AERODYNAMIC ROUGHNESS AND DRAG MEASURED FROM FLIP

Abstract

The atmospheric roughness length, z_0, is an experimentally determined parameter that attempts to encapsulate the physics at the air-sea interface. For numerical modeling, z_0 is central to defining the exchange of momentum across the ocean for both meteorological and oceanographic forecasting. Thus, characterizing roughness over the ocean is important for the U.S. Navy marine forecasting mission. However, z_0 does not have a universal scaling with a bulk meteorological parameter, such as wind speed, sea state, etc. Using near-surface profile measurements collected from the R/P FLIP (Floating Instrumentation Platform), a unique platform for science applications, this research study will examine the variability in z_0 as observed during the Coupled Air Sea Processes and EM ducting Research (CASPER) field study. The variability of the atmospheric friction velocity, drag coefficient, and z_0 was examined, with a particular focus on evaluating the effect vertical flux divergence had on the observed scatter. After controlling for the logarithmic wind profile and non-divergent stress, a novel parameterization for z_0 is presented and compared to widely-used bulk relations. After examining the natural flux footprint variability, a conceptual approach to identifying spatial changes in z_0 is presented and the implications for feature detection are discussed. This work holds significance for air-sea interaction modeling and the bulk parameterization of ocean surface roughness.