The impact of resolving the Rossby radius at mid-latitudes in the ocean: results from a high-resolution version of the Met Office GC2 coupled model

Abstract

Abstract. There is mounting evidence that resolving mesoscale eddies and western boundary currents as well as topographically controlled flows can play an important role in air-sea interaction associated with vertical and lateral transports of heat and salt. Here we describe the development of the Met Office Global Coupled Model version 2 (GC2) with increased resolution relative to the standard model: the ocean resolution is increased from 1/4 to 1/12 • (28 to 9 km at the Equator), the atmosphere resolution increased from 60 km (N216) to 25 km (N512) and the coupling period reduced from 3 hourly to hourly. The technical developments that were required to build a version of the model at higher resolution are described as well as results from a 20-year simulation. The results demonstrate the key role played by the enhanced resolution of the ocean model: reduced sea surface temperature (SST) biases, improved ocean heat transports, deeper and stronger overturning circulation and a stronger Antarctic Circumpolar Current. Our results suggest that the improvements seen here require high resolution in both atmosphere and ocean components as well as high-frequency coupling. These results add to the body of evidence suggesting that ocean resolution is an important consideration when developing coupled models for weather and climate applications.

The Impact of Horizontal Resolution on Energy Transfers in Global Ocean Models

“…Less energetic currents and eddies can cause biases in e.g., the strength of overturning circulations [3], oceanic heat uptake [4], and mixed-layer depth [5] as well as model drifts [6]. To understand what sets the energy levels in ocean models at different horizontal resolutions and what parameterisations may be needed, we must understand how KE is transfered between length scales.…”

The Benefits of Global High Resolution for Climate Simulation: Process Understanding and the Enabling of Stakeholder Decisions at the Regional Scale

“…At this grid spacing, the first baroclinic Rossby radius is resolved only near the equator (Hallberg 2013). Hewitt et al (2017) reviewed the improvements found in going toward eddy-poor/ eddy-rich regimes (1/4°-1/10°), with important consequences for large-scale biases (McClean et al 2011;Delworth et al 2012;Small et al 2014a;Hewitt et al 2016), heat uptake (e.g., Griffies et al 2015;Kuhlbrodt et al 2015), and ocean marine ecosystems (Saba et al 2016;McKiver et al 2015;Stock et al 2011). Coupled simulations with ocean resolutions up to 1/16° will enable investigation of the impact of eddies on the mean state and variability of the coupled system.…”

Explicit representation and parametrised impacts of under ice shelf seas in the <i>z</i><sup>∗</sup> coordinate ocean model NEMO 3.6

“…We follow a similar strategy to introduce ice-shelf-ocean interactions into the NEMO framework (Madec and the NEMO team, 2016). The work is a first step towards adding an ice sheet component and its interaction within NEMO, and including these interactions within climate models such as IPSL (Dufresne et al, 2013), the Hadley Centre models (Hewitt et al, 2011(Hewitt et al, , 2016, EC earth (Hazeleger et al, 2010), CNRM (Voldoire et al, 2013) and CMCC (Scoccimarro et al, 2011).…”