IBM supports regional weather
forecasting at the United States Air Force Global Weather Center
Based upon the success of the approach at the Olympics, AMS and China,
several meteorological agencies world-wide have determined that it fulfills
a critical need in their operational requirements. But they are using
different components of the overall system. For example, the United
States Air Force Global Weather Center (AFGWC)
at Offutt Field, Nebraska is using a different mesoscale weather model
-- MM5 running
on an IBM SP. The Fifth-Generation Mesoscale Model (MM5) is the latest
in a series developed by the Pennsylvania
State University and the National
Center for Atmospheric Research. MM5 is a limited-area, hydrostatic
or nonhydrostatic, sigma-coordinate model designed to simulate or predict
mesoscale and regional-scale atmospheric circulation. AFGWC is also
using LAPS as a data assimilation, pre-processing step similar to the way
it has been used with RAMS, as described above.
To illustrate the role of appropriate visualization in such a system,
a sample MM5 model run over Bosnia and surrounding territories was provided.
Two Data Explorer (DX)-based applications for the visualization of the
example model results were created for AFGWC. The first is a browser.
It has the ability to view and interact with the data in a latitude-longitude
(from the model's stereographic grid)-altitude (from the model's height
calculations) coordinate system. The view is annotated with base
maps. The focus of this application is qualitative assessment (browsing)
of the model output. You have the ability to create both time-based
and key-frame (flyover) animation. There is a control panel, which
gives you the ability to select specific surface and upper air variables
to visualize with pre-defined methods. It also gives you control
over the creation of key-frame animation. Additional information
about these options is available via the Help button in the control panel.
This is a screen dump of the application.
For this and any of the subsequent images, you can view a higher-resolution
version by simply clicking on it.
There are two other windows of interest. The primary one is the
Image window, within which you may view and directly interact with the
model output. There are several options available, including changing
viewing modes (Options pull-down, View-Control) such as rotation or pan/zoom,
and saving/printing images/animations (File pull-down). The coordinates
can be optionally annotated with an axes box be turning on AutoAxes from
the Options pull-down.
The other window is the Sequence Control, a graphical widget with the
appearance of a VCR. It gives you the ability to specify a time step
or frame within the model run you are currently examining. You can
move forward or backward in sequence, single step, pause, loop continuously
or loop back and forth. The default settings for the Sequencer are
to have the program operate on each individual time step from the model
as a frame in the animation. If you click on the box in the upper
right of the Sequencer, you will notice that you have the ability to change
the increment setting. By reducing the size of the increment, for
example, you will lengthen the animation. The program will interpolate
between the time steps of the model output to calculate the additional
frames of animation that you request. You can also manually control
which time steps are available.
The control panel in the browse application allows you to select specific
visualization techniques and data. The visualization coordinate system
(latitude, longitude, altitude) is annotated with base coastlines, political
boundary, river and topographic maps. The vector/line maps are draped
over a topographic surface and registered in this three-dimensional coordinate
system with the model output.
You may choose one of several surface scalar parameters to show on the
map, which include temperature, dew point, relative humidity, precipitation,
heat index and pressure. The data are shown as a continuous pseudo-color
field. Most variables (e.g., temperature) are shown with a continuous
colormap from cyan to red. Variables related to moisture (e.g., humidity
and precipitation) are illustrated with a continuous colormap from
brown (implying dry) through green (for modest moisture) to deep blue (implying
wet). The data are shown as a shaded colored surface that is deformed
vertically by local topography, and overlaid with vector maps. Alternatively,
you can select topography, then the surface will be colored like a topographic
map, where color is a redundant way of indicating altitude with the height
of the surface. You also have the ability to adjust the scaling range
for the variable that you have selected via a pair of stepper widgets.
This panel also allows you to optionally visualize surface winds through
one of several techniques, which will be pseudo-colored by speed.
The maximum value for scaling may also be set. The continuous colormap
ranges from a deep violet for very calm winds to white for the maximum
speed specified. These techniques include vector arrows of fixed
size draped over the topographic surface, which point to indicate the direction
of the wind, streamlines with directional arrows, which show the continuous
flow of wind at the particular time step, or flags distributed over the
domain of the model run. The flags are rigid, which point to indicate
the direction of the wind.
The model contains several parameters related to clouds. You may
select an isosurface of total cloud water (sum of ice and liquid) to be
generated, which can correspond to cloud boundaries. The isosurface
is colored white with variation in darkness and opacity according to the
data. Keep in mind that these surfaces are three-dimensional analogues
of contour threshold levels and thus, do not necessarily represent a true
"cloud surface". If the isosurface threshold value is low, then the
surface can often be considered an outer cloud "boundary". You may
indicate one or more threshold values in gm/m^3 via a widget.
In addition, you may also show a surface corresponding to one of the
cloud structure parameters. This surface is translucent yellow.
It can be derived from cloud base, top or ceiling data from the model.
Alternatively, cloud cover can be shown, which is illustrated with a flat
surface.
Here is a sample image and animation. The animation
illustrates the formation of rain storms in this vicinity.
A surface variable (total precipitation) has been selected for display
as pseudo-color, which is overlaid on a topographic map. Rivers (blue),
political boundaries (white) and coastlines (black) are draped on the surface.
The only upper air variable available to show is total cloud water density
(sum of liquid and ice), which can be shown via one or more isosurfaces,
colored white but with increasing darkness and opacity at high densities.
The surface at 0.001 gm/m^3 is visible. Surface winds are shown via
vector arrows of uniform size pointing in the direction of the wind.
They are pseudo-colored by speed. The winds can also be shown as
pseudo-colored streamlines with directional arrows or flags. Given
the coarseness of the temporal resolution for this model run (3 hour steps),
the ability to produce smooth animations for presentation purposes via
interpolation between time steps is available, which is illustrated.
Currently, the interpolation is linear, so there is some jerkiness to the
animation.
You have the ability to create a flyover key-frame animation along either
one of two fixed paths or one that you can specifiy interactively with
the mouse. The first path is a spiral through the domain. The
second is a simulated path from Aviano, Italy to Sarajevo, Bosnia.
To change the latter, go to Cursors Mode (Options pull-down in the Image
window, View-Control). You will see a set of little probe points
in the volume. With the left mouse button, you can drag individual
points around, which will show coordinates in the upper left. You
can indicate a new location by double clicking with the left mouse button
at the desired place. You can also delete one of the extant locations
by pointing at it with the cursor and double-clicking the left mouse button.
The locations that have been specified will serve as control points for
the animation. When you want to view the animation, select the Show
Animation button and hit Execute (or Ctrl-O). Another image window
will pop up and be the view of the model output of the current time step
along the flight path. The main window will show the model output
with the flight path and a little cursor corresponding to the location
being viewed in the animation window. Here is a sample image and
animation for the path from Aviano
to Sarajevo.
The second application is viewer for the model results. You have
the ability to view and interact with the data in a latitude-longitude
(from the model's stereographic grid)-pressure coordinate system.
The coordinates are annotated with an axes box and base maps. The
focus of this application is the analysis (visualization and interrogation)
of the model output. There is a control panel, which gives you the
ability to select any of the surface and upper air variables to visualize
with pre-defined methods. Additional information about these options
is available via the Help button in the control panel. This is a
screen dump of the application.
There are two other windows of interest. The primary one is the
Image window, within which you may view and directly interact with the
model output. There are several options available, including changing
viewing modes (Options pull-down, View-Control) and saving/printing images/animations
(File pull-down).
The other window is the Sequence Control, a graphical widget with the
appearance of a VCR. It gives you the ability to specify a time step
or frame within the model run you are currently examining. You can
move forward or backward in sequence, single step, pause, loop continuously
or loop back and forth. If you hit the button in the upper right,
you can manual control the time steps available as well as the increment
between steps to be examined.
The control panel in the viewer application allows you to select specific
visualization techniques and data. The visualization coordinate system
(latitude, longitude, pressure) is annotated with an axes box and base
coastlines, political boundary, river and topographic maps. The vector/line
maps are draped over a topographic surface and displaced below the lower
vertical boundary. Alternatively, the topographic surface may be
replaced with a time-dependent pressure surface derived from the model
output. The surface may be pseudo-colored by any one of over two
dozen surface, scalar, two-dimensional variables produced by the model.
This may also include topographic height.
The model contains several upper air, three-dimensional fields.
For each of 11 upper air scalar fields, you may choose to realize the data
as an isosurface, vertical slice and horizontal (isobaric) slice.
For the isosurface, you may choose a specific threshold value. The
isosurface is colored according to a segmented colormap. When you
change the variable of interest, the default value for the isosurface is
the mean. You may indicate the desired value via a stepper widget.
For the vertical slice, you may select a grid position, and whether
the slice is meridional or zonal. The slice is color-filled, pseudo-colored
with a segmented colormap and line contoured. For the horizontal
slice, you may choose what pressure level is to be shown. The slice
is pseudo-colored with a continuous colormap.
You may probe the volume for specific values at selected locations within
the model output. If the probe button is pushed, the variable that
was selected for isosurface representation will be interrogated.
The results will be displayed in a dialog box that will pop up on the screen.
To change the location, go to Cursors Mode (Options pull-down in the Image
window, View-Control) and select probe_volume. You will see a little
probe point in the volume. With the left mouse button, you can drag
the point around, which will show coordinates in the upper left.
In execute-on-change mode, when you release the mouse button, the results
will be shown.
The upper air three-dimensional wind velocity is visualized via interactive
marking of geographic locations of interest. You may define one or
more geographic locations for "virtual soundings" within the model atmosphere.
This is also done in Cursors Mode. You should select profilers.
You can either grab and move one of the locations already set with the
mouse or indicate a new location by double clicking with the left mouse
button at the desired place. You can also delete one of the extant
locations by pointing at it with the cursor and double-clicking the left
mouse button. At the locations that have been specified, a vertical
profile is extruded through the entire model atmosphere, which is realized
as a tube. The sounding location is used to derive information about
wind velocity. The wind velocity along the profile is shown by a
set of vector arrows that point in the direction of the wind. Horizontal
speed at these points are indicated by the color and length of the arrows.
Optionally, the locations on each "virtual wind profiler" can be used for
seed particles for particle advection, which is realized as streamlines.
These lines, which are also pseudo-colored by horizontal speed, indicate
the instantaneous direction of the modelled wind from these locations.
If a variable has been selected for realization as an isosurface, then
the values along each profile of that variable are also shown as pseudo-colored,
filled contour bands using the same segmented colormap as is employed for
the isosurface.
Here is a some sample image and animation.
A surface variable (mean sea level pressure) has been selected for
display as pseudo-color, which is overlaid on a topographic map.
Rivers (blue), political boundaries (white) and coastlines (black) are
draped on the surface. An upper air variable (specific humidity)
has been selected for display via surface extraction. The surface
at 6.0 kg/kg is shown in translucent light brown. Another field (temperature)
has been selected to show as a vertical slice, which is pseudo-color contoured.
Any of the three-dimensional fields available from the model can be visualized
with either of these methods. The upper air wind data are shown via
streamribbons. The seed points are along vertical profiles, which
are specified interactively. The direction of the model wind field
along this "virtual sounding" is shown via vector arrows. Both the
arrows and ribbons are pseudo-colored by horizontal wind speed. The
length of the arrows also corresponds to the horizontal speed. The
profile is realized as a pseudo-colored tube, which is contoured by the
variable selected for isosurface realization (i.e., specific humidity).
This next example shows turbulent kinetic energy as the upper air variable,
which is realized as pseudo-color-filled contours. The winds are
shown only as vector arrows along the vertical profiles. No surface
variable is illustrated, but a topographic surface, pseudo-colored by height
is used instead. An animation of this model
output through time can be viewed.
lloydt@watson.ibm.com
