Variability of Optical Turbulence in the Coastal Marine Environment During CASPER-West

The performance of optical systems operating in the marine atmospheric boundary layer (MABL) and marine atmospheric surface layer (MASL) are subject to scintillation effects due to turbulence along the path. Nearshore MABL/MASLs provide optically heterogeneous and complex turbulent environments that can be difficult to model accurately. The structure function parameter (Cn2) is the atmospheric variable relevant to optical turbulence, and extensive measurements were taken during the 2017 CASPER-West fieldcampaign to investigate the variability of Cn2 in the coastal environment from multiple land, sea, and airborne based observations under a variety of atmospheric forcing conditions. Temporal varaiblities of mean and turbulent state variables relevent to the magnitude of Cn2 were directly measured in the MASL from a multi-level mast on the R/P FLIP anchored 26 NM from the coast, and spatial variabilities of the same were measured in the MABL and MASL from the Twin Otter aircraft and Controlled Towed Vehicle (CTV) operating in the experimental domain.

Case studies show distinct spatial and temporal characteristics of the optical turbulence behavior in a thermally unstable cold front event and a thermally stable Santa Ana Wind event. Cn2 in the cold front event displayed features consistent with traditional surface layer and mixed layer scaling theory in the lower half of the boundary layer. However, in the upper half of the convective boundary layer, Cn2 were higher suggesting influence from the entrainment zone turbulence above. Closer to shore less agreement with models is found due to the influence of the continental boundary layer turbulent dynamics. Several profiling models were analyzed and results are discussed. In the Santa Ana Wind event the formation of a stably stratified internal boundary layer (IBL) provided a spatially and temporally dynamic optical environment that maximized Cn2 unevenly along the IBL interface. Spectral analysis revealed non-Kolmogorov characterisitic turbulence near the IBL interface that calls into quetion the validity of Cn2 measurements in these cases.