Ocean influence on the atmosphere on hourly to seasonal time scales
August 26, 2026
Kyle Shackelford
Committee: Peter Jan van Leeuwen (Advisor); Charlotte DeMott (Co-advisor); Michael Bell; Eric Maloney; Chien-Yung Tseng (Civil and Environmental Engineering)
Abstract
In the tropical warm pool region, the atmosphere forces upper ocean temperature and salinity through diurnal heating, nocturnal cooling, wind stirring, and surface freshening. As atmospherically-forced changes to the upper ocean accumulate, they also feed back to the atmosphere and influence atmospheric evolution. Ocean feedbacks to the atmosphere modify the short-term evolution of atmospheric convection as well as intraseasonal atmospheric variability. This dissertation investigates ocean influence on atmospheric convection and tropical-extratropical teleconnections, over hourly to seasonal timescales, organized in three separate studies.The first study investigates the influence of interactive sea surface temperatures (SST) on the organization of convection in radiative-convective equilibrium (RCE) simulations. RCE is an idealized representation of the tropical atmosphere and is generally achieved in simulations by prescribing constant solar heating, horizontally uniform initial temperature and moisture profiles, uniform, fixed lower boundary forcing, and doubly periodic boundaries. Random thermal perturbations embedded within uniform initial temperature fields in RCE simulations self-organize into distinct regions of suppressed and active convection, making it a suitable idealization for studying convective organization. We conduct RCE simulations coupled to a 2 m (S2) and a 20 m (S20) slab ocean model in a 3D channel domain to evaluate the influence of interactive SSTs on convective organization. S2 exhibits enhanced convective variability compared to S20, corroborating previous findings that the strength of convective organization in coupled RCE simulations is proportional to slab ocean depth. Notably, convection in S2 continually evolves over the 100-day simulation, whereas convection in S20 reaches an approximate equilibrium after ~40 days. Low cloud-SST feedbacks on the periphery of deep convection drive a zonal contraction of convection in S2 and are responsible for initial enhanced convective variability. Near the end of the S2 simulation, differential shortwave heating of the ocean within the convectively suppressed region produces SST gradients that excite fresh atmospheric convection, and is responsible for later enhanced convective variability.
The second study evaluates the influence of rain-induced SST gradients on upscale convective growth over the tropical warm pool. Coupled simulations are conducted with realistic initialization and boundary forcing to assess how rain-driven SST perturbations modify convective organization under realistic large-scale forcing. A control simulation is conducted (RL) where rain falling on the ocean surface can form ocean surface rain layers, alongside a mechanism denial experiment in which rainfall does not freshen and cool the ocean surface (no-RL). Our results demonstrate that low SST patches in RL drive anomalous circulations in the lower atmosphere, with upward motion detected in the lower free troposphere. Additionally, rain-driven cooling of the ocean surface modifies the convective organization of a mesoscale convectively-coupled n=3 gravity wave, while convective variability not connected to rain-cooled SST patches also plays a significant role in this modification.
The final study focuses on the role of SSTs as source of seasonal prediction skill for North Atlantic atmospheric circulation. A machine learning (ML) methodology is developed for detecting specific configurations of northern hemisphere SST that enhance prediction skill for North Atlantic atmospheric circulation on seasonal time scales. We identify four distinct SST regimes that result in more confident ML predictions and inform understanding of how interannual, decadal, and multidecadal SST variability modifies El Nino Southern Oscillation teleconnections to the extratropics.