Tropical synoptic-scale wave disturbances over the western Pacific simulated by a global cloud-system resolving model
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Lower-tropospheric tropical synoptic-scale disturbances (TSDs) are associated with severe weather systems in the Asian Monsoon region. Therefore, exact prediction of the development and behavior of TSDs using atmospheric general circulation models is expected to improve weather forecasting for this region. Recent state-of-the art global cloud-system resolving modeling approaches using a Nonhydrostatic Icosahedral Atmospheric Model (NICAM) may improve representation of TSDs. This study evaluates TSDs over the western Pacific in output from an Atmospheric Model Intercomparison Project (AMIP)-like control experiment using NICAM. Data analysis compared the simulated and observed fields. NICAM successfully simulates the average activity, three-dimensional structures, and characteristics of the TSDs during the Northern summer. The variance statistics and spectral analysis showed that the average activity of the simulated TSDs over the western Pacific during Northern summer broadly captures that of observations. The composite analysis revealed that the structures of the simulated TSDs resemble the observed TSDs to a large degree. The simulated TSDs exhibited a typical southeast- to northwest-oriented wave-train pattern that propagates northwestward from near the equator around 150 ∘ E toward the southern coast of China. However, the location of the simulated wave train and wave activity center was displaced northward by approximately a few degrees of latitude from that in the observation. This displacement can be attributed to the structure and strength of the background basic flow in the simulated fields. Better representation of the background basic states is required for more successful simulation of TSDs.
KeywordsTropical synoptic-scale wave disturbances Western Pacific Global cloud-system resolving model
The authors thank anonymous reviewers for their comments on an earlier version of the paper. We also thank Kazuyoshi Oouchi and Tomoe Nasuno for their constructive comments and discussions. The JRA-55 data set was obtained from the Japan Meteorological Agency (JMA). The OLR dataset was provided from the Earth System Research Laboratory (ESRL) of NOAA. The experiment is performed on the K computer at the Advanced Institute for Computational Science, RIKEN (Proposal number hp120279, hp130010, and hp140219). This research is supported by Strategic Programs for Innovative Research (SPIRE) Field 3 (Projection of Planet Earth Variations for Mitigating Natural Disasters), which is promoted by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
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