Surface air temperature is one of the basic climate system variables that were identified by the National Research Council as relevant to the detection, attribution, and direct societal impacts of climate change. Unfortunately, drawbacks and changes in instrument systems could cause problems of biases and inhomogeneity in temperature data collected and blended from past and present national observing systems. High-quality measurements from the instrument system with superior performance, such as the one from the U.S. Climate Reference Network (USCRN), are therefore needed to identify and correct those biases and hence to create long-term homogeneious observations. The USCRN is a National Oceanic and Atmospheric Administration (NOAA)-sponsored network and research initiative. The first and foremost objective of the USCRN instrument suite is to provide benchmark quality air temperature and precipitation measurements free of time-dependent biases.

A comparative study of temperature measurements from Automated Surface Observing System (ASOS) and CRN will be presented, based on measurements from two locations, Sterling, VA and Asheville, NC. The Sterling, VA facility is the site that was selected to support the National Intercomparison of National Weather Service (NWS) and USCRN Sensors under the same environmental conditions. At the Asheville site, the ASOS station is located nearby the Asheville Regional Airport, which is about 1.5-miles away from the CRN station at the Horticultural Crops Reservation Center. Effects of the siting difference at the Asheville site can be significant. The objective of this study is to evaluate the influence of solar radiation, infrared radiation, and ambient wind speed on the accuracy of ASOS temperature measurements. Influence of different reporting practices (ASOS vs. CRN) and siting difference effect are also discussed.