Mesoscale ensemble prediction for model improvement: atmospheric ducting example

We present an example of the use of a mesoscale ensemble prediction system to elucidate model inadequacies relevant to Navy applications. RIMPAC08, the 2008 Rim of the Pacific Exercise, was the largest naval exercise in the world. Participating nations included the USA (Navy, Marines, and Coast Guard), the UK, Australia, Canada, Chile, Japan, Netherlands, Peru, Korea, and Singapore. The exercise took place between June 29 and July 31, 2008 in the waters surrounding Hawaii with an overarching aim to test the interoperability of coordinated, combined, and joint international operations. The Naval Research Laboratory developed METOC guidance products aimed at enabling Navy decision makers to better manage uncertainty. Mesoscale ensemble forecasts were utilized to provide objective uncertainty guidance for electro-magnetic (EM) ducting conditions. Ensemble forecast verification using independent observations indicates that the Coupled Ocean Atmosphere Mesoscale Prediction System* (COAMPS®) at a 5km resolution a) systematically under-predicts duct frequency, b) places too many ducts at cloud base, and c) places ducts at cloud top at too low an altitude. This analysis indicates that COAMPS at this resolution is lacking in its ability to produce realistic shallow convection, and may not be producing adequate mixing at the trade-wind inversion.