Two-way feedback between the Madden-Julian Oscillation and diurnal warm layers in a coupled ocean-atmosphere model

Karlowska, Eliza ORCID:, Matthews, Adrian ORCID:, Webber, Ben ORCID:, Graham, Tim and Xavier, Prince (2024) Two-way feedback between the Madden-Julian Oscillation and diurnal warm layers in a coupled ocean-atmosphere model. Quarterly Journal of the Royal Meteorological Society. ISSN 0035-9009 (In Press)

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Diurnal warm layers develop in the upper ocean on sunny days with low surface wind speeds. They rectify intraseasonal sea surface temperatures (SSTs), potentially impacting intraseasonal weather patterns such as the Madden--Julian Oscillation (MJO). Here we analyse 15-lead-day forecast composites of coupled ocean--atmosphere and atmosphere-only Numerical Weather Prediction (NWP) models of the UK Met Office to reveal that the presence of the diurnal warming of SST (dSST) leads to a faster MJO propagation in the coupled model compared with the atmosphere-only model. To test the feedback between the MJO and the dSST, we designed a set of experiments with instantaneous vertical mixing over the top 5 m or 10 m of the ocean component of the coupled model. Weaker dSST in the mixing experiments leads to a slower MJO over 15 lead days. The dSST produces a 3% increase in the MJO phase speed between the coupled and the atmosphere-only model. An additional 5% increase is found for other coupling effects, unrelated to the dSST. A two-way feedback manifests in the coupled model over the 15 lead days of the forecast between the MJO and the dSST. The MJO regime dictates the strength of the dSST and the dSST rectifies onto the intraseasonal anomalies of SST in the coupled model. Stronger dSST in the coupled model leads to stronger intraseasonal anomalies of SST. The MJO convection responds to these SSTs on a 7-lead-day timescale, and feeds back onto the SST anomalies within the next 3 lead days. Overall, this study demonstrates the importance of high vertical resolution in the upper ocean for predicting the eastward propagation of the MJO in an NWP setting, which is potentially impactful for seasonal predictions and climate projections should this feedback be unrepresented in the models.

Item Type: Article
Uncontrolled Keywords: sdg 13 - climate action ,/dk/atira/pure/sustainabledevelopmentgoals/climate_action
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: 25 Jun 2024 13:30
Last Modified: 25 Jun 2024 13:30

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