Madden-Julian oscillation winds excite an intraseasonal see-saw of ocean mass that affects Earth’s polar motion

Abstract

Strong large-scale winds can relay their energy to the ocean bottom and elicit an almost immediate intraseasonal barotropic (depth independent) response in the ocean. The intense winds associated with the Madden-Julian Oscillation over the Maritime Continent generate significant intraseasonal basin-wide barotropic sea level variability in the tropical Indian Ocean. Here we show, using a numerical model and a network of in-situ bottom pressure recorders, that the concerted barotropic response of the Indian and the Pacific Ocean to these winds leads to an intraseasonal see-saw of oceanic mass in the Indo-Pacific basin. This global-scale mass shift is unexpectedly fast, as we show that the mass field of the entire Indo-Pacific basin is dynamically adjusted to Madden-Julian Oscillation in a few days. We find this large-scale ocean see-saw, induced by the Madden-Julian Oscillation, has a detectable influence on the Earth’s polar axis motion, in particular during the strong see-saw of early 2013.

The Global Patterns of Interannual and Intraseasonal Mass Variations in the Oceans from GRACE and GRACE Follow-On Records

“…The South Indian Ocean pattern (~#2) involves both barotropic and baroclinic processes at the annual scale [74]. Other recent studies present further evidence of barotropic processes at intraseasonal timescales over the Indian Ocean [25,26,75]. In a region that is close to our Pattern #14, a sea-level trend that is associated with the Atlantic subtropical gyre has been shown in [76,77].…”

“…Yet relationships with the SLA and WSC are not systematically significant (Table 1, |𝜌 #, 𝑆𝐿𝐴 |,|𝜌 #, 𝑊𝑆𝐶 |), whereas such a relationship is expected from the literature [30]. This implies significant remote forcing of SLA by WSC, as already evidenced in some regions of the world ocean [25,26], and/or a prominent fraction of SLA variability that is baroclinic in nature. In Figure 4, correlations between WSC and the load patterns from Table 1 are plotted against latitude.…”

“…The effect of the atmosphere tends to cancel out at timescales longer than a few days [22]. Oceanic barotropic signals are supposed to be prominently related to high frequencies [21,23,24] but were also reported at intraseasonal [25,26] and interannual scales [20]. Besides land-ocean transfers, the ocean circulation, mass, and sealevel variations result from water density gradients or wind-driven Ekman transport [27].…”

“…At lower latitudes, OBP variations potentially have a baroclinic contribution, typically at the subcentimetric level [31]. However, instances of regional-scale barotropic sea-level variability were reported [24][25][26]31]. Climate dynamics also impact sea level and mass variation no matter the triggered mechanism [32,33].…”

On two formulations of polar motion and identification of its sources

“…. ) are seen as potential causes of this trend (e.g Rochester (1984); Gross et al (2004); Landerer et al (2007); Chen et al (2019); Afroosa et al (2021)). Also, the recent acceleration of rotation velocity, that contradicts previous models, may find a simple explanation with Laplace's formalism (e.g.…”