19990428: Bug in XCD SYN decoder

One of our sites, TASC - The Analytic Sciences Corporation, has recently 
made us aware of a bug in the synoptic data decoder. As best we can tell
this bug has been around since September 1990.

This bug affects all users of the SSEC Data Center's synoptic data and
all sites that have been running McIDAS-XCD.  We are testing a fix for 
-XCD now. The fix will be included in McIDAS-XCD 7.6 that will be
available in late May-early June. If your site would like to get an
addendum to -XCD before then, please contact me or the Help Desk. 

The SSEC Data Center will be redecoding and archiving the corrected data
from 1996 to present. Previous to 1996 the Data Center did not archive
the text data, so redecoding is not an option.

A description of the problem follows.    
  
The problem occurs in the decoding of the "height above surface of the
base of the lowest cloud seen" which is filed in the ZCB parameter of
the SYN point files. The bug is in the decoding of the h code of the
iR ix h VV group in section 1 of the synoptic code form. There was
an error while converting the code figure to a cloud base height.
See table 1600 in the WMO Manual on Codes, Part A.

Below is a table of the reported height versus the incorrectly
decoded height.

                                Incorrectly
Code figure (h)   Reported        Decoded
---------------   ---------     ------------
     0              25            MISSING
     1              75            25
     2              150           75
     3              250           150
     4              450           250
     5              800           450
     6              1250          800
     7              1750          1250
     8              2250          1750
     9              2500 or more  2250
                    or no clouds 


Please feel free to contact me or the Help Desk if you have any
questions.
We are sorry for any inconvenience this may have caused.

Dee Wade
-- 
Dee Wade
McIDAS User Services and Data Center
Space Science and Engineering Center
University of Wisconsin-Madison
Email:     address@hidden
Phone:     (608) 263-0527
Fax:       (608) 263-6738