Office of Science and Technology Integration

Climate Prediction Center Ocean Briefing

Is an El Niño coming?
         - Possible impacts of ocean initial conditions on CFSv2 ENSO forecast

May 10, 2018  In Climate Prediction Center (CPC) May Ocean Briefing, forecaster discussions led by Dr. Zeng-Zhen Hu focused on potential El Niño development and the possible impact of Climate Forecast System Reanalysis (CFSR) biases on ENSO forecast. Investigations revealed the depth of 20°C isotherm anomaly of CFSR minus Global Ocean Data Analysis System (GODAS) reached -10 m before 1999 and after 2015. The shift around 1999 was related to the sudden onset of positive trade wind bias resulted from assimilation of the Advanced TIROS Operational Vertical Sounder (ATOVS) satellite observations (Xue et al. 2011; Zhang et al. 2012). The shift around 2015 was partially related to the reset of CFSR ocean conditions with a parallel GODAS run to control a cold bias growth in the tropical Atlantic Ocean in CFSR and partially to the warm bias in the 1999-2010 climatology used to define anomalies. The periodic reset of the CFSR ocean with the parallel GODAS run not only removed the cold bias in the tropical Atlantic, but also removed the warm bias in the eastern Pacific that has persisted from 1999 until 2015 when the reset started. According to Dr. Yan Xue, the CPC Global Ocean Monitoring Lead, the cooler subsurface temperature anomalies in CFSR after 2015 likely contributed to somewhat cooler NINO3.4 anomaly forecast in CFSv2, as shown in the North American Multi-Model Ensemble (NMME) plume, since the CFSv2 SST hindcast has been also bias-corrected with the 1999-2010 climatology. The discussion materials are available at current.ppt.

NMME Teleconferences

Predictability assessment of winter 2015/16 precipitation over the west coast of the US

April 5, 2018  Dr. Arun Kumar, Principal Scientist at NOAA Climate Prediction Center, gave a presentation on a research challenge on the predictability of 2015/16 winter precipitation anomaly

Climate Prediction S&T Digest, 42nd NOAA Climate Diagnostics and Prediction Workshop, Norman, OK, 23-26 2017, NWS OSTI and CPC, 202pp.  DOI: 10.7289/V5/CDPW-NWS-42nd-2018

over the west coast of the U. S., where the observation was opposite to the mean El Niño signal. Key research questions were raised. 1) Were the differences due to unpredictable noise having an influence on individual seasonal mean? 2) Were the differences due to changes in atmospheric response to differences in ENSO SSTs, atmospheric response to other boundary forcing, or changes in ENSO teleconnections in a changing climate? Were those factors predictable? Using CFSv2 hindcasts (1982-2011) and real-time forecasts (2012-2015), Dr. Kumar demonstrated the model forecasts with DJF 2015/16 SST forcings were consistent with historical expectations; the contribution from noise could lead to subtle changes in circulation and could appreciably change seasonal mean precipitation outcomes from the “expected response”. For better understanding, there are further questions that need to be answered, e.g. 1) What is the PDF of seasonal mean atmospheric states during different El Niño conditions? 2) How does the “response and noise” vary from one event to another? 3) How predictable are the variations in SSTs themselves? “Though we know the approach, i.e. ensemble of GCM simulations with multiple models to pursue attribution studies, we don’t know how to build confidence in answering some of the questions and bringing them to a closure. With such a view, the use of probabilistic forecasts in decision making on an individual forecast basis is a hard dilemma to come to grips with”, said Dr. Kumar.

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