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

[Gerardo Montoya]

 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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