[ncl-talk] Unrealistic (strange) wind values using obj_anal_ic interpolation function

[Dennis Shea]

Hello,

A few questions/comments/suggestions:

[1]
I am not sure where you get 10m wind 1st guess.  Adding "*.grb2*" on the
command line and looking at the *lv_HGT2 *variable:

*%>*  *ncl_filedump*   gfs.t18z.pgrb2.0p25.anl*.grb2*    *-v lv_HTGL2*   |
less

*GRD_P0_L103_GLL0 *(* lv_HTGL2*, lat_0, lon_0 )       ; <= 3D

*lv_HTGL2*:    80.00       100.0      <== meters

[2]  Apparently, you have created a 10 m wind: EG
          g = addfile (DirAnData+"*wind10m.nc <http://wind10m.nc>"*,"r")
      I have no idea how this was created.

[3]  Inverting and the latitude and longitude coordinates does *NOT* result
in the actual grid being reordered

;invert the latitude order
lati=lat_g(::-1)
;convert to west latitude
loni=lon_g-360.0

[4] Please *carefully *examine the *coordinates* after each operation

  dirg = "./"
  filg = "gfs.t18z.pgrb2.0p25.anl"
  pthg = dirg+filg+".grb2"            ; add .grb extension
  fg   = *addfile*(pthg, "r")
 ;print(fg)                           ; ncl_filedump
gfs.t18z.pgrb2.0p25.anl.grb2| less

  uh   = fg->UGRD_P0_L103_GLL0        ; ( lv_HTGL2, lat_0, lon_0)
  *printVarSummary*(uh)
  print("---")

  uh   = uh(:,*::-1*,:)                 ; Invert the grid (S->N)  via NCL
syntax
  printVarSummary(uh)
  print("---")

  uh   =* lonFlip*(uh)                  ; -180 to 180
  printVarSummary(uh)
  print("---")

  lat  = uh*&*lat_0                     ; extract the latitudes *associated
with the variable*
  lon  = uh*&*lon_0                    ;             longitudes
  print(lat)                              ; look at values
  print(lon)

If, after you makes changes, you still have problens
I will take a look. However, I would need the files:

VarMetar1H.txt
VieMetar1H.txt

On Tue, Mar 5, 2019 at 7:55 AM Gerardo Montoya <gemonga at gmail.com> wrote:

>  Dear NCL talk colleagues
>
> I’m interpolating wind, extracted from METAR, using  obj_anal_ic function.
>
> I take as first guess the wind at 10m (UGRD_P0_L103_GLL0 and VGRD_P0_L103_GLL0 variables) from GFS analysis at 2019-02-28:18Z (gfs.t18z.pgrb2.0p25.anl <https://nomads.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/gfs.2019022818/gfs.t18z.pgrb2.0p25.anl>)and use a rscan=(/0.1,0.01/).
>
> The METAR information is also taken for this data and time.
>
>
>
> Fig. Vgfs_A20190228_1800png  shows the GFS analysis wind and Fig. CressmanInterpolation19-02-28_18Z.png, the interpolated wind.
>
> These Figs, also contain wind barbs (plotted in black) at airports.
>
>
>
> Comparing these two Figs., it can be seen that, in some regions and in the
> vicinity of airports, The interpolation function works as expected: the
> interpolated wind deviates from the large scale flow (trade winds) and
> tends to curve in the direction indicated by wind barbs (see the areas
> highlighted with green arrow). Although, in some areas, specially over
> complex terrain (central Colombia)  and Cuba, the interpolated wind is
> extremely strong (see the areas highlighted with red arrow). It there is
> the possibility I made a mistake in my code. However, I can’t find it. I
> also noted that Cressman interpolation is very sensible to the rscan
> values. I’m attaching the code. The NCL 6.5 version is used.
>
> Any suggestion will be greatly appreciated.
> Gerardo Montoya, full professor (retired) at Universidad Nacional de
> Colombia
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