Impacts of vertical resolution in the Coupled Ocean / Atmosphere Mesoscale Prediction System on atmospheric boundary layer structure and radio refractivity over the Sea of Japan

Due in part to the affordability of increased vertical resolution, mesoscale numerical weather prediction (NWP) has gained acceptance in recent years as a tool to resolve four dimensional radio refractivity gradients found in stable internal boundary layers (SIBL), mixing layers and entrainment layers. These radio refractivity gradients have the potential to trap radio frequency energy over long distances and compromise the performance of marine radar and communication systems. SIBLs and entrainment layers tend to be shallow and are difficult to resolve without significant NWP vertical resolution. This paper will describe the results of a multi vertical level modeling study of a significant radio refractivity event during a cold frontal passage over the Sea of Japan. The Coupled Ocean / Atmosphere Mesoscale Prediction System (COAMPS®) was employed using three vertical resolutions of 40, 58, and 70 sigma levels with a 3 km horizontal resolution. Vertical profiles of potential temperature, water vapor mixing ratio, modified refractivity and winds were analyzed to understand how the vertical resolution variations affect the modified refractivity profiles and related surface-based ducting. Understanding the variations in trapping layer or duct height and strength caused by differing vertical resolutions will allow optimization of mesoscale NWP models for the radio frequency propagation decision support systems.