ABSTRACT:The study describes significant outcomes of the 'Metrology for Meteorology' project, MeteoMet, which is an attempt to bridge the meteorological and metrological communities. The concept of traceability, an idea used in both fields but with a subtle difference in meaning, is at the heart of the project. For meteorology, a traceable measurement is the one that can be traced back to a particular instrument, time and location. From a metrological perspective, traceability further implies that the measurement can be traced back to a primary realization of the quantity being measured in terms of the base units of the International System of Units, the SI. These two perspectives reflect long-standing differences in culture and practice and this project -and this study -represents only the first step towards better communication between the two communities. The 3 year MeteoMet project was funded by the European Metrology Research Program (EMRP) and involved 18 European National Metrological Institutes, 3 universities and 35 collaborating stakeholders including national meteorology organizations, research institutes, universities, associations and instrument companies. The project brought a metrological perspective to several long-standing measurement problems in meteorology and climatology, varying from conventional ground-based measurements to those made in the upper atmosphere. It included development and testing of novel instrumentation as well as improved calibration procedures and facilities, instrument intercomparison under realistic conditions and best practice dissemination. Additionally, the validation of historical temperature data series with respect to measurement uncertainties and a methodology for recalculation of the values were included.

Launched in 2011 within the European Metrology Research Programme (EMRP) of EURAMET, the joint research project "MeteoMet" -Metrology for Meteorology -is the largest EMRP consortium: National Metrology Institutes, Universities, meteorological and climate agencies, Research Institutes, collaborators and manufacturers are working together, developing new metrological techniques, as well as improving already existing ones, for meteorological observations and climate records. The project focuses on: humidity in the upper and surface atmosphere, air temperature, surface and deep-sea temperatures, soil moisture, salinity, permafrost temperature, precipitation and snow albedo effect on air temperature. All tasks are performed under rigorous metrological approach and include design and study of new sensors, new calibration facilities, investigation of sensors characteristics, improved techniques for measurements of Essential Climate Variables with uncertainty evaluation, traceability, laboratory proficiency and inclusion of field influencing parameters, long-lasting measurements, and campaigns in remote and extreme areas. MeteoMet vision is to make a further step towards establishing full data comparability, coherency, consistency and long-term continuity, through a comprehensive evaluation of the measurement uncertainties for the quantities involved in the global climate observing systems and the derived observations. The improvement of quality of Essential Climate Variables records, through the inclusion of measurement uncertainty budgets, will also highlight possible strategies for the reduction of the uncertainty. This contribution presents selected highlights of the MeteoMet project and reviews the main ongoing activities, tasks and deliverables, with a view to its possible future evolution and extended impact.

A World Meteorological Organization (WMO) committee officially evaluated temperature record extremes of 54.0°C at two locations, one in Mitribah, Kuwait on July 21, 2016 and a second in Turbat, Pakistan on May 28, 2017. The committee agreed that quantity and quality of documentation of both observations were excellent. Additional metrological testing of the equipment focused on three aspects: the calibration of both thermometers, an effort to estimate the factors influencing the measurements and a direct comparison of the two thermometers when exposed simultaneously to 54°C. The metrological analysis's conclusion for the Mitribah value is a temperature estimated to be 53.87°C with an expanded uncertainty of ±0.08°C. Correspondingly, for the Turbat value the temperature is estimated to be 53.72°C with an expanded uncertainty of ±0.40°C. Following that analysis, the committee recommended acceptance of the calibrated observations to the first decimal digit such that the Mitribah observation is accepted as 53.9 ± 0.1°C and the Turbat as 53.7 ± 0.4°C. The Mitribah, Kuwait temperature is now accepted by the WMO as the highest temperature ever recorded for Asia (WMO RA II) and the two observations are the third (tied within uncertainty limits) and fourth highest WMO‐recognized temperature extremes and, significantly, they are the highest, officially recognized temperatures to have been recorded in the last 76 years. This evaluation has involved the most extensive temperature extremes analysis ever to be undertaken by an international evaluation committee of the WMO CCl Archive of Weather and Climate Extremes.

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A low frost-point generator (INRIM 03) operating at sub-atmospheric pressure has been designed and constructed at the Istituto Nazionale di Ricerca Metrologica (INRIM) as part of a calibration facility for upper-air sounding instruments. This new humidity generator covers the frost-point temperature range between  −99 °C and  −20 °C and works at any controlled pressure between 200 hPa and 1100 hPa, achieving a complete saturation of the carrier gas (nitrogen) in a single passage through a stainless steel isothermal saturator. The generated humid gas contains a water vapour amount fraction between 14  ×  10−9 mol mol−1 and 5  ×  10−3 mol mol−1. In this work the design of the generator is reported together with characterisation and performance evaluation tests. A preliminary validation of the INRIM 03 against one of the INRIM humidity standards in the common region is also included. Based on experimental test results, an initial uncertainty evaluation of the generated frost-point temperature, Tfp, and water vapour amount fraction, xw, in the limited range down to  −75 °C at atmospheric pressure is reported. For the frost-point temperature, the uncertainty budget yields a total expanded uncertainty (k  =  2) of less than 0.028 °C, while for the mole fraction the budget yields a total expanded uncertainty of less than 10−6 mol mol−1.