Son Seok-Woo

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Son
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Seok-Woo
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  • Article
    Revisiting the relationship among metrics of tropical expansion
    (American Meteorological Society, 2018-08-08) Waugh, Darryn W. ; Grise, Kevin M. ; Seviour, William J. M. ; Davis, Sean M. ; Davis, Nicholas ; Adam, Ori ; Son, Seok-Woo ; Simpson, Isla R. ; Staten, Paul W. ; Maycock, Amanda C. ; Ummenhofer, Caroline C. ; Birner, Thomas ; Ming, Alison
    There is mounting evidence that the width of the tropics has increased over the last few decades, but there are large differences in reported expansion rates. This is, likely, in part due to the wide variety of metrics that have been used to define the tropical width. Here we perform a systematic investigation into the relationship among nine metrics of the zonal-mean tropical width using preindustrial control and abrupt quadrupling of CO2 simulations from a suite of coupled climate models. It is shown that the latitudes of the edge of the Hadley cell, the midlatitude eddy-driven jet, the edge of the subtropical dry zones, and the Southern Hemisphere subtropical high covary interannually and exhibit similar long-term responses to a quadrupling of CO2. However, metrics based on the outgoing longwave radiation, the position of the subtropical jet, the break in the tropopause, and the Northern Hemisphere subtropical high have very weak covariations with the above metrics and/or respond differently to increases in CO2 and thus are not good indicators of the expansion of the Hadley cell or subtropical dry zone. The differing variability and responses to increases in CO2 among metrics highlights that care is needed when choosing metrics for studies of the width of the tropics and that it is important to make sure the metric used is appropriate for the specific phenomena and impacts being examined.
  • Article
    Tropical widening from global variations to regional impacts
    (American Meteorological Society, 2020-06-01) Staten, Paul W. ; Grise, Kevin M. ; Davis, Sean M. ; Karnauskas, Kristopher B. ; Waugh, Darryn W. ; Maycock, Amanda C. ; Fu, Qiang ; Cook, Kerry ; Adam, Ori ; Simpson, Isla R. ; Allen, Robert J. ; Rosenlof, Karen H. ; Chen, Gang ; Ummenhofer, Caroline C. ; Quan, Xiao-Wei ; Kossin, James P. ; Davis, Nicholas A. ; Son, Seok-Woo
    Over the past 15 years, numerous studies have suggested that the sinking branches of Earth’s Hadley circulation and the associated subtropical dry zones have shifted poleward over the late twentieth century and early twenty-first century. Early estimates of this tropical widening from satellite observations and reanalyses varied from 0.25° to 3° latitude per decade, while estimates from global climate models show widening at the lower end of the observed range. In 2016, two working groups, the U.S. Climate Variability and Predictability (CLIVAR) working group on the Changing Width of the Tropical Belt and the International Space Science Institute (ISSI) Tropical Width Diagnostics Intercomparison Project, were formed to synthesize current understanding of the magnitude, causes, and impacts of the recent tropical widening evident in observations. These working groups concluded that the large rates of observed tropical widening noted by earlier studies resulted from their use of metrics that poorly capture changes in the Hadley circulation, or from the use of reanalyses that contained spurious trends. Accounting for these issues reduces the range of observed expansion rates to 0.25°–0.5° latitude decade‒1—within the range from model simulations. Models indicate that most of the recent Northern Hemisphere tropical widening is consistent with natural variability, whereas increasing greenhouse gases and decreasing stratospheric ozone likely played an important role in Southern Hemisphere widening. Whatever the cause or rate of expansion, understanding the regional impacts of tropical widening requires additional work, as different forcings can produce different regional patterns of widening.
  • Article
    Basin-dependent response of Northern Hemisphere winter blocking frequency to CO2 removal
    (Nature Research, 2024-05-23) Hwang, Jaeyoung ; Son, Seok-Woo ; Martineau, Patrick ; Sung, Mi-Kyung ; Barriopedro, David ; An, Soon-Il ; Yeh, Sang-Wook ; Min, Seung-Ki ; Kug, Jong-Seong ; Shin, Jongsoo
    Atmospheric blocking has been identified as one of the key elements of the extratropical atmospheric variabilities, controlling extreme weather events in mid-latitudes. Future projections indicate that Northern Hemisphere winter blocking frequency may decrease as CO2 concentrations increase. Here, we show that such changes may not be reversed when CO2 concentrations return to the current levels. Blocking frequency instead exhibits basin-dependent changes in response to CO2 removal. While the North Atlantic blocking frequency recovers gradually from the CO2-induced eastward shift, the North Pacific blocking frequency under the CO2 removal remains lower than its initial state. These basin-dependent blocking frequency changes result from background flow changes and their interactions with high-frequency eddies. Both high-frequency eddy and background flow changes determine North Atlantic blocking changes, whereas high-frequency eddy changes dominate the slow recovery of North Pacific blocking. Our results indicate that blocking-related extreme events in the Northern Hemisphere winter may not monotonically respond to CO2 removal.