Subtropical Eastern North Pacific SST Bias in Earth System Models

Abstract

The subtropical eastern boundary regions in the global oceans play a key role in the climate of the earth system. These are regions with shallow marine stratocumulus cloud decks that modulate the planet's greenhouse gas forcing, and consequently, the radiative balance (Richter, 2015). Stratus clouds are maintained partly by cold sea surface temperatures (SSTs) associated with the equatorward flowing eastern boundary currents that form the eastern branch of subtropical gyres (Kessler, 2006). Alongshore winds drive these currents and Ekman divergence along the coast (Bakun & Nelson, 1991), causing the upwelling of cold nutrient-rich waters making these regions some of the most biologically productive globally (Chavez & Messié, 2009). This makes modeling of these processes really important not only for improving our understanding of them but also to accurately project their response under climate change (Ashfaq et al., 2011;García-Reyes et al., 2015;Richter, 2015).However, most coupled climate models incorrectly simulate various processes occurring in these regions and suffer from warm SST biases (Richter, 2015). Misrepresentation of stratocumulus clouds has been identified as one of the primary reasons for this bias. Model inability to produce stratocumulus decks can lead to absorption of excessive shortwave radiation in the upper-ocean and warm SSTs, which in turn induces a positive feedback to the initial error (Richter, 2015;Zuidema et al., 2016). Further, model resolution and

The Improvements of the Upper Zonal Currents by SST Assimilation Over the Tropical Pacific in a Coupled Climate Model

“…The present study highlights the importance of improved tropical SST in reproducing tropical upper zonal ocean currents in coupled models. The reduction in SST bias can be achieved to some extent by increasing the spatial resolution (Balaguru et al, 2021) and oceanic parameterization scheme (Noh et al, 2016).…”