PMEL Publications Abstract
FY 2026
Increases in Southeast Pacific low-cloudiness during ENSO warm phases
Manapat, A., M.J. McPhaden, and R. Wood
Geophys. Res. Lett., 53(13), e2026GL122913, doi: 10.1029/2026GL122913, View open access article at AGU/Wiley (external link) (2026)
Changes in cloud fraction associated with Central Pacific and Eastern Pacific El Niños are analyzed using monthly cloud data from the International Satellite Cloud Climatology Project, meteorological variables from the European Center for Medium Range Weather Forecasting reanalysis version 5, and radiation data from the Clouds and the Earth's Radiant Energy System. We observe robust increases in low cloud fraction in the tropical Southeast Pacific (SEP, 120°–80°W 0°–20°S) during El Niños. The increases in SEP low-cloudiness are associated with CP-El Niño variability. Increases in SEP Sea Surface Temperature during CP-El Niños are accompanied by a warmer tropical free troposphere, increased cold advection, and reduced overlying cirrus, facilitating the growth of low clouds. Northeast Pacific cloud decks decrease during El Niños, consistent with weaker free-tropospheric heating outside the tropics. Coupled CMIP6 model experiments are unable to replicate increased SEP low cloud due to a misrepresentation of El Niño Southern Oscillation diversity.
Plain Language Summary. The El Niño Southern Oscillation (ENSO) is a semi-periodic fluctuation in the tropical Pacific. Sea Surface Temperatures (SSTs) in this region transition between a cold pattern (La Niña) and a warm (El Niño) pattern every 3–7 years. Recently, there has been more recognition that clouds play an important role in modulating this cycle. Different cloud types differ in both their ability to block incoming sunlight and their effectiveness at trapping heat radiating from Earth. As such, various cloud types can either dampen or accentuate the growth of SST anomalies in the Pacific. However, how cloud properties change in response to ENSO remains uncertain. In this study, we find that during El Niño events, low clouds in the Southeast Pacific increase in area—even though low clouds typically decrease as SSTs rise. We show that this unexpected response is linked to atmospheric heating and a reduction in high cloud cover, which together counteract SST increases to promote the formation of low clouds. Coupled climate models are unable to replicate this phenomenon, likely due to them misrepresenting ENSO diversity. These findings reveal a more complex relationship between ENSO and clouds than previously understood, and underscores the need to better understand cloud behavior in a warming world..