Unstructured grid Antarctic weather forecast system

Weather forecasting in and around Antarctica is notoriously difficult. This arises in part because of the failure of current models to include the important orographic and coastal features of the continent and problems with basic surface and boundary layer physics and cloud processes. The weather of Antarctica is dominated by three processes: (1) the polar high and the baroclinic waves that circumnavigate the continent leading to incursions into the continental landmass; (2) terrain forcing as the synoptic circulation interacts with the steep terrain and coastal and ice boundaries; and (3) katabatic processes that arise from strong radiative cooling of the surface and the downslope acceleration of the flow. These processes then couple with the moisture and surface features leading to rapid degradation in ceiling and visibility and high wind situations that preclude air operations. This has a severe impact on flight operations including aborting operations in progress.

SAIC has explored the use of the Operational Multiscale Environment model with Grid Adaptivity (OMEGA), an unstructured grid numerical weather prediction capability, that can simultaneously resolve all of the important surface features of the continent of Antarctica. SAIC is exploring the enhancement of the OMEGA surface and boundary layer physics to include those processes that are unique to the polar situation. Our intent is to use the modified system to explore the interactions between the larger scale flow driven by the polar high, the baroclinic waves, and the meso-b and meso-g scale terrain and surface and planetary boundary layer processes responsible for the terrain and katabatic forced circulations.

OMEGA has two fundamental advantages in polar forecasting: (1) the unstructured grid has no singularity at the pole eliminating a common problem (cf. Figure 1, which shows an OMEGA grid constructed for all of Antarctica) and (2) the variable resolution and adaptive nature of the OMEGA grid structure permit resolving all of the important scales of motion and the multiscale interactions.

This paper will present the basic modifications made to the OMEGA system to support Antarctic forecasting and some initial studies performed using the model.

Figure 1. Part of a 20-200 km resolution OMEGA grid, constructed for the entire Antarctic continent.