McIDAS Learning Guide
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MD Files - Plotting and Contouring Point Data
The SFCCON, SFCPLOT, RAOBCON,
and RAOBPLOT commands display
surface and upper-air point data. These commands are designed to allow for
shorter command entries by having commonly used defaults for displaying their
data types, and using positional parameters instead of keywords for values
that are always or often specified.
For example, the default for the DATASET keyword is to use the real-time datasets.
When looking at real-time data you will never have to specify the DATASET keyword.
However, in these examples, you will be using the historical BLIZZARD dataset
and will still have to specify the DATASET keyword.
These commands are easier to use for plotting or contouring their specific
data types than the generic "toolbox" commands PTDISP and PTCON.
However, the "toolbox" commands are still useful for calculating complicated
mathematical equations and for creating output that is completely controlled
by the user instead of by the command defaults.
In this exercise, you will plot and contour observed parameters, as well as
calculate the changes in these parameters over time and between different levels
in the atmosphere. You will also plot some derived parameters and plot the
results of your own mathematical equation.
- Erase both the images and graphics in frames 1 through 6.
- Type: ERASE F 1 6
- Display the two latest Meteosat-3 Vis images on frames 1 and 2 centered
on Florence, South Carolina, with the resolution magnified by a factor of
2. Show each frame and add a map in graphics color level 5.
- Type: IMGDISP BLIZZARD/M3-VIS.2 1 STA=KFLO MAG=2 REPEAT=2 SF=YES
REFRESH='MAP H 5'
- Show frame 1 and plot the snow depth at 18 UTC on 13 March 1993 on the
satellite image using data from the BLIZZARD/SFCHOURLY dataset by creating
and using an alias with the AKA command. The X in the map positional
parameter means to use the default, which is to use the frame's current navigation.
- Type: AKA ADD SFC BLIZZARD/SFCHOURLY
- Type: SF 1;SFCPLOT SNO X 18 1993/03/13 DATASET=SFC.1
- Contour the snow depth over the plot using the same data and conditions
as in the previous step.
- Type: SFCCON SNO X 18 13/MAR/93 DATA=SFC.1
- On frame 2, contour the pressure change from 00 UTC to 23 UTC.
- Type: SFCCON PRE X 23-00 93072 DAT=SFC GRA=2;SF 2
In addition to plotting the observed parameters, these commands can also calculate
and plot some derived parameters, such as windchill, vorticity, and temperature
advection. If you have a more complicated equation that you would like to use,
you can use the PTCON or PTDISP commands to plot the results of your equation.
- Display a map of the United States in color level 8 (gray) on frames 3
- Type: SF 3;MAP USA 8 GRA=3-4
- Contour the 850-500 mb thickness on frame 3.
- Type: RAOBCON Z 500-850 X 12 93072 DAT=BLIZZARD/UPPERMAND.1
- Contour the 850 mb temperature over the United States at 12 UTC on 13 March
- Type: SF 4;RAOBCON T 850 X 12 93072 DAT=BLIZZARD/UPPERMAND.1
- Plot the 850 mb streamlines over the temperature contours.
- Type: RAOBCON STREAML 850 X 12 93072 DAT=BLIZZARD/UPPERMAND.1
- Contour the 850 mb temperature advection on frame 5, using a contour interval
- Type: SF 5;RAOBCON TADV 850 USA 12 93072 DAT=BLIZZARD/UPPERMAND
- Compare frames 4 and 5.
Notice that the areas of positive temperature advection (warm air advection)
calculated and plotted in frame 5 match the areas in frame 4 where streamlines
are passing from warmer to colder air.
- Press: Alt B
- Press: Alt A
- Use the Hypsometric Equation to calculate the 1000-500 mb thickness in
Only stations reporting both a 1000 mb and 500 mb temperature are included
in the equation, so stations that are above 1000 mb (e.g. Rocky Mountain
stations) will not appear in the display.
- Type: PTDISP BLIZZARD/UPPERMAND 6 SEL='DAY 93072;TIME 12'
MAP=USA PARAM='THIK[M]=(287/9.8)*((P1+P2)/2)*LOG(1000/500)' P1=T[K] 'P 1000'
P2=T[K] 'P 500' ; SF 6
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