The effect of ocean–atmosphere coupling on the Madden–Julian Oscillation in UK Met Office forecast models

Karlowska, Eliza (2024) The effect of ocean–atmosphere coupling on the Madden–Julian Oscillation in UK Met Office forecast models. Doctoral thesis, University of East Anglia.

Preview

PDF Download (38MB) | Preview

Abstract

The Madden–Julian Oscillation (MJO) is the main mode of intraseasonal weather variability in the tropics. The air–sea interactions during the MJO can modulate the intraseasonal sea surface temperature (SST) anomalies, and influence the MJO through surface flux exchange. Such feedbacks are absent in atmosphere-only Numerical Weather Prediction (NWP) models, potentially leading to a degraded model performance in predicting the MJO. Coupled ocean–atmosphere models can help to understand how these feedbacks affect the MJO, and the MJO prediction skill.

Here, global coupled and atmosphere-only NWP systems of the UK Met Office are assessed to reveal skilful predictions of the MJO in both models at least out to 15 lead days. The coupled model predicts erroneously fast MJO propagation compared with the atmosphere-only model. Numerical experiments reveal that half of the MJO phase speed increase between the models is due to diurnal warm layers (DWLs), unaccounted for in the atmosphere-only model. Enhanced (suppressed) MJO convection weakens (strengthens) DWLs in the coupled model. DWLs rectify intraseasonal SST anomalies such that stronger diurnal warming leads to stronger intraseasonal SST anomalies. The peak response in the MJO convection to these SST anomalies in this coupled model occurs within the next seven days. Such feedback is realistic and consistent with observations, however, the added complexity slightly degrades the model performance in predicting the MJO.

A further analysis of the coupled model shows that ocean advection and net surface heat fluxes are equally important in modulating the intraseasonal mixed layer temperature (MLT) anomalies during the MJO. The net surface heat flux drives the large-scale MLT anomalies in this coupled model, while ocean advection dominates at horizontal scales smaller than 10°. Overall, this work demonstrates the importance of ocean–atmosphere feedbacks during the MJO.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Kitty Laine
Date Deposited:	11 Jun 2025 10:58
Last Modified:	11 Jun 2025 10:58
URI:	https://ueaeprints.uea.ac.uk/id/eprint/99453
DOI:

Downloads

Actions (login required)

View Item