Changes in southeastern Pacific Ocean cloud fractions: cloud radiative effects and cloud controlling factors

Abstract

Clouds play a critical role in Earth’s radiative balance through their radiative effects. Recent studies suggest that the current planetary energy imbalance is associated with a reduction in global albedo, largely resulting from decreases in cloud fraction. However, the southeastern Pacific Ocean, where maritime stratocumulus clouds dominate off the west coast of South America, shows increasing albedo associated with enhanced low cloud cover. In this study, PATMOS-x v6.0, a satellite-based long-term climate data record derived from the AVHRR instruments aboard polar orbiting satellites, and CERES EBAF are used to investigate changes in cloud fraction and albedo, respectively. Both datasets show increases in anomalies of water cloud amount (1.21%∙decade −1 ) and albedo (0.25%∙decade −1 ), and these variables have been strongly correlated since 2000. Applying the cloud-controlling factors framework using 6 atmospheric variables from the ERA5 reanalysis dataset and ridge regression method indicates that these changes are primarily driven by an increase in estimated inversion strength (0.31 K∙decade −1 ). The slope between water cloud amount and EIS anomalies is 2.81%∙K −1 from Pv6.0 and 2.37%∙K −1 from ridge regression model. The increase in EIS is associated with enhanced lower tropospheric stability, resulting from a decrease in surface temperature (−0.07 K∙decade −1 ) and an increase in atmospheric temperature at 700 hPa (0.24 K∙decade −1 ) over the last four decades. The long-term decrease in surface potential temperature is closely associated with ENSO variability, whereas the increase in potential temperature at 700 hPa is incompatible with an ENSO-only explanation, implying that other thermodynamic or circulation changes are contributing to enhanced lower tropospheric stability.