The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature.

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.

The CCT has completed the guide summarizing the uncertainties in the realization of the SPRT subranges of ITS-90 between the triple point of neon (24.5561 K) and the freezing point of silver (961.78 • C). This article identifies aspects of standard platinum resistance thermometry where either data or models are lacking and further research is required. In the calibration of SPRTs, the two main concerns are the need for data on liquidus slopes for the different impurities in the fixed points and improved understanding of the impact of the thermal environment of the fixed point on the realized temperature. In the use of SPRTs, the two largest sources of uncertainty are Types 1 and 3 non-uniqueness and oxidation. The causes of Type 3 non-uniqueness are not yet understood, especially at low temperatures, and there is a paucity of data for the high-temperature subranges. In respect of oxidation, there is a need for validation of the models developed in the 1980s, especially in light of the reduced partial pressure of oxygen used in modern SPRTs. A range of other effects including vacancy effects in SPRTs, isotopic effects in fixed points, and improved statistical methods are discussed.

The International Committee for Weights and Measures (CIPM), at its meeting in October 2017, followed the recommendation of the Consultative Committee for Units (CCU) on the redefinition of the kilogram, ampere, kelvin and mole. For the redefinition of the kelvin, the Boltzmann constant will be fixed with the numerical value 1.380 649 × 10−23 J K−1. The relative standard uncertainty to be transferred to the thermodynamic temperature value of the triple point of water will be 3.7 × 10−7, corresponding to an uncertainty in temperature of 0.10 mK, sufficiently low for all practical purposes. With the redefinition of the kelvin, the broad research activities of the temperature community on the determination of the Boltzmann constant have been very successfully completed. In the following, a review of the determinations of the Boltzmann constant k, important for the new definition of the kelvin and performed in the last decade, is given.

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.