Scintillation in the coastal atmospheric surface layer

The scintillation of a beam propagating in the Marine Atmospheric Boundary Layer (MABL) can be expressed in terms of the index of refraction structure parameter, C_n². The parameter may be determined from MABL models that make use of bulk meteorological measurements and Monin-Obukhov similarity theory. Similarity theory is used to determine the structure parameters involving temperature (T ) and absolute humidity (Q ), namely C_T², C_TQ and C_Q². These structure parameters are then combined to yield the C_n² values, using a formula described by Andreas (1988). This paper shows the results of our comparison of scintillation measurements obtained by SPAWAR, as part of the EOPACE campaign, with MABL models developed at DREV and NPS. It is found that the NPS model performs well under unstable conditions, while having certain problems under neutral and stable conditions. The DREV model, however, performs well only in near-neutral conditions. We also show that by relaxing the constant total pressure assumption used by Andreas, we obtain a good fit to the data for all stability conditions. Possible physical mechanisms explaining the modified pressure assumption are proposed and discussed.