P69 Optical turbulence estimation using WRF model

Wang, Yao, and Sukanta Basu, North Carolina State University

Small-scale atmospheric turbulence in the inertial-convective range is referred as optical turbulence, because the wave phase and amplitude of the optical and electromagnetic wave is highly affected by the small-scale variation of temperature and specific humanity. Documentation and prediction of optical turbulence are significant to a wide range of applications: environmental monitoring, optical communication, astronomy, sensing with detection, reconnaissance and identification, guiding systems or directed-energy systems. The refractive index structure parameter Cn2 which depends on temperature structure parameter, Ct2 (if the minor wavelength and humidity dependence are ignored) is chosen to describe the effect of the optical turbulence.

Meso-scale models can be utilized to estimate and predict the Ct2 from calculated heat and momentum fluxes by using the traditional Monin-Obukhov similarity theory (MOST) based functions. The functions in these M-O similarity are empirically derived from fast-response turbulence observations collected during different field campaigns where fluxes are estimated over an area. In this study, surface heat flux, friction velocity, temperature and pressure from Weather Research Forecasting (WRF) model with Fast Four Dimensional Assimilation (FDDA) (surface data observational nudging) was utilized to estimate the Ct2 in the case study. Three nights (23-26 October 1999) during CASES-99 study are selected because the turbulence intensities of these nights differ significantly. The first night is intermittently turbulent, the second is fully turbulent, and the third is mainly driven by radiative cooling (hardly turbulent). The estimated results of Ct2 are evaluated by the observed Ct2 value from the state-of-the-art optical turbulence measurement instrument, scitillometer to see the performance of these traditional MOST based functions under different atmospheric boundary layer turbulent stabilities.