0:long_name = "longitude" ;

x0:units = "degrees_east" ;

x0:axis = "X" ;

float y0(y0) ;

y0:standard_name = "latitude" ;

y0:long_name = "latitude" ;

y0:units = "degrees_north" ;

y0:axis = "Y" ;

float z0(z0) ;

z0:long_name = "surface" ;

z0:units = "level" ;

z0:positive = "up" ;

z0:axis = "Z" ;

double time(time) ;

time:standard_name = "time" ;

time:long_name = "Data time" ;

time:units = "seconds since 1970-01-01 00:00:00" ;

time:calendar = "standard" ;

float terrain(time, z0, y0, x0) ;

terrain:standard_name = "terrain" ;

terrain:long_name = "Terrain height" ;

terrain:units = "m" ;

terrain:_FillValue = -1.677065f ;

terrain:missing_value = -1.677065f ;

float land_use(time, z0, y0, x0) ;

land_use:standard_name = "land_use" ;

land_use:long_name = "Land use category" ;

land_use:units = "Cat" ;

land_use:_FillValue = 255.f ;

land_use:missing_value = 255.f ;

// global attributes:

:CDI = "Climate Data Interface version 1.6.3 (http://code.zmaw.de/projects/cdi)" ;

:source = "DTRA Project, RAL, NCAR. See document describing CFDDA runs used to

produce global climatography" ;

:Conventions = "CF-1.0" ;

:history = "Sat Jul 19 11:11:09 2014: ncatted -a history,global,d,,

terrain_new.nc" ;

}

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