Mathematics Programs

Raw Data File Mathematics

The program to perform mathematics on raw data file is called rawmath. Raw data can be either entered by hand or created by a program such as sfcwx or upairwx. Once a raw data file has been created, math can be performed on it using this program. The output of these computations can either be sent to mapplt for plotting or grid for gridding and contouring. The operations available with rawmath are:

`rawmath rawa add rawb = rawc rawmath rawa sub rawb = rawc rawmath rawa mul rawb = rawc rawmath rawa div rawb = rawc rawmath rawa mod rawb = rawc`	Standard functions add, subtract, multiply, divide and modulus rawa, rawb, rawc are raw data files
`rawmath rawa add #number = rawb`	Add a constant number to a station.
`rawmath rawa mul #number = rawc`	Scale a value by number
`rawmath sum rawa rawb ... = rawd`	Sum station values
`rawmath ext rawa = rawd`	Extract a field from a raw file
`rawmath rawa merge rawb = rawd`	Merge two like raw files
`rawmath series rawa rawb ...= rawd`

Also "-" can be used for a filename to read from standard input or write to standard output. This can be used to change units or to scale output. For operations between files, stations are matched before the operation is performed. This can be used to get a plot of 24 hour temperature change:

( sfcwx -re=us -pr=3 -va=st -of=std -dr=none -cu ; \
  sfcwx -re=us -pr=3 -va=st -of=std -dr=none -cu=24 ) | \
  rawmath - sub - = - "24 hour Temp change (F)" | \
  mapplt -re=us -if=raw -de=d -

Grid File Mathematics

A program to perform mathematics on grid files is called grdmath. Grid data files are generally not entered by hand but are generated from a gridding program such as sfccalc, upcalc, and grid or by directly referencing a GRIB file. Once the grid file exists, grdmath can be called and the output sent to programs such as contour or vector. The operations available with grdmath are:

`grdmath grida add gridb = gridc grdmath grida sub gridb = gridc grdmath grida mul gridb = gridc grdmath grida div gridb = gridc`	Standard functions add, subtract, multiply and divide grida, gridb, gridc, gridu, gridv are grid files
`grdmath grida add #number = gridb`	Add a constant number to a grid
`grdmath grida mul #number = gridc`	Scale a grid by number
`grdmath sum grida gridb ... = gridd`	Sum grids
`grdmath avg grida gridb ... = gridd`	Average grids
`grdmath dx grida = gridb`	Finite difference in x
`grdmath dy grida = gridb`	Finite difference in y
`grdmath cvg gridu gridv = gridb`	Convergence
`grdmath vort gridu gridv = gridb`	Vorticity
`grdmath adv grida gridu gridv = gridb`	Advection of grida
`grdmath spd gridu gridv = gridb`	Speed given u and v wind components
`grdmath interp grida factor gridb = gridc`	Interpolates between two grids using factor
`grdmath grida add #cor = gridb`	Add coriolis parameter to grida

Also "-" can be used for a filename to read from standard input or write to standard output. For example, to convert the temps to Celsius:

sfccalc -re=us -va=st -pl=none -of=std -cu -pf=calc | \
  grdmath - sub #32 = - | grdmath - mul #.555555 = - "Temperature (C)" |
  contour -in=5 -pl=cf -de=d -

Multiple grids can be moved around by using ():

( grdmath uwind.grd sub ugeos.grd = - ;
  grdmath vwind.grd sub vgeos.grd = - ) |
  vector -de=p -la "500 mb Ageos Wind vectors" - -

This will plot ageostrophic wind vectors. Notice that both the U and V component is read in through standard input.

Last updated June 8, 1998