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On the choice of ensemble mean for estimating the forced signal in the presence of internal variability

Citation

Frankcombe, LM and England, MH and Kajtar, JB and Mann, ME and Steinman, BA, On the choice of ensemble mean for estimating the forced signal in the presence of internal variability, Journal of Climate, 31 pp. 5681-5693. ISSN 0894-8755 (2018) [Refereed Article]


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DOI: doi:10.1175/JCLI-D-17-0662.1

Abstract

In this paper we examine various options for the calculation of the forced signal in climate model simulations, and the impact these choices have on the estimates of internal variability. We find that an ensemble mean of runs from a single climate model [a single model ensemble mean (SMEM)] provides a good estimate of the true forced signal even for models with very few ensemble members. In cases where only a single member is available for a given model, however, theSMEMfrom other models is in general out-performed by the scaled ensemble mean from all available climate model simulations [the multimodel ensemble mean (MMEM)]. The scaled MMEM may therefore be used as an estimate of the forced signal for observations. The MMEM method, however, leads to increasing errors further into the future, as the different rates of warming in the models causes their trajectories to diverge. We therefore apply the SMEM method to those models with a sufficient number of ensemble members to estimate the change in the amplitude of internal variability under a future forcing scenario. In line with previous results, we find that on average the surface air temperature variability decreases at higher latitudes, particularly over the ocean along the sea ice margins, while variability in precipitation increases on average, particularly at high latitudes. Variability in sea level pressure decreases on average in the Southern Hemisphere, while in the Northern Hemisphere there are regional differences.

Item Details

Item Type:Refereed Article
Keywords:climate variability, CMIP5
Research Division:Earth Sciences
Research Group:Atmospheric Sciences
Research Field:Atmospheric Dynamics
Objective Division:Environment
Objective Group:Climate and Climate Change
Objective Field:Global Effects of Climate Change and Variability (excl. Australia, New Zealand, Antarctica and the South Pacific) (excl. Social Impacts)
UTAS Author:Kajtar, JB (Mr Jules Kajtar)
ID Code:133140
Year Published:2018
Web of Science® Times Cited:2
Deposited By:Oceans and Cryosphere
Deposited On:2019-06-13
Last Modified:2019-06-13
Downloads:0

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