NOUS41 KWBC 251605

PNSWSH

 

Technical Implementation Notice 16-09

National Weather Service Headquarters Washington DC

1205 PM EDT Fri Mar 25 2016

 

To:       Subscribers:

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network

          -NOAAPORT

          -Other NWS Partners, Users and Employees

 

From:     Tim McClung

          Chief Operating Officer

          NWS Office of Science and Technology Integration

 

Subject:  Reset of ocean initial conditions in the operational

          Climate Forecast System version 2 (CFSv2) to remove

          Atlantic Ocean cold bias March 28, 2016

         

Beginning with the 0600 Coordinated Universal Time (UTC) model

run on Monday, March 28, 2016, the National Centers for

Environmental Prediction (NCEP) Central Operations will

implement a fix to the Global Ocean Data Assimilation System

used in the Climate Forecast System (CFSv2). This fix is

expected to remove an erroneous cold anomaly in the equatorial

and South Atlantic Ocean temperature.

 

A large temperature cold bias emerged in the ocean initial

conditions along the equator in the spring of 2015 and grew to

include the South Atlantic in the summer of 2015. These cold

biases have translated into cold biases in the same regions in

CFSv2 forecasts. The ENSO forecasts from the CFSv2 from December

2015 show unusual behavior, in that the El Nino event does not

transition to neutral but rather experiences a double-dip 

El Nino, which is not realistic. A fix has been tested that

re-initialized the ocean initial conditions in the operational

CFSv2 from an offline GODAS, which uses a weak relaxation to

climatology (the NODC WOD09) to control the noise.

 

EMC tested this re-initialization strategy for 4 initial months

(December 2015 through March 2016). Results can be viewed here:

 

http://www.nco.ncep.noaa.gov/pmb/changes/downloads/CFSv2_Atlantic_cold_bias_problem.pdf

 

EMC found that there was no Atlantic cold bias in the initial

states as compared to current operational CFSv2. The long lead

forecasts evolved from the current El Nino event into neutral or

La Nina conditions during the next 9 months in the Nino3.4 SST

plumes.

 

Based on the positive results of the CFSv2 tests and the

severity of the cold bias anomaly in the Atlantic Ocean, NCEP

will implement this change outside of the normal upgrade

process. Users do not need to take any action and will continue

receiving data as they do today.

 

For questions regarding the correction to the CFS GODAS and

resulting improvement to the Atlantic cold bias please contact:

 

  Suranjana Saha

  NCEP EMC/College Park, Maryland

  301-683-3727

  Suranjana.Saha@noaa.gov

 

NWS national TINS are online at:

 

http://www.weather.gov/os/notif.htm

 

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