Christian Feliciano The Ohio State University Atmospheric Science

Overview EP and CP El Nino First Paper ENSO Flavors Frequency of each flavor. Second Paper Natural variability Future Research Questions

Eastern Pacific ENSO…. Typical El Nino Pattern Centered over the eastern Pacific Sea surface anomalies in the Nino 3.4 region. (+0.5°C) 5°S-5°N and °W Kao & Yu 2007

Central Pacific El Nino… Newly recognize Centered near the International Date Line Unique global impacts and global warming trends Increase d frequency of Central Pacific El Nino? Kao & Yu 2007

EP vs. CP ENSO Examples of the eastern-Pacific and central-Pacific types of ENSO: (a) SST anomalies averaged from November 1997 to January 1998 of the 1997/98 El Nino event and (b) SST anomalies averaged from November 1977 to January 1978 of the 1977/78 El Nino event

Nathaniel C. Johnson International Pacific Research Center, School of Ocean and Earth Science and Technology, University of Hawaii Manoa, Honolulu, Hawaii

Data and Methodology Self-organizing map analysis (SOM) Grouping tool ENSO flavors defined by SOM SST anomaly patterns in the equatorial Pacific September–February mean SST data from 1950 through 2011 derived from the Extended Reconstructed Sea Surface Temperature Dataset Pacific region between 120°E and 50°W and between 25°S and 25°N

SOM Patterns Johnson 2012

Frequency Johnson 2012

Results/Conclusion Pattern 6, 7, and 8 represent CP ENSO Pattern 9 represents EP ENSO (also the strongest El Nino events) A transition from La Nina–like patterns with weak or negative SST anomalies in the western Pacific warm pool (1 and 2) to La Nina–like patterns with positive SST anomalies in the western Pacific warm pool (3 and 4)  Drought? Natural variability or global warming?

Matthew Newman Sang-Ik Shin Michael A. Alexander Geophysical Research Journal 2007

Background Based off of the paper “The Optimal Growth of Tropical Seas Surface Temperature Anomalies” by Cecile Penland and Prashant D. Sardeshmukh Used many of the same techniques SST precursor patterns Correlate optimal SST patters to observed ENSO events

Findings

Motivation 1)Dynamics that lead to various ENSO flavors 2) Does the recent increase in CP ENSO a result of decadal change 3)Does the recent increase in CP ENSO a result of anthropogenic climate change

Data and Methodology Linear Inverse Modeling (LIM) 3‐month running mean anomalies of observed SST, thermocline depth(depth of 20°C isotherm) and surface zonal wind stress in the Tropics (30°S–30°N) during 1959–2000. multivariate, “patterns‐based”, red noise approach to 42 years of observed tropical SST, thermocline depth, and zonal wind stress seasonal anomalies

ENSO Dynamics Newman 2011

1) Tropical SST growth factor for the EP pattern is almost 4 times greater than for the CP pattern 2) CP ENSO has a cold phase

Results/Conclusion EP ENSO events form as a result of the discharge-recharge theory  lead to stronger El Nino CP ENSO events have no thermocline-surface interactions. SST anomalies are advected into the region  lead to longer lasting weaker El Nino Natural random variations can account for the observed variability of Central Pacific (CP) and Eastern Pacific (EP) ENSO events Increasing trend in the frequency of CP El Nino events may be indistinguishable from natural variability Data set to small

Future Research Global impacts of CP ENSO Similar to EP ENSO? Stronger/Weaker? Better understanding of the variability and dynamics of CP/EP ENSO flavors/events Will the warming trend in the west Pacific for La Nina events continue? What are the global impacts

Questions??

References Hsun-Ying Kao and Jin-Yi Yu, 2009: Contrasting Eastern-Pacific and Central- Pacific Types of ENSO. J. Climate, 22, 615–632. doi: Nathaniel C. Johnson, 2013: How Many ENSO Flavors Can We Distinguish?*. J. Climate, 26, 4816–4827. doi: Michael A. Alexander, Ludmila Matrosova, Cécile Penland, James D. Scott, and Ping Chang, 2008: Forecasting Pacific SSTs: Linear Inverse Model Predictions of the PDO. J. Climate, 21, 385–402. doi: Newman, M., S.-I. Shin, and M. A. Alexander (2011), Natural variation in ENSO flavors, Geophys. Res. Lett., 38, L14705, doi: /2011GL /2011GL047658