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Hiroaki Kawase, Shunichi Watanabe, Yasutaka Hirockawa, and Yukiko Imada
Open access
Akihiko Murata, Masaya Nosaka, Hidetaka Sasaki, and Hiroaki Kawase

Abstract

Dynamic and thermodynamic factors involved in future changes in local-scale short-term extreme summertime precipitation on the mesoscale and hourly time scale in Japan were examined using convection-permitting regional climate model simulations under the Representative Concentration Pathway 8.5 scenario. The change in the dynamic component primarily contributes to the total change in vertically integrated moisture flux convergence over the analysis domain that located off Okinawa Island, while the thermodynamic component is dominant over the analysis domain that located off Kyushu Island. Differences in the amount of the dynamic and thermodynamic components are noticeable in these two domains. These results are explained by the difference in the vertical profiles of the convergence term, and hence, the convergence itself between the two specific domains. A mesoscale low-pressure system on the seasonal rain front—termed the Baiu front—is a key factor underlying the difference in the magnitudes and vertical profiles of convergence between the two specific domains. In the vicinity of the domain off Okinawa Island, a mesoscale low-pressure system on the Baiu front enhances low-level convergence in the future climate when compared to the present climate. This atmospheric state is attributable to the location of the Baiu front itself that is located relatively southward in the future climate and is affected by the domain off Okinawa Island. In the domain where the dynamic component is dominant such as the domain off Okinawa Island, the total moisture flux convergence follows a super Clausius-Clapeyron scaling.

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Satoru Kasuga, Meiji Honda, Jinro Ukita, Shozo Yamane, Hiroaki Kawase, and Akira Yamazaki

Abstract

We propose a new scheme based on geopotential height fields to detect cutoff lows starting in the preexisting trough stage. The intensity and scale derived from the proposed scheme will allow for a better understanding of the cutoff low life cycle. These cutoff lows often accompany mesoscale disturbances, causing adverse weather-related events, such as intense torrential rainfall and/or tornadoes. The proposed scheme quantifies the geometric features of a depression from its horizontal height profile. The height slope of a line intersecting the depression bottom and the nearest tangential point (optimal slope) locally indicates the intensity and scale of an isolated depression. The strength of the proposed scheme is that, by removing a local background height slope from a geopotential height field, the cutoff low and its preexisting trough are seamlessly detected as an identical depression. The distribution maps for the detected cutoff lows and preexisting troughs are illustrated along with their intensities, sizes, and local background flows estimated from snapshot height fields. We conducted climatological comparisons of cutoff lows to determine the utility of the proposed scheme.

Open access
Hiroaki Kawase, Yukiko Imada, Hiroshige Tsuguti, Toshiyuki Nakaegawa, Naoko Seino, Akihiko Murata, and Izuru Takayabu
Free access
Akihiko Murata, Shun-ichi I. Watanabe, Hidetaka Sasaki, Hiroaki Kawase, and Masaya Nosaka

Abstract

Goodness of fit in daily precipitation frequency to a gamma distribution was examined, focusing on adverse effects originating from the shortage of sampled tropical cyclones, using precipitation data with and without the influence of tropical cyclones. The data used in this study were obtained through rain gauge observations and regional climate model simulations under the RCP8.5 scenario and the present climate. An empirical cumulative distribution function (CDF), calculated from a sample of precipitation data for each location, was compared with a theoretical CDF derived from two parameters of a gamma distribution. Using these two CDFs, the root-mean-square error (RMSE) was calculated as an indicator of the goodness of fit. The RMSE exhibited a decreasing tendency when the influence of tropical cyclones was removed. This means that the empirical CDF derived from sampled precipitation more closely resembled the theoretical CDF when compared with the relationship between empirical and theoretical CDFs, including precipitation data associated with tropical cyclones. Future changes in the two parameters of the gamma distribution, without the influence of tropical cyclones, depend on regions in Japan, indicating a regional dependence on changes in the shape and scale of the CDF. The magnitude of increases in no-rain days was also dependent on regions of Japan, although the number of no-rain days increased overall. This simplified approach is useful for analyzing climate change from a broad perspective.

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Izuru Takayabu, Roy Rasmussen, Eiichi Nakakita, Andreas Prein, Hiroaki Kawase, ShunIchi Watanabe, Sachiho A. Adachi, Tetsuya Takemi, Kosei Yamaguchi, Yukari Osakada, and Ying-Hsin Wu
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Izuru Takayabu, Roy Rasmussen, Eiichi Nakakita, Andreas Prein, Hiroaki Kawase, Shun-Ichi Watanabe, Sachiho A. Adachi, Tetsuya Takemi, Kosei Yamaguchi, Yukari Osakada, and Ying-Hsin Wu
4th International Convection-Permitting Modeling Workshop for Climate Research

What:

The purpose of the workshop was to discuss the performance of convection-permitting models (<4-km horizontal grid spacing) at global and local scales and also to discuss the potential of CPMs data for hazard and impact studies. Recent advancements in CPM research were highlighted and key challenges discussed. The workshop also focused on the potential of applying CPMs to the Asian region.

When:

2–4 September 2020

Where:

Online

The 4th International Convection-Permitting Modeling Workshop, originally planned as an in-person meeting for September 2020 in Kyoto, Japan, was converted to

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Ryo Mizuta, Akihiko Murata, Masayoshi Ishii, Hideo Shiogama, Kenshi Hibino, Nobuhito Mori, Osamu Arakawa, Yukiko Imada, Kohei Yoshida, Toshinori Aoyagi, Hiroaki Kawase, Masato Mori, Yasuko Okada, Tomoya Shimura, Toshiharu Nagatomo, Mikiko Ikeda, Hirokazu Endo, Masaya Nosaka, Miki Arai, Chiharu Takahashi, Kenji Tanaka, Tetsuya Takemi, Yasuto Tachikawa, Khujanazarov Temur, Youichi Kamae, Masahiro Watanabe, Hidetaka Sasaki, Akio Kitoh, Izuru Takayabu, Eiichi Nakakita, and Masahide Kimoto

Abstract

An unprecedentedly large ensemble of climate simulations with a 60-km atmospheric general circulation model and dynamical downscaling with a 20-km regional climate model has been performed to obtain probabilistic future projections of low-frequency local-scale events. The climate of the latter half of the twentieth century, the climate 4 K warmer than the preindustrial climate, and the climate of the latter half of the twentieth century without historical trends associated with the anthropogenic effect are each simulated for more than 5,000 years. From large ensemble simulations, probabilistic future changes in extreme events are available directly without using any statistical models. The atmospheric models are highly skillful in representing localized extreme events, such as heavy precipitation and tropical cyclones. Moreover, mean climate changes in the models are consistent with those in phase 5 of the Coupled Model Intercomparison Project (CMIP5) ensembles. Therefore, the results enable the assessment of probabilistic change in localized severe events that have large uncertainty from internal variability. The simulation outputs are open to the public as a database called “Database for Policy Decision Making for Future Climate Change” (d4PDF), which is intended to be utilized for impact assessment studies and adaptation planning for global warming.

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