Air temperature measurement errors in a naturally ventilated multi-plate radiation shield

In observational networks of air temperature, mechanically aspirated radiation shields are often replaced by naturally ventilated radiation shields because of the operational costs. As a multi-plate shield relies on the ambient wind for ventilation, radiative errors tend to occur when radiative forcing on the radiation shield is large and the ambient wind speed is low. Radiative errors need to be considered in correctly interpreting air temperature data collected in a multi-plate shield.

A series of field experiments are conducted to investigate the sources of the radiative errors of a commonly-used system consisting of the Onset HOBO Pro Data Logger external thermistor enclosed in the Davis Instruments multi-plate shield. The amount of solar radiation reaching inside the shield is positively correlated with the ground surface albedo. The deviation of the shield surface temperature from the ambient air temperature generally becomes positive during the daytime and negative at nighttime. The effective thermal inertia of the thermistor-shield system increases with decreasing wind speed. The magnitude of the systematic radiative error within the thermistor-shield system is assessed by comparing it with a RTD sensor in a mechanically aspirated shield. Empirical models are developed for correcting temperature errors using information on wind speed and net or solar radiation. The same empirical models may be applicable for systems consisting of different sensors and multi-plate shields by empirically determining new coefficients in the models.