CPT-GCE

Climate Process Team on Gravity Current Entrainment

The CPT (Climate Process Team) is a new paradigm established by the U.S. CLIVAR program for linking process-oriented research and coupled climate model development. A CPT is a group of scientists funded by the National Science Foundation and the National Oceanic and Atmospheric Administration to

1. speed the transfer of theoretical and process-model understanding into improved treatment of processes in climate model systems,

2. identify process study activities necessary to further refine climate model fidelity, and

3. develop sustained observational requirements for climate model systems.

Overview

The CPT on Gravity Current Entrainment aims to develop parameterizations of dense gravity currents in the ocean for inclusion in climate models. Dense water formed through cooling or evaporation in marginal seas (e.g. Greenland-Iceland-Norwegian sea, Mediterranean Sea) or coastal shelves (e.g. Antarctic shelf) enters the general ocean circulation by flowing over topographic features including narrow channels (e.g. Denmark Straits, Gibraltar Straits) and down the continental slope. As the dense water descends it entrains ambient water, which mixes with the dense water, modifying the tracer properties and volume of the dense water. Present climate models do not have sufficient resolution to capture the small scale processes responsible for entrainment, and hence cannot correctly simulate the properties of the dense water masses which result, some of which (e.g. North Atlantic Deep Water, Mediterranean Overflow water, Antarctic Bottom Water) play very important roles in the large-scale ocean circulation. The goal of the CPT on Gravity Current Entrainment is to use knowledge gained from recent observations of dense overflows and laboratory and numerical process studies to improve the representation of dense gravity currents and their entrainment in climate models, thereby enhancing their ability to predict current and future climate.

Objectives

(a) Closely examine entrainment in recent observations, especially those of Denmark Straits Overflow, Faroe Bank Channel, Mediterranean Outflow, Red Sea Overflow and Antarctic slope overflows, as well as laboratory and numerical process studies.

(b) Use this knowledge to develop new and enhanced parameterizations of entrainment.

(c) Implement and test the new parameterizations in Ocean General Circulation models.