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Blind use of reanalysis data: apparent trends in Madden–Julian Oscillation activity driven by observational changes

Citation

Oliver, ECJ, Blind use of reanalysis data: apparent trends in Madden-Julian Oscillation activity driven by observational changes, International Journal of Climatology, 36, (10) pp. 3458-3468. ISSN 0899-8418 (2016) [Refereed Article]

Copyright Statement

Copyright 2015 Royal Meteorological Society

DOI: doi:10.1002/joc.4568

Abstract

Atmospheric and oceanic reanalyses are used widely by the climate science community. These products provide full three-dimensional state fields and gapless time series, along with the confidence of being constrained by observational measurements, for atmospheric scientists and oceanographers to use in analyses of the climate system. However, as ubiquitous as reanalysis data are, it is not often considered how a scarcity of measurements in certain poorly observed regions, or over the course of a long period of time in which the observational system has changed significantly, impacts the realism of the data. This study explores this question using tropical surface pressures from the Twentieth Century Reanalysis to hindcast an index of the Madden–Julian Oscillation (MJO) over the 20th century. We show that by changing the choice of surface pressure predictor locations, and being aware of the observational measurements that have been assimilated by the reanalysis system, it is possible to control the estimated centennial-scale trend in MJO activity from nearly zero to an increase of 30% over the 20th century. We emphasize that this is an apparent trend as it arises solely from the use of reanalyzed surface pressures from locations that have either been poorly observed or have experienced significant changes in the observing system over the 20th century. This highlights the need to be aware of the observational measurements (or lack of them), particularly their density in space and time, that have been assimilated by a reanalysis system.

Item Details

Item Type:Refereed Article
Keywords:Madden-Julian Oscillation, reanalysis, data assimilation, multidecadal variability, climate trends
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Physical Oceanography
Objective Division:Environment
Objective Group:Climate and Climate Change
Objective Field:Climate Variability (excl. Social Impacts)
Author:Oliver, ECJ (Dr Eric Oliver)
ID Code:107954
Year Published:2016
Web of Science® Times Cited:2
Deposited By:Centre for Oceans and Cryosphere
Deposited On:2016-04-01
Last Modified:2017-11-17
Downloads:0

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