Test case mini-tutorial

A small case has been set up for a quick and simple test run. Input files, configuration files, and namelists have all been set up for this test case.

From the top-level AOSPRE directory, move to the working directory for the test case:

cd test

This directory will be your working directory for running the test case.

Several components are required for a successful run of AOSPRE. All of these components have been prepared in a simple configuration for this test case. Do a listing of the current working directory:

ls -l

The various files required for a run of AOSPRE are described below.

WRF-formatted model output files

The principal data from which simulated radar sweep will be constructed are contained in model output files from a high-resolution weather model. In this example, the CM1 model running with 500-m grid spacing simulated an idealized supercell. For this example, three vertical slices from the full model run have been extracted at two output times. This is enough for a couple of RHI sweeps as a demonstration. These data are found in the "wrfout" files in this directory:

wrfout_test_4650.nc
 wrfout_test_4660.nc

The 4650 and 4660 numerals in these sample filenames indicate the number of seconds since model initialization. You can use the NetCDF utility program ncdump to examine the contents of these model output files, and the ncview graphics utility program (if available) to get a quick look at the meteorological fields in these files.

Scanning tables

AOSPRE relies on user-provided scanning tables to define the beams and sweeps that will be used to sample the atmospheric state as represented in the model output files. For this example, these files are:

scanning_bot.txt
scanning_lhs.txt
scanning_rhs.txt
scanning_top.txt

where "bot", "lhs", "rhs", and "top" indicate the bottom panel of the APAR platform, the left-hand (port) side panel, the right-hand (starboard) side panel, and the top panel.

The bulk of these scanning table files is a series of beam directions, expressed in terms of rotation and tilt angles in the "type-Z" coordinate system (cf. CfRadial documentation), These particular files have been set up for this test case to produce sweeps in the plane perpendicular to the direction of flight.

CR-SIM configuration table

The components of CR-SIM used by AOSPRE use a configuration file to specify characteristics of the simulated radar. This configuration file is:

CONFIG_crsim

Details of the CR-SIM configuration may be found in the CR-SIM documentation. Note that only certain entries in this configuration setup are used by AOSPRE; the entries related to radar position, lidar, Micropulse lidar (MPL) and postprocessing are not used by AOSPRE.

AOSPRE namelist files

AOSPRE processing is controlled by one or more Fortran namelist files:

namelist.BOT
namelist.LHS
namelist.RHS
namelist.TOP

Where the bottom, left-hand side, right-hand side, and top panels each have their own namelist files.

The namelist files specify the flight path and radar scanning strategy for a flight, and the input and output files for the AOSPRE processing.. See the namelist documentation for details of the namelist entries. Several of the critical namelist entries are described below:

wrf_glob_pattern

The wrf_glob_pattern entry defines how AOSPRE finds the atmospheric model output files. Any file matching the glob pattern (using standard wildcard matching where '?' matches any single character and '*' matches any number of characters) will be interpreted as a model output file. In this example, the wrf_glob_pattern has been set up to match the names of both WRF output files provided for the test.

output_filename_format_string

The output_filename_format_string determines how the CfRadial-formatted files produced by AOSPRE will be named. This entry must specify a Fortran format string with exactly two 'A' format specifiers, used to build output file names. The 'A' format specifiers will resolve to the beginning and ending time of the sweeps in any particular output file. With each panel of the APAR platform producing its own set of output volumes, the file name construction should be unique for each panel. Compare the output_filename_format_string for each namelist in the test directory.

leg_initial_time

The leg_initial_time entry specifies the time (in seconds from model initialization) to start a data-collection flight leg. Since the example WRF output files contain only 10 seconds of data (model output times at 4650 to 4660 seconds past initialization), we've set up the namelists for an 8-second flight leg starting at time 4651 seconds past initialization.

leg_time_seconds

The leg_time_seconds entry specifies the duration in seconds of the data-collection fligh leg. As mentioned above, only a minimal set of data is provided for this small test. An 8-second flight will fit within the data provided.

flight_waypoints_x, y, and z

The entries flight_waypoints_x, flight_waypoints_y, and flight_waypoints_z specify the flight path taken through the model output files. The X and Y coordinates are specified in terms of grid-point indices in the model grid (x and y both equal 1 at the lower left grid point). The Z coordinate may be specified in meters above MSL, or as pressure in hPa, depending on the setting of flight_level_coordinate.

The test dataset (in the wrfout files) consists of three vertical slices, in the south-north direction, from a larger model grid. The dimensions of this subset grid (X x Y) are 3 x 400. Our initial flight is set up to move from west to east at y=105, south of the main body of the storm, at 2000 meters above sea level.

When running AOSPRE with for multiple APAR panels, the namelists for each panel must be set up with the same flight path and flight time information.

CRSIM_Config

The CRSIM_Config entry must specify the file name of the CR-SIM configuration file, in this case, "CONFIG_crsim".

scanning_table

The entry specifies the name of the file that contains the details of the radar beam directions for the panel represented by the namelist. Compare the scanning_table entries for the four namelists provided.

Run the AOSPRE program

The AOSPRE executable takes as command-line arguments the names of one or more namelist files. As a first run of AOSPRE, invoke a flight using the original namelist settings, with only the left-hand side panel active:

../code/embed_crsim/aospre namelist.LHS

If you get an immediate segmentation fault, you may need to unlimit the stacksize in your terminal session:

ulimit -s unlimited for bash shell,

unlimit stacksize for csh shell,

and try again.

A successful run will result in several CfRadial-formatted files from the left-hand side panel of the APAR platform. E.g.:

LHS_rhi_20010101_011731.092_to_20010101_011732.149.nc
LHS_rhi_20010101_011732.244_to_20010101_011733.301.nc
LHS_rhi_20010101_011733.396_to_20010101_011734.453.nc
LHS_rhi_20010101_011734.548_to_20010101_011735.605.nc
LHS_rhi_20010101_011735.700_to_20010101_011736.757.nc
LHS_rhi_20010101_011736.852_to_20010101_011737.909.nc

These contents of these files may be examined with the NetCDF utility program ncdump, and may be explored with the ncview utility program. Since these files are in radar coordinates, it is often difficult to make sense of the quick-look views provided by the ncview program. Other graphics capabilities that work with the radar coordinates, such as those in the LROSE package, are beyond the scope of this mini-tutorial.

Note also the file flightpath.ascii. This file preserves details of the aircraft's flight through the simulation, with locations, directions, and wind values at the aircraft location, every tenth of a second.

Modify the flightpath to run again

To explore the multi-panel capability, edit all the namelists to move the flight_waypoints_y entries to somewhere near the middle of the supercell, at Y index about 150, where the various panels may all see interesting weather.

Rerun the flight with the left panel:

../code/embed_crsim/aospre namelist.LHS

And do a repeat flight with the right panel:

../code/embed_crsim/aospre namelist.RHS

Note the additional RHS CfRadial files produced by this second run.

You can also run multiple APAR panels in the same run, by specifying multiple namelists on as command-line arguments to the AOSPRE executable.

E.g., try:

../code/embed_crsim/aospre namelist.RHS namelist.LHS

or

../code/embed_crsim/aospre namelist.BOT namelist.TOP

or

../code/embed_crsim/aospre namelist.BOT namelist.TOP namelist.LHS namelist.RHS

and note the output generated.

Further exploration

As noted before, the minimal WRF output dataset allows only limited AOSPRE runs. But there are a variety of runs you can do to further explore the data or familiarize yourself with AOSPRE configuration. E.g.:

  • Try setting up flights north of the storm.
  • Try setting up flights from west to east.
  • See how results change with flights at different levels.
  • Change the direction of the flight and the corresponding orientation of the beams in the scanning tables and still get sweeps within the slices of the WRF output data.