domain gathers information from its parent domain each timestep, then it runs three timesteps, and then delivers the information back to its parent domain. There are three different ways to do two-way nesting: Nest interpolation, nest analysis input, and nest terrain input. Interpolation occurs when the terrain is smooth, such as water. There is no input that is required for this type of two-way nesting. Nest input requires a file called MMINPUT, and that file contains the meteorological and the terrain information so that initially, a better analysis can be done. Finally terrain input requires a TERRAIN file. Then the meteorological fields are interpolated. When multi-tasking occurs, the variables must be marked as either shared or private. Shared implies that the processors all have access to the same part of memory, while private implies that each processor must have its own private copy of an array with its personal memory location. The multi-tasking occurs specifically in the subroutines Solve1, Solve3, and Sound. Requirements MM5 can be run in many different ways, depending on the computer. The model can be run on a single processor computer, shared memory architecture or distributed memory architecture. It can be run on many different platforms as well such as IBM, SGI origin 200/2000, CRAYs (J90, C90, T3E), DEC Alphas, Alphas running Linux, Sun, and more. The computer it is run on must have a Fortran 90 and 77 compilers and a C compiler. Additionally, it can have NCAR graphics and MPI tools for running the MPI MM5 model. However, this is not necessary. The MM5 model takes up at least half a gigabyte of memory and a few gigabytes of disk space. Source code The MM5 code itself has over 220 subroutines, with more than 55,000 lines of code. It uses Standard Fortran 77 with “Cray” pointers. A list of the subroutines of all of the functions within the MM5, with a short description and the routines that are called within it can be found here. Use The MM5 had been adapted for use in many different types of atmospheric simulations: Real-time regional weather forecasts Tropical cyclone prediction Climate change simulation and projection Developments and improvements TERRAIN's latest update uses USGS global 30 sec terrain elevation data, which looks at the entire world, where before was only used in the continental United States. This new update also allows for a better quality terrain image that