The effect of diurnal warming of sea surface temperatures on the propagation speed of the Madden-Julian Oscillation

Karlowska, Eliza ORCID:, Matthews, Adrian J. ORCID:, Webber, Benjamin ORCID:, Graham, Tim and Xavier, Prince (2023) The effect of diurnal warming of sea surface temperatures on the propagation speed of the Madden-Julian Oscillation. Quarterly Journal of the Royal Meteorological Society. ISSN 0035-9009

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The diurnal warm layer in the upper ocean develops during low surface winds and high incoming solar radiation conditions, often increasing sea surface temperatures (SSTs) by up to 1 degC. The suppressed phase of the Madden–Julian Oscillation (MJO) favours the formation of such a layer. Here we analyse the coupled ocean–atmosphere and atmosphere-only Numerical Weather Prediction systems of the UK Met Office to reveal that important differences arise from the representation of the diurnal warm layer in the coupled model. While both models are skilful in predicting the MJO to at least 7-day lead time, the coupled model predicts approximately 12% faster MJO RMM phase speed than the atmosphere-only model due to the ability to resolve diurnal warming in the upper ocean that rectifies onto MJO-associated SST anomalies. The diurnal warming of SST (dSST) in the coupled model leads to an increase in daily mean SST compared with the atmosphere-only model persisted foundation SST. The strength of the dSST in the coupled model is modulated by MJO conditions. During suppressed MJO conditions on lead day 1, the dSST is enhanced leading to 0.2 degC warmer daily mean MJO-associated SST anomalies and increased convection in the coupled model by lead day 7. During active MJO convection, the dSST is suppressed, leading to 0.1 degC colder MJO-associated SST anomalies in the coupled model and reduced convection by lead day 7. This variability in dSST further amplifies the MJO propagation speed, underlining the importance of the two-way feedback between the MJO and the diurnal cycle of SST and the need to accurately represent this process in coupled models.

Item Type: Article
Additional Information: Funding information: Natural Environment Research Council (NERC) and ARIES DTP [grant NE/S007334/1] and Terra Maris project [grant NE/R016704/1].
Faculty \ School: Faculty of Science
Faculty of Science > School of Environmental Sciences
Faculty of Science > School of Natural Sciences
University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups: Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Faculty of Science > Research Groups > Climatic Research Unit
Depositing User: LivePure Connector
Date Deposited: 17 Oct 2023 00:43
Last Modified: 21 Oct 2023 00:50
DOI: 10.1002/qj.4599

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