Ocean Convective Available Potential Energy. Part I: Concept and Calculation

Thermobaric convection (type II convection) and thermobaric cabbeling (type III convection) might substantially contribute to vertical mixing, vertical heat transport, and deep-water formation in the World Ocean. However, the extent of this contribution remains poorly constrained. The concept of oce...

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Bibliographic Details
Published in:Journal of Physical Oceanography
Main Authors: Su, Zhan, Ingersoll, Andrew P, Stewart, Andrew L, Thompson, Andrew F
Format: Article in Journal/Newspaper
Language:unknown
Published: eScholarship, University of California 2016
Subjects:
Life Below Water
Fluxes
Deep convection
Convection
Conditional instability
Diapycnal mixing
Energy transport
Circulation/ Dynamics
Oceanography
Maritime Engineering
Weddell Sea
Online Access:https://escholarship.org/uc/item/4734n4kg
https://escholarship.org/content/qt4734n4kg/qt4734n4kg.pdf
https://doi.org/10.1175/jpo-d-14-0155.1
Description
Summary:Thermobaric convection (type II convection) and thermobaric cabbeling (type III convection) might substantially contribute to vertical mixing, vertical heat transport, and deep-water formation in the World Ocean. However, the extent of this contribution remains poorly constrained. The concept of ocean convective available potential energy (OCAPE), the thermobaric energy source for type II and type III convection, is introduced to improve the diagnosis and prediction of these convection events. OCAPE is analogous to atmospheric CAPE, which is a key energy source for atmospheric moist convection and has long been used to forecast moist convection. OCAPE is the potential energy (PE) stored in an ocean column arising from thermobaricity, defined as the difference between the PE of the ocean column and its minimum possible PE under adiabatic vertical parcel rearrangements. An ocean column may be stably stratified and still have nonzero OCAPE. The authors present an efficient strategy for computing OCAPE accurately for any given column of seawater. They further derive analytical expressions for OCAPE for approximately two-layer ocean columns that are widely observed in polar oceans. This elucidates the dependence of OCAPE on key physical parameters. Hydrographic profiles from the winter Weddell Sea are shown to contain OCAPE (0.001-0.01 J kg-1), and scaling analysis suggests that OCAPE may be substantially enhanced by wintertime surface buoyancy loss. The release of this OCAPE may substantially contribute to the kinetic energy of deep convection in polar oceans.

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