Metrological evaluation of the effect of the presence of a road on near‐surface air temperatures

Abstract

With the purpose of revising World Meteorological Organization's Commission for Instruments and Methods of Observation (WMO/CIMO) Guide #8 on weather stations siting, an experiment to evaluate metrologically the maximum influence of a paved road on 2-m air temperature measurements ("road siting effect") has been designed, installed and run in Italy. It consists of a 100-m long array of seven measurement stations, at increasing distances from a local road, equipped with shielded Pt100 thermometers and ancillary sensors.Data coming from 1 year of observations have been analysed for daily climatological metrics, finding that the road mostly effects minimum temperatures, with average values of $0.30 ± 0.18 C at a distance of 1 m; then, in order to quantify the instrumental effect on the measurement, data were filtered by applying a generalized additive model, selecting only times when the effect is more intense (during nights, in presence of low winds coming from the road), and the road siting effect has been calculated by modelling the maximum temperature differences by using extreme values analysis. The 1-year return value on 10-min measurements is 1.22 ± 0.30 C at 1 m from the road, with a gradual decline ($0.1 CÁm −1 ), while an extrapolation to 100-year return level gives a value of 1.71 ± 0.79 C with a decline rate of about 0.17 CÁm −1 . This is a first step towards a redefinition of the weather station classification scheme of WMO/CIMO Guide #8, together with building and tree effects experiments which have been run in parallel with the road siting experiment here presented and which will be presented elsewhere.

Effect of snow-covered ground albedo on the accuracy of air temperature measurements

“…In any case, this would go beyond the scope of the work, given that it focused on relative differences caused by reflected radiation only, and that there is much more literature dealing with the effect of incident radiation. Erell et al (2005), for instance, showed that no shield provides complete protection from incident radiation, with relative uncertainties up to 1.5 • C. Lopardo et al (2014), showed that an aged, darkened screen can introduce uncertainties up to a similar values, especially at daily maxima.…”

“…Only a 3 m wide local road with almost no traffic and a small unoccupied building were present in the area at a distance of more than 50 m from the measuring point. Coppa et al (2021b) performed a metrological quantification of the influences on air temperature measurements introduced by the proximity of roads that revealed a significant effect only at closer distances (less than 50 m) and mainly at very low or even null values of incident radiation; the presence of this infrastructure was therefore considered negligible. According to a similar experiment for the evaluation of the effect of buildings (Garcia Izquierdo et al, 2021), a building of the size of the hut and at that distance causes no influence in air temperature records.…”

“…In other, similar, experiments about obstacle effects on near-surface temperature measurements, it often emerges that wind dominates radiation. For instance, Coppa et al (2021b) showed that, in the case of strong winds, turbulent mixing of heat to higher atmospheric layers has an influence on temperature 2 m lower than where the sensors are located. Differently from the pas- sive screen systems, fan-aspirated type A seems to be independent from wind speed (Fig.…”

Effect of snow-covered ground albedo on the accuracy of air temperature measurements

“…Only a 3-m wide local road with almost no traffic and a small unmanned building were present in the area, at more than 50 m from the measuring point. Coppa et al, (2021) performed a metrological quantification of the influences on air temperature measurements introduced by the proximity of roads, that revealed a significant effect only at closer distances (less than 50 m) and mainly at very low or even null values of incident radiation. Since for this experiment only records associated to sun radiation are relevant and the road is at more than 50 m, its presence was considered negligible.…”

Air temperature dependencies on the structure of thermometer screens in summer at Daejeon, South Korea

“…Therefore, a thermometer screen with various structures is designed and used to observe air temperature (van der Meulen & Brandsma, 2008). However, the thermometer screens of various designs have different structures, therefore, they have their thermal characteristics (Coppa et al, 2021). While observing the temperature, the inherent thermal characteristics of the thermometer screen get influenced, causing differences between the structures of the thermometer screen even in the same weather station (WS) (Aoshima et al, 2010).…”