Response times of meteorological air temperature sensors

Burt, Stephen; Podesta, Michael de

doi:10.1002/qj.3817

Cited by 18 publications

(15 citation statements)

References 16 publications

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“…Data availability. Original raw data are available at https://doi.org/10.5281/zenodo.5126973 (Coppa et al, 2021a).…”

Section: Discussionmentioning

confidence: 99%

“…Among the numerous observed essential climate variables (ECVs), near-surface (1.25-2 m; WMO, 2012) atmospheric air temperature measurements have been collected for 150 years. Such data series form the basis of scientific knowledge on local and global climate trends (Camuffo and Jones, 2002). Land-based stations are equipped with different kinds of thermometers whose performances have constantly improved.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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Abstract. Solar radiation is one of the main factors which introduce significant deviations between thermometers reading and true air temperature value. Techniques to protect the sensors from direct radiative influence have been adopted almost since the beginning of meteorological observations. Reflected radiation from a snow-covered surface can also cause extra warming to thermometers hosted in solar shields, which are not always optimised to protect the sensors from this further radiative heat transfer. This phenomenon can cause errors in near-surface temperature measurements results, with a relevant impact on the quality of data records and series. This study experimentally evaluates the effect of reflected radiation from a snow-covered surface on the accuracy of air temperature measurements. The investigation is based on the evaluation of temperature differences between pairs of identical instruments, positioned above ground covered by natural vegetation, with one instrument in snow-free conditions and the other above a snow-covered surface, at the same time and at the same site. The work involved a representative number of sensors and shields, in terms of different typologies, technologies and engineering solutions, from different manufacturers. A mountain site with acceptable field conditions, offering long-lasting snow presence to maximise data availability, was selected to perform the experiment. Quantities of influence, such as relative humidity, wind speed and direction and solar radiation (global and reflected), were constantly measured. The main findings of this work show that none of the involved instruments were immune to the extra heating due to the snow-reflected radiation. Excluding nighttimes and days of high wind or low incident radiation, the differences among sensors positioned above natural soil and identical ones exposed to snow albedo ranged up to more than 3 ∘C. Solar screens with forced ventilation showed a partially reduced effect compared to most of the naturally ventilated ones. A full data analysis is reported here, together with complete results and uncertainties.

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“…Data availability. Original raw data are available at https://doi.org/10.5281/zenodo.5126973 (Coppa et al, 2021a).…”

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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“…9 of an instantaneous 5 K fall in temperature (and constant 85 % RH) at t = 0 s, assuming response times that are given in Table 2. It should be noted that the response times set out in Table 2 are representative of the fastest commercial Pt100 sensors available in 2020 (Burt and de Podesta, 2020) and that the response times of typical Pt100 sensors are almost certainly slower still. Table 3.…”

Section: Implications For Sensor Averaging Timementioning

confidence: 99%

“…Comparison of calculated response times (s) for a nominal "bare" PRT of 3 mm diameter in varying airflow, and for the same sensor sleeved in a (dry) wick -here representing two identical sensors where the response time differences are due solely to the presence of the wick around the sensor. Based upon experimental work and empirical relationships described inBurt and de Podesta (2020).…”

mentioning

confidence: 99%

Measurements of natural airflow within a Stevenson screen and its influence on air temperature and humidity records

Burt

2022

Geosci. Instrum. Method. Data Syst.

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Abstract. Climate science depends upon accurate measurements of air temperature and humidity, the majority of which are still derived from sensors exposed within passively ventilated louvred Stevenson-type thermometer screens. It is well-documented that, under certain circumstances, air temperatures measured within such screens can differ significantly from “true” air temperatures measured by other methods, such as aspirated sensors. Passively ventilated screens depend upon wind motion to provide ventilation within the screen and thus airflow over the sensors contained therein. Consequently, instances of anomalous temperatures occur most often during light winds when airflow through the screen is weakest, particularly when in combination with strong or low-angle incident solar radiation. Adequate ventilation is essential for reliable and consistent measurements of both air temperature and humidity, yet very few systematic comparisons to quantify relationships between external wind speed and airflow within a thermometer screen have been made. This paper addresses that gap by summarizing the results of a 3-month field experiment in which airflow within a UK-standard Stevenson screen was measured using a sensitive sonic anemometer and comparisons made with simultaneous wind speed and direction records from the same site. The mean in-screen ventilation rate was found to be 0.2 m s−1 (median 0.18 m s−1), well below the 1 m s−1 minimum assumed in meteorological and design standard references, and only about 7 % of the scalar mean wind speed at 10 m. The implications of low in-screen ventilation on the uncertainty of air temperature and humidity measurements from Stevenson-type thermometer screens are discussed, particularly those due to the differing response times of dry- and wet-bulb temperature sensors and ambiguity in the value of the psychrometric coefficient.

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“…The characterization was then performed in a controlled environment with slow temperature change, to keep into account possible effects, without being affected too much by the sensors' dynamics. Too rapid air temperature transients will in fact not be included in the final data analysis, since sensors dynamics can predominantly influence the trueness of the analysis (Burt and de Podesta, 2020). All sensors underwent the laboratory characterisation in order to obtain the information reported in table 3.…”

Section: Laboratory Activitiesmentioning

confidence: 99%

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

Musacchio¹,

Coppa²,

Beges³

et al. 2021

Preprint

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Abstract. Solar radiation is one of the main factors introducing significant deviations between thermometers reading and true air temperature value. Techniques to protect the sensors from direct radiative influence have been adopted almost since the beginning of meteorological observations. Reflected radiation from snow-covered surface can also cause extra warming to thermometers hosted in solar shields, not always optimized to protect the sensors from this further backward radiative heat transfer. This phenomenon can cause errors in near-surface temperature data series, with relevant impact on the quality of data records. The study here presented experimentally evaluates the effect of albedo radiation from snow-covered surface, on the accuracy of air temperature measurements. The investigation is based on evaluating temperature differences between couples of identical instruments positioned above ground covered by natural vegetation, being one in snow-free conditions and the other above snow-covered surface, at the same time in the same site in close vicinity. The work involved a representative number of different typologies of sensors and shields from different manufactures. A mountain site with appropriate field conditions, offering long-lasting snow presence to maximize data availability, was selected to host the experiment. Quantities of influence such as relative humidity, wind speed and direction, solar radiation (direct and reflected) were constantly measured. The effect was evaluated to range up to more than 3 °C for some typologies of sensors. Full data analysis is here reported, together with complete results. This main scope of this work is to report on an experimental estimation and method to evaluate and include this effect as a component of uncertainty in temperature data series for near-surface stations above snowy areas.

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Response times of meteorological air temperature sensors

Cited by 18 publications

References 16 publications

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

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

Measurements of natural airflow within a Stevenson screen and its influence on air temperature and humidity records

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

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