Effects of Initial and Boundary Conditions of Mesoscale Models on Simulated Atmospheric Refractivity

Abstract

Radar ducting is caused by sharp vertical changes in temperature and, especially, water vapor at the top of the atmospheric boundary layer, both of which are sensitive to variations in the underlying surface conditions, local mesoscale weather, and synoptic weather patterns. High-resolution numerical weather prediction (NWP) models offer an alternative to observation to determine boundary layer (BL) structure and to assess the spatial variability of radar ducts. The benefit of using NWP models for simulating ducting conditions very much depends on the initial state of sea surface temperature (SST) and the model spinup time, both of which have a great impact on BL structure. This study investigates the effects of variation of NWP-model initial conditions and simulation length on the accuracy of simulating the atmosphere's refractive index over the Wallops Island, Virginia, region, which has pronounced SST variability and complex BL structure. The Met Office Unified Model (MetUM) with horizontal resolution of 4 km (4-km model) was used to simulate the atmospheric environment when observations were made during the Wallops-2000 experiment. Sensitivity tests were conducted in terms of the variability of SST and model spinup time. The evaluation of the model results was focused on low-level moisture, temperature, and surface ducting characteristics including the frequency, strength, and the height of the ducting layer. When provided with more accurate SST and adequate simulation length, the MetUM 4-km model demonstrated an improved ability to predict the observed ducting.

Impact of mesoscale meteorological processes on anomalous radar propagation conditions over the northern Adriatic area

“…Wang et al . [] also reported that an enhanced SB can result in more numerous surface ducts. At an altitude of 100–400 m agl (Figures c and b), a region of subrefractive conditions (~70 km offshore from the western Istrian coast) formed because of the drier layer at the top of the lower branch of the SB cell.…”

“…Considering the relatively low sampling frequency (usually every 6 or 12 h) and the infrequent and irregular spatial distribution of radio sounding measurements, improvements can be achieved be employing a mesoscale model with a high resolution (both vertically and horizontally). Such studies [e.g., Burk et al ., ; Atkinson and Zhu , , ; Bech et al ., ; Haack et al ., ; Thompson and Haack , ; Wang et al ., ; Karimian et al ., ] are relatively recent, having been conducted within the last decade, because they are highly dependent on the development of atmospheric models and the increase in available computer capacity. On the California coast, based on extensive research (radio sounding and aircraft measurements) in combination with a numerical model, Haack and Burk [] related the structure and depth of the marine ABL, finding variations in trapping primarily at the top of the ABL, where the gradients in humidity and temperature were the most pronounced.…”

Observation- and numerical-analysis-based dynamics of the Uttarkashi cloudburst

“…To overcome this problem, we used gravity wave drag as a momentum-damping mechanism. The model vertical atmospheric structure strongly depends on the initialization of surface fields and model spin-up time (Wang et al, 2012). As mesoscale convective systems evolve due to specific vertical atmospheric structure, we performed sensitivity analysis of the spin-up time to properly calibrate the model.…”

Influence of heterogeneous refractivity on optical wave propagation in coastal environments

“…Some of these variables can be used to diagnose the spatiotemporal variation of atmospheric refractivity for simulating or forecasting optical phenomena such as optical ducting and mirage formation. This technique has been adopted in a handful of research studies to document the influences of heterogeneous refractivity on propagation of radio wave (Burk and Thompson 1997;Atkinson et al 2001;Haack et al 2010;Wang et al 2012). In our recent work , a coupled mesoscale modeling and ray tracing framework was utilized to investigate the impacts of anomalous refractivity, induced by the periodic shedding of island wake vortices, on long-range optical wave propagations.…”

“…In some cases, these uncertainties may be high and often times sensitive to the particular flow being simulated (Wang et al 2012). This paper concentrates on modeling of optical ray trajectories originating, and traveling through, the planetary boundary layer (PBL).…”