Abstract
Retrieving information concerning the interior of the ocean using satellite remote sensing data has a major impact on studies of ocean dynamic and climate changes; however, the lack of information within the ocean limits such studies about the global ocean. In this paper, an artificial neural network, combined with satellite data and gridded Argo product, is used to estimate the ocean heat content (OHC) anomalies over four different depths down to 2000 m covering the near-global ocean, excluding the polar regions. Our method allows for the temporal hindcast of the OHC to other periods beyond the 2005–2018 training period. By applying an ensemble technique, the hindcasting uncertainty could also be estimated by using different 9-year periods for training and then calculating the standard deviation across six ensemble members. This new OHC product is called the Ocean Projection and Extension neural Network (OPEN) product. The accuracy of the product is accessed using the coefficient of determination (R2) and the relative root-mean-square error (RRMSE). The feature combinations and network architecture are optimized via a series of experiments. Overall, intercomparison with several routinely analyzed OHC products shows that the OPEN OHC has an R2 larger than 0.95 and an RRMSE of <0.20 and presents notably accurate trends and variabilities. The OPEN product can therefore provide a valuable complement for studies of global climate changes.
Highlights
In recent decades, with the continuous emission of greenhouse gases the imbalance in the top-of-atmosphere radiation has intensified, leading to continued global warming
The EEI is caused by the difference between the energy absorbed and that reflected by the Earth, i.e., the net thermal energy trapped inside the Earth system [3]
It is necessary to study the sensitivity of the results to the artificial neural networks (ANN) architecture, to the number of hidden layers, the number of neurons in each layer, and the activation function σ
Summary
With the continuous emission of greenhouse gases the imbalance in the top-of-atmosphere radiation has intensified, leading to continued global warming. This imbalance, termed the Earth’s energy imbalance (EEI, [1]), is a vital issue because it intensifies and promotes changes in the global climate system. More than 93% of the EEI passes through the atmosphere into the ocean and is stored in the form of ocean heat content (OHC) changes [4,5]. OHC is the most suitable variable for detecting and tracking EEI changes [3]
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