[Dart-dev] obs_diag update - important - please read

Tim Hoar thoar at ucar.edu
Thu Feb 7 10:46:57 MST 2008

Perhaps the subject line should be 'obs_diag bugfix pending' ...

For the purpose of this email

'old' obs_diag is anything before revision 3180.
'new' obs_diag is 3180 and later ... all of which output the netCDF  

Only the new version tracks the U, V wind components individually ...  
they are (still) correct.

The new obs_diag has what I consider a 'bug' in that it tracks  
statistics of the
scalar wind speed rather than the vector wind velocity. The old  
obs_diag was
designed to compare to NCEP and tracks the vector wind velocity.

The sticky point is the old obs_diag accurately called this the  
and the new obs_diag calculates the speed and accurately calls it  

Clearly ... comparisons between the old and the new are not appropriate.
Since the primary intent of this routine is to allow accurate  
comparisons with NCEP,
I will be changing obs_diag to track the vector wind velocity and  
create a netCDF variable
called 'WIND_VELOCITY' (I'm dropping the HORIZONTAL part because the  
names are so long already).

There are some other enhancements in obs_diag that will allow a  
simpler interface
to the plot_observation_locations.m script, the ability to ingest  
observation sequences
that have not been assimilated, and the ability to define regions  
that span the prime meridian.
What the heck ... I might even update the documentation. So stay  
tuned - I have not completed
testing on all the platforms but feel this information needs to go  
out now.

Please also note that the ONLY rejection mechanism in the new  
obs_diag is based
on the DART QC flag. The old version could be used in a misleading  
fashion by lowering the
value of 'rat_cri' (a namelist variable) so that any observations  
whose increments were greater
than 'rat_cri' were summarily rejected by obs_diag - regardless of  
whether they were assimilated or not.
Before the DART QC flag existed, this was the only way we had to  
discriminate 'good' observations from
'bad' observations.

Tim Hoar, Associate Scientist
National Center for Atmospheric Research
thoar at ucar.edu
303 497 1708

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