WMO (World Meteorological Organization) Glossary

The World Meteorological Organization (WMO) is the United Nations’ specialized agency responsible for coordinating global activities in meteorology, climatology, hydrology, and related fields. Established in 1950, WMO connects 193 Member States and Territories through a network of National Meteorological and Hydrological Services (NMHSs). Its mission is to promote the international exchange of weather, climate, and water data and to ensure that countries have access to standardized observations and services for disaster risk reduction, sustainable development, and environmental protection.

WMO develops and maintains a suite of international standards—technical regulations, manuals, and guidelines—that underpin the reliability, consistency, and interoperability of meteorological, climatological, and hydrological data. These standards are essential for global monitoring, operational forecasting, climate assessment, and supporting sectors like aviation, marine transport, agriculture, and public health.

WMO Standards: Definition and Scope

WMO standards are authoritative international benchmarks for the observation, reporting, calibration, management, and exchange of meteorological, climate, and hydrological data. Developed through scientific consensus and adopted formally by WMO’s governing bodies, these standards are articulated through Technical Regulations (WMO-No. 49), manuals, and guides (such as WMO-No. 8).

Their scope covers:

• Instrument specifications, calibration, and maintenance
• Observational practices (e.g., exposure, siting)
• Data formats (e.g., BUFR, GRIB, SYNOP)
• Coding systems and metadata schemas
• Data quality assurance and quality control (QA/QC)
• Protocols for real-time and historical data exchange

Uniform application of WMO standards ensures that data from diverse sources and environments are comparable and can be integrated into global datasets. This underpins everything from daily weather forecasts to climate change assessments and early warning systems for natural hazards.

Climatological Normals

Climatological Normals are 30-year averages of climate variables (such as temperature, precipitation, or wind speed) calculated for a specific site or region. The WMO recommends using periods like 1961–1990, 1981–2010, and 1991–2020 for calculating these reference values. Climatological normals are vital for:

• Contextualizing current weather and climate conditions
• Identifying anomalies and long-term trends
• Supporting infrastructure design, insurance, agriculture, and public health

Calculation and reporting of normals follow strict WMO guidelines (e.g., WMO-No. 1203), ensuring accuracy, consistency, and inclusion of necessary metadata (station location, period covered, instrument details, etc.).

Meteorological Instruments and Methods of Observation

WMO’s Guide to Meteorological Instruments and Methods of Observation (WMO-No. 8) details standards for the installation, operation, and calibration of all instruments used in atmospheric and hydrological monitoring. Covered instruments include thermometers, barometers, hygrometers, anemometers, rain gauges, pyranometers, ceilometers, and radiosondes.

Key principles:

• Siting: Minimizing microclimate and artificial influences (e.g., temperature sensors in ventilated Stevenson screens at 1.25–2.0 m height)
• Calibration: Regular checks against recognized standards to eliminate bias
• Quality control: Automated and manual procedures for detecting and correcting errors

These standards ensure data reliability for integration into global systems and operational use in forecasting, hazard warnings, and environmental management.

Data Exchange and the WMO Information System (WIS 2.0)

The WMO Information System (WIS 2.0) is the backbone of global meteorological, climate, and hydrological data sharing. It provides a decentralized, standards-based architecture for real-time, secure exchange and discovery of data.

Features include:

• Open APIs (OGC standards) for data access and metadata discovery
• Multiple data formats (GeoJSON, NetCDF, WaterML)
• Event-driven dissemination (MQTT), enabling automated, real-time updates
• Global Brokers, Caches, and Discovery Catalogues for efficient data flow

WIS 2.0 promotes open access, interoperability, and scalability, enabling researchers, forecasters, and emergency managers worldwide to access and integrate data seamlessly.

WMO Unified Data Policy

Adopted in 2021, the WMO Unified Data Policy mandates free and unrestricted sharing of specified core weather, climate, and water data among Members. This policy:

• Eliminates data gaps and fragmentation
• Improves accessibility and quality of global datasets
• Supports research, innovation, and disaster risk reduction

The policy is harmonized with international frameworks like the Global Framework for Climate Services (GFCS) and the Global Earth Observation System of Systems (GEOSS), and it underpins the operation of WIS 2.0 and GBON.

Global Basic Observing Network (GBON)

The Global Basic Observing Network (GBON) sets quantitative requirements for minimum surface and upper-air observations worldwide, addressing critical gaps in data coverage. GBON specifies:

• Types and frequency of observations (e.g., hourly surface data, 12-hourly upper-air profiles)
• Compliance with WMO standards for instrumentation, calibration, and data management
• Real-time data dissemination via WIS 2.0

GBON’s implementation ensures baseline, high-quality data are available globally, improving weather prediction, climate monitoring, and early warning, especially in data-sparse regions.

Quality Management and Calibration

Quality management encompasses all procedures and policies ensuring the accuracy, reliability, and consistency of meteorological and hydrological data:

• Calibration: Regular comparison of instruments against recognized standards under controlled conditions, with detailed records maintained for traceability
• Quality Assurance (QA): Preventative measures (e.g., training, SOPs, maintenance)
• Quality Control (QC): Detection and correction of errors via automated/manual checks, intercomparisons, and cross-validation

WMO guidance (e.g., WMO-No. 8) and adoption of ISO 9001-aligned Quality Management Systems (QMS) are increasingly common, underpinning confidence and interoperability in global datasets.

Key Terms and Concepts

Automatic Weather Station (AWS)

An Automatic Weather Station (AWS) is a modular, unmanned system equipped with sensors (temperature, humidity, wind, pressure, precipitation, solar radiation) and telemetry for remote, real-time data collection and transmission. AWSs are crucial for dense observing networks supporting aviation, flood forecasting, and climate monitoring. WMO standards cover AWS sensor performance, siting, calibration, power supply, data logging, and metadata documentation.

Calibration

Calibration is the process of verifying and adjusting instrument readings against a reference standard to ensure accuracy and traceability. Schedules are based on instrument type and usage, with detailed records maintained for every calibration event. WMO and ISO guidelines define calibration protocols.

Climatological Elements

Climatological elements are the individual climate variables measured and recorded (temperature, precipitation, pressure, humidity, wind, sunshine, cloud cover, soil temperature, etc.). Their measurement and reporting are governed by WMO standards to ensure comparability.

Composite Data File

A Composite Data File aggregates station-level climatological data (normals, extremes, time series) across multiple locations or regions, structured in standardized formats (CSV, NetCDF) and accompanied by metadata for integration and analysis.

Data Granule

A Data Granule is the smallest indivisible unit of data in a dataset (e.g., hourly temperature from a station), supporting efficient storage, retrieval, and analysis.

Exposure

Exposure refers to the placement and surroundings of an instrument or station. Proper exposure ensures representative measurements, minimizing local distortions from heat sources, obstructions, or reflective surfaces. WMO provides specific criteria for instrument exposure.

Metadata

Metadata are structured, descriptive information about data (e.g., station location, elevation, instrument type, calibration history, data quality indicators) that enable discovery, interpretation, and reuse of datasets. WMO standards require comprehensive metadata to accompany all observations.

Further Reading

• WMO Official Website
• WMO-No. 8 Guide to Meteorological Instruments and Methods of Observation
• WMO Unified Data Policy

For more detailed information on WMO standards, data exchange, and quality management, consult official WMO technical documents and manuals.