Basin-wide sea level coherency in the tropical Indian Ocean driven by Madden–Julian Oscillation

Changes in sea level may be attributed either to barotropic (involving the entire water column) or baroclinic processes (governed by stratification). It has been widely accepted that barotropic sea level changes in the tropics are insignificant at intraseasonal time scales (periods of 30–80 days). Based on bottom pressure records, we present evidence for significant basin-wide barotropic sea level variability in the tropical Indian Ocean during December–April with standard deviations amounting to ∼30–60% of the standard deviation in total intraseasonal sea level variability. The origin of this variability is linked to a small patch of wind over the Eastern Indian Ocean, associated with boreal winter Madden–Julian Oscillations (MJO). These large fluctuations are likely to play a prominent role in the intraseasonal sea level and mass budgets. Because of their much faster propagation than baroclinic processes, they allow the basin to adjust to climatic perturbations much more rapidly than was previously thought

The MJO-driven Indo-Pacific barotropic see-saw

International audienc

The Anomalous 2012–13 Boreal Winter Oceanic Excitation of Earth’s Polar Motion

International audienc

Basin-wide sea level coherency in the tropical Indian Ocean driven by Madden-Julian Oscillation

Changes in sea level may be attributed either to barotropic (involving the entire water column) or baroclinic processes (governed by stratification). It has been widely accepted that barotropic sea level changes in the tropics are insignificant at intraseasonal time scales (periods of 30-80 days). Based on bottom pressure records, we present evidence for significant basin-wide barotropic sea level variability in the tropical Indian Ocean during December-April with standard deviations amounting to similar to 30-60% of the standard deviation in total intraseasonal sea level variability. The origin of this variability is linked to a small patch of wind over the Eastern Indian Ocean, associated with boreal winter Madden-Julian Oscillations (MJO). These large fluctuations are likely to play a prominent role in the intraseasonal sea level and mass budgets. Because of their much faster propagation than baroclinic processes, they allow the basin to adjust to climatic perturbations much more rapidly than was previously thought

Investigating the robustness of the intraseasonal see-saw in the Indo-Pacific barotropic sea level across models

International audienceAn intraseasonal see-saw has been observed in the Indo-Pacific barotropic sea level anomaly during boreal winters. This see-saw carries a significant amount of energy and is crucial for the tropical sea level and angular momentum budget. Here, we evaluate the performance of several state-of-the-art ocean general circulation models (OGCMs), including the Modular Ocean Model (MOM), the Nucleus for European Modeling of the Ocean (NEMO), Massachusetts Institute of Technology general circulation model (MITgcm), and the HYbrid Coordinate Ocean Model (HYCOM) in reproducing the see-saw. Regardless of differences in model physics, forcings, setup, and resolution, all OGCMs simulate see-saw in the Indo-Pacific oceanic mass, making it a robust oceanic phenomenon. The models with horizontal resolutions ranging from 25 to 9 km, particularly those with higher resolution, are successful at simulating the qualitative characteristics of the see-saw. We show that a proper representation of the Indonesian straits is vital for a reasonable simulation of the see-saw. Furthermore, we show that the inclusion of the polar ocean in the models has little impact on the see-saw structure, implying that OGCMs with semi-global domain are appropriate tools for capturing the see-saw dynamics

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

International audienceAbstract 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