McIDAS User's Guide
Version 2018.1

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MDX

Plots or grids data from MD files or grids.

Formats

MDX CLE PREFIX =
MDX LIST PREFIX=
MDX PLT [keywords]
MDX PLT ugrid vgrid [keywords]
MDX grid [keywords]
MDX parm [keywords]

Parameters

CLE

restores strings with the specified prefix to their default values

LIST

lists the values of the strings with the specified prefix

PLT

plots one or more parameters as defined in the prefixed strings

ugrid

grid number containing the u-component of the wind

vgrid

grid number containing the v-component of the wind

grid

one or more grid numbers of the parameters to plot or contour

parm

one or more MD file keys or derived parameters; see the Remarks

Keywords

MDX has many keywords for fetching and displaying data. They are divided into five groups for discussion.

Parameter Keywords

COLOR=

graphics color level of the plotted data graphics; use keyword GCOLOR for contours (default=3)

DIVIDE=

divides the data values before plotting; to multiply, use a number from 0 to 1 (default=1)

FORMAT=

FORTRAN format specification for the output (default=I12; character data default=A4)

LSIZE=

label height in pixels; if LSIZE=5, all data is plotted; the numbers can overwrite each other (default=8)

 

u v

if the parameter WNV is specified, a negative LSIZE plots vectors of constant length; if the parameter WIN is specified, a positive LSIZE defines a relative length of the wind barb; specify u and v lengths with the same value

MISS=

missing data code (default=Z80808080)

OFFSET=

operates on the data before output; data value=(data - OFFSET)/DIVIDE; the UNIT keyword uses the DIVIDE and OFFSET keywords (default=0)

PLACE=

place to plot the data relative to the station location; the station is located at 41 in a 9 x 9 matrix starting at 1 in the upper-left corner, increasing along a row; use when plotting more than one parameter (default=41)

UNIT=

units to plot the parameter; possible conversions are: K to C, F; MB to INHG; MPS, MPH, KT (any); KM, M, CM, MM, MI, NMI, YD, FT, IN (any) (default=the MD file original units)

 

SYMB

plots weather symbols (default=CHAR)

Output Keywords

GELE=

beg end

graphics element extents (default=depends on the frame size)

GLINe=

beg end

graphics line extents (default=depends on the frame size)

GRA=

graphics frame number (default=current)

IMA=

image frame number (default=current)

OUT=

PLO

plot (default)

 

CON

grid and contour

PELE=

beg end

CRT/printer element extents (default=1 60 for the CRT; 1 120 for the printer)

PLIN=

beg end

CRT/printer line extents (default=1 19 for the CRT; 1 60 for the printer)

Grid/Contour Keywords

CINT=

grid contour interval (default=2)

DER=

WNV

plots wind vectors from the grid file data

DRAW=

YES

draws contours after gridding (default)

 

NO

does not draw contours

GCOLor=

graphics color level (default=2)

GRIDF=

destination grid file to store grids (default from IGU SET)

GUESS=

grid to use as first guess (default=none)

INC=

grid increment in degrees (default=1.0)

SMOOTH=

smoothing parameter (default=40)

Map Keywords

LAT=

min max

minimum and maximum latitude extents

LON=

min max

minimum and maximum longitude extents

MAP=

NA

North America

 

USA

USA

 

MID

Midwest USA

 

State Post Office Abbreviation

MCHAR=

map character for the CRT/printer output (default= . . .)

MCOLOR=

graphics map color level (default=1)

 

0

for no map

PRO=

CONF

conformal projection for polar stereographic or Lambert conformal

 

MERC

pseudo-Mercator projection (default)

 

SAT

satellite projection

SCALE=

map scale ratio for PRO=CONF (default=not true to scale)

SLAT=

lat1 lat2

standard latitudes; for polar stereographic, specify lat1; for Lambert conformal, specify lat1 lat2; used with keyword PRO=CONF (default=60, polar projection)

SLON=

specifies the normal longitude for polar stereographic or Lambert conformal; used with the keyword PRO=CONF (default=centers longitude of the map limits)

Miscellaneous Keywords

DERIVE=

temp dewpoint pressure (elevation)

if THAE, THA or MIX is displayed when the parameter does not appear in the MD file (it will be calculated); use elevation with sea level pressure

for an SVCA or ISFC file, use: DERIVE=T TD PSL ZS

for a RAOB or IRAB file, use: DERIVE=T TD P

GRIDF=

grid file number to read (default=from IGU SET)

MDf=

MD file number to read; you can combine up to six MD files using the PREFIX keyword (default=from MDU SET)

PREFIX=

MDX stores options and defaults in the string table with a prefix at the beginning of the string name; the prefix can be any printable character except a numeric or the pound sign (#) (default=$)

 

You can set up two prefixed string tables using keyword PREFIX to run these arithmetic operations: - (subtract), * (multiply), + (add), / (divide), : (catenate).

 

For all operations except catenate, the MD file must have the same schema; if LAT/LON is not contained in the column header, only one row can be operated on, for example: PREFIX=$ - !

SORT=

keyword1 loval1 [hival] keyword2 . .

selects data from the MD file that meets its conditions; in the SORT keyword list, do not use an equals sign (=) between keywords and loval, hival; hival is optional if loval is numeric; do not specify hival if loval is alphabetic; keyword is any parameter from an MD file or a ROW and COL number, for example: SORT=TIME 12 13 ST WI

SOU=

MDF

data source is an MD file (default)

 

GRID

data source is a grid file

Remarks

MDX is a flexible routine that plots or contours from any schema MD file or grid. When plotting or contouring ISFC, SVCA, IRAB or RAOB schema MD file data, it is easier to use commands SFCPLOT, SFCCON, RAOBPLOT and RAOBCON. When contouring grid data, it's easier to use command GRDDISP.

MDX is the general MD file plotter/gridder. It is intended for use in macros, not entered directly.

With each MDX command entry, the information (i.e., parm, time, date, map boundaries, display colors) is stored in strings with a special character prefix. The default prefix is a dollar sign ($), but you can define a prefix using keyword PREFIX with any single character except a pound sign (#) or alphanumeric character.

The parm parameter may be any key name in the MD file (use command MDL to list the keys), or one of these derived parameters: ABV, ADV, DVG, MIX, SPD, STR, THA, THAE, VOR, WIN, WNV.

When you use the plus sign (+) as the last positional parameter, the command information is stored in the string table but not plotted. This allows you to run arithmetic operations on the data using the PLT option with the keyword PREFIX.

The most basic command to display data is MDX parm, where parm is any parameter found in an MD file. The command plots all of this parameter from the current MD file (from MDU SET) on the current graphics frame on a map as determined by the limits of the data. To do anything more with MDX, you must know something about the type of data in the MD file. For example, if you want to plot 500 mb heights for day 97250 at 12 UTC over the Midwest, you must know that the height, pressure, day and time are referenced through parameters Z, P, DAY and TIME in the MD file.

The command to enter (with IRAB schema data in MD file 5000) is:

MDX Z MAP=MID MDF=5000 SORT=P 500 DAY 97250 TIME 12

Keyword SORT provides a way of limiting the data to a specific subset of interest. This is probably the most used keyword along with a map specification keyword (MAP or LAT, LON). When using history data, the contour plot does not indicate a day unless you indicate that day as a SORT condition. Do NOT use an equals sign (=) between the keys and values in the SORT list.

Keywords LAT and LON default to limits that guarantee complete coverage of the data distribution, rounded to the nearest whole degree.

When MDX creates and interpolates data to a grid, the amount of extrapolation into data void regions is controlled via SYSKEY word 897. It has a range of 2 to 20 and a default of 10. Use command SYSVAL to list or change its value. Grid points beyond its value are assigned missing value codes, and are not contoured. Note that data density, grid spacing and smoothing can affect a data value's results.

You can use the ADDE command GRDDISP in place of MDX SOU=GRID,
and the ADDE command PTDISP in place of MDX SOU=MDF OUT=PLO.

Examples

Before using this example, enter MDX CLE to clear and initialize the string entries that MDX uses.

1. Plot the weather data from MD file 4000 at 18 UTC.

MDX WX1 MDF=4000 SORT=TIME 1

2. Contour the temperature advection from MD file 3020 over the Midwest at 15 UTC.

MDX T ADV MDF=3020 MAP=MID OUT=CON SORT=TIME 15

3. Plot T in degrees Fahrenheit for MD file 4050, for Wisconsin.

MDX T + MDF=4050 UNIT=F MAP=WI

This command will not plot because + is the last positional parameter. Now plot in graphics color level 2 (MDF, UNIT and MAP are the same).

MDX T COLOR=2

4. Plot the temperature from the current surface data for 15 UTC for a lat/lon box. The MD file is the last digit of the Julian day (if zero, MD=10); today is 97322 so use MD file 2.

MDX T MDF=2 LAT=30 50 LON=90 105 SORT=TIME 15

We forgot to specify hourlies (no specials) and degrees C. So, when MDX is done plotting, enter the command below.

EG; MDX T SORT=TIME 15 TYPE 0 UNIT=C

5. Plot 1000-500 mb thickness over the USA, 12 UTC, MD file 1030, by entering the following command sequence.

MDX CLEAR

MDX Z + SORT=P 500 TIME 12 MAP=USA MDF=1030 PREFIX=$

MDX CLEAR PREFIX=!

MDX Z + SORT=P 1000 TIME 12 MAP=USA MDF=1030 PREFIX=!

MDX PREFIX=$ - !

6. Grid the winds from MD files 2020 and 2045 for streamlines.

MDX STR + MDF=2020 PREFIX=$

MDX STR + MDF=2045 PREFIX=!

MDX PREFIX=$ : !

7. Use THAE, THA and MIX. It is easier to use the macros (SFCPLOT, RAOBPLOT, etc.) to display these derived parameters. When using MDX, an extra keyword, DERIVE, is necessary.

MDX MIX MDF=3 MAP=MID DERIVE=T TD PSL ZS SORT=TIME 17 DAY 92003 TYPE 0

This entry plots a mixing ratio from the surface data for day 92003.

8. Plot the grid points on the graphics for grid 10, grid file 6512, which contains temperature data.

MDX 10 SOU=GRID GRIDF=6512 MAP=MID UNIT=C

9. Plot the wind flags at the grid points for u grid 1 and v grid 2. When plotting wind flags, you cannot change the units.

MDX PLT 1 2 SOU=GRID PRO=SAT SORT=TIME 12

10. Plot parameters T and TD from MD file 4000 at 12 UTC over Wisconsin. Position the temperature above the dew points with the PLACE keyword. First, set it up with no plot.

MDX T TD + MDF=4000 SORT=TIME 12 MAP=WI PLACE=41 50

Now plot the data.

MDX PLT

11. Plot the u- and v-component vectors on the graphics from grids 1 and 2. When plotting wind vectors, you cannot change the units.

MDX PLT 1 2 SOU=GRID DER=WNV MAP=MID

12. Plot the weather symbols for 18 UTC on day 97301.

MDX WX1 UNIT=SYMB MDF=1 MAP=MID SORT=TIME 18 TYPE 0 DAY 97301

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