Trouble with EOFs

[Gerhard Krinner <gerhard@xxxxxxxxxxxxxxxxxxxxxxx>]

Dear ferret users,

I have some trouble using the external EOF functions.
EOF_SPACE sometimes gives no results (that is, "NO VALID DATA" for the
whole domain).

The strange thing is that the results are reasonable for some months,
but "no valid data" for some other months of the same data set.

Here's the script I use:

$> cat eof.jnl

set data pmer.clim.nc
 
set axis/modulo mois
 
set memory/size=10
 
set reg/y=50:90
 
repeat/k=1:12:3 ( let eof_vector =
eof_space(pmer[d=1,k=`k-1`:`k+1`@ave],2,.5);
save/file=pmer_eof_N_clim_mois`k-1`+`k`+`k+1`.nc eof_vector[l=1:6] )

---

In this case, the results are fine for k=4,7,10 but the problem occurs
for k=1 (with another file of the same kind, I had similar problems, but
for other months).

The problem also disappears if I choose a smaller region.
The variable itself (pmer) looks fine (no missing data etc.)

What did I do wrong? Could you please help me?

Cheers
Gerhard

_____________________________________________

  Gerhard Krinner
  LGGE / CNRS
  54 Rue Moliere, DU BP 96
  38402 Saint Martin d'Heres Cedex, FRANCE
  telephone: (33) 4 76 82 42 41
  facsimile: (33) 4 76 82 42 01
  courriel: krinner@glaciog.ujf-grenoble.fr  
_____________________________________________


Here's the header of the input file:

netcdf pmer.clim {
dimensions:
        nav_lon = 96 ;
        nav_lat = 73 ;
        mois = 12 ;
        annee = 15 ;
variables:
        float nav_lon(nav_lon) ;
                nav_lon:units = "degrees_east" ;
                nav_lon:long_name = "Longitude" ;
                nav_lon:valid_min = -180.f ;
                nav_lon:valid_max = 176.25f ;
        float nav_lat(nav_lat) ;
                nav_lat:units = "degrees_north" ;
                nav_lat:long_name = "Latitude" ;
                nav_lat:valid_min = -90.f ;
                nav_lat:valid_max = 90.f ;
        float annee(annee) ;
                annee:units = "-" ;
                annee:valid_min = 1.f ;
                annee:valid_max = 15.f ;
                annee:title = "annee" ;
                annee:long_name = "Annee" ;
        float pmer(annee, mois, nav_lat, nav_lon) ;
                pmer:units = "Pa" ;
                pmer:long_name = "Sea Level Pressure" ;
                pmer:short_name = "pmer" ;
                pmer:valid_min = 1.e+20f ;
                pmer:valid_max = -1.e+20f ;
                pmer:missing_value = 1.e+20f ;
                pmer:online_operation = "ave(X)" ;
                pmer:axis = "TYX" ;
                pmer:interval_operation = 2400.f ;
                pmer:interval_write = 2592000.f ;
data:
...