- 著者
- Tetsuya Takemi Takashi Unuma
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.15A, pp.60-65, 2019 (Released:2019-09-19)
- 参考文献数
- 32
- 被引用文献数
- 25
This study documented the environmental properties of precipitation systems that produced the July 2018 Heavy Rainfall event in Japan. The gridded analysis data were used to diagnose the potential for the development of convective systems in terms of thermodynamic environmental indices. Precipitable water vapor was extremely larger than that seen in the climatology of warm-season quasi-stationary convective clusters (QSCCs). Such an extreme moisture content was realized by very humid conditions at the middle-levels. In contrast, temperature lapse rate in a convectively unstable layer was not so significant in comparison to the QSCC climatology. Among the environmental indices, K Index was shown to describe the potential for the rainfall development. Based on the analysis, the roles of moisture content and profile on the convection development were discussed. It was suggested that the middle-level high humidity contributes to the occurrence of the present heavy rainfall by minimizing negative effects of environmental mixing and by decreasing vertical displacements to reach levels of free convection. In regions where heavy rainfall occurred, an automated algorithm detected the development of QSCCs, which were mostly categorized as a linear type.
- 著者
- Tetsuya Takemi Takashi Unuma
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- pp.2020-006, (Released:2020-01-21)
- 被引用文献数
- 33
This study investigated the environmental factors responsible for the development of heavy rainfall in eastern Japan during the passage of Typhoon Hagibis (2019) by using mesoscale gridded analysis data as well as observed data. Environmental indices for diagnosing stability and moisture conditions were examined. It was found that the whole troposphere is almost saturated and the column total water vapor content is extremely large. In the lower troposphere we identified layers of moist absolutely unstable states with the thickness deeper than 2 km. Such deep moist absolutely unstable layers as well as abundant moisture content and almost saturated troposphere set a high potential for convective development. Under these favorable environmental conditions, the fact that the heights of the absolutely unstable layers' bottom are comparable to the mountain elevations is considered to be favorable for topographic lifting of unstable, moist air, which will trigger and activate strong convection and hence heavy rainfall. In spite of a moderate amount of convective available potential energy and a nearly moist-adiabatic lapse rate, moist absolute instability, abundant moisture, and high humidity jointly play a key role to increase the potential for generating the present heavy rainfalls.
- 著者
- Tetsuya Takemi Takashi Unuma
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- pp.15A-011, (Released:2019-08-26)
- 被引用文献数
- 25
This study documented the environmental properties of precipitation systems that produced the July 2018 Heavy Rainfall event in Japan. The gridded analysis data were used to diagnose the potential for the development of convective systems in terms of thermodynamic environmental indices. Precipitable water vapor was extremely larger than that seen in the climatology of warm-season quasi-stationary convective clusters (QSCCs). Such an extreme moisture content was realized by very humid conditions at the middle-levels. In contrast, temperature lapse rate in a convectively unstable layer was not so significant in comparison to the QSCC climatology. Among the environmental indices, K Index was shown to describe the potential for the rainfall development. Based on the analysis, the roles of moisture content and profile on the convection development were discussed. It was suggested that the middle-level high humidity contributes to the occurrence of the present heavy rainfall by minimizing negative effects of environmental mixing and by decreasing vertical displacements to reach levels of free convection. In regions where heavy rainfall occurred, an automated algorithm detected the development of QSCCs, which were mostly categorized as a linear type.
- 著者
- Tetsuya Takemi Takashi Unuma
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.16, pp.30-36, 2020 (Released:2020-02-22)
- 参考文献数
- 23
- 被引用文献数
- 33
This study investigated the environmental factors responsible for the development of heavy rainfall in eastern Japan during the passage of Typhoon Hagibis (2019) by using mesoscale gridded analysis data as well as observed data. Environmental indices for diagnosing stability and moisture conditions were examined. It was found that the whole troposphere is almost saturated and the column total water vapor content is extremely large. In the lower troposphere we identified layers of moist absolutely unstable states with the thickness deeper than 2 km. Such deep moist absolutely unstable layers as well as abundant moisture content and almost saturated troposphere set a high potential for convective development. Under these favorable environmental conditions, the fact that the heights of the absolutely unstable layers' bottom are comparable to the mountain elevations is considered to be favorable for topographic lifting of unstable, moist air, which will trigger and activate strong convection and hence heavy rainfall. In spite of a moderate amount of convective available potential energy and a nearly moist-adiabatic lapse rate, moist absolute instability, abundant moisture, and high humidity jointly play a key role to increase the potential for generating the present heavy rainfalls.
- 著者
- Takashi Unuma Hiroshi Yamauchi Akihito Umehara Teruyuki Kato
- 出版者
- 公益社団法人 日本気象学会
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- pp.2023-020, (Released:2023-06-09)
- 被引用文献数
- 1
We investigated the microphysical mechanisms for the enhancement of rainfall in a precipitating system that spawned heavy rainfall over the central part of the Kanto Plain in eastern Japan on 12 July 2022. Optical disdrometer observations confirmed the existence of an equilibrium state in the raindrop size distribution, especially when the precipitation intensity was high (e.g., 20 mm hr−1). As the raindrop size distribution approached equilibrium, raindrop sizes centered around 1.5 mm were observed initially, and then the number concentration of smaller and larger size raindrops increased simultaneously. The raindrop size distribution was closely related to the vertical profile of the parameters of raindrop size distribution that were estimated from polarimetric radar observations. These results suggest that the formation of equilibrium raindrop size distributions is important to produce substantial rainfall in the midlatitude as well as in the tropics.
- 著者
- Takashi Unuma Tetsuya Takemi
- 出版者
- (公社)日本気象学会
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.12, pp.111-115, 2016 (Released:2016-05-06)
- 参考文献数
- 27
- 被引用文献数
- 1 20
A role of environmental shear on the organization mode of warm-season quasi-stationary convective clusters (QSCCs) was statistically investigated by using operational weather radar and radiosonde data from May to October during 2005-2012. With the use of an ellipse-fitting method, the total number of QSCCs whose shape was determined was 2549. It was found that 87% of the QSCCs have an aspect ratio of larger than 1.4, suggesting that the elongated mode is dominant during the warm season in Japan. The elongated QSCCs were mostly oriented southwest–northeast. The analyses of the environmental shear direction with respect to the orientation of the elongated QSCCs showed that the wind shear direction at the lower troposphere is mainly parallel to the orientation of the elongated QSCCs. A comparison between the elongated and the circular QSCCs with the environmental parameters showed that the lower convective instability and stronger intensity of the low-level shear clearly characterize the elongated QSCC environments. A parameter combining convective instability and shear, bulk Richardson number, characterizes the environmental conditions for determining the organization mode of the QSCCs, suggesting that a back-building mechanism should play a role in generating the elongated QSCCs.
- 著者
- Takashi Unuma Hiroshi Yamauchi Akihito Umehara Teruyuki Kato
- 出版者
- 公益社団法人 日本気象学会
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.19, pp.150-156, 2023 (Released:2023-07-22)
- 参考文献数
- 28
- 被引用文献数
- 1
We investigated the microphysical mechanisms for the enhancement of rainfall in a precipitating system that spawned heavy rainfall over the central part of the Kanto Plain in eastern Japan on 12 July 2022. Optical disdrometer observations confirmed the existence of an equilibrium state in the raindrop size distribution, especially when the precipitation intensity was high (e.g., 20 mm hr−1). As the raindrop size distribution approached equilibrium, raindrop sizes centered around 1.5 mm were observed initially, and then the number concentration of smaller and larger size raindrops increased simultaneously. The raindrop size distribution was closely related to the vertical profile of the parameters of raindrop size distribution that were estimated from polarimetric radar observations. These results suggest that the formation of equilibrium raindrop size distributions is important to produce substantial rainfall in the midlatitude as well as in the tropics.