[gradsusr] How to calculate precipitable water

[lzf]

Dear grads user，
I am calculating precipitable water by integrating spefific humidity of entire layers
Below is the script for calculating precipitable water of summer (6,7,8,9) during 1979-2010. Its unit should be mm?
 'reinit'
'sdfopen shum.mon.mean.nc'
'sdfopen pres.mon.mean.nc'
'set z 1 8'
'define w=vint(pres.2(z=1),shum.1,300)/1000'
'set z 1'
'define w6=ave(w,t=378,t=756,12)'
'define w7=ave(w,t=379,t=756,12)'
'define w8=ave(w,t=380,t=756,12)'
'define w9=ave(w,t=381,t=756,12)'
'define sw=(w6+w7+w8+w9)'
'define ww=aave(sw,lon=100,lon=120,lat=25,lat=35)'
'd ww'
 
Is it right?   Thanks in advance!
Liu
 
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