Assimilation of Refractivity from Clutter to Improve Forecasts of Atmospheric Electromagnetic Propagation Conditions near the Ocean Surface

Four-dimensional variational (4DVar) data assimilation techniques were developed at the Naval Research Laboratory (NRL) to assimilate refractivity from clutter (RFC) profiles from radar observations into the US Navy’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS^®) to improve prediction of the lower atmospheric boundary layer. RFC profiles from the Wallops Island field experiment in 2000 are used to test the 4DVar refractivity data assimilation system, and the vertical profiles of temperature, pressure and relative humidity of the lower atmospheric boundary layer observed by an instrumented helicopter (HELO) during the field experiment are used for verification of model forecasts. Studies show that assimilation of RFC profiles significantly impacts the vertical structure of the modeled atmospheric boundary layer. It improves the forecasts of refractivity in the lower boundary layer for more than 15 hours of forecast lead time. Further investigation also reveals that the length of the data assimilation time window and the estimation of observational errors play an important role in optimizing the data assimilation impact.