scholarly journals Errors of Naturally Ventilated Air Temperature Measurements in a Spatial Observation Network

2008 ◽  
Vol 25 (11) ◽  
pp. 2145-2151 ◽  
Author(s):  
Matthias Mauder ◽  
R. L. Desjardins ◽  
Zhiling Gao ◽  
Ronald van Haarlem
Keyword(s):  
Solar Radiation ◽  
Air Temperature ◽  
Agricultural Land ◽  
Sensible Heat Flux ◽  
Temperature Sensors ◽  
Radiative Heating ◽  
Temperature Measurements ◽  
Observation Network ◽  
Temporal Averaging ◽  
Radiation Shields

Abstract A spatial network of 25 air temperature sensors was deployed over an area of 3.5 km × 3.5 km of agricultural land, aiming to calculate the sensible heat flux by spatial averaging instead of temporal averaging. Since temperature sensors in naturally ventilated solar radiation shields were used for these measurements, a correction for radiative heating had to be applied. In this study, the approach of Anderson and Baumgartner was adapted to the cube-shaped HOBO solar radiation shields. This semiempirical correction depends on the shield’s area normal to the sun in addition to solar radiation and wind speed. The required correction coefficients, which can be universally applied for this type of shield, were obtained through comparison with fan-aspirated temperature measurements at one site. The root-mean-square error of the HOBO temperature measurements was reduced from 0.49° to 0.15°C after applying this radiation correction.

Solar and Thermal Radiation Errors on Upper-Air Radiosonde Temperature Measurements

2013 ◽  
Vol 30 (10) ◽  
pp. 2382-2393 ◽  
Author(s):  
R. Philipona ◽  
A. Kräuchi ◽  
G. Romanens ◽  
G. Levrat ◽  
P. Ruppert ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Thermal Radiation ◽  
Air Temperature ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Atmospheric Temperature ◽  
Radiative Heating ◽  
Temperature Measurements ◽  
High Quality

Abstract Atmospheric temperature and humidity profiles are important for weather prediction, but climate change has increased the interest in upper-air observations asking for very high-quality reference measurements. This paper discusses an experimental approach to determine the radiation-induced error on radiosonde air temperature measurements. On the one hand, solar shortwave and thermal longwave radiation profiles were accurately measured during radiosonde ascents from the surface to 35-km altitude. On the other hand, air temperature was measured with several thermocouples on the same flight, simultaneously under sun-shaded and unshaded conditions. The radiation experiments reveal that thermal radiation errors on the very thin thermocouple of the Meteolabor SRS-C34 radiosonde are similar during night- and daytime. They produce a radiative cooling in the lower troposphere and the upper stratosphere, but a radiative heating in the upper troposphere and lower stratosphere. Air temperature experiments with several thermocouples, however, show that solar radiation produces a radiative heating of about +0.2°C near the surface, which linearly increases to about +1°C at 32 km (~10 hPa). The new solar radiation error profile was then applied to SRS-C34 measurements made during the Eighth WMO Intercomparison of High Quality Radiosonde Systems, held in Yangjiang, China, in July 2010. The effects of thermal and solar radiation errors are finally shown in contrast to the 10 other internationally used radiosonde systems, which were flown during this international campaign.

Mechanically Aspirated Solar Radiation Shields: A CFD and Neural Network Design Analysis

2001 ◽  
Author(s):  
B. M. Fichera ◽  
R. L. Mahajan ◽  
T. W. Horst
Keyword(s):  
Neural Network ◽  
Solar Radiation ◽  
Temperature Sensor ◽  
Temperature Measurements ◽  
Analysis And Design ◽  
Computational Fluid Dynamics Analysis ◽  
Radiation Shields ◽  
Input Variables ◽  
The Relationship

Abstract Accurate air temperature measurements made by surface meteorological stations are demanded by climate research programs for various uses. Heating of the temperature sensor due to inadequate coupling with the environment can lead to significant errors. Therefore, accurate in-situ temperature measurements require shielding the sensor from exposure to direct and reflected solar radiation, while also allowing the sensor to be brought into contact with atmospheric air at the ambient temperature. The difficulty in designing a radiation shield for such a temperature sensor lies in satisfying these two conditions simultaneously. In this paper, we perform a computational fluid dynamics analysis of mechanically aspirated radiation shields (MARS) to study the effect of geometry, wind speed, and interplay of multiple heat transfer processes. Finally, an artificial neural network model is developed to learn the relationship between the temperature error and specified input variables. The model is then used to perform a sensitivity analysis and design optimization.

scholarly journals Outdoor Air Temperature Measurement: A Semi-Empirical Model to Characterize Shelter Performance

Climate ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 26
Author(s):  
Jérémy Bernard ◽  
Pascal Kéravec ◽  
Benjamin Morille ◽  
Erwan Bocher ◽  
Marjorie Musy ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Response Time ◽  
Air Temperature ◽  
Empirical Model ◽  
Regression Coefficient ◽  
Radiation Sensitivity ◽  
Temperature Sensors ◽  
Outdoor Air ◽  
The One ◽  
Semi Empirical

Shelters used to protect air temperature sensors from solar radiation induce a measurement error. This work presents a semi-empirical model based on meteorological variables to evaluate this error. The model equation is based on the analytical solution of a simplified energy balance performed on a naturally ventilated shelter. Two main physical error causes are identified from this equation: one is due to the shelter response time and the other is due to its solar radiation sensitivity. A shelter intercomparison measurement campaign performed by the World Meteorological Organization (WMO) is used to perform a non-linear regression of the model coefficients. The regression coefficient values obtained for each shelter are found to be consistent with their expected physical behavior. They are then used to simply classify shelters according to their response time and radiation sensitivity characteristics. Finally, the ability of the model to estimate the temperature error within a given shelter is assessed and compared to the one of two existing models (proposed by Cheng and by Nakamura). For low-response-time shelters, our results reduce the root mean square error by about 15% (0.07 K) on average when compared with other compensation schemes.

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

2021 ◽  
Vol 14 (9) ◽  
pp. 6195-6212
Author(s):  
Chiara Musacchio ◽  
Graziano Coppa ◽  
Gaber Begeš ◽  
Christina Hofstätter-Mohler ◽  
Laura Massano ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Air Temperature ◽  
Incident Radiation ◽  
Data Availability ◽  
Temperature Measurements ◽  
Natural Soil ◽  
Quality Of Data ◽  
Full Data ◽  
Near Surface ◽  
Meteorological Observations

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.

Radiation Effects on Natural Convection Between Horizontal Walls With Heated Upper Plate

2000 ◽  
Author(s):  
Giuseppe Guidotti ◽  
Oronzio Manca ◽  
Sergio Nardini ◽  
Biagio Morrone
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Air Temperature ◽  
Radiation Effects ◽  
Fluid Layer ◽  
Radiation Heat Transfer ◽  
Mean Value ◽  
Radiative Heating ◽  
Temperature Measurements ◽  
Secondary Motion

Abstract Radiation heat transfer affects natural convection of air inside an open ended cavity with a heated horizontal upper plate and an unheated lower parallel plate. The influence is mainly due to radiative heating of the lower plate, and plane fluid layer secondary motion could arise. In this paper an experimental study is carried out to describe and to detect the influence of radiation on air flow and on heat transfer coefficient by means of wall temperature profiles, smoke visualization, and air temperature measurements. The analysis is obtained for an emissivity of the horizontal plates equal to 0.8, for distances between the plates of 20.0, 32.3, and 40.0 mm. By means of flow visualization and local air temperature measurements in the cavity as a function of time, remarkable secondary motion in the cavity is observed when qΩ is equal to 120 W/m2. Measurement of the air temperature in the cavity also shows that radiation causes and damps secondary motion at the same time. Profiles of the mean value of the air temperature as a function of the x and y coordinates confirm both the main flow path inside the cavity and radiation effects on convective heat transfer. Finally, correlations related to average Nusselt number are proposed for natural convection as well as for heat transfer as a whole, that is convection along with radiation.

scholarly journals Solar radiation exposure of shielded air temperature sensors and measurement error evaluation in an urban environment: a preliminary study in Florence, Italy

2009 ◽  
Vol 3 (1) ◽  
pp. 9-12 ◽  
Author(s):  
M. Petralli ◽  
L. Massetti ◽  
S. Orlandini
Keyword(s):  
Solar Radiation ◽  
Radiation Exposure ◽  
Air Temperature ◽  
Urban Areas ◽  
Thermal Conditions ◽  
Surface Characteristics ◽  
Temperature Sensors ◽  
Island Effect ◽  
Synoptic Conditions ◽  
Solar Radiation Exposure

Abstract. Particularly in summer, thermal conditions in urban areas are influenced by solar radiation and human health can be strongly affected by the higher temperature regime increased by the Urban Heat Island effect (UHI). Many studies have been carried out to estimate the temperature distribution in urban areas and some of these use or are based on data collected by meteorological instruments placed within the cities. At microscale, temperature collected by sensors can be influenced by the underlying surface characteristics and the closeness to warm surfaces. The aim of this study is to investigate how different exposure to solar radiation can affect air temperature measurement in streets and gardens. The study was carried out on two different areas in Florence during summer 2007. Shielded air temperature sensors were placed in a street of a high density built-up area and in a green area. Each area was monitored by two sensors, sited in different solar radiation exposure: one in a sunny area and the other in a shaded one. A preliminary data analysis showed a difference in every site between the air temperature values collected by the two sensors especially from the morning to the afternoon. The relationship between air temperature differences and synoptic meteorological conditions were also analyzed. In conclusion, the solar radiation exposure of a monitoring station is an important parameter that must be considered both during the instruments siting and the analysis of data collected by sensors previously placed. The result of this study shows that during particular synoptic conditions, data collected by the two sensors of the same area can be different.

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

2021 ◽  
Author(s):  
Chiara Musacchio ◽  
Graziano Coppa ◽  
Gaber Begeš ◽  
Christina Hofstätter-Mohler ◽  
Laura Massano ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Air Temperature ◽  
Temperature Data ◽  
Data Availability ◽  
Temperature Measurements ◽  
Data Series ◽  
Quality Of Data ◽  
Full Data ◽  
Near Surface ◽  
Meteorological Observations

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.

Thermometry

2001 ◽  
Author(s):  
Fred V. Brock ◽  
Scott J. Richardson
Keyword(s):  
Air Temperature ◽  
Temperature Difference ◽  
Initial Conditions ◽  
Numerical Models ◽  
Global Climate ◽  
Global Climate Model ◽  
Temperature Sensors ◽  
Physical Principle ◽  
Absolute Temperature ◽  
Temperature Measurements

Air temperature is one of the most fundamental of all meteorological measurements and directly effects our everyday lives. It has been measured for centuries, using countless different techniques. One might assume that accurate air temperature measurements are readily made. Indeed, it is possible to make very accurate air temperature measurements but it can be a remarkably hard task, especially when limitations such as power consumption, reliability, and cost are involved. Errors in the measurement of air temperature in excess of 2 to 3°C are not uncommon in many networks. Errors of this magnitude are generally acceptable for the general public who is most interested in what clothes to wear for the day. However, numerical models at all scales of motion (mesoscale, synoptic scale, or climate models) are greatly affected by errors even as large as 1°C. Errors of just 1°C in a mesoscale model have been shown to be the deciding factor between no storms initiated and intense storms (Crook, 1996). In addition, errors as small as 0.2°C can change the prediction of a global climate model, depending on its dependency on initial conditions (DeFelice, 1998). Measurement of air temperature near the surface of the earth is facilitated by the vast array of temperature sensors and supporting electronic modules that are readily available. Accuracy is limited not by technology but by our ability to use it and by our ability to avoid exposure error, that is, to provide adequate coupling with the atmosphere. The preferred temperature scales are Celsius and Kelvin. These scales can be used almost interchangeably (except when absolute temperature is required) because a temperature difference of 1 K is equal to a temperature difference of 1°C. The Fahrenheit scale is still in general use by the U.S. public. Some common temperature reference points are shown in table 4-1. The triple point of water is the temperature and pressure where all three phases, gas, liquid, and solid, can coexist. Temperature sensors can be categorized according to the physical principle that they use: thermal expansion, thermoelectric, electrical resistance, electrical capacitance and some other effects.

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