Thesis or Dissertation Dynamical downscaling of future sea-level change in the western North Pacific using ROMS

劉, 昭君

The future regional sea-level (RSL) rise in the western North Pacific is investigatedby dynamical downscaling with the Regional Ocean Modeling System (ROMS) with aneddy-permitting 0.25° resolution based on three Coupled Model Intercomparison ProjectPhase 5 (CMIP5) climate models— MIROC-ESM, CSIRO-Mk3.6.0, and GFDL-CM3—under the highest greenhouse-gas emission Representative Concentration Pathway (RCP)8.5 scenario. The dynamical downscaling is performed for two epochs, historical run(1950–2000) and future run (2051–2100). The historical run, ROMS-Hist, is forced withthe air-sea fluxes calculated from Coordinated Ocean Reference Experiment version 2(COREv2). Three future runs— ROMS-MIROC, ROMS-CSIRO, and ROMS-GFDL—are forced with an atmospheric field constructed by adding the difference between theclimate model parameters for the 21st and 20th century to the forcing fields in ROMS-Hist.The downscaled future RSLs commonly exhibit strong, bullseye-like RSL risemaxima centered on 41°N, 142°E to the east of the Tsugaru Strait, and three zonallyaligned maxima along 37°N between 140°E and 160°E. In all ROMS downscaling, theRSL rise along the eastern coast of Japan is generally one-third or less of the RSL risemaxima off the eastern coast of Japan. The projected regional (total) sea level rises alongHonshu coast during 2081–2100 relative to 1981–2000 are 22–29 (101–108), 8–15 (73–80), and 8–18 (80–90) cm in ROMS-MIROC, ROMS-CSIRO, and ROMS-GFDL,respectively. The largest downscaled RSL rise along the Japan coast occurs at the Sanrikucoast in all models. Although the CMIP5 models substantially underestimate the maximaof the offshore RSL rise compared with the ROMS downscaling, the discrepancies of theRSL rise along the Honshu coast between the climate models and ROMS downscalingare less than 10 cm. The maxima of the RSL rise to the east of the Tsugaru Strait andthose along 37°N are probably related to the enhanced northward intrusion of theKuroshio Current along the eastern coast of Japan and to the northward shift of theKuroshio Extension, respectively. The projected RSL change along Hokkaido coastduring 2081–2100 relative to 1981–2000 is smaller than that on Honshu coast. AtOkinawa Island, RSL changes are nearly 30 cm in ROMS-MIROC and ROMS-CSIRO,which is higher than those along Honshu. The difference of RSL rise at Okinawa Islandbetween ROMS-CSIRO and CSIRO-Mk3.6.0 exceeds 10 cm.ROMS-MIROC and ROMS-GFDL simulations suggest that the RSL changes arelikely induced by wind stress changes rather than heat or freshwater fluxes at the surface,whereas ROMS-CSIRO suggests that heat and freshwater fluxes play relatively largerroles than other two models. All ROMS simulations commonly show that thethermosteric components give the major features of regional dynamic height (RDH) andthus major regional sea-level changes, while halosteric components contribute to yieldoverall meridional gradients in regional sea-level changes.
Hokkaido University(北海道大学). 博士(理学)

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