Enhancing Weather Observations: Bridging The Gap Between Airborne Measurements and ASOS data

Abstract

Diagnosing the intensity of precipitation during winter is a challenge due to observational uncertainty and representativeness. Automated Surface Observing System (ASOS) stations are widely distributed across the United States, providing on-site current weather conditions to help with go/no-go decisions at airports and other purposes. Despite their many capabilities, previous research highlighted ASOS limitations with regards to precipitation type classification (e.g., ice pellets, drizzle, freezing drizzle and freezing rain) and snow accumulation rates. This study enhances these studies by investigating how well ASOS captures precipitation intensity and spatial variability during winter storms. ASOS reported intensities are compared against those derived from airborne ground-based reflectivity collected during the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign. Using radar reflectivity from the Ku and Ka-band High Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) on the NASA ER-2 aircraft, 50 samples from IMPACTS 2020, 2022, and 2023 collocated with ASOS stations were analyzed. Cases were identified when the NASA ER-2 passed within 6.5 km of an ASOS station. Mean reflectivies taken at 0.1 km above the surface were converted to mass fluxes using Z-R and Z-S relationships and compared to ASOS-reported rates for light and moderate intensity cases. For both rain and snow cases, ASOS light intensity reports often missed areas of enhanced reflectivity captured by the HIWRAP. Additionally, statistical analysis revealed an overlap in mean reflectivities between ASOS-reported light and moderate intensities, suggesting ASOS intensity reports may not fully represent precipitation surrounding the site. Further research can explore environmental conditions leading to these discrepancies and expanding cases by using other airborne field campaigns to examine ASOS performance.