Advanced Research WRF (ARW) Technical Note - MMM - University ...

Chapter 5
Initial Conditions
The ARW may be run with initial conditions that are defined analytically for idealized simulations,
or it may be run using interpolated data from either a large-scale analysis or forecast
for real-data cases. Both 2D and 3D tests cases for idealized simulations are provided. Several
sample cases for real-data simulations are provided, which rely on pre-processing from an external
package that converts the large-scale GriB data into a format suitable for ingest by the
ARW’s real-data processor.
The programs that generate the specific initial conditions for the selected idealized or realdata
case function similarly. They provide the ARW with:
• input data that is on the correct horizontal and vertical staggering;
• hydrostatically balanced reference state and perturbation fields; and
• metadata specifying such information as the date, grid physical characteristics, and projection
details.
For neither the idealized nor the real-data cases are the initial conditions enhanced with observations.
However, output from the ARW system initial condition programs is suitable as input
to the WRF variational assimilation package (see Chapter 9).
5.1 Initialization for Idealized Conditions
The ARW comes with a number of test cases using idealized environments, including mountain
waves (em hill2d x), squall lines (em squall2d x, em squall2d y), supercell thunderstorms
(em quarter ss), gravity currents (em grav2d x), and baroclinic waves (em b wave). A brief description
of these test cases can be found in the README test cases file provided in the ARW
release. The test cases include examples of atmospheric flows at fine scales (e.g., the gravity
current example has a grid-spacing of 100 meters and a time step of 1 second) and examples of
flow at large scales (e.g., the baroclinic wave test case uses a grid-spacing of 100 km and a time
step of 600 s), in addition to the traditional mesoscale and cloudscale model simulations. The
test suite allows an ARW user to easily reproduce these known solutions. The test suite is also
the starting point for constructing idealized flow simulations by modifying initializations that
closely resemble a desired initialization.
All of these tests use as input a 1D sounding specified as a function of geometric height z
(except for the baroclinic wave case that uses a 2D sounding specified in [y, z]), and, with the
33