Abstract
AbstractSea surface temperatures (SSTs) north of Australia in the Indonesian–Australian Basin are significantly influenced by Madden–Julian oscillation (MJO), an eastward-moving atmospheric disturbance that traverses the globe in the tropics. The region also has large-amplitude diurnal SST variations, which may influence the air–sea heat and moisture fluxes, that provide feedback to the MJO evolution. During the 2018/19 austral summer, a field campaign aiming to better understand the influences of air–sea coupling on the MJO was conducted north of Australia in the Indonesian–Australian Basin. Surface meteorology from buoy observations and upper-ocean data from autonomous fast-profiling float observations were collected. Two MJO convective phases propagated eastward across the region in mid-December 2018 and late January 2019 and the second MJO was in conjunction with a tropical cyclone development. Observations showed that SST in the region was rather sensitive to the MJO forcing. Air–sea heat fluxes warmed the SST throughout the 2018/19 austral summer, punctuated by the MJO activities, with a 2°–3°C drop in SST during the two MJO events. Substantial diurnal SST variations during the suppressed phases of the MJOs were observed, and the near-surface thermal stratifications provided positive feedback for the peak diurnal SST amplitude, which may be a mechanism to influence the MJO evolution. Compared to traditionally vessel-based observation programs, we have relied on fast-profiling floats as the main vehicle in measuring the upper-ocean variability from diurnal to the MJO time scales, which may pave the way for using cost-effective technology in similar process studies.
Highlights
Sea surface temperatures (SSTs) north of Australia in the Indonesian–Australian Basin are significantly influenced by Madden–Julian oscillation (MJO), an eastward-moving atmospheric disturbance that traverses the globe in the tropics
The strongest large-scale intraseasonal sea surface temperature (SST) variations in austral summer in the tropics are found north of Australia in the Indonesian–Australian Basin, forced by air–sea heat flux and wind-driven current anomalies associated with the MJO (Vialard et al 2013; Marshall and Hendon 2014)
The air–sea coupling at these two time scales can have significant influences on the MJO and its forecasts (DeMott et al 2015), which has motivated a number of observation programs in the Indian Ocean: the Mirai Indian Ocean Cruise for the Study of the MJO (MISMO; Yoneyama et al 2008), the air–sea interactions at several time scales in the Indian Ocean (Cirene; Vialard et al 2009), Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the Madden–Julian Oscillation (CINDY-DYNAMO; Yoneyama et al 2013; Moum et al 2014), and Ocean Mixing and Monsoon/Air–Sea Interactions in the Northern Indian Ocean Regional Initiative (OMM-ASIRI; Wijesekera et al 2016), mostly focused on the equatorial central Indian Ocean
Summary
Sea surface temperatures (SSTs) north of Australia in the Indonesian–Australian Basin are significantly influenced by Madden–Julian oscillation (MJO), an eastward-moving atmospheric disturbance that traverses the globe in the tropics. The air–sea coupling at these two time scales can have significant influences on the MJO and its forecasts (DeMott et al 2015), which has motivated a number of observation programs in the Indian Ocean: the Mirai Indian Ocean Cruise for the Study of the MJO (MISMO; Yoneyama et al 2008), the air–sea interactions at several time scales in the Indian Ocean (Cirene; Vialard et al 2009), Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the Madden–Julian Oscillation (CINDY-DYNAMO; Yoneyama et al 2013; Moum et al 2014), and Ocean Mixing and Monsoon/Air–Sea Interactions in the Northern Indian Ocean Regional Initiative (OMM-ASIRI; Wijesekera et al 2016), mostly focused on the equatorial central Indian Ocean Both observation and model studies show that the increase of daily mean SST can enhance the latent and sensible heat fluxes into the atmosphere, providing important feedbacks to the evolution of the MJO (Seo et al 2014; Moum et al 2014). Regional oceanography and changes of diurnal thermocline can affect the magnitude of diurnal SST variations nonlinearly, exploring the diurnal variation of vertical mixing in the upper ocean is critical to improve the MJO forecasting
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