Spatial variations of refractivity significantly dictate the characteristics of optical wave propagation through the atmosphere. Consequently, the ability to simulate such propagation is highly dependent upon the accurate characterization of refractivity along the propagation path. Unfortunately, the scarcity of high spatiotemporal resolution observational data has forced many past studies of optical wave propagation to assume horizontally homogeneous (HH) atmospheric conditions. However, the (adverse) impact of such an assumption has not been quantified in the literature. In this paper, we attempt to fill this void by utilizing a mesoscale modeling-based approach to explicitly simulate atmospheric refraction. We then compare the differences of the HH refractivity fields to the mesoscale model-derived refractivity fields by means of a realistic atmospheric event and through ray tracing simulations. In this study, we model a coastal low-level jet, a common coastal atmospheric phenomenon which is associated with heterogeneous thermal and refractivity fields. Observational data from a radiosonde and a radar wind profiler near the northeastern region of the United States are used for model validation. The observed characteristics of low-level jet (e.g., evolution, intensity, location) and associated temperature inversion are found to be reasonably well captured by the mesoscale model. The simulated nighttime refractivity gradient field manifests significant spatial heterogeneity; over land, the refractivity gradient is much stronger and amplified near the ground, whereas it becomes much weaker over the ocean. We quantify the effect of this heterogeneity on optical ray trajectories by simulating a suite of rays and documenting the variability of their altitudes at certain propagation ranges. It is found that the altitude of optical rays may vary tens of meters during a diurnal cycle, and at nighttime the rays may bend downward by more than 150 m at a range of 100 km. We run additional ray tracing simulations using refractivity profiles from a single location and assuming HH refractivity along the propagation path. It is observed that the HH approach yields instantaneous ray bending magnitudes up to 30 % less than the ray bending based on the refractivity simulated by the mesoscale model. At the same time, it is found that the mesoscale model-based refractivity fields may have uncertainty introduced by different factors associated with the model configuration. Of these factors, turbulence parameterization is explored in-depth and found to be responsible for more uncertainty than spatial grid resolution. To be more specific, different turbulence parameterizations are found to produce significantly varying temperature inversion parameters (e.g., height, magnitude), which are critical factors influencing ray trajectories. Collectively, these results highlight the potential advantages and disadvantages of utilizing a mesoscale model to simulate refractivity in coastal areas as opposed to assuming HH refractivity.@en

Optical wave propagation through the atmosphere is complicated by organized atmospheric structures, spanning a wide range of length and time scales, which induce spatio-temporal variability in refraction. Therefore, when considering long-range optical ray trajectories, the influence of such structures on the propagation path becomes significantly more complex compared to a hypothetically homogeneous atmosphere. In this paper, we use a coupled mesoscale model and ray tracing framework to analyze the refractive anomalies associated with the wake vortices induced by three geographically diverse islands under various meteorological conditions. We identify organized mesoscale wake vortices (e.g., von Kármán vortices) which are sometimes capable of distorting optical ray trajectories, through ray bending, tens of meters at a range of approximately 50 km. In addition, we find in some cases that vertical oscillations, or perturbations, to the simulated ray trajectories share a frequency with the vortex shedding frequency on the order of hours. At the same time, it is also observed that the intensity and predictability of the wake vortex-induced ray bending varies from case to case. Collectively, these results highlight the value of using mesoscale models in optical wave propagation studies above conventional approaches which do not explicitly consider horizontally heterogeneous atmospheres.@en