FY 2021 ENSO Observations McPhaden, M.J., T. Lee, S. Fournier, and M.A. Balmaseda Chapter 3 in El Niño Southern Oscillation in a Changing Climate, M.J. McPhaden, A. Santoso, and W. Cai (eds.), Geophysical Monograph 253, American Geophysical Union, Wiley, 39–63, doi: 10.1002/9781119548164.ch3, View online (2020) Summary. Observations of the ocean‐atmosphere system sustained over decades are essential for describing, understanding, modeling, and predicting variations associated with El Niño and the Southern Oscillation (ENSO). Here we discuss the history of observing system development in the tropical Pacific and profile the mix of satellite and in situ components that currently make up the sustained observing system. To illustrate key physical processes that give rise to ENSO variations, we focus on the period 2014–2019, which encompassed the first extreme El Niño of the 21st century in 2015–2016. We also provide an overview of model‐based oceanic and atmospheric reanalysis products that are used for monitoring climate variability and initializing seasonal to decadal timescale climate forecasts. In addition, we highlight new developments in coupled ocean‐atmosphere data assimilation and century‐long reanalyses. We conclude by addressing some of the challenges in sustaining and evolving the observing system over time. Feature Publications | Outstanding Scientific Publications Contact Sandra Bigley | Help
