5 day precipitation

[Arindam Chakraborty]

hi Ben,
        your modified expression is correct if you want 'prec' to be
undefined rather than 'sum(prec,t+0,t+4)'. But both of these are going
to give the same result if you do not have undefined values in the
original data (prec) since at last we are not taking the value of the
variable to calculate anything but the number of time points it is
defined (i.e., greater than or equal to tenpanave).
        Why do you feel that the results are very close but not exact?

regards,

arindam
----------------------------
 ARINDAM CHAKRABORTY
 Department of Meteorology
 Florida State University
 Tallahassee, FL-32306, USA
 Tel: +001-850-6443524 (Off)
      +001-850-5758550 (Res)
 Fax: +001-850-6449642
____________________________

On Thu, 9 Feb 2006, Ben Burford wrote:

> Hello Arindam,
>
> This is amazing!  Thank you very much.
>
> I've been working on figuring out the functions and the logic, and I think t
> here is a mistake in your answer (but its very close).  I'd appreciate it if
>  you would check this.
>
> In the innermost part you have:
> maskout(sum(prec,t+0,t+4),sum(prec,t+0,t+4)-tenpanave)
>
> I think this means: "if the sum (of the 5 days of prec) is not greater than
> tenpanave, then change 'sum(prec,t+0,t+4)' to missing value".
>
> I think the logic should be "if the sum (of the 5 days of prec) is not great
> er than tenpanave, then change 'prec' to missing value".
>
> So I think the innermost part should be:
> maskout(prec,sum(prec,t+0,t+4)-tenpanave)
>
>
> and the overall function would be:
> 'count = sum(  const(  const(  maskout(prec,sum(prec,t+0,t+4)-tenpanave)  ,1
> )  ,0,-u)  ,t=1,t=2918)'
>
>
> Is this right (or perhaps wrong)?
>
> Thank you very much,
>
> Ben
>
>
>
>
> At 15:21 2006/02/07 -0500, you wrote:
> > hi Ben,
> >         you have an interesting problem to solve in grads. Probably
> > it is possible to get the count and I'm giving the expression below,
> > although I've not checked the answer thoroughly for my own data.
> > You may try it out and see if it makes sense.
> >
> > If the threshold precipitation value is 'tenpanave' (you can
> > define it the way you want before the expression to calculate
> > the count, the way you showed the example in your mail).
> > Then, the count is nothing but
> > 'count = sum(const(const(maskout(sum(prec,t+0,t+4),sum(prec,t+0,t+4)-tenpa
> nave),1),0,-u),t=1,t=2918)'
> > ...
> >
> >
> > Hope this helps,
> > ----------------------------
> >  ARINDAM CHAKRABORTY
> >  Department of Meteorology
> >  Florida State University
> >  Tallahassee, FL-32306, USA
> >  Tel: +001-850-6443524 (Off)
> >       +001-850-5758550 (Res)
> >  Fax: +001-850-6449642
> > ____________________________
> >
> > On Tue, 7 Feb 2006, Ben Burford wrote:
> >
> > > Hello All,
> > >
> > > I'm trying to implement a script.  I studied functions (e.g. tloop) and
> look
> > > ed in the archives for help, but so far its over my head as a beginner,
> I'm
> > > not even sure if Grads can do this.
> > >
> > > I have an 8 year (t=1,2922) global gridded daily precipitation data set.
>   Fo
> > > r each grid cell I want to go through the time series and check each fiv
> e da
> > > y period (2918 possible 5 day periods) to see if the total of the precip
> itat
> > > ion for the five days is greater than a certain level, if it is I want t
> o in
> > > crement a counter.  The result will be a single value (total count) for
> each
> > >  grid cell (global grid of a single value per grid cell).
> > >
> > > The value that I want to check the five day total against is "10% of the
>  ann
> > > ual average rainfall" (tenpanave) which I'm calculating as follows (add
> up a
> > > ll the daily values for 8 years, divide by 8 to get the annual average,
> then
> > >  take 10% of that):
> > > tenpanave = 0.1*((sum(prec,t=1,t=2922))/8)
> > >
> > > A flow chart for the script might look like:
> > > * Calculate "10% of the annual average rainfall" (tenpanave)
> > > tenpanave = 0.1*((sum(prec,t=1,t=2922))/8)
> > >
> > > * calculate the precipitation over 5 days (5dayprec), if that 5 day tota
> l is
> > >  greater than or equal to ten percent of the annual average precipitatio
> n (t
> > > enpanave) for that grid cell, then increment the counter for that grid c
> ell.
> > >   Perform this process for all grid cells, over the full time period of
> 2922
> > >  days (x from 1 to 2918).
> > > x=1
> > > 5dayprec=sum(prec,t=x,t=x+4)
> > > if 5dayprec is greater than or equal to tenpanave then count=count+1
> > > x=x+1
> > > if x=2919 then quit, else go up three steps and calculate the next 5 day
>  win
> > > dow (5dayp)
> > >
> > > * Display results
> > > d count
> > >
> > >
> > > As I say, I don't know if this can be done with Grads.  Any help would b
> e gr
> > > eatly appreciated.
> > >
> > > Thank you,
> > >
> > > Ben
> > >
> >
>
>