Global Diurnal Sea Surface Temperature Variability and the Role of Ocean-Atmosphere Interactions

Abstract

Diurnal variations in sea surface temperature (SST) influence the atmospheric boundary layer and the hydrological cycle. Using a decade of satellite data, we identify global patterns of diurnal SST variability, capturing both warming and cooling phases. We highlight diurnal cooling as a distinct and previously underrecognized phenomenon, accounting for over 38% of observed cases. By focusing on extreme cooling and warming events, defined as diurnal SST changes exceeding $\pm 3.16°C$ from the mean, we explore the spatial distribution, seasonality, and mechanisms driving transitions between three SST states: diurnal warming, a balanced state, and diurnal cooling. These states correspond to distinct upper-ocean mixing regimes: minimal, neutral, and strong, each shaped by atmospheric forcing, including wind stress, cloud cover, and precipitation. In the tropics and mid-latitudes, extreme warming events dominate, occurring primarily during the transition and summer seasons under calm winds, clear skies, and little to no rain. In contrast, high-latitude regions are characterized by frequent diurnal cooling during winter, with passing storms emerging as key modulators of SST variability. Storms that occur during the day typically trigger strong cooling, while those passing at night can occasionally result in warming. By integrating seasonal context and focusing on extreme events, this study provides new insights into the atmospheric drivers of diurnal SST variability, an important step in constructing and tuning models that capture diurnal layer dynamics. These findings have implications for understanding energy budgets, air–sea interactions, and feedbacks in the coupled climate system.