# [ncl-talk] Help : calculation of Total precipitable water, overestimated values

Jim Means jim at weatherextreme.com
Wed Jun 7 09:14:02 MDT 2017

```Dhirendra,

Since I don't have access to the netcdf file that you're using, perhaps
I'm mistaken, but aren't the plev the pressure levels? I think the dp
that's used in the function prcwater_dp are the differences between the
levels (the layer thicknesses), if you're trying to do an integration to
get the precipitable water.

I think if you used the levels instead of their thicknesses that would
definitely give you a value that was too large.

Hope that helps.

Jim

On 6/7/2017 12:37 AM, Dhirendra Kumar wrote:
> I am trying to calculate total precipitable water from 6 hourly data
> containing specific humidity (kg/kg) at different pressure levels
> (hPa). I am able to write the output successfully but I think the
>  values are overestimated 10 times of the usual value.
>
> I checked my code but could not figure out the mistake.
>
> I will appreciate if people here can help me finding the error. The
> NCL version for me is 6.4. The code written is following:
>
> begin
> sphum=f->qas
> lat=f->lat
> lon=f->lon
> time=f->time
> dp=f->plev*100                                          ; conversion
> into Pa
> print(dp)
> ps=f->ps(time|:,lat|:,lon|:)
> re_sphum=sphum(time|:,lat|:,lon|:,plev|:)
> pw = prcwater_dp (re_sphum, dp)
> pw at long_name = "total column precipitable water"
> pw at units     = "kg/m2"
> printVarSummary(pw)
> pw at coordinates = "lat lon"
> copy_VarCoords(ps,pw)
> out->pw=pw
> out->lat=lat
> out->lon= lon
> out->time= time
> end
>
>
> Thanks in anticipation
> Dhirendra
>
> --
> ========================================
> Dhirendra Kumar
> PhD Student
> School of Environmental Sciences, JNU
> New Delhi (India)
> Contact: +91 9910778043
> Alternate email: dhirendra.cub at outlook.com
> <mailto:dhirendra.cub at outlook.com>
> =========================================
>
>
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