GEMPAK Mapping Programs: SFMAP

Your first experience with the GEMPAK user interface will be with the program SFMAP

SFMAP plots any parameters which can be derived from the data in a GEMPAK surface data file.

These are the program defaults and allow us to list/plot data immediately when starting to use GEMPAK.

By default, surface obs from "Hurricane Bob" in 1991 are displayed, centered around West Virginia. At this point we are going to use a shortcut for real-time metar observations:

AREA determines the data area, while GAREA determines the graphics area (see below)

The map projection directly affects the way the map looks on the screen, and can be specified as a simple map projection or as a full map projection, which requires a set of angles.

PROJ and GAREA together give you the flexibility to generate very specific map projections.

GEMPAK comes equiped with these simple map projections that will work with standard graphical areas (mostly over the US). Simply define PROJ:

For stereographic STR and azimuthal AZM projections, angle1 is the standard latitude through which the projection plane passes and angle2 is the central longitude (i.e. the longitude that lies parallel to the grid columns). These azimuthal projections require you to specify these two angles, and because angle3 isn't used, GEMPAK expects 0.

When GEMPAK draws a new map or graph to the X-Window (also for GIF), clearing the screen is an option. CLEAR = YES will erase whatever has been previously draw to the x-window, and the new graphic is drawn on a blank screen. CLEAR=NO ensures that the screen is not cleared, allowing you to overlay fields.

Exercise: Exercise!

Plot a standard surface chart for CO area for this morning (1200 UTC).

The parameter's position in SFPARM corresponds to placement around station (except for wind barbs which are always centered on the station)...

For Example if:

sfparm = skyc; tmpf; wsym; rmsl; ; dwpf

The parameter's position (SKYC : 1, TMPF : 2, WSYM : 3, RMSL : 4, DWPF : 6 ) will correspond to the chart position:

    18      14      8       16      22
    19      2       10      4       23
    12      3       1       5       13
    20      6       11      7       24
    21      15      9       17      25

Help: Why in that order? To corresponed to the standard ordering of data on a surface chart:

The GEMPAK four letter SFPARM abbreviations would therefore be:

    TMPF            RMSL 
    WSYM    SKYC    PTND
    DWPF    &BRBK

Does the default file already set for a standard surface chart? Let's find out:

GEMPAK-SFMAP>restore $GEMPAK/defaults/sfmap.nts
GEMPAK-SFMAP>l
 AREA    =
 GAREA   = 
 SFPARM  = skyc;tmpf;wsym;rmsl;pt03;dwpf;p03i; brbk:.7:2
 DATTIM  =                       
 SFFILE  =        
 COLORS  = 1;2;3;25;5;6;7;9 
 MAP     = 3/1/2
 LATLON  = 0
 TITLE   = 1/-2
 CLEAR   = YES
 PANEL   = 0
 DEVICE  = xw
 PROJ    = nps
 FILTER  = yes
 TEXT    = 1.3/23//HW
 SKPMIS  = no
 GEMPAK-SFMAP>

Now simply define the area, date/time and file:

 GEMPAK-SFMAP>AREA = CO- 
 GEMPAK-SFMAP>GAREA = CO
 GEMPAK-SFMAP>DATTIM = /1200
 GEMPAK-SFMAP>SFFILE = metar
 GEMPAK-SFMAP>r

Look okay? Save your output:

 GEMPAK-SFMAP>save sf.nts

we'll use it again soon.

SNMAP plots any parameters which can be derived from the data in a GEMPAK sounding data file for specified levels and vertical coordinate.

SNMAP runs similarly to SFMAP. The only fundamental difference is that SNMAP will map sounding (upper air) data instead of surface data. As a result, you must define the level GLEVEL and vertical coordinate GVCORD on which to map the data.

Notice area and date/time remain the same from SFMAP, inherited from last.nts.

GDMAP is very similar to SFMAP and SNMAP. The only fundamental difference is that GDMAP will plot gridded data points on a map. Usually, however, we use contours, streamlines, or vectors to view gridded data, so this program is of limited use. We'll discuss the new variables unique to grid programs in the Grid Programs section. Consult the on-line help file, or the User's Manual for information on how to use this program.

Before moving on to the next chapter, test your GEMPAK skill by working through the Mapping Program Exercises. After each question, there will be a answer window Answer:

. Work through the exercise, and then check your results against the answers.

The next chapter discusses graphing programs. These programs are used to represent data without the geo-referencing. Examples include meteograms and Skew T-Log P plots. Cross section programs are also included in this category.

You won't find this variable on any user interface, it is a hidden variable.

The default map is a medium-resolution political boundary map of the world. Alternate maps, such as lakes, rivers and more detailed political boundaries, can be called using $MAPFIL.

For global maps, low resolution is fine. For small scale maps, high resolution can make an impressive graphic.

Exercise: Plot a chart over North America, using a coastal boundary map.

Use 1200 UTC surface data from this morning.
Choose a low resolution coastal boundary map:
```
$MAPFIL=LOCONH.GSF
```
Plot sky cover, temperature, and dew point: Put SKYC in position 1, TMPC in position 2 and DWPT in position 7:
```
SFPARM=skyc;tmpc;blnk;blnk;blnk;blnk;dwpc
```
or
```
SFPARM=barb;tmpc;;;;;dwpc
```
Use full map projection (Remember, you can't abbreviate with a non-standard area)
```
PROJ=STR/90;-100;0
```
AREA and GAREA set for North America:
```
AREA=dset
GAREA=10;-125;50;-20
```
Date/time (abbreviation):
```
DATTIM=/1200
```

Remember to list or l to check your defintiions. Now run it:

GEMPAK-SFMAP>r
 SFMAP PARAMETERS:
 

 GEMPAK-SFMAP>r
Creating process: xw for queue 9928711
 SFMAP PARAMETERS:

 Data area:          dset                                                       
 Graphics area name: 10;-125;50;-20                                                         
 Valid parameters:    BRBM TMPC BLNK BLNK BLNK BLNK DWPC
 Parameter colors:     1    2    0    0    0    0    3
 Time:              101014/1200
 File:              $GEMDATA/surface/20101014_sao.gem
 Map:               3/1/2                                                       
 Title:             1/-2                                                        
 Device:            XW                                              
 Projection:        STR/90;-100;0                                                         
 Clear screen:      YES
 Filter:            YES
 Filter factor:      1.00
 Panel:             0   
 
 Enter  to accept parameters or type EXIT:

Don't use the window manager to get rid of the XWindow graphic. Either iconify the window for use later, or run GPEND

Great, now if you think that that isn't much data you can adjust the filter to 0.7 and see the difference.

And one more thing, what would you have seen if you left PROJ set to NPS as it was in the defaults files sfmap.nts?

Not so great, eh? If you often like to look at North American plots, you may want to keep the PROJ and GAREA settings we just used in their own defaults file. (I do!) Here's a copy of my file namerica.nts:

PROJ    str/+90;-100;0/0;3;0;2                                                  
GAREA   10;-125;50;-20

Pretty simple, huh? Whenever I want to draw a graph of North America, all I do is:

GEMPAK-SFMAP> restore $GEMPAKHOME/defaults/namerica.nts

warning: Before you move on, be sure to set the $MAPFIL back to the default!!!

GEMPAK-SFMAP>$MAPFIL=MEPOWO.GSF
GEMPAK-SFMAP>e