Capturing characteristics of atmospheric refractivity using observation and modeling approaches

Abstract

Electromagnetic wave propagation is sensitive to gradients of refractivity derived from atmospheric temperature, humidity, and pressure. It is thus critical to understand the atmospheric conditions leading to the formation of the gradient layers and explore methods to better represent the gradients in forecast models. This study first examines the sensitivity of the surface evaporative ducts to key physical parameters of the atmospheric surface layers. This analytical study is followed by analyses of relationships between the ducting/propagation variables and air-sea interaction parameters using input from buoy-based measurements in diverse meteorological conditions. We further explore numerical simulations using a single column model (SCM) forced by the 3-dimensional Coupled Ocean- Atmosphere Mesoscale Prediction System (COAMPS). This hybrid modeling approach leverages the mesoscale model’s strength to provide large-scale forcing while using high vertical resolution simulations to capture the strong gradient layers. The SCM approach works effectively for the stratocumulus-topped boundary layers. Its performance for the cloud-free cases from Trident Warrior 2013 was limited due to the complexity of external forcing in coastal regions. A new blending technique is developed based on SCM to effectively patch the surface evaporative duct to forecasts from COAMPS with consistent model physics throughout the entire atmospheric column.