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Assessing the role of the ocean–atmosphere coupling frequency in the western Maritime Continent rainfall

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Abstract

High-frequency interactions between the ocean and atmosphere have the potential to affect lower frequency or mean state climate in various regions. Here we examine the importance of sub-daily air-sea interactions over the Maritime Continent region to the rectification of longer timescale variation. In order to determine the importance of these high-frequency interactions, we conducted two regional ocean–atmosphere coupled simulations over the Maritime Continent where exchanges between the oceanic and atmospheric components are performed either every hour (i.e. resolving diurnal changes) or every day. We find that coupling frequency has a significant influence on mean sea surface temperature (SST) and the mean state and diurnal cycle of rainfall over certain regions of the western Maritime Continent where air-sea interactions are strong during the Asian monsoon season, with little effect in other regions or seasons. Without sub-daily air-sea interactions, the mean SST along the southwest off Sumatra is ~ 2 °C warmer during the period from June to October as a result of a deepening of thermocline along the coast. This deepening is linked to anomalous downwelling equatorial eastward propagating Kelvin waves triggered by westerly anomalies in the eastern equatorial Indian Ocean. In addition, the mean rainfall in the vicinity of ocean warming increases, thereby producing an enhanced barrier layer that also provides a positive warming feedback. Although the coupling frequency has little impact on the timing of the rainfall diurnal cycle, suppression of sub-daily coupling significantly changes the diurnal rainfall amplitude causing a relative decrease (increase) in amplitude over the coast of Northwestern (Southwestern) Sumatra during the South Asian monsoon season.

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Acknowledgements

This work was supported by ARC Centre of Excellence for Climate System Science (ARCCSS) in Australia. The collaboration with NCAR was supported by the Graduate Student Visitor Scholarship under Advanced Study Program (ASP). The WRF model was provided by the University Corporation for Atmospheric Research (https://www2.mmm.ucar.edu/wrf/users/download/get_source.htm). All the simulations were performed on the Australian National Computational Infrastructure (NCI). NJ is supported by the TROIS-AS ANR project (ANR-15-CE01-0005-01).

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Correspondence to Jing-Jia Luo.

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382_2020_5266_MOESM1_ESM.eps

Supplementary file1 (EPS 14138 kb) Suppl. Fig. 1 The seasonal mean biases of SST (10-m wind) for (a) NOW1h and (b) NOW24h against AVHRR-OISSTv2 (QuickSCAT) in JJASO. The seasonal mean biases of precipitation for (c) NOW1h and (d) NOW24h against TRMM-3B43. All biases are obtained by subtracting the observational mean from the simulation for the period of 2006-2009

382_2020_5266_MOESM2_ESM.eps

Supplementary file2 (EPS 7903 kb) Suppl. Fig. 2 (a) The annual mean difference of velocity potential at 950hPa between NOW24h and NOW1h. (b) As (a), but for the mean averaged over the months from June to October. (c) As (a), but the mean for the remainder of months

382_2020_5266_MOESM3_ESM.eps

Supplementary file3 (EPS 5090 kb) Suppl. Fig. 3 Differences in mean precipitation between WRF24h and NOW1h simulations (i.e., WRF24h-NOW1h) for the period of 2006-2009

382_2020_5266_MOESM4_ESM.eps

Supplementary file4 (EPS 13272 kb) Suppl. Fig. 4 Monthly mean SST averaged from June to November for (a) NOW1h and (b) NOW24h

382_2020_5266_MOESM5_ESM.eps

Supplementary file5 (EPS 2001 kb) Suppl. Fig. 5 Mean seasonal cycles of vertical velocity from surface to 500 m averaged over the region where difference of mean SST between NOW24h minus NOW1h exceeds 1 °C during JJASO (see Fig. 3a-I) for (a) NOW1h and (b) NOW24h-NOW1h. (c) shows the timeseries of averaged vertical velocity from surface to 100 m during the period of 2006-2009. The positive and negative indicate upward and downward movement, respectively

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Li, Y., Gupta, A.S., Taschetto, A.S. et al. Assessing the role of the ocean–atmosphere coupling frequency in the western Maritime Continent rainfall. Clim Dyn 54, 4935–4952 (2020). https://doi.org/10.1007/s00382-020-05266-7

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  • DOI: https://doi.org/10.1007/s00382-020-05266-7

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