Terrain

Terrain slope magnitude and aspect from elevation gradients. Migrated from WildlandFire.jl@126976f2 src/coupling.jl:205 (`TerrainSlope` @component). Observed-only: dzdx and dzdy are inputs (parameters); tan_phi, slope_aspect, dzdx_out, dzdy_out are algebraic outputs.

USGS 3DEP regridding model — the coupler half of the usgs3dep loader+regridding-model split (RFC pure-io-data-loaders §6/§7; bead esm-3nc.4). Exposes USGS 3D Elevation Program terrain elevation (a pure-I/O loader passthrough) for terrain coupling in EarthSciML systems.

USGS 3DEP regridding model — the coupler half of the usgs3dep loader+regridding-model split (RFC pure-io-data-loaders §6/§7; bead esm-3nc.4). Exposes USGS 3D Elevation Program terrain elevation (a pure-I/O loader passthrough) for terrain coupling in EarthSciML systems.

"Witch of Agnesi" bell-shaped mountain topography from Clark (1977) "A Small-Scale Dynamic Model Using a Terrain-Following Coordinate Transformation", Equation 7.1 — the canonical idealized terrain for mountain-wave simulations. Algebraic component: from the mountain half-width a, peak height h_mtn, and horizontal position x relative to the mountain center it computes the terrain surface height z_s = a^2 h_mtn / (a^2 + x^2) (Eq. 7.1) and the terrain slope dz_s_dx = d(z_s)/dx. Migrated from AtmosphericDynamics.jl@816cc391 src/clark1977.jl:107 (`WitchOfAgnesi` @component); z_s and dz_s_dx are upstream `@variables` bound by algebraic equations and migrate as state-typed variables.