Meso-simulation

Phenomena in the atmosphere take on a very wide range of spatial scales: from turbulence (1 mm to 1 km); to events like thunderstorms, mountain/valley winds, sea breezes, fronts (1 km to 100 km, also called the meso-scale); to the large scales of low/high pressure systems, jet streams, and global climate (hundreds to thousands of km). Historical ERA5 weather data resolves these largest scales very well, and the LES is tailored for the smallest scales. It is the meso-scale, the scale in between those two, that neither is very good at simulating. That is why Whiffle Wind uses a meso-scale model in between the driving weather data and the LES.

The meso-simulation runs at a resolution of 2 km and has a domain of 256 km by 256 km, by which it can capture the effects of land-sea transitions, and large-scale orography. This meso-simulation directly drives the LES, and gives more realistic boundary conditions than pure ERA5. Its implementation is based on the LES code, but has several modifications that allow it to run at coarser resolutions.