Exploring ENSO-Related Global Ocean Heat Content Variations in ECCOv4

 

 

This month we spotlight work from researchers from China and Australia who have been using the ECCOv4 dataset, an MITgcm product, to investigate ENSO-Related Global Ocean Heat Content Variations.

The ocean’s large heat capacity gives it a leading role in Earth’s energy budget. Over 90% of the energy imbalance at the top of the atmosphere is stored in the ocean, making the full-depth globally integrated ocean heat content (GOHC) a fundamental metric of climate change. Recent observational and modeling efforts have suggested that internal climate variability has the potential to modulate the GOHC on interannual-to-decadal time scales, complicating the detection and attribution of the anthropogenic climate signal.

A recent, well-documented example is the rapid reduction of the full-depth GOHC after the 1997/98 El Niño event. The El Niño–Southern Oscillation (ENSO) is the most energetic source of climate variability on interannual timescales. Originating in the tropical Pacific via air-sea coupling, ENSO’s impacts are felt globally via atmospheric teleconnections. Although efforts had been made to establish a statistical relationship between the ENSO index and the GOHC, the mechanisms at work are still uncertain.

In a new study published this month in the Journal of climate, researchers from the State Key Laboratory of Marine Environmental Science at Xiamen University in China Jianyu Hu and Quran Wu (now working at University of Reading, UK); and Xuebin Zhang (Centre for Southern Hemisphere Oceans Research, CSIRO) and John A. Church (Climate Change Research Centre, University of New South Wales) from Australia report on their use of ECCOv4 to study the large-scale integrated heat content variations during ENSO events for the global ocean.

As a dynamically consistent global estimate of recent ocean state, the ECCOv4 data set, a solution of the MIT general circulation model (MITgcm) covering the period from 1992 to 2011 has two characteristics that make it particularly well suited to this study. First, ECCOv4 is a global scale analysis optimized to fit global hydrographic data. In particular, the ENSO-related ocean heat content anomalies from ECCOv4 have been shown to be in good agreement with Argo observations. Second, unlike other types of data assimilation products, no artificial source/sink is induced in adjoint-based ECCOv4’s solution, thus the ocean heat content changes can be fully attributed to well-defined physical processes.

The team finds that the full depth GOHC exhibits a cooling tendency during the peak and decaying phases of El Niño events, mainly caused by the negative surface heat flux (SHF) anomaly in the tropics (30°S–30°N), but is partially offset by the positive SHF anomaly at higher latitudes. The tropical SHF anomaly acts as a lagged response damping the convergence of oceanic heat transport, which redistributes heat from the extratropics and the subsurface layers (100–440 m) into the upper tropical oceans (0–100 m) during the onset and peak of El Niño events. While confirming the global nature of the heat redistribution during ENSO events, Wu et al’s results reveal how the regional processes are integrated to cause significant interannual variations of GOHC.

Mechanisms of heat redistribution processes are explored as well. They report that the meridional heat exchange across 30°S and 30°N are mainly driven by ocean current anomalies, while multiple heat advection terms contribute to the vertical heat exchange across 100 m simultaneously. Heat advection due to unbalanced mass transport is distinguished from the mass balanced one, and significant contributions from the meridional and zonal overturning cells to the vertical heat advection are found in the latter component.

They also used ECCOv4 product to study variability and change of sea level and its components in the Indo-Pacific, which was published earlier by Journal of Geophysical Research (doi:10.1002/2016JC012345).

To find out more about this work contact Xuebin and Quran

This Month’s Featured Publication

Other New Publications this Month

Arbic et al (2018), Primer on Global Internal Tide and Internal Gravity Wave Continuum Modeling in HYCOM and MITgcm, diginole.lib.fsu, doi: 10.17125/gov2018.ch13

Andrew S. Delman, Tong Lee, Bo Qiu (2018), Interannual to Multidecadal Forcing of Mesoscale Eddy Kinetic Energy in the Subtropical Southern Indian Ocean, Journal of Geophysical Research – Oceans, doi: 10.1029/2018JC013945

Ian Grooms and William Kleiber (2019), Diagnosing, modeling, and testing a multiplicative stochastic Gent-McWilliams parameterization, Ocean Modelling, doi: 10.1016/j.ocemod.2018.10.009

Xia Lin and Zhaomin Wang (2018), Simulated impact of Southern Hemisphere westerlies on Antarctic Continental Shelf Bottom Water temperature, Advances in Polar Science, Vol. 29, Issue 3, pp. 215-221, doi: 10.13679/j.advps.2018.3.00215

Mu Liu, Daizhao Chen, Xiqiang Zhou, Wei Yuan, Maosheng Jiang, Lijing Liu (2019), Climatic and oceanic changes during the Middle-Late Ordovician transition in the Tarim Basin, NW China and implications for the Great Ordovician Biodiversification Event, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 514, Pages 522-535, doi: 10.1016/j.palaeo.2018.10.032

Losa, S.N., Oelker, J., Soppa, M.A., Losch, M., Dutkiewicz, S., Dinter, T., Richter, A. ,Rozanov, V. V., Burrows, J. P. and Bracher, A. (2018), Investigating the phytoplankton diversity in the Great Calcite Belt: perspective from modelling and satellite retrievals, Ocean Optics Conference XXIV, Dubrovnik (Croatia), 7 October 2018 – 12 October 2018, http://epic.awi.de/48397

Keisuke Nakayama, Taro Kakinuma, Hidekazu Tsuji (2019), Oblique reflection of large internal solitary waves in a two-layer fluid, European Journal of Mechanics – B/Fluids, Volume 74, Pages 81-91, doi: 10.1016/j.euromechflu.2018.10.014

Vasileios Pefanis et al (2018), Assessing bio-physical feedbacks in the shelf areas of Laptev Sea, poster http://epic.awi.de/48479/1/AC3_template_poster_clusC_Pefanis.pdf

K.J. Quinn, R.M. Ponte, P. Heimbach, I. Fukumori, J-M Campin (2018), Ocean angular momentum from a recent global state estimate, with assessment of uncertainties, Geophysical Journal International, doi: 10.1093/gji/ggy452

D. A. Slater, F. Straneo, S. B. Das, C. G. Richards, T. J. W. Wagner, P. W. Nienow (2018), Localized Plumes Drive Front‐Wide Ocean Melting of A Greenlandic Tidewater Glacier, Geophysical Research Letters, doi: 10.1029/2018GL080763

Peiran Yang, Zhao Jing, Lixin Wu (2018), An Assessment of Representation of Oceanic Mesoscale Eddy‐Atmosphere Interaction in the Current Generation of General Circulation Models and Reanalyses, Geophysical Research Letters, doi: 10.1029/2018GL080678

Peng Zhan, Ganesh Gopalakrishnan, Aneesh C. Subramanian, Daquan Gu, Ibrahim Hoteit (2018), Sensitivity Studies of the Red Sea Eddies Using Adjoint Method, Journal of Geophysical Research – Oceans, doi: 10.1029/2018JC014531

Do you have news about research using MITgcm? We are looking for contributions to these pages. If you have an interesting MITgcm project (ocean, atmosphere, sea-ice, physics, biology or otherwise) that you want to tell people about, get in touch. To make a post, contact Helen