Comparisons of New York State Mesonet (NYSM) and ASOS Data: Implication to Users

The New York State Mesonet (NYSM) consists of 126 stations across the state with an average spacing of 19 miles (see map below). All stations collect measurements of standard meteorological variables with additional soil moisture at three levels, solar radiation, snow depth and still camera images. In addition, in a first for a state mesonet, NYSM has three sub-networks (“Profiler”, “Flux”, and “Snow”) comprised of 17, 17, and 20 sites to provide atmospheric vertical profiles, the surface energy budget, and snow water equivalent, respectively. In comparison, there are 27 Automated Surface Observing System (ASOS) stations in NYS. Comparing the two networks, the 27 ASOS stations are very sparse with gaps in mountainous regions and are mostly located at airports, which raises the issue of ASOS representativeness. ASOS has been in operation since 1947 and has been widely used for a variety of applications. In contrast, NYSM just became operational 15 August 2015, but it is very promising given its better spatial coverage, more variables and more advanced instruments. Therefore, it is important to compare the data from the two networks for cross-validation, investigate impacts of potential biases in each dataset on prior and future studies and inform the user community.

Six pairs of NYSM and ASOS stations are located within 10 km of one another and are selected for comparison (see map below). Temperature, humidity, pressure, wind and precipitation are compared for one year of data (July 2017-June 2018). Preliminary results show that ASOS temperature is systematically warmer than NYSM by a monthly mean of ~0.5°C during daytime, but colder by as much as 2°C in summer on average. As a result, ASOS would significantly overestimate diurnal temperature range (DTR). The small warm bias in ASOS data exists in both day and night, but there are large cold biases in ASOS data for some days when wind is calm. It seems that land cover difference (NYSM grass land vs. ASOS concrete airport) is the primary reason for temperature discrepancies. It would be interesting to study how the biases in ASOS data affect prior research using ASOS data, such as long-term trends of surface temperature and DTR. The comparisons for other variables and the impacts of the results will also be studied.

Figure Map of 126 NYSM stations (in green nails), 27 ASOS stations (small white circles) and 6 matched stations (large white circles).