2023/01/13 14:00 Dr. Yu-Chun Lin(Center of Excellence for Ocean Engineering, NTOU)

Poster:Post date:2023-01-11
NCU IHOS Seminar Announcement

Title:The amplifying Great Lakes ice cover in responses to changing teleconnections and modeling the landfast ice of Lake Superior


Speaker:Dr. Yu-Chun Lin

Center of Excellence for Ocean Engineering, NTOU


Place:S-325, Science Building 1

  The interannual variability of the annual maximum ice cover (AMIC) of the Great Lakes, the largest fresh lakes of the world, is strongly influenced by large-scale atmospheric circulations that drive regional weather patterns. Statistical analyses show a reduced number of accumulated freezing degree days across the winter months in recent decades, a step-change decrease of AMIC after the winter of 1997/98, and an increased interannual variability of AMIC since 1993. Furthermore, the climate indices that are significantly correlated with AMIC is changing from El Niño–Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), and the Pacific–North American pattern (PNA) before the winter of 1997/98 to the tropical–Northern Hemisphere pattern (TNH) and Eastern Pacific Oscillation (EPO) after 1997/98. Singular value decomposition of the 500-hPa geopotential height and surface air temperature shows a dipole pattern over the northeast Pacific and North America, demonstrating the ridge–trough system. This dipole pattern shifts northward to the northern Rocky Mountains, placing the Great Lakes region in the trough after 1997/98. This shift coincides with the increased interannual variability of the EPO index, as well as the change in the sea surface temperature (SST) over the northeast Pacific, where the second mode of the empirical orthogonal function on SST shows a warm blob-like feature manifested over the Gulf of Alaska. The regression of wave activity flux onto the SST EOF shows that the source of upward and eastward propagation of a stationary Rossby wave shifts to the west coast of North America, likely moving the ridge–trough system eastward after the winter of 1997/98.
  Landfast ice plays an important role in the nearshore hydrodynamics of large lakes, such as the dampening of surface waves and currents. In this study, previously developed landfast ice basal stress parameterizations were added to an unstructured grid hydrodynamic ice model to represent the effects of grounded ice keels and tensile strength of ice cover. Numerical experiments using this model were conducted to evaluate the development of coastal landfast ice in Lake Superior. A sensitivity study of the free parameters was conducted from December 2018 to May 2021 to cover both high and low ice cover winters in Lake Superior and was compared against observations from the United States National Ice Center. Experiments show that the growth of landfast ice is mainly controlled by the free parameter that controls the critical ice thickness for the activation of basal stress.
Last modification time:2023-01-11 PM 5:14

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