McIDAS Learning Guide
Version 2015

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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.

Displaying Surface Data

  1. Erase both the images and graphics in frames 1 through 6.
    Type:  ERASE F 1 6
  2. 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.
  3. 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:  SF 1;SFCPLOT SNO X 18 1993/03/13 DATASET=SFC.1
  4. 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
  5. 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

Displaying Upper-air Data

  1. Display a map of the United States in color level 8 (gray) on frames 3 and 4.
    Type:  SF 3;MAP USA 8 GRA=3-4
  2. Contour the 850-500 mb thickness on frame 3.
    Type:  RAOBCON Z 500-850 X 12 93072 DAT=BLIZZARD/UPPERMAND.1
  3. Contour the 850 mb temperature over the United States at 12 UTC on 13 March 1993.
    Type:  SF 4;RAOBCON T 850 X 12 93072 DAT=BLIZZARD/UPPERMAND.1 COL=9
  4. Plot the 850 mb streamlines over the temperature contours.

Displaying Calculated Parameters

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.
  1. Contour the 850 mb temperature advection on frame 5, using a contour interval of 5.
  2. Compare frames 4 and 5.
    Press:  Alt B
    Press:  Alt A
    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.

  3. Use the Hypsometric Equation to calculate the 1000-500 mb thickness in meters.
    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
    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.

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