Observational Perspectives from U.S. Climate Reference Network (USCRN) and Cooperative Observer Program (COOP) Network: Temperature and Precipitation Comparison

Abstract

The U.S. Cooperative Observer Program (COOP) network was formed in the early 1890s to provide daily observations of temperature and precipitation. However, manual observations from naturally aspirated temperature sensors and unshielded precipitation gauges often led to uncertainties in atmospheric measurements. Advancements in observational technology (ventilated temperature sensors, well-shielded precipitation gauges) and measurement techniques (automation and redundant sensors), which improve observation quality, were adopted by NOAA's National Climatic Data Center (NCDC) into the establishment of the U.S. Climate Reference Network (USCRN). USCRN was designed to provide high-quality and continuous observations to monitor long-term temperature and precipitation trends, and to provide an independent reference to compare to other networks. The purpose of this study is to evaluate how diverse technological and operational choices between the USCRN and COOP programs impact temperature and precipitation observations. Naturally aspirated COOP sensors generally had warmer (10.488C) daily maximum and cooler (20.368C) minimum temperatures than USCRN, with considerable variability among stations. For precipitation, COOP reported slightly more precipitation overall (1.5%) with network differences varying seasonally. COOP gauges were sensitive to wind biases (no shielding), which are enhanced over winter when COOP observed (10.7%) less precipitation than USCRN. Conversely, wetting factor and gauge evaporation, which dominate in summer, were sources of bias for USCRN, leading to wetter COOP observations over warmer months. Inconsistencies in COOP observations (e.g., multiday observations, time shifts, recording errors) complicated network comparisons and led to unique bias profiles that evolved over time with changes in instrumentation and primary observer.

Inconsistency in precipitation measurements across the Alaska–Yukon border

“…It is also important for climate change analyses over the cold regions. Leeper et al (2015), in comparison of USCRN with the COOP station network precipitation measurements, averaged the USCRN hourly temperature data during precipitation periods into an event mean and used it to group precipitation events into warm (mean temperature > 5 • C), near-freezing (mean temperature between 0 and 5 • C), and freezing (mean temperature < 0 • C) conditions. Yang et al (2005) used the daily mean air temperature to estimate precipitation types (snow, mixed, and rain) when this information was not available for the northern regions.…”

“…Efforts have been reported to examine the precipitation discontinuity within a country (Groisman and Easterling, 1994;Sanderson, 1975). Leeper et al (2015) found that the US Cooperative Observer Program (COOP) Network stations reported slightly more precipitation overall (1.5 %), with network differences varying seasonally. The COOP gauges were sensitive to wind biases, particularly over winter when COOP observed (10 %) less precipitation than the US Climate Refer- ence Network (USCRN).…”

Making better sense of the mosaic of environmental measurement networks: a system-of-systems approach and quantitative assessment

“…Several networks remarked upon completion that the exercise had been useful and had led to discussions around potential innovations or improvements which could yield increased assessment scores in any future assessment but, more importantly, increase accessibility, usability and robustness of their measurement systems. This benefit was felt most strongly for those networks with a central mission to provide the highest possible quality measurements such as USCRN (Diamond et al, 2013;Leeper et al, 2015), TCCON, NDACC and EARLINET. For example, the results of the NDACC assessment were discussed in depth at their most recent annual meeting and this led to several suggestions for improvements.…”

Evaporation from weighing precipitation gauges: impacts on automated gauge measurements and quality assurance methods

“…However, recent research comparing USCRN with COOP stations indicate gauge evaporation can bias observations even when taken frequently at a sub-hourly rate (Leeper et al, 2015a). The USCRN monitors precipitation at a 5 min frequency from a well-shielded automated funnel-less gauge whereas COOP stations operate a manual funnel-capped gauge that is checked daily.…”