Uncovering a Missing Factor in Marine Low Cloud Formation

[Geoengineering News]

https://essopenarchive.org/doi/full/10.22541/essoar.15001799/v1

Authors: Ehsan Erfani  

09 April 2026

Abstract

Marine low clouds (MLCs) play a critical role in regulating Earth’s radiation budget due to their extensive coverage and strong reflection of incoming solar radiation. Despite their importance, the extent to which large-scale climate oscillations modulate MLC properties is not well understood. In this report, the influence of the El Niño–Southern Oscillation (ENSO) on MLCs over the Pacific Ocean is investigated using satellite observations and reanalysis data. Cloud properties, including cloud fraction, liquid water path, and shortwave cloud radiative effect, are analyzed alongside meteorological variables such as inversion strength and lower-tropospheric geopotential height.

Results reveal a pronounced regional asymmetry in MLC response to ENSO. During El Niño conditions, MLCs decrease over the Northeast Pacific, leading to weaker shortwave cooling, while an opposite response is observed over the Southeast Pacific, where cloudiness and radiative cooling are enhanced. These contrasting behaviors are linked to ENSO-driven changes in large-scale circulation and boundary-layer stability. Specifically, reduced inversion strength and lower geopotential height suppress MLCs in the Northeast Pacific, whereas strengthened inversion and a poleward- and westward-shift of the Southeast Pacific high favor MLC formation in this region. These findings highlight the importance of both dynamical and thermodynamical controls in shaping regional cloud responses to climate variability and provide insights for improving cloud representation in Earth system models.

Source: ESS Open Archive