Comparison of Maximum–Minimum Resistance and Liquid-in-Glass Thermometer Records

Abstract

The replacement of liquid-in-glass (LIG) thermometers with electronic thermometers in the National Weather Service (NWS) cooperative (co-op) network and concern for homogeneous temporal temperature records prompted this comparison study between the two temperature sensors. This study shows that the new National Weather Service maximum-minimum temperature sensors (MMTS) underestimate LIG maximum temperatures by as much as 0.6°C, but are virtually equal to LIG minimum temperatures. The magnitude of differences increases with increasing solar loading and decreased wind speeds, apparently due to better ventilation characteristics of the MMTS shelter compared to those of a cotton-region shelter. Any comparison of MMTS records with the LIG record will therefore require wind and solar observations. Unfortunately, neither wind nor solar is measured at NWS co-op sites, requiring the use of data from the nearest observing station. Obviously, the time of change from LIG sensors to the MMTS is of paramount importance when evaluating long-term temperature change.