Work supported by the Climate Program Office's Climate Observation Division (authors: C. Seethala, et al. from the Scripps Institution of Oceanography) has been published online for early release in the Journal of Climate.
The paper--How has subtropical stratocumulus and associated meteorology changed since the 1980s?--assesses how low-level cloud amount and meteorological conditions have changed in recent decades in subtropical stratocumulus regions.
The importance of low-level cloud feedbacks to climate sensitivity motivates an investigation of how low-level cloud amount and related meteorological conditions have changed in recent decades in subtropical stratocumulus regions. Using satellite cloud datasets corrected for inhomogeneities, we find that during 1984-2009 low-level cloud amount substantially increased over the northeast Pacific, southeast Pacific, and southeast Atlantic, decreased over the northeast Atlantic, and weakly increased over the southeast Indian subtropical stratocumulus regions. Examination of meteorological parameters from four reanalyses indicates that positive trends in low-level cloud amount are associated with cooler sea surface temperature, greater inversion strength, and enhanced cold-air advection. The converse holds for negative trends in low-level cloud amount. A multilinear regression model based on these three meteorological variables reproduces the sign and magnitude of observed cloud amount trends in all stratocumulus regions within the range of observational uncertainty. Changes in inversion strength have the largest independent effect on cloud trends, followed by changes in advection strength. Changes in sea surface temperature have the smallest independent effect on cloud trends. Differing signs of cloud trends and differing contributions from meteorological parameters suggest that observed changes in subtropical stratocumulus since the 1980s may be due to natural variability rather than a systematic response to climate change.
To access the early online release of this paper, visit: http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0120.1