SOLA
Online ISSN : 1349-6476
ISSN-L : 1349-6476
Volume 19A, Issue Special_Edition
Research on Extreme Weather Events That Occurred around East Asia in 2017-2021
Displaying 1-4 of 4 articles from this issue
Editorial
  • Shingo Shimizu
    2023 Volume 19A Issue Special_Edition Pages i-iii
    Published: 2023
    Released on J-STAGE: October 24, 2023
    JOURNAL OPEN ACCESS
    Catastrophic disasters triggered by mesoscale convective systems occur annually in East Asia, with a notable increase in casualties and extensive damages between 2019 and 2021 due to record-breaking rainfall in Japan. There is an urgent need for a comprehensive understanding of the physical processes and dynamic mechanisms behind these extreme rainfall events. This requires the integration of various research approaches, including observational analysis, statistical data analysis, and weather forecasting with data assimilation. Additionally, we must consider the impact of large-scale atmospheric circulation on extreme weather in East Asia. In this special edition, jointly coordinated with Journal of the Meteorological Society of Japan, we have published nine articles covering extreme events in East Asia from 2017 to 2022. Here, we provide an overview of these papers.
    From a large-scale view perspective, Horinouchi et al. (2021) and Ueda et al. (2021) examined the influence of synoptic-scale moisture conditions and sea surface temperatures on severe rainfall events in Kyushu, Japan during the summer of 2020. Additionally, Takemura et al. (2022) investigated the large-scale atmospheric factors contributing to the record-breaking early onset of Baiu season in most parts of western Japan in 2021. Furthermore, Kuramochi et al. (2021) conducted a study on the causes of the anomalous warm conditions in winter 2019 and 2020 over East Asia, utilizing large-scale atmospheric analysis and global simulations.
    Three papers focused on the statistical features of environmental conditions suitable for the occurrence of “senjo-kousuitai” (Kato 2020). Goto and Satoh (2022) applied a similar definition of senjo-kousuitai as proposed by Kato 2020 to a satellite-based precipitation dataset covering 20 years from 2000 to 2019. They confirmed a high occurrence frequency in Kyushu, the Nansei Islands (South of Kyushu), and the East China sea. Based on analysis using reanalysis datasets, it was determined that low-level water vapor flux and vertical wind shear are essential for the development of senjo-kousuitai. Sato and Hosotani (2023) also confirmed the importance of these two factors based on reanalysis data spanning the past 20 years. Additionally, Naka and Takemi (2023) proposed the significance of moist absolutely unstable layers (MAULs) in enhancing heavy rainfall in the preceding hours.
    Numerical simulations were also employed in research efforts. Tochimoto et al. (2022) conducted sensitivity experiments to investigate the impact of the upper-level trough on the heavy rainfall. In another study, Terasaki and Miyoshi (2022) demonstrated the high predictability of heavy rainfall by utilizing data assimilation with 1024-ensemble members. Doyle et al. (2023) indicated the importance of a mesoscale convective system, orographic ascent, and equatorial wave components in contributing to the extreme flood that occurred in southwestern Sulawesi, Indonesia in January 2019 by conducting adjoint model simulations and the sensitivity analysis.
    To mitigate the damages caused by various extreme weather events, it is essential to consolidate our research achievements and further enhance the predictability of these events.
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Article
  • Masaki Satoh, Keisuke Hosotani
    2023 Volume 19A Issue Special_Edition Pages 1-8
    Published: 2023
    Released on J-STAGE: February 10, 2023
    Advance online publication: December 28, 2022
    JOURNAL OPEN ACCESS
    Supplementary material

    A sequence of heavy rainfall events due to quasi-stationary band-shaped precipitation systems, or “senjo-kousuitai“, was observed in the Kyushu region, Japan, from 3 to 8 July 2020. In this study, we investigate two of six indices that have previously been used to determine conditions favorable for senjo-kousuitai, i.e., water vapor flux at the height of 500 m and storm-relative environmental helicity. We examine the relationship between these indices and the occurrence of senjo-kousuitai over the past 20 years using the Japan Meteorological Agency 55-year reanalysis data. We show that the anomaly in wind speeds rather than humidity contributes more to anomalous water vapor flux. The vertical shear of zonal winds and the meridional flow in the lower layer contribute more to the storm-relative environmental helicity. We conducted 20-member ensemble experiments with a 14 km mesh Nonhydrostatic Icosahedral Atmospheric Model (NICAM) for the senjo-kousuitai event. We found that the initial variabilities of the water vapor over the area stretching from the East China Sea to the South China Sea and the wind fields over the western periphery of the North Pacific High are sensitive to the water vapor flux over the senjo-kousuitai area in Kyushu.

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  • Nanami Naka, Tetsuya Takemi
    2023 Volume 19A Issue Special_Edition Pages 9-16
    Published: 2023
    Released on J-STAGE: July 15, 2023
    Advance online publication: June 05, 2023
    JOURNAL OPEN ACCESS
    Supplementary material

    Using mesoscale gridded analysis data and radar/raingauge-analyzed precipitation products, this study investigated the environmental conditions for the occurrence of extremely heavy rain events that occurred in northern Kyushu during the warm season in recent years. In all cases, the environmental conditions were not particularly unstable but were almost saturated in the deep layer of the troposphere. The existence of moist absolutely unstable layers (MAULs) was confirmed in and around the rainfall areas. A positive correlation was found between the volume of deep MAULs and the area total rainfall. A large convergence of the water vapor flux is observed in the lower troposphere, which appears to maintain very humid conditions and MAULs. The moisture convergence in the lower troposphere and the presence of deep MAULs is considered to enhance the heavy rainfall in the preceding hours. Humid conditions form deep MAULs that appear to precede the heavy rainfalls.

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  • James D. Doyle, Carolyn A. Reynolds, Maria Flatau, Beata Latos
    2023 Volume 19A Issue Special_Edition Pages 17-26
    Published: 2023
    Released on J-STAGE: August 05, 2023
    Advance online publication: June 13, 2023
    JOURNAL OPEN ACCESS
    Supplementary material

     The Makassar Peninsula in southwestern Sulawesi, Indonesia, experienced its largest flood in its recorded history in January 2019. Four-day accumulated rainfall exceeded 350 mm with devastating impacts on the community, including 53 perished and over 14000 evacuated. Previous studies find a convectively coupled Kelvin wave and convectively coupled equatorial Rossby wave associated with the Madden-Julian Oscillation to be likely contributors to the onset of the mesoscale convective system responsible for the flooding. We employ an adjoint model to identify and dynamically link specific components of the mesoscale and environmental flow affecting the flooding event.

     The adjoint simulations indicate that enhancing the moisture and low-level convergence associated with the mesoscale convective system can substantially increase rainfall. The sensitivity patterns are complex, with low-level convergence and vorticity sensitivity in quadrature and projecting onto the larger-scale Kelvin and Rossby waves. The vorticity sensitivity enhances waves along the dynamic equator. Small adjoint-based perturbations made to the initial state can increase the 36-h rainfall maximum by greater than 30%. The sensitivity analysis supports the importance of a mesoscale convective system, orographic ascent, and equatorial wave components in contributing to the flood. The rapid growth of small initial perturbations underscores the need for probabilistic forecasts.

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