The Effectiveness of the ASOS, MMTS, Gill, and CRS Air Temperature Radiation Shields

Abstract

Periodic upgrades of air temperature measurement systems in surface weather station networks cause data discontinuities. From a climatological viewpoint, it is necessary to evaluate the air temperature data discontinuities when air temperature radiation shields are upgraded. This study was undertaken to investigate the effectiveness of four common air temperature radiation shields including the Automated Surface Observing System (ASOS), the Maximum?Minimum Temperature System (MMTS), the Gill, and the Cotton Region Shelter (CRS) shields. The solar radiation shielding effectiveness for each shield under typical grass ground surface and different artificial surfaces (black, white, and aluminum) were investigated. The shield effectiveness was evaluated by measuring the interior solar irradiance and the inner surface temperatures of radiation shields. Parabolic curves describe the fraction of solar radiation entering shields, which increased as the solar reflectivity of the underlying surface increased. The rank of solar radiation shield effectiveness was ASOS > CRS > MMTS > Gill (i.e., total interior solar irradiance loading in relative terms was ASOS:CRS:MMTS:Gill = 1:1.3:1.7:2.5), under typical grass surface conditions. The increase in interior solar irradiance from the typical grass surface to the white surface went up by a factor of 1.2, 2.3, 1.6, and 1.9, respectively, for the ASOS, MMTS, Gill, and CRS shields. The ASOS shield had an obvious drawback for the infrared radiation effectiveness due to using the chilled mirror heating/cooling system as the dewpoint temperature measuring system located in the middle portion of the shield. The rank of the infrared radiation shielding effectiveness was CRS > MMTS > Gill > ASOS during daytime and Gill ≥ MMTS > CRS ≈ ASOS during nighttime.