著者

HARADA Yayoi ENDO Hirokazu TAKEMURA Kazuto

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-062, (Released:2020-08-12)

被引用文献数

5

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To explore large-scale atmospheric factors causing heavy rainfall events that occurred widely in western Japan, a composite analysis of atmospheric fields during the past heavy rainfall events in the region is performed using the Japanese 55-year Reanalysis. During heavy rainfall events, atmospheric fields are characterized by an upper-tropospheric trough over the Korean Peninsula (KP), an upper-tropospheric ridge to the east of Japan, a surface high-pressure system to the southeast of Japan, and southwesterly moisture flux. The composite analysis indicates that a clear wave train due to quasi-stationary Rossby wave-packet propagation (RWPP) along the polar front jet (PFJ) over Siberia tends to occur just before extreme events. Further analysis considering various time-scale variabilities in the atmosphere reveals that surface high-pressure anomalies to the southeast of Japan are dominated by variability with a 25–90-day period, whereas variability with an 8–25-day period dominates lower-pressure anomalies over the East China Sea (ECS) in relation to the development of the upper-tropospheric trough around the KP. We also investigate atmospheric fields during an extreme heavy rainfall event that occurred in early July 2018 (HR18). Atmospheric features during HR18 are generally similar to those of the other heavy rainfall events. However, a remarkable RWPP occurred along the sub-tropical jet (STJ) in late June 2018 and intensified a surface high-pressure system to the southeast of Japan. In addition, a low-pressure system with an 8–25-day period to the south of Japan developed in association with wave breaking induced by the remarkable RWPP along the STJ and propagated northwestward toward the ECS and then to Japan. The simultaneous development of high- and low-pressure systems contributed to the extreme southerly moisture flux into western Japan. HR18 is also characterized by a sharp upper-tropospheric trough over the KP that is dominated by high-frequency variability with a period < 8 days.

著者

IQBAL Waheed HANNACHI Abdel HIROOKA Toshihiko CHAFIK Léon HARADA Yayoi

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-037, (Released:2019-02-15)

被引用文献数

1

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The interaction between the troposphere and the stratosphere has attracted the attention of climate scientists for several decades not least for the benefit it has on understanding dynamical processes and predictability. This interaction has been revived recently in regard to downward disturbance propagation effects on tropospheric circulations. The current study investigates such interactions over the North Atlantic region in relation to the eddy-driven jet stream. The atmospheric low-frequency variability in the winter over the North Atlantic sector is mainly associated with variations in the latitudinal positions of the North Atlantic eddy-driven jet stream. The Japanese Reanalysis JRA-55 data has been used to analyse the jet latitude statistics. The results reveal robust trimodality of the North Atlantic jet reflecting the latitudinal (i.e., northern, central and southern) positions in agreement with other reanalysis products. Thirty major sudden stratospheric warming events were analysed in relation to the three modes or regimes of the eddy-driven jet. The frequency of occurrence of the eddy-driven jet to be in a specific latitudinal position is largely related to the wave amplitude. The stratospheric polar vortex experiences significant changes via upward wave propagation associated with the jet positions. It is found that when the jet is close to its central mode the wave propagation of zonal wave number 2 from the troposphere to the stratosphere is significantly high. Eliassen-Palm fluxes from all waves and zonal wave number 1 depict deceleration of the stratospheric polar vortex for the eddy-driven jet with latitudinal position close to the northern mode. Plumb wave activity variations originate mainly in the Atlantic sector depending on the North Atlantic eddy-driven jet states. These significant associations between preferred latitudinal positions of the North Atlantic eddy-driven jet and the stratospheric dynamics may be a source of predictability.

著者

KOSAKA Yuki KOBAYASHI Shinya HARADA Yayoi KOBAYASHI Chiaki NAOE Hiroaki YOSHIMOTO Koichi HARADA Masashi GOTO Naochika CHIBA Jotaro MIYAOKA Kengo SEKIGUCHI Ryohei DEUSHI Makoto KAMAHORI Hirotaka NAKAEGAWA Tosiyuki TANAKA Taichu Y. TOKUHIRO Takayuki SATO Yoshiaki MATSUSHITA Yasuhiro ONOGI Kazutoshi

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2024-004, (Released:2023-11-02)

被引用文献数

4

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The Japan Meteorological Agency (JMA) has developed the third Japanese global atmospheric reanalysis, the Japanese Reanalysis for Three Quarters of a Century (JRA-3Q). The objective of JRA-3Q is to improve quality in terms of issues identified in the previous Japanese 55-year Reanalysis (JRA-55) and to extend the reanalysis period further into the past. JRA-3Q is based on the TL479 version of the JMA global Numerical Weather Prediction (NWP) system as of December 2018 and uses results of developments in the operational NWP system, boundary conditions, and forcing fields achieved at JMA since JRA-55. It covers the period from September 1947, when Typhoon Kathleen brought severe flood damage to Japan, and uses rescued historical observations to extend its analyses backwards in time about 10 years earlier than JRA-55. This paper describes the data assimilation system, forecast model, observations, boundary conditions, and forcing fields used to produce JRA-3Q as well as the basic characteristics of the JRA-3Q product. The initial quality evaluation revealed major improvements from JRA-55 in the global energy budget and representation of tropical cyclones (TCs). One of the major problems in JRA-55—global energy imbalance with excess upward net energy flux at the top of the atmosphere and at the surface—has been significantly reduced in JRA-3Q. Another problem—a trend of artificial weakening of TCs—has been resolved through the use of a method that generates TC bogus based on the JMA operational system. There remain several problems such that volcanic-induced stratospheric warming is smaller than expected. This paper discusses the causes of such problems and possible solutions in future reanalyses.