High-Latitude Ocean Convection and Gyre Dynamics

• Main Author: Su, Zhan
• Format: Thesis
• Language: English
• Published: 2016
• Subjects: Weddell Sea; Weddell; North Atlantic; Sea ice
• Online Access: https://thesis.library.caltech.edu/9777/; https://thesis.library.caltech.edu/9777/7/su_zhan_2016.pdf; https://resolver.caltech.edu/CaltechTHESIS:05262016-174848616

High-latitude ocean deep convection substantially contributes to vertical mixing, vertical heat transport, deep-water formation, and sea-ice budget in the World Ocean. However, the extent of this contribution remains poorly constrained. The concept of ocean convective available potential energy (OCAPE) have been developed to improve the understanding and the prediction for these deep convection events. The kinetic energy (KE) budget of deep convection is explored analytically and numerically based on the observations in the Weddell Sea. OCAPE, which is derived from thermobaricity, is identified as a critical KE source to power ocean deep convection. Other significant contributions to the energetics of convection, including diabatic processes related to cabbeling and stratification, are also carefully quantified. An associated theory is developed to predict the maximum depth of convection. This work may provide a useful basis for improving the convection parameterization in ocean models. As an application of the theory above, basin-scale OCAPE is found to be significantly built up in the North Atlantic at the end of Heinrich Stadial 1 (~17,000 years ago). This OCAPE is ultimately released to power strong ocean deep convection in North Atlantic as simulated by numerical models. This causes a ~2 °C sea surface warming for the whole basin (~700 km) within a month and exposes a huge heat reservoir to the atmosphere. This may invigorate the Atlantic meridional overturning circulation and provide an important mechanism to explain the abrupt Bolling-Allerod warming. Mesoscale turbulence is another crucial process for high-latitude ocean dynamics. From the physical nature of baroclinic instability, the framework of eddy-size- constrained Available Potential Energy (APE) density is developed, which is capable of well-detecting individual eddies and local eddy kinetic energy (EKE) in the World Ocean. This new framework is likely useful in parameterizing mesoscale eddies in ocean GCMs. Mesoscale turbulence are found to be ...