Re: [ferret_users]wind frequency from zonal, meridional wind

[Halldór Björnsson <halldor@xxxxxxxxxxxx>]

It seems to me that you are trying to  draw a windrose

If you google "ferret wind rose" you get the following thread 
from the help archives.
http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2004/msg00770.html


Sincerely

Halldŕo
----- Original Message -----
From: "Peter Szabo" <szabpet83@xxxxxxxxx>
To: "ferret users" <ferret_users@xxxxxxxx>
Sent: Tuesday, 12 August, 2008 7:48:29 AM GMT +00:00 Casablanca / Monrovia
Subject: [ferret_users]wind frequency from zonal, meridional wind



Dear Ferreters, 

I have daily data set. I want to visualize the most frequent wind direction for a region. I have u and v variables. 

1. First i count the number of days belonging to (16) directions with "tan" function (N, NNE, NE, ENE...) 

let ENE=if (u lt 0 and v lt 0) and (tan(u/v) le 0.6682) and (tan(u/v) gt 0.1989) then 1 
let enedir=ene[l=@sum] 

and so on... 

2. Then i try to write out for every (lon-lat) point the frequency of the direction (actually the number of the most frequent direction): 

repeat/j=1:61:1 (repeat/i=1:97:1 (let freq={`ndir`,`nnedir`,`nedir`,`enedir`,`edir`,`esedir`,`sedir`,`ssedir`,`sdir`,`sswdir`,`swdir`,`wswdir`,`wdir`,`wnwdir`,`nwdir`,`nnwdir`} ;\ 
let winddirmax=freq[x=@max]; let wind=freq[x=@loc:`winddirmax`];\ 
save/file="./ winddir.6190.nc "/ilimits=1:97/jlimits=1:61/i=`i`/j=`j`/clobber wind)) 

It works, it says: 

!-> REPEAT: I=63 
!-> DEFINE VARIABLE freq={28,12,16,28,165,78,75,47,29,10,21,38,221,82,83,67} 
!-> DEFINE VARIABLE wind=freq[x=@loc:221] 
!-> LIST/FORMAT=CDF/file="..."/ilimits=1:97/jlimits=1:61/i=63/j=1/append/clobber wind 
listing to file ... 

But as for the output file, it seems, it didnt work: 
yes? use ... 
name title I J K L 
WIND FREQ[X=@LOC:221] ... ... ... ... 
yes? list wind 
VARIABLE : FREQ[X=@LOC:221] 
FILENAME : winddir.6190.nc 
FILEPATH : /home/szabop/aladin_arpege/ 
13.00 

Any suggestion will be appreciated (either in solving the technical problem). Thanks a lot, 

Peter szabo