plotting the time-averaged wind barbs over a domain

[Paul S. Wichansky]

Hello, fellow GrADs users!  Using a time series of u and v components, I am
seeking to plot the mean wind direction (in the form of a barb),
time-averaged over a month, at a given vertical level.  This is not at a
single grid point, but over a domain.  I've read through the GrADs tutorial
and also searched through each year of the online listserv (and read through
many responses) for assistance and to see if someone else asked this
question, but I have still come up empty-handed.

I have my script below, which produces a contoured plot of mean wind
direction, rather than the barbs.  The length of the barbs would indicate
the mean wind speed at the given level.

'open lowlvl_winds.ctl'
'set t 1'
'set x 1 142'
'set y 1 142'
'set z 1'
'set gxout barb'
'set grads off'
'define wdir = 2*3.141592654 - atan2(u,-v)'
'define wdir = (wdir * 180.0/3.141592654) - 180.0'
*  plot the mean wind direction during the month
'd ave(wdir,t=1,t=720)'

Alternately, I have attempted to draw vectors directly within the ave()
command, which would precisely be the plot I want to create (if this would
theoretically work!):

'd ave(skip(u,4);skip(v,4),t=1,t=720)

but the semicolon is not recognized in this specific GrADs command.

Thanks in advance for your insights and clarifications.

Paul

-- -- --

Paul Stuart Wichansky
Department of Environmental Sciences
Rutgers University, Cook College
pstuart at cep.rutgers.edu