MM5 Modeling System Overview
Brief Description
The PSU/NCAR mesoscale model is a limited-area, nonhydrostatic
or hydrostatic (Version 2 only), terrain-following sigma-coordinate
model designed to simulate or predict mesoscale and regional-scale
atmospheric circulation. It has been developed at Penn State and
NCAR as a community mesoscale model and is continuously being improved
by contributions from users at several universities and government
laboratories.
The Fifth-Generation NCAR / Penn State Mesoscale Model (MM5) is
the latest in a series that developed from a mesoscale model used
by Anthes at Penn State in the early 70's that was later documented
by Anthes and Warner (1978). Since that time, it has undergone many
changes designed to broaden its usage. These include (i) a multiple-nest
capability, (ii) nonhydrostatic dynamics, which allows the model
to be used at a few-kilometer scale, (iii) multitasking capability
on shared- and distributed-memory machines, (iv) a four-dimensional
data-assimilation capability, and (v) more physics options.
The model (known as MM5) is supported by several auxiliary programs,
which are referred to collectively as the MM5 modeling system.
A schematic diagram is provided
to facilitate discussion of the complete modeling system. It is
intended to show the order of the programs and the flow of the data,
and to briefly describe their primary functions. Documentationfor
various programs in the modeling system is available online (see
Documents and Publications above).
Terrestrial and isobaric meteorological data are horizontally
interpolated (programs TERRAIN and REGRID) from a latitude-longitude
mesh to a variable high-resolution domain on either a Mercator,
Lambert conformal, or polar stereographic projection. Since the
interpolation does not provide mesoscale detail, the interpolated
data may be enhanced (program RAWINS or little_r) with observations
from the standard network of surface and rawinsonde stations using
either a successive-scan Cressman technique or multiquadric scheme.
Program INTERPF performs the vertical interpolation from pressure
levels to the sigma coordinate system of MM5. Sigma surfaces near
the ground closely follow the terrain, and the higher-level sigma
surfaces tend to approximate isobaric surfaces. Since the vertical
and horizontal resolution and domain size are variable, the modeling
package programs employ parameterized dimensions requiring a variable
amount of core memory. Some peripheral storage devices are also
used.
Since MM5 is a regional model, it requires an initial condition
as well as lateral boundary condition to run. To produce lateral
boundary condition for a model run, one needs gridded data to cover
the entire time period that the model is integrated.
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