January 16, 2008

We discovered an error in our processing of AMSU data from NOAA-15 for TLT.  A new version,
version 3.1 is now available and should be used for all applications.  This new version
is in much better agreement with other sources of tropospheric temperature.  We apologize for
any inconvenience.

What was the error?

Last January, I made a small change in the way TLT is calculated that reduced the absolute
Temperatures by 0.1K.  But I only used the new method for 2007 (the error).  
When the data are merged with MSU, MSU and AMSU are forced to be as close as possible to each 
other over the 1999-2004 period of overlap.  This caused the error to show up as a downward 
jump in JAnuary 2007.  To fix the problem, I reprocessed the 1998-2006 AMSU data using the new
code (like I should have done in the first place), and merged it with the MSU data. 

We would like to thank John Christy and Roy Spencer, who were very helpful during the diagnosis 
process.

Carl Mears, RSS, January 16 2008