Factors Causing Stratocumulus to Deviate from Subtropical High Variability on Seasonal to Interannual Timescales

Abstract. Stratocumulus (Sc) covers the eastern flanks of maritime subtropical high pressure systems and exerts an influence on the global energy budget comparable to CO₂. Previous studies have identified the temperature difference between 700 hPa and the surface as the primary driver of Sc variability. However, the mechanistic linkages between subtropical highs and this critical temperature gradient, which defines lower tropospheric stability, remain unresolved. While subsidence modulates temperatures at 700 hPa and wind-driven cooling affects surface temperatures, the observed decoupling between subtropical high intensity and Sc fraction on seasonal to interannual timescales lacks a mechanical explanation. This study uses reanalysis data to test two hypothesized pathways linking the strength of the subtropical highs to the lower tropospheric stability. Results demonstrate that neither pathway dominates, as correlations between Sc-regime temperatures and subtropical high dynamics exhibit strong regional and temporal dependencies, indicating that correlation does not apply causation. Additionally, Sc-regime conditions do not systematically align with subtropical high variability, highlighting the need for further investigation into the dynamical processes governing temperatures in the lower troposphere.