Mesoscale circulations in a hydrostatic model: coastal convergence and orographic lifting

Abstract

A hydrostatic two-dimensional K-theory model (Δx = 4 km, 10 σ levels) is described and used to simulate mesoscale circulations developing in a neutral atmospheric boundary layer when wind blows over or along a 80 km wide sea gulf. On-shore geostrophic wind of 10 m s^-1 induces rising motion ˜ 1 cm/s at 300 m level above the coastline due to roughness difference (coastal convergence) and ˜ 1.6 cm s^-1 further inland over sloping land (orographic lifting). Off-shore wind produces sinking motion. When the geostrophic wind 10 m s^-1 blows along the coastline with lower pressure over the sea, the coastal convergence induces rising motion ˜ 0.5 cm s^-1 25 km off-shore at 600 m level, weak sinking motion just over the coastline below 200 m, and the topography induces sinking motion further inland. The results are opposite for reversed wind direction. The two effects are additive.