# Earth System Atlas — sources and model scope

Eight interactive educational studies of natural Earth processes. Geometry, particle paths, temperature fields, and traces are generated by the application. **No captured climate or seismic simulation dataset is included. No CESM, NVIDIA Earth-2, or SPECFEM solver is running or represented as running.** Natural Earth coastlines are the only geographic dataset. Human emissions, land use, infrastructure, and intervention are absent. These demonstrations do not establish what Earth would actually be like without historical human influence.

## Scientific context

- [NCAR Community Earth System Model](https://www.cesm.ucar.edu/): a coupled Earth system model connecting atmosphere, ocean, land, ice, and other components. A model configuration determines its forcing; CESM is not intrinsically restricted to natural forcing.
- [NVIDIA Earth-2](https://www.nvidia.com/en-us/high-performance-computing/earth-2/): weather and climate AI models, libraries, and frameworks. The application uses no Earth-2 inference, weights, or forecast output.
- [SPECFEM3D Cartesian](https://specfem3d.readthedocs.io/en/latest/01_introduction/): a regional seismic wave solver based on the spectral-element method. [SPECFEM3D GLOBE](https://github.com/SPECFEM/specfem3d_globe) addresses global propagation. Neither replaces a long-timescale mantle-convection solver.
- [Meta WebXR mixed reality](https://developers.meta.com/horizon/documentation/web/webxr-mixed-reality/): immersive-ar session mode. Rendering occurs in the headset; the headless Hetzner server only delivers static assets over HTTPS.

## Equations and visual encodings

1. **Radiation balance.** S = 1361 W/m², incoming = S/4, reflected = αS/4, absorbed = (1−α)S/4, effective emission temperature T = [(1−α)S/(4σ)]^(1/4), σ = 5.670374419×10⁻⁸ W m⁻² K⁻⁴. Gold, teal, and orange paths encode incoming, reflected, and emitted energy. Flow counts and ray positions are decorative encodings, not photon Monte Carlo transport. T is not surface temperature. The color field is schematic. [NASA energy budget](https://science.nasa.gov/earth/earth-observatory/climate-and-earths-energy-budget/).

2. **Convection.** Surface temperature 28 °C. Magnus dew point Td uses a = 17.625 and b = 243.04 °C. Approximate cloud base = 0.125(T−Td) km. Unsaturated parcels cool at 9.8 K/km; saturated parcels use a fixed illustrative 6 K/km. The displayed cloud base and rain origin follow this calculation. Tracers follow prescribed overturning paths. No stability profile, entrainment, microphysics, precipitation budget, or Navier–Stokes dynamics is solved. [NOAA atmospheric circulation context](https://www.weather.gov/source/zhu/ZHU_Training_Page/winds/Wx_Terms/Flight_Environment.htm).

3. **Global circulation.** Six zonal-mean cells are prescribed at 0–30°, 30–60°, and 60–90° in both hemispheres, with surface easterlies/westerlies. f = 2Ω sin φ with Ω = 7.2921159×10⁻⁵ s⁻¹. The rotation knob rescales f and zonal drift. It does not recompute cell widths or the general circulation. Ferrel cells are eddy-driven indirect circulation, not simple tropical-style thermal cells. [NOAA circulation](https://www.weather.gov/source/zhu/ZHU_Training_Page/winds/Wx_Terms/Flight_Environment.htm).

4. **Ocean overturning.** Linear density ρ = 1027[1−2×10⁻⁴(T−10)+7.6×10⁻⁴(S−35)] kg/m³. Surface box: 22 °C, salinity 35 g/kg. Polar box: 3 °C and salinity 35 minus freshening. Signed flow proxy = clamp((ρpolar−ρsurface)/3.9026, −1.5, 1.5). Paths reverse if the proxy becomes negative and stop at zero. This is not a TEOS-10 equation of state or a forecast of circulation collapse or reversal; winds, mixing, geometry, and pressure are omitted. [NOAA thermohaline circulation](https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor1.html/).

5. **Ice–albedo feedback.** Ice fraction I(T) = 1/[1+exp((T−268)/5)] with T in K. α = 0.26+0.34I. C dT/dt = (1−α)S/4 − εσT⁴, C = 4×10⁸ J m⁻² K⁻¹, ε = 0.61. Initial temperature is 278 K. RK4 integration splits steps at one model day. One animation second = 2 model years (365.25 days/year). The ice caps occupy the corresponding fraction of sphere area; latitude boundaries are a geometric visualization, not an ice-sheet model. The solar exploration range 1150–1450 W/m² is hypothetical and much broader than contemporary solar-cycle changes. All other forcing stays fixed. [NASA albedo](https://science.nasa.gov/earth/earth-observatory/measuring-earths-albedo-84499/).

6. **Seismic waves.** Uniform example K = 100 GPa, μ = 60 GPa, ρ = 3300 kg/m³. Vp = sqrt[(K+4μ/3)/ρ] ≈ 7.39 km/s; Vs = sqrt(μ/ρ) ≈ 4.26 km/s. Local receiver distance = sqrt[(200 km)²+depth²]; arrivals = distance/velocity. Trace = two damped sinusoidal pulses with no signal before arrival. Trace playback uses 5 s per animation second. The global front has a separate illustrative 20-second loop, constant relative P/S speed ratio, and direct-S shadow mask when the segment crosses the outer core. Neither refraction, attenuation, mode conversion, realistic focal mechanisms, nor surface waves are computed. The drawn receiver on the cutaway is a generic symbol; the local 200 km receiver calculation is separate. Layer radii approximate inner core 1221 km, outer core 3480 km, Earth 6371 km; crust is exaggerated for visibility. [USGS interior](https://pubs.usgs.gov/gip/interior/index.html), [USGS wave paths](https://www.usgs.gov/media/images/p-wave-and-s-wave-paths-through-earth).

7. **Plate boundaries.** Subduction is an extruded, layered section. Distance in km = 10 × rate in cm/yr × time in Myr. Animation second = 0.25 Myr. Tracers illustrate relative plate and melt motion; the slab remains in a steady shape. The descending plate releases water that promotes mantle-wedge melting; it is not shown as melting wholesale. Relief, thickness, magma paths, and travel lengths are exaggerated. No lithosphere stress, rupture, or viscoplastic dynamics is solved. [USGS plate motions](https://pubs.usgs.gov/gip/dynamic/understanding.html).

8. **Mantle convection.** Ra = ρgαΔTD³/(ηκ), with ρ = 3300 kg/m³, g = 9.81 m/s², α = 3×10⁻⁵ K⁻¹, D = 2.89×10⁶ m, η = 10²¹ Pa·s, κ = 10⁻⁶ m²/s. The knob changes this calculated diagnostic and prescribed tracer speed. The mantle is solid rock deforming by creep; orange coloring is heat, not an entirely molten mantle. Global flow paths and temperature are schematic and do not solve Stokes or heat-advection equations. [USGS Earth interior](https://pubs.usgs.gov/gip/interior/index.html).

## Assets and software

- Coastlines: Natural Earth 1:110m land, [source GeoJSON](https://github.com/nvkelso/natural-earth-vector/blob/master/geojson/ne_110m_land.geojson), [public-domain terms](https://www.naturalearthdata.com/about/terms-of-use/). Reused from the already bundled local copy downloaded September 5, 2026. Rasterized to a texture at startup. No satellite imagery, bathymetry, elevation, or measured temperature is implied.
- Three.js and OrbitControls: bundled same-origin under the MIT license; see `vendor/THREE-LICENSE.txt`. No runtime CDN, account, paid API, or graphics server is required.
- All rendering geometry, shaders, text, and UI code are authored for this atlas.

## XR limitations and controls

Quest Browser uses an HTTPS immersive-ar session and a transparent renderer background. White panels and labels remain visible in the room. Local-floor placement is recentered from the headset pose; it is not a persistent anchor. No camera capture, scene mesh, or physical-room occlusion is used. Controller triggers or hand select/pinch activate controls; grips translate; left stick rotates the exhibit and right stick changes scale. The entire collection and all explanation steps are available on the spatial panels. Physical headset rendering, tracking, readability, and performance must be checked on Quest 3.