Abstract
Abstract. A coordinated set of Arctic modelling experiments, which explore how the Arctic responds to changes in external forcing, is proposed. Our goal is to compute and compare climate response functions (CRFs) – the transient response of key observable indicators such as sea-ice extent, freshwater content of the Beaufort Gyre, etc. – to abrupt step changes in forcing fields across a number of Arctic models. Changes in wind, freshwater sources, and inflows to the Arctic basin are considered. Convolutions of known or postulated time series of these forcing fields with their respective CRFs then yield the (linear) response of these observables. This allows the project to inform, and interface directly with, Arctic observations and observers and the climate change community. Here we outline the rationale behind such experiments and illustrate our approach in the context of a coarse-resolution model of the Arctic based on the MITgcm. We conclude by summarizing the expected benefits of such an activity and encourage other modelling groups to compute CRFs with their own models so that we might begin to document their robustness to model formulation, resolution, and parameterization.
Highlights
Much progress has been made in understanding the role of the ocean in climate change by computing and thinking about “climate response functions” (CRFs), i.e., perturbations to the climate induced by step changes in, for example, greenhouse gases, freshwater (FW) fluxes, or ozone concentrations
To illustrate our approach here we focus on perturbations to the wind field over the Beaufort Gyre and the Greenland Sea (GS), the heat flux through the Fram Strait, and river runoff
A focus on the transient response of Arctic models is of direct relevance to Arctic climate change, enabling us to engage and overlap with the climate change community
Summary
Much progress has been made in understanding the role of the ocean in climate change by computing and thinking about “climate response functions” (CRFs), i.e., perturbations to the climate induced by step changes in, for example, greenhouse gases, freshwater (FW) fluxes, or ozone concentrations (see, e.g., Good et al, 2011, 2013; Hansen et al, 2011; Marshall et al, 2014; Ferreira et al, 2015). A successful coordinated activity has a low bar for entry, is straightforward to carry out, involves models of all kinds – low resolution, high resolution, coupled and ocean only – is exciting and interesting scientifically, connects to observations and, in the context of the Arctic, to climate change and the climate change community. This paper stems from those discussions and sets out in a more formalized way how to compute CRFs for the Arctic, what they might look like, and proposed usage. Convolutions with observed time series of the forcing 2 we describe how we propose to compute CRFs for key observables and forcing functions in the Arctic.
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