Bathymetric Influence on Mean Currents in two High-Resolution, Bathymetric Influence on Mean Currents in two High-Resolution, Near-Global Ocean ModelsNear-Global Ocean Models Bill Merryfield

Canadian Centre for Climate Modelling and Analysis Rob ScottUniversity of Texas Institute for Geophysics

Environment Canada

Environnement Canada

Meteorological Service

of Canada

Service météorologique

du Canada

AcknowledgementsThe authors are grateful to Mat Maltrud and Hideharu Sasaki for providing results from the LANL/NPS POP and OFES ocean models. This work was funded by NSF through award # 0327520.

References(3) Holloway, G., 1992: J. Phys. Oceanogr. 22,

OS16J-14

Arctic

NH Subtrop

SH Subtrop

NH Subpolar

Tropics

SH Subpolar

NCEP mean wind stress curl (10**8 Pa/m)

● Unsteady motions over sloping topography tend to drive steady alongslope currents such that shallower water lies to the right of the current vector in the Northern Hemisphere.1,2 ● This is a consequence of partial mixing of potential vorticity, and has been termed the ‘neptune effect”.3

● The extent to which such a ttendency is prevalent in the oceans is uncertain due to a paucity of current measurements, particularly in the deep ocean.● High resolution models provide a means (albeit imperfect) for inferring current structures where few measurements exist.● On the basis of theory and idealized process models, expect high-resolution, eddy-active models to exhibit greater neptune tendency than lower-resolution models.

Introduction

● OFES (OGCM for Earth Simulator)4

- 0.1º resolution x 54 levels - Partial cell topography - Biharmonic friction (-27x109 m4s-1) - 10-year average● LANL/NPS POP5

- 0.1º resolution x 40 levels - Full cell topography - Biharmonic friction (-27x109 m4s-1) - 3-year average

● LANL POP - 0.4º resolution x 40 levels - Full cell topography - Biharmonic friction (-8.6x1011 m4s-1) - 3-year average● CCCma CGCM3 - 1.87º resolution x 29 levels - Full cell topography - Laplacian friction (1.4x105 m2s-1) - 50-year average

High-resolution ocean models

Lower-resolution comparison models

● Unsteady motions over sloping topography tend to drive steady alongslope currents such that shallower water lies to the right of the current vector in the Northern Hemisphere.1,2 This has been termed the ‘neptune effect”.3

● The extent to which this tendency is prevalent in the oceans is uncertain due to a paucity of current measurements, particularly in the deep ocean.● High resolution models provide a means (albeit imperfect) for inferring current structures where few measurements exist.

● Unsteady motions over sloping topography tend to drive steady alongslope currents such that shallower water lies to the right of the current vector in the Northern Hemisphere.1,2 This has been termed the ‘neptune effect”.3

● The extent to which this tendency is prevalent in the oceans is uncertain due to a paucity of current measurements, particularly in the deep ocean.● High resolution models provide a means (albeit imperfect) for inferring current structures where few measurements exist.

● Consider volume averages of “topostrophy”6, defined as ûûN , where û = unit vector in direction of mean current

ûN=● We plot

Diagnostics

● Unsteady motions over sloping topography tend to drive steady alongslope currents such that shallower water lies to the right of the current vector in the Northern Hemisphere.1,2 This has been termed the ‘neptune effect”.3

● The extent to which this tendency is prevalent in the oceans is uncertain due to a paucity of current measurements, particularly in the deep ocean.● High resolution models provide a means (albeit imperfect) for inferring current structures where few measurements exist.

Example 1: Arctic ocean