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Climate Prediction Center Ocean Briefing

Is an El Niño coming? - Possible impact of CFSR biases on 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. It was learned that the shift of the CFSR bias around 1999 was related to the shift of CFSR surface 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 of the CFSR bias around 2015 may be 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. A periodic reset of the CFSR ocean with the parallel GODAS run is used to remove the cold bias. For the impact on North American Multi-Model Ensemble (NMME) forecast, NCEP-CFSv2 and NCAR-CCSM4 both models respond to the CFSR re-re-adjustment with flat forecasts, while NASA-GEOS5, GFDL-FLOR, and GFDL-CanCM3&4 models are sticking with weak-moderate El Niño. The ensemble means of both original and PDF-adjusted call for Ocean Niño Index (ONI) about +1°C, peaking in OND/NDJ. Overall, the probabilities are confident for El Niño, but the magnitude is pretty borderline. The discussion materials are available at _briefing_gif/global_ocean_monitoring_current.ppt.

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

NMME Teleconference

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 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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