Links between subtropical high-pressure systems and stratocumulus clouds variation

Stratocumulus clouds contribute significantly to the global energy budget as they are the Earth’s predominant cloud type and contribute strongly to Earth’s albedo. They are known to predominate in the subtropics, especially on the eastern edge of the subtropical highs. Previous studies have confirmed the importance of these highs for stratocumulus clouds, but how much it varies can influence the cloudiness hasn’t been quantified, yet. Our study investigates this relation for both the annual cycle and deseasonalized time series for the five major subtropical high-pressure regions. It has been shown that the estimated cloud top entrainment index (ECTEI) is a useful predictor for the stratocumulus cloud fraction for both time scales. We show, however, that the variation of the highs provides additional information on the fraction change on an annual cycle. The Northern Hemisphere is more sensitive to the highs change compared to the Southern Hemisphere. Variations in the structure, area, and location of subtropical highs are not considered the dominant influencing factors (correlations about 0.3~0.4). Nevertheless, we found a qualitative preference that stratocumulus clouds prefer a flatter, large, and westward subtropical high.