Frequently Asked Questions (FAQ)

From EPICwiki

1. What does EPIC stand for? Explicit Planetary Isentropic-Coordinate. Explicit refers to the timestep (as opposed to an implicit or semi-implicit one), Planetary refers to the fact that the model is implemented in principle for all known atmospheres (one for all!), Isentropic-Coordinate refers to the vertical coordinate, which provides motion-following accuracy and limits vertical numerical truncation errors, which are a major source of errors in general circulation models.
2. What is the difference between EPIC 3 and EPIC 4? EPIC Version 3.x uses a pure isentropic vertical coordinate (potential temperature, theta), whereas EPIC 4.x uses a hybrid coordinate that transitions for potential temperature aloft into a terrain-following sigma coordinate for terrestrial planets, or a pressure coordinate for gas-giant planets.
3. Should I use EPIC Version 3 or Version 4? Use Version 3.x if you want a shallow-water model for process studies or idealized simulations. Also, the full model's pure-isentropic coordinate implies that its pressure-gradient force is given by a single term, which makes initializing full-strength vortices and waves easier than with a hybrid coordinate, which is useful for gas-giant simulations. However, it is not implemented for terrestrial-planet applications (because the potential-temperature coordinate surfaces intersect the bottom surface at a steep angle), nor can it be extended into the isentropic interiors of gas giants. Use Version 4.x for terrestrial-planet applications, where the terrain-following coordinate handles topography while the isentropic coordinate aloft minimizes vertical truncation errors. Also, use it for gas-giant applications where the bottom of the model extends deeply into the planet.
4. Is there a nonhydrostatic version of EPIC? A nonhydrostatic (anelastic) version (EPIC Version 5) is in the planning stage. Versions 3 and 4 are hydrostatic.