4.3. Glossary


To transport substances in the atmostphere by advection.


According to the American Meteorological Society (AMS) definition, advection is “The process of transport of an atmospheric property solely by the mass motion (velocity field) of the atmosphere.” In common parlance, advection is movement of atmospheric substances that are carried around by the wind.


The Air Quality Model (AQM) is a UFS Application that dynamically couples the Community Multiscale Air Quality (CMAQ) model with the UFS Weather Model through the NUOPC Layer to simulate temporal and spatial variations of atmospheric compositions (e.g., ozone and aerosol compositions). The CMAQ, treated as a column chemistry model, updates concentrations of chemical species (e.g., ozone and aerosol compositions) at each integration time step. The transport terms (e.g., advection and diffusion) of all chemical species are handled by the UFS Weather Model as tracers.


Convective Available Potential Energy.


Climatology-Calibrated Precipitation Analysis (CCPA) data. This data is required for METplus precipitation verification tasks within the SRW App. The most recent 8 days worth of data are publicly available and can be accessed here.


The Common Community Physics Package is a forecast-model agnostic, vetted collection of code containing atmospheric physical parameterizations and suites of parameterizations for use in Numerical Weather Prediction (NWP) along with a framework that connects the physics to the host forecast model.


The preprocessing software used to create initial and boundary condition files to “cold start” the forecast model. It is part of UFS_UTILS.


Convective Inhibition.


The Community Multiscale Air Quality Model (CMAQ, pronounced “cee-mak”) is a numerical air quality model that predicts the concentration of airborne gases and particles and the deposition of these pollutants back to Earth’s surface. The purpose of CMAQ is to provide fast, technically sound estimates of ozone, particulates, toxics, and acid deposition. CMAQ is an active open-source development project of the U.S. Environmental Protection Agency (EPA). Code is publicly available at https://github.com/USEPA/CMAQ.

cron table

Cron is a job scheduler accessed through the command-line on UNIX-like operating systems. It is useful for automating tasks such as the rocotorun command, which launches each workflow task in the SRW App (see Chapter 4.1 for details). Cron periodically checks a cron table (aka crontab) to see if any tasks are are ready to execute. If so, it runs them.


The Community Radiative Transfer Model (CRTM) is a fast and accurate radiative transfer model developed at the Joint Center for Satellite Data Assimilation (JCSDA) in the United States. It is a sensor-based radiative transfer model and supports more than 100 sensors, including sensors on most meteorological satellites and some from other remote sensing satellites.


A software element that has a clear function and interface. In Earth system models, components are often single portions of the Earth system (e.g. atmosphere, ocean, or land surface) that are assembled to form a whole.

Component Repository

A repository that contains, at a minimum, source code for a single component.


Docker describes a container as “a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another.”


Continental United States

convection-allowing models

Convection-allowing models (CAMs) are models that run on high-resolution grids (usually with grid spacing at 4km or less). They are able to resolve the effects of small-scale convective processes. They typically run several times a day to provide frequent forecasts (e.g., hourly or subhourly).


An hour of the day on which a forecast is started.


Describes a workflow task that needs to be run at the start of each cycle of an experiment.


Describes a workflow task that only needs to be run once per experiment, regardless of the number of cycles in the experiment.

data assimilation

Data assimilation is the process of combining observations, model data, and error statistics to achieve the best estimate of the state of a system. One of the major sources of error in weather and climate forecasts is uncertainty related to the initial conditions that are used to generate future predictions. Even the most precise instruments have a small range of unavoidable measurement error, which means that tiny measurement errors (e.g., related to atmospheric conditions and instrument location) can compound over time. These small differences result in very similar forecasts in the short term (i.e., minutes, hours), but they cause widely divergent forecasts in the long term. Errors in weather and climate forecasts can also arise because models are imperfect representations of reality. Data assimilation systems seek to mitigate these problems by combining the most timely observational data with a “first guess” of the atmospheric state (usually a previous forecast) and other sources of data to provide a “best guess” analysis of the atmospheric state to start a weather or climate simulation. When combined with an “ensemble” of model runs (many forecasts with slightly different conditions), data assimilation helps predict a range of possible atmospheric states, giving an overall measure of uncertainty in a given forecast.

dynamical core

Global atmospheric model based on fluid dynamics principles, including Euler’s equations of motion.

echo top

The radar-indicated top of an area of precipitation. Specifically, it contains the height of the 18 dBZ reflectivity value.


The Environmental Modeling Center.


The Earth Prediction Innovation Center seeks to accelerate scientific research and modeling contributions through continuous and sustained community engagement in order to produce the most accurate and reliable operational modeling system in the world.


Extended Schmidt Gnomonic (ESG) grid. The ESG grid uses the map projection developed by Jim Purser of NOAA EMC (Purser et al. [PJK+20]).


Earth System Modeling Framework. The ESMF defines itself as “a suite of software tools for developing high-performance, multi-component Earth science modeling applications.”


Scripting layer (contained in ufs-srweather-app/scripts/) that should be called by a J-job for each workflow componentto run a specific task or sub-task in the workflow. The different scripting layers are described in detail in the NCO Implementation Standards document


The Finite-Volume Cubed-Sphere dynamical core (dycore). Developed at NOAA’s Geophysical Fluid Dynamics Laboratory (GFDL), it is a scalable and flexible dycore capable of both hydrostatic and non-hydrostatic atmospheric simulations. It is the dycore used in the UFS Weather Model.


Finite Volume Community Ocean Model. FVCOM is used in modeling work for the Great Lakes Coastal Forecasting System (next-gen FVCOM) conducted by the Great Lakes Environmental Research Laboratory.


Global Forecast System. The GFS is a National Centers for Environmental Prediction (NCEP) weather forecast model that generates data for dozens of atmospheric and land-soil variables, including temperatures, winds, precipitation, soil moisture, and atmospheric ozone concentration. The system couples four separate models (atmosphere, ocean, land/soil, and sea ice) that work together to accurately depict weather conditions.


NASA’s Goddard Chemistry Aerosol Radiation and Transport (GOCART) model simulates the distribution of major tropospheric aerosol types, including sulfate, dust, organic carbon (OC), black carbon (BC), and sea salt aerosols. The UFS Weather Model integrates a prognostic aerosol component using GOCART. The code is publicly available on GitHub at https://github.com/GEOS-ESM/GOCART.


The second version of the World Meterological Organization’s (WMO) standard for distributing gridded data.


NOAA Global Systems Laboratory is one of ten NOAA Research laboratories and is located in Boulder, Colorado. Its research improves environmental prediction models, develops state-of-the-science decision support tools and visualization systems, and uses high-performance computing technology to support a Weather-Ready Nation.


A strip of cells on the edge of the regional grid. The wide halo surrounds the regional grid and is used to feed the lateral boundary conditions into the grid. The HALO_BLEND parameter refers to a strip of cells inside the boundary of the native grid. This halo smooths out mismatches between the external and internal solutions.


High-Performance Computing.


The HPC-Stack is a repository that provides a unified, shell script-based build system for building the software stack required for numerical weather prediction (NWP) tools such as the Unified Forecast System (UFS) and the Joint Effort for Data assimilation Integration (JEDI) framework. View the HPC-Stack documentation here.


High Performance Storage System (HPSS).


High Resolution Rapid Refresh. The HRRR is a NOAA real-time 3-km resolution, hourly updated, cloud-resolving, convection-allowing atmospheric model initialized by 3km grids with 3km radar assimilation. Radar data is assimilated in the HRRR every 15 min over a 1-h period adding further detail to that provided by the hourly data assimilation from the 13km radar-enhanced Rapid Refresh.


Initial conditions/lateral boundary conditions


Initial conditions


Scripting layer (contained in ufs-srweather-app/jobs/) that should be directly called for each workflow component (either on the command line or by the workflow manager) to run a specific task in the workflow. The different scripting layers are described in detail in the NCO Implementation Standards document


The Joint Effort for Data assimilation Integration (JEDI) is a unified and versatile data assimilation (DA) system for Earth System Prediction. It aims to enable efficient research and accelerated transition from research to operations by providing a framework that takes into account all components of the Earth system in a consistent manner. The JEDI software package can run on a variety of platforms and for a variety of purposes, and it is designed to readily accommodate new atmospheric and oceanic models and new observation systems. The JEDI User’s Guide contains extensive information on the software.

JEDI is developed and distributed by the Joint Center for Satellite Data Assimilation, a multi-agency research center hosted by the University Corporation for Atmospheric Research (UCAR). JCSDA is dedicated to improving and accelerating the quantitative use of research and operational satellite data in weather, ocean, climate, and environmental analysis and prediction systems.


Limited Area Model (grid type), formerly known as the “Stand-Alone Regional Model,” or SAR. LAM grids use a regional (rather than global) configuration of the FV3 dynamical core.


Lateral boundary conditions


The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is a modeling system for estimating the emission of gases and aerosols from terrestrial ecosystems into the atmosphere. It has been integrated into a number of chemistry and transport models, including NEXUS.


The Modern-Era Retrospective analysis for Research and Applications, Version 2 provides satellite observation data back to 1980. According to NASA, “It was introduced to replace the original MERRA dataset because of the advances made in the assimilation system that enable assimilation of modern hyperspectral radiance and microwave observations, along with GPS-Radio Occultation datasets. It also uses NASA’s ozone profile observations that began in late 2004. Additional advances in both the GEOS model and the GSI assimilation system are included in MERRA-2. Spatial resolution remains about the same (about 50 km in the latitudinal direction) as in MERRA.”


MPI stands for Message Passing Interface. An MPI is a standardized communication system used in parallel programming. It establishes portable and efficient syntax for the exchange of messages and data between multiple processors that are used by a single computer program. An MPI is required for high-performance computing (HPC) systems.


Multi-Radar/Multi-Sensor (MRMS) System Analysis data. This data is required for METplus composite reflectivity or echo top verification tasks within the SRW App. A two-day archive of precipitation, radar, and aviation and severe weather fields is publicly available and can be accessed here.


North American Mesoscale Forecast System. NAM generates multiple grids (or domains) of weather forecasts over the North American continent at various horizontal resolutions. Each grid contains data for dozens of weather parameters, including temperature, precipitation, lightning, and turbulent kinetic energy. NAM uses additional numerical weather models to generate high-resolution forecasts over fixed regions, and occasionally to follow significant weather events like hurricanes.


A namelist defines a group of variables or arrays. Namelists are an I/O feature for format-free input and output of variables by key-value assignments in Fortran compilers. Fortran variables can be read from and written to plain-text files in a standardised format, usually with a .nml file ending.


The National Center for Atmospheric Research.


National Centers for Environmental Prediction (NCEP) is an arm of the National Weather Service consisting of nine centers. More information can be found at https://www.ncep.noaa.gov.


The software libraries created and maintained by NCEP that are required for running chgres_cube, the UFS Weather Model, and the UPP. They are included in the HPC-Stack.


A collection of third-party libraries required to build NCEPLIBS, chgres_cube, the UFS Weather Model, and UPP. They are included in the HPC-Stack.


An interpreted programming language designed specifically for scientific data analysis and visualization. Stands for NCAR Command Language. More information can be found at https://www.ncl.ucar.edu.


NAM Data Assimilation System (NDAS) data. This data is required for METplus surface and upper-air verification tasks within the SRW App. The most recent 1-2 days worth of data are publicly available in PrepBufr format and can be accessed here. The most recent 8 days of data can be accessed here.


The NOAA Environmental Modeling System is a common modeling framework whose purpose is to streamline components of operational modeling suites at NCEP.


A binary format for atmospheric model output from NCEP’s Global Forecast System (GFS).


NetCDF (Network Common Data Form) is a file format and community standard for storing multidimensional scientific data. It includes a set of software libraries and machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data.


The National Operational Hydrologic Remote Sensing Center, which provides the National Snowfall Analysis, an observation-based, gridded estimate of recent snowfall, now an operational product.


The National Severe Storms Laboratory.


The National Unified Operational Prediction Capability Layer “defines conventions and a set of generic components for building coupled models using the Earth System Modeling Framework (ESMF).”


Numerical Weather Prediction (NWP) takes current observations of weather and processes them with computer models to forecast the future state of the weather.


The National Weather Service (NWS) is an agency of the United States government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the purposes of protection, safety, and general information. It is a part of the National Oceanic and Atmospheric Administration (NOAA) branch of the Department of Commerce.


The branch of physical geography dealing with mountains.


Simplified functions that approximate the effects of small-scale processes (e.g., microphysics, gravity wave drag) that cannot be explicitly resolved by a model grid’s representation of the earth.


Rapid Refresh. The continental-scale NOAA hourly-updated assimilation/modeling system operational at NCEP. RAP covers North America and is comprised primarily of a numerical forecast model and an analysis/assimilation system to initialize that model. RAP is complemented by the higher-resolution 3km High-Resolution Rapid Refresh (HRRR) model.


NOAA Research & Development High-Performance Computing Systems.


A central location in which files (e.g., data, code, documentation) are stored and managed.


The Rapid Refresh Forecast System (RRFS) is NOAA’s next-generation convection-allowing, rapidly-updated, ensemble-based data assimilation and forecasting system currently scheduled for operational implementation in 2024. It is designed to run forecasts on a 3-km CONUS domain.


Suite Definition File. An external file containing information about the construction of a physics suite. It describes the schemes that are called, in which order they are called, whether they are subcycled, and whether they are assembled into groups to be called together.


Spack is a package management tool designed to support multiple versions and configurations of software on a wide variety of platforms and environments. It was designed for large supercomputing centers, where many users and application teams share common installations of software on clusters with exotic architectures.


The spack-stack is a collaborative effort between the NOAA Environmental Modeling Center (EMC), the UCAR Joint Center for Satellite Data Assimilation (JCSDA), and the Earth Prediction Innovation Center (EPIC). spack-stack is a repository that provides a Spack-based method for building the software stack required for numerical weather prediction (NWP) tools such as the Unified Forecast System (UFS) and the Joint Effort for Data assimilation Integration (JEDI) framework. spack-stack uses the Spack package manager along with custom Spack configuration files and Python scripts to simplify installation of the libraries required to run various applications. The spack-stack can be installed on a range of platforms and comes pre-configured for many systems. Users can install the necessary packages for a particular application and later add the missing packages for another application without having to rebuild the entire stack.


According to the American Meteorological Society (AMS) definition, a tracer is “Any substance in the atmosphere that can be used to track the history [i.e., movement] of an air mass.” Tracers are carried around by the motion of the atmosphere (i.e., by advection). These substances are usually gases (e.g., water vapor, CO2), but they can also be non-gaseous (e.g., rain drops in microphysics parameterizations). In weather models, temperature (or potential temperature), absolute humidity, and radioactivity are also usually treated as tracers. According to AMS, “The main requirement for a tracer is that its lifetime be substantially longer than the transport process under study.”


The Unified Forecast System is a community-based, coupled, comprehensive Earth modeling system consisting of several applications (apps). These apps span regional to global domains and sub-hourly to seasonal time scales. The UFS is designed to support the Weather Enterprise and to be the source system for NOAA’s operational numerical weather prediction applications. For more information, visit https://ufscommunity.org/.


A collection of code used by multiple UFS apps (e.g., the UFS Short-Range Weather App, the UFS Medium-Range Weather App). The grid, orography, surface climatology, and initial and boundary condition generation codes used by the UFS Short-Range Weather App are all part of this collection. The code is publicly available on Github.

Umbrella repository

A repository that houses external code, or “externals,” from additional repositories.

Updraft helicity

Helicity measures the rotation in a storm’s updraft (rising) air. Significant rotation increases the probability that the storm will produce severe weather, including tornadoes. See http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/modl/fcst/params/hel.rxml for more details on updraft helicity.


The Unified Post Processor is software developed at NCEP and used operationally to post-process raw output from a variety of NCEP’s NWP models, including the FV3. See https://epic.noaa.gov/unified-post-processor/ for more information.

Weather Enterprise

Individuals and organizations from public, private, and academic sectors that contribute to the research, development, and production of weather forecast products; primary consumers of these weather forecast products.

Weather Model

A prognostic model that can be used for short- and medium-range research and operational forecasts. It can be an atmosphere-only model or an atmospheric model coupled with one or more additional components, such as a wave or ocean model. The SRW App uses the UFS Weather Model.


The sequence of steps required to run an experiment from start to finish.