Written by: Huug van den Dool (7/2000) adjustments 1/2001, 7/2002 , 8/2003 2/2005 2/2006 3/2007 2/2008 5/2009 2/2010 4/2011

For your perusal I have placed updated (untampered) OCN on a web page:

http://www.cpc.ncep.noaa.gov/products/people/wd51hd/index.html

then click on menu OCN.

Shown is the last 10 (T), 15(P) years averaged minus a 30 year climatology for each of 12 seasons.

Units are st.dev., i.e. 40 is 40% of the local standard deviation.

Data is 102 'super'CDs.

You will find all maps wrt current 71-2000 normals. Column 9 is the most recent OCN estimate, Columns 1, 2 , 3, 4, 5,6,7 and 8 are eight, seven, six, five, four, three, two and one year's ago best estimate, respectively. The lst column on the right shows the difference in the (1971-2000) and (1961-1990),climos, in physical units, C X 100 for Temp and mm/month X 10 for Precip.

What is shown in column (1) - (7) is untampered OCN, i.e. no skill mask

and no damping.

The untampered OCN shown here differs from what is operationally used only in the following ways:

-) operationally we have a skill mask, i.e. where a-priori correlation is less than 0.3 no forecast is shown. The a-priori skill is determined from 1962 up the moment of issuance.

-) the amplitude of the operational OCN is reduced by a factor that relates to the a-priori skill so as to minimize RMS error.

-) We update these set of 12 maps only once a year with final CD data, while operational OCN is up-to-date with (prelim) data thru last month.

OTHER COMMENTS:

-) Operational OCN can be found under item 30 of long lead briefing package:90-day tools

-) Related use of OCN can be consulted in trendadjusted ENSO composites at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/total.html

-) Other Related use of OCN, on an EOF by EOF basis, can be found under item 18 of long lead briefing package: E-OCN developed by Peitao Peng

-) Long Lead briefing package, see: http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing/index.pri.html

Reference: J. Huang, H. M. van den Dool and A. G. Barnston, 1996: Long-Lead Seasonal Temperature Prediction Using Optimal Climate Normals. J. Climate., 9, 809-817.