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Lag‐time effects on a naturally ventilated large thermometer screen
Author(s) -
Harrison R. G.
Publication year - 2011
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.745
Subject(s) - thermometer , daytime , wind speed , lag , atmospheric sciences , environmental science , ventilation (architecture) , time lag , meteorology , air temperature , radiation , materials science , physics , optics , thermodynamics , computer network , computer science
Systematic natural ventilation effects on measured temperatures within a standard large wooden thermometer screen are investigated under summer conditions, using well‐calibrated platinum resistance thermometers. Under low ventilation (2 m wind speed u 2 < 1.1 m s −1 ), the screen slightly underestimates daytime air temperature but overestimates air temperature nocturnally by 0.2°C. The screen's lag time L lengthens with decreasing wind speed, following an inverse power law relationship between L and u 2 . For u 2 > 2 m s −1 , L ∼ 2.5 min, increasing, when calm, to at least 15 min. Spectral response properties of the screen to air temperature fluctuations vary with wind speed because of the lag changes. Ventilation effects are particularly apparent at the higher (>25° C ) temperatures, both through the lag effect and from solar heating. For sites where wind speed decreases with increasing daytime temperature, thermometer screen temperatures may consequently show larger uncertainties at the higher temperatures. Under strong direct beam solar radiation (>850 W m −2 ) the radiation effect is likely to be <0.4° C . Copyright © 2011 Royal Meteorological Society