Safe assessment of climate change crucially depends on the robustness of climate data and on the uncertainties associated with measurements. Metrology, the science of measurement, is now playing a new role in climate science, providing expertise and funded projects aiming at improving measurements capabilities and traceability of data.

Reliable assessments of climate change depend crucially on data quality, but measurement of Essential Climate Variables (ECVs), as defined by the Global Climate Observing System (GCOS), are still often expressed without the inclusion of measurement uncertainty, or a clear traceability statement. Nowadays the scientific community is moving to fill this gap.

Background

In 2010, the World Meteorological Organization (WMO) signed the Mutual Recognition Arrangement (MRA) of the CIPM (Comité international des Poids et Mesures/International Committee for Weights and Measures) during a joint workshop with the Bureau International des Poids et Mesures (BIPM). On this occasion the two international associations recognised the need for improving meteo-climatic measurements and discussed ways in which they could collaborate, as well as effective actions to be undertaken by National Metrological Institutes (NMIs).

Addressing those needs is now becoming a priority of the metrological community. The CCT (Consultative Committee for Thermometry) recommendation to CIPM encourages a strong cooperation between NMIs and meteorological organisations and the European Association of NMIs (EURAMET) launched a call, the same year, for funding projects aiming at practically addressing those metrological needs.

After a selective evaluation process, following two phases of the proposal stage, in 2011 EURAMET funded a research project called ‘MeteoMet – Metrology for Meteorology’. The project, operating in the framework of the European Metrology Research Programme (EMRP) aims to ensure the metrological traceability to the International System of Units (SI) through national standards in meteorological observations and climate data, and groups a wide consortium of 18 NMIs, 12 universities, research centres, hydro-meteorological agencies, private companies and manufacturers. The major challenge of the project is the propagation of a metrological measurement perspective to meteorological observations, in order to better meet the expressed requirement of reliable data and robust datasets over a large scale and for the long term.

The project covers several aspects of meteorological observations, from upper air to ground based measurements. It includes development and testing of novel instruments as well as improved calibration procedures and facilities, insitu practical calibrations, instrument intercomparison under real dynamic conditions and best practise dissemination. Historical temperature data series will be validated with respect to measurement uncertainties and a methodology for recalculation of the values will be provided.

Scientific and technical objectives

The Joint Research Project (JRP) structure reflects two main aspects of metrology: scientific innovation and practical traceability for end users. It includes development and testing of novel instruments as well as improved calibration procedures and facilities for ground based observations, insitu practical calibrations and best practise dissemination. The work addresses the following topics:

Upper air measurements

• Realisation of traceable, self-calibrating tunable diode laser (TDLAS) hygrometers and the study of absorption lines of water molecules

• Implementation of new hygrometers based on microwave resonances in quasi-spherical cavities, innovative multisensors for free-space non-contact atmospheric measurements, ultrasonic anemometers, novel methods for GPS and Galileo-based measurements. Traceability of radiosonde-based measurements

• Intercomparison of airbone field humidity sensors of different types (AquaVIT2 campaign)

• Generation of new data to improve the water vapour formulae and proposition of a new equation for the water vapour pressure curve

Ground based measurements

• Proposition of calibration methods and protocols for weather stations, evaluation of the effect of solar radiance, traceability in wind speed measurements. Evaluation of realistic calibration uncertainties for air temperature sensors

• Development of facilities for laboratory and insitu simultaneous calibration of temperature, humidity and pressure sensors in weather stations, also working in extreme environmental conditions

• Organisation of the first metrological inter-comparison and testing of weather stations

• Development of protocols for software validation of automatic weather stations (AWSs)

Assessment of the historical temperature measurement data with respect to uncertainties

• Methods and software for taking into account inhomogeneity in historical data measurement including Type B uncertainties

• Software development as a tool for climatologists, to include temperature scale definition change correction over time

Recent MeteoMet results have been:

Upper air measurements

• The second international comparison of airborne hygrometers AquaVIT2 took place at the AIDA chamber at KIT Institute. Twelve research groups from 11 countries participated in the comparisons. This work offered for the first time the possibility to trace back the calibration devices and the hygrometers to the international humidity scale by means of a traceable calibrated frost point hygrometer and a commercial two-pressure generator. The evaluation of the outcome is in progress. This intercomparison promises a reasonable improvement of measurement uncertainty during atmospheric measurements by research airplanes and balloons

• Tests of the measurement chamber system and the saturators of the new radiosonde calibration system have been carried out. Two experimental methods were investigated in order to determine the effect of contamination on the equilibrium state in a saturator, intended to be used as a primary source of traceability. The two methods, based on electrical conductivity and density measurements were compared for the first time

• The new microwave resonators have been realised at CNAM. Setup is in progress and preliminary measurements show sharp resonances and fast thermal equilibration. Humidity measurements should be considerably improved with these new resonators

• The free-space acoustic thermometer and adapted water vapour spectrometer have both been made operational independently.

Work is in progress for the mounting of the two together to operate in the same multi-sensor combined system

Assessment of the historical temperature measurement data with respect to uncertainties

• The software conversion tool to convert the historical temperature data from the ITS90 predecessors to the current ITS90 temperature scale was developed. This tool provides a safe and effective conversion of historical data. These converted values can be easily compared with the current data thus easily see the temperature trend in the present and in history

Ground based measurements

• Questionnaire dedicated to collect data about European weather stations in use was prepared and sent to MeteoMet partners, collaborators, and stakeholders

• The laser based measurements of wind speed were performed by evaluating the scattered light of single aerosols. The local and temporal resolution reached in the measurements had not been realised until now

The environment monitoring by automatic weather stations (AWSs) is growing, driven by the requirement for increasing the number and reliability of surface observations. To ensure data traceability and to obtain more comprehensive data on the performance of AWSs a new calibration chamber was manufactured, which is equipped with reference sensors directly traceable to national standards to obtain meteorological data with well defined calibration uncertainty.

In this chamber temperature and pressure can be controlled simultaneously and independently so that all combinations over the ranges are possible. The nominal ranges of the chamber are: absolute pressure 500-1100 hPa, temperature -25°C to 50°C. The target uncertainty (k=2) of pressure and temperature are 10 Pa and 0.076°C.

The control of the two quantities allows both the AWS calibration in a large atmospheric variability range and the study of the mutual influencing effects on sensors’ response.

This apparatus is also designed to allow the humidity control to complete the characterisation of the whole AWS pressure-temperature-humidity modulus. In fact, the final version of the chamber will be equipped with a humidity generator for hygrometers’ calibrations in variable temperature and pressure conditions, and also allowing the calibration of thermometers and barometers under different humidity values as quantity of influence.

Finally, the chamber was designed to be easily transportable to allow the calibration of AWSs located in sites that are difficult to access. Further prototypes of this chamber have been designed and assembled for use in extreme areas like the Everest pyramid observatory and the Ny-Alesund, Svalbard stations.

The experience acquired with this first chamber and in the collaboration with the Ev-K2 CNR committee on measurement in extreme environments highlighted the need for a new portable climatic chamber, specifically designed to address high altitude challenges.

High altitude metrology

Climatic variables observation carried out in extremely high mountainous environments are important because they permit a long term series of data to be recorded in the absence of direct human activities, which influence and change the environmental conditions.

Such data series are therefore of great value also in climatic changes assessments. Aiming to obtain traceable data series, the Italian National Metrology Institute (INRiM), in collaboration with Ev-K2-CNR committee, launched research that led to the installation of a special portable climatic chamber in the Pyramid Observatory Laboratory at an altitude of 5,000m on the Nepalese side of mount Everest. This was in September, 2013.

Ev-K2-CNR is a high mountain oriented research agency operating mainly in the Himalayas. Environmental observations in high altitude areas allow the acquisition of unique information about the background conditions of the environment, also facilitating the study of the role played by natural or anthropic processes in disturbing this pristine habitat.

In 2008 the 78th UN General Assembly plenary meeting on sustainable mountain development recognised that ”mountains provide indications of global climate change through phenomena such as modifications of biological diversity, the retreat of mountain glaciers and changes in seasonal runoff that may impact major sources of freshwater in the world, and stresses the need to undertake actions to minimise the negative effects of these phenomena.” The Assembly encouraged governments to collaborate with scientists to improve knowledge on mountain climate and on the effects of its change on local communities.

To promote high altitude measurement, Ev-K2-CNR launched the SHARE project – Stations at High Altitude for Research on the Environment. This aims to produce high quality and long lasting data series. The collaboration with MeteoMet is essential to improve metrological quality of the data acquired in the Khumbu Valley, Nepal.

Accurate calibration campaigns, made possible by the installation of the climatic chamber in the Pyramid Observatory Laboratory, guarantee data quality and bring traceability. Furthermore, the definition of specific procedures for the periodic calibration of the instrument should guarantee a long lasting homogeneity of these series of data in the future.

The Pyramid Observatory Laboratory was built in 1990 in collaboration with the Nepal Academy of Science and Technology (NAST) and several sponsors. It is very remote, and only accessible after six days of trekking and acclimatisation. Helicopter flights are often available for delivering equipment but are not guaranteed, and the nearest landing field is half an hour on foot from the Pyramid.

Traditional Himalayan Sherpas are therefore important in the management of the laboratory. Another important challenge imposed by this remote area is represented by its power supply and communication system. The Pyramid has a completely self-sufficient renewable energy supply and satellite telecommunications systems.

In the laboratory and in the whole Khumbu Valley there are many scientific instruments – environmental observation and monitoring equipment which continuously collects data that is transmitted to researchers’ institutes in real time.

The SHARE project aims to establish a mitigation policy against climate change based on reliable assessments. Eight weather stations have now been installed in the Khumbu valley: two at Pyramid (5,050m and 5,079m ASL), and one in Lukla (2,800m ASL), in Namche Bazar (3,560m ASL), in Pheriche (4,200m ASL), at Kala Patthar (5,600m ASL), at Changri Nup (5,700m ASL) and at Everest South Col (8,000m ASL).

The special climatic chamber used at these sites has been carefully constructed at INRiM using primary instruments, and equipping the system with traceable high level standards of temperature and pressure.

In July 2013 the chamber was transported from Torino to Kathmandu, then from Kathmandu to Lukla, by airplane. From Lukla to Namche the chamber had to wait for appropriate weather conditions for helicopter flights.

Then, the weather conditions prevented the helicopters from bringing the instruments up to the 5,000m altitude at Lobuche, close to the Pyramid. The load was left in the last airport available, in Namche, at 3,600m.

Sherpa porters were then recruited to bring the complete system up to the Pyramid at 5,050m. This motivated a very special design of the calibration chamber, being reduced in weight to components of a maximum 30kg. A key point of this new facility design is that besides a mass reduction, the weight reduction allows a faster thermal stability which is a useful attribute, because of the high value of the energy in this remote laboratory.

The calibration chamber was delivered to the Pyramid after three days of trekking through the Kunbu valley, from Namche, via Tengboche, Periche, Lobuche. When it arrived at the Pyramid, accompanied by INRiM and EV-K2 staff, the equipment was reassembled, and the Nepalese Pyramid staff were trained so that the first calibration campaign could begin.

The Pyramid laboratory, which was already the headquarters of the whole Khumbu valley network, now became the calibration centre for all of these instruments – the highest metrology laboratory in the world.

EURAMET Impact prize, 2013

Since the JRP commenced, activities have consisted of setting up communication systems, engaging stakeholders and disseminating information. In July 2013, these efforts prompted the EURAMET General Assembly to award Andrea Merlone, the coordinator of the project, the EURAMET Impact Prize.

An extraordinary impact was achieved through the establishment of fruitful collaboration and liaisons with international organisations, key institutions and bodies, universities, manufacturers and a number of stakeholders.

A relevant part of the impact achieved by EMRP ENV07 MeteoMet project was based on the personal proposal, organisation and involvement of the coordinator in the dissemination of activities such as workshops in different nations outside Europe; seminars at universities in different countries; visits to meteorological sites; the constant exchange of technical information; the involvement of JCGM chair regarding the adoption of the GUM and VIM by meteorological institutions in the dissemination of their recommendations, guides and manuals.

In addition, Andrea Merlone’s personal membership of international bodies played a part. These bodies include CIPM CCT, IMEKO, EURAMET TC-T, GCOS-GRUAN, ISTI, WMO-*CIMO Expert Team on Standardisation. This created a direct involvement and exchange of documents between the Metrology and Meteorology communities.

The prize was awarded to Andrea Merlone in October, 2013, during TEMPMEKO Conference in Madeira.

Published: 27th May 2014 in AWE International