Dr. Sang-Ki Lee

Oceanographer


NOAA/AOML/PHOD
4301 Rickenbacker Causeway
Miami, FL 33149, USA
Phone: (305) 361-4521
sang-ki.lee@noaa.gov

Research interests

    I am a physical oceanographer interested in a range of topics related to ocean, climate and extreme weather. My research aims to better understand atmosphere-ocean processes that affect and control the Earth's physical, chemical, and biological systems by using both observations and mathematical modeling tools. Currently, my research lies in the areas of inter-ocean transports of heat, salt and carbon; El Nino diversity and its remote impact on North American climate; Atlantic Nino diversity; atmosphere-ocean processes conducive to extreme weather; and Antarctic sea-ice and ocean interactions


Research highlights

    Spatiotemporal diversity of Atlantic Nino: A phenomenon known as Atlantic Nino is characterized by the appearance of warm sea surface temperature anomalies (SSTAs) in the eastern equatorial Atlantic in northern summer. When it attains its full strength, it increases rainfall and the frequency of extreme flooding over the West African countries bordering the Gulf of Guinea and in northeastern South America. However, not all Atlantic Nino events are alike. Some appear earlier than others or persists longer. These variabilities during the onset and dissipation phases are well captured by the four most recurring Atlantic Nino varieties identified in this study. Largely consistent with the differences in the timings of onset and dissipation, these four varieties display remarkable differences in rainfall response over West Africa and South America. Most of the varieties are subject to preconditioning in northern spring by cold SSTAs in the North Atlantic or El Nino in the Pacific, except for one variety with no clear source of external forcing. (Valles-Casanova et al. 2020) [ENSO Blog: Do you know that El Nino has a little brother?].

    Contrasting sea-ice trends around West Antarctica: Since late 1978, Antarctic sea-ice extent has overall expanded in all seasons in stark contrast to the retreating Arctic sea-ice extent. However, while the sea-ice extent around East Antarctica has increased monotonically, the sea-ice around West Antarctica exhibits regionally and seasonally inhomogeneous trends. For instance, Antarctic sea-ice extent in the East Pacific has decreased substantially in Austral summer. We used an ocean and sea-ice coupled model to show that the increased wind-driven upwelling of the relatively warm subsurface water, known as upper Circumpolar Deep Water, is mainly responsible for the declining sea-ice extent. This study also explains how the changes in Weddell Gyre circulations and associated meridional heat transport contributed to the increasing Antarctic sea ice in the Atlantic during Austral summer (Lee et al. 2017) [JGR editor's highlight].

    Abrupt increase in Indian Ocean heat content during the warming hiatus: Global mean surface warming has stalled since the end of the 20th century, but the net radiation imbalance at the top of the atmosphere continues to suggest an increasingly warming planet. This apparent contradiction has been reconciled by an anomalous heat flux into the Pacific Ocean, induced by a shift toward a La Nina-like state over the past decade or so. This study found that the enhanced heat uptake by the Pacific Ocean has been compensated by an increased heat transport from the Pacific Ocean to the Indian Ocean, carried by the Indonesian throughflow. As a result, Indian Ocean heat content has increased abruptly during the warming hiatus (Lee et al. 2015) [highlighted in EOS and Nature].

    What caused the significant increase in Atlantic ocean heat content since the mid-20th century?: As the upper layer of the world ocean warms gradually during the 20th century, the inter-ocean heat transport from the Indian to Atlantic basin should be enhanced, and the Atlantic Ocean should therefore gain extra heat due to the increased upper ocean temperature of the inflow via the Agulhas leakage. Consistent with this hypothesis, instrumental records indicate that the Atlantic Ocean has warmed substantially more than any other ocean basin since the mid-20th century. A surface-forced global ocean-sea ice coupled model is used to confirm this hypothesis (Lee et al. 2011) [highlighted in Nature as Community Choice].


Work in progress

    Kim, D. S.-K. Lee, H. Lopez, G. R. Foltz and C. Wen, 2021: On the role of Atlantic Nino/Nina in seasonal Atlantic tropical cyclone activity. To be submitted.

    Lopez, H., S.-K. Lee, D. Kim, A. T. Wittenberg, and S.-Y. Yeh, 2021: Projected increase in fast-growing and slow-dissipating El Nino events in the 21st Century. Submitted.


Publications