A cautionary note on the computation of daily mean temperatures and their trends

Abstract

There are different methodologies to compute daily mean temperatures (DMT), including averaging the 24-hourly temperature values, readings at specific times throughout the day or simply averaging the minimum and maximum daily temperatures. This study provides an intercomparison of some of such methods applied to six meteorological stations in Argentina with continuous hourly measurements for a period of more than 24 years. Results show that differences arising from the various methodologies are largely dependent on the local weather conditions, particularly those related to cloud cover and wind intensity, while the role of air moisture is less important. Furthermore, trends derived from DMT estimates using different methodologies are found to be highly sensitive to the chosen method. In fact, statistically insignificant trends could be significant should other methodologies to calculate DMT had been used. This result could be of importance for diverse scientific areas such as agriculture or climate warming studies.