Premium
Ventilation effects on humidity measurements in thermometer screens
Author(s) -
Harrison R. G.,
Wood C. R.
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.985
Subject(s) - hygrometer , thermometer , humidity , relative humidity , thermocouple , meteorology , wet bulb temperature , environmental science , wind speed , ventilation (architecture) , dew point , atmospheric sciences , dry bulb temperature , materials science , thermodynamics , physics , composite material
Abstract Relative humidity (RH) measurements, as derived from wet‐bulb and dry‐bulb thermometers operated as a psychrometer within a thermometer screen, have limited accuracy because of natural ventilation variations. Standard RH calculations generally assume a fixed screen psychrometer coefficient, but this is too small during poor ventilation. By comparing a reference humidity probe—exposed within a screen containing a psychrometer—with wind‐speed measurements under controlled conditions, a wind‐speed correction for the screen psychrometer coefficient has been derived and is applicable when 2‐metre wind speeds fall below 3 m s −1 . Applying this to hourly‐averaged data reduced the mean moist RH bias of the psychrometer (over the reference probe) from 1.2% to 0.4%, and reduced the interquartile range of the RH differences from 2.0% to 0.8%. This correction is particularly amenable to automatic measurement systems. Copyright © 2011 Royal Meteorological Society