Abstract

Coastal Stratocumulus clouds have a diurnal cycle influenced by solar heating and sea-breeze dynamics. These clouds typically thin after sunrise, and some of them fragment and then dissipate, a transition that has proven difficult to predict. In this work, we study the role of sea breeze in the dissipation transition by analyzing observations at two coastal sites, Antofagasta, Chile, and San Diego, CA. Surface measurements of solar irradiance and wind speed allow us to diagnose cloud fragmentation time, dissipation time, and the onset of sea breeze. While both locations differ in meteorological conditions, the transition has a distinctive sequence with similar average times: sunrise, then sea breeze (43 min later), and finally fragmentation (1.25 h) and dissipation (4.1 h). While the sequence suggests that sea breeze may be causing fragmentation, correlations do not support that hypothesis; instead, solar and thermodynamic variables gain relevance. Later dissipation shows correspondence to stronger wind speed, more markedly in Antofagasta. Causality between wind speed and solar irradiance was assessed using Convergent Cross Mapping, showing a bidirectional positive correlation that is dominated by wind speed, more strongly in Antofagasta than in San Diego, highlighting the role of sea breeze in causing changes in cloudiness.