著者
Shinya KOBAYASHI Yukinari OTA Yayoi HARADA Ayataka EBITA Masami MORIYA Hirokatsu ONODA Kazutoshi ONOGI Hirotaka KAMAHORI Chiaki KOBAYASHI Hirokazu ENDO Kengo MIYAOKA Kiyotoshi TAKAHASHI
出版者
(公社)日本気象学会
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.93, no.1, pp.5-48, 2015 (Released:2015-03-18)
参考文献数
128
被引用文献数
213 1132

The Japan Meteorological Agency (JMA) conducted the second Japanese global atmospheric reanalysis, called the Japanese 55-year Reanalysis or JRA-55. It covers the period from 1958, when regular radiosonde observations began on a global basis. JRA-55 is the first comprehensive reanalysis that has covered the last half-century since the European Centre for Medium-Range Weather Forecasts 45-year Reanalysis (ERA-40), and is the first one to apply four-dimensional variational analysis to this period. The main objectives of JRA-55 were to address issues found in previous reanalyses and to produce a comprehensive atmospheric dataset suitable for studying multidecadal variability and climate change. This paper describes the observations, data assimilation system, and forecast model used to produce JRA-55 as well as the basic characteristics of the JRA-55 product. JRA-55 has been produced with the TL319 version of JMA’s operational data assimilation system as of December 2009, which was extensively improved since the Japanese 25-year Reanalysis (JRA-25). It also uses several newly available and improved past observations. The resulting reanalysis products are considerably better than the JRA-25 product. Two major problems of JRA-25 were a cold bias in the lower stratosphere, which has been diminished, and a dry bias in the Amazon basin, which has been mitigated. The temporal consistency of temperature analysis has also been considerably improved compared to previous reanalysis products. Our initial quality evaluation revealed problems such as a warm bias in the upper troposphere, large upward imbalance in the global mean net energy fluxes at the top of the atmosphere and at the surface, excessive precipitation over the tropics, and unrealistic trends in analyzed tropical cyclone strength. This paper also assesses the impacts of model biases and changes in the observing system, and mentions efforts to further investigate the representation of low-frequency variability and trends in JRA-55.
著者
Kazuto Takemura Shunya Wakamatsu Hiroki Togawa Akihiko Shimpo Chiaki Kobayashi Shuhei Maeda Hisashi Nakamura
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.49-54, 2019 (Released:2019-08-09)
参考文献数
21
被引用文献数
1 1

This study investigates the influence of strong southerly moisture flux on an extreme rainfall event over western Japan in early July 2018, by using a global atmospheric reanalysis dataset. During its peak period from 5 to 7 July, extensive and unprecedented rainfall observed along the well-defined quasi-stationary Baiu front was attributed to two branches of extremely moist inflow from the southern confluence into western Japan. One was a shallow southerly airstream enhanced by the surface North Pacific Subtropical High, and the other was a deeper southwesterly airstream accompanying enhanced convection over the East China Sea. Both the vertically integrated moisture flux from the south and its convergence into western Japan reached the highest levels for 60 years due to an overwhelming contribution from the intensified southerlies. Anomalous diabatic heating associated with the active convection over the East China Sea acted to maintain the southwesterly moisture flux by inducing low-level cyclonic potential vorticity anomalies. During the rainfall event, a strong meander of the upper-level subtropical jet associated with the intensified surface North Pacific Subtropical High accompanied an amplified upper-level trough over the Korean Peninsula, which acted to induce ascent dynamically along the Baiu front.
著者
Chiaki Kobayashi Ichiro Ishikawa
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.31-36, 2019 (Released:2019-07-03)
参考文献数
11

During summer 2018, zonally averaged tropospheric temperatures were higher than normal in the northern mid-latitudes, and this contributed to the extreme warmth experienced in eastern and western Japan. These northern-mid-latitudes warm anomalies, along with enhanced convective activity in the northern subtropics, persisted from autumn 2017 until autumn 2018. This paper demonstrates that both the persistent zonal pattern, and the circulation anomaly pattern, that developed during summer 2018 are well predicted by a reforecast experiment using an operational seasonal prediction system. As variation in zonally averaged convective activity in the northern subtropics is statistically closely related to northern-mid-latitude tropospheric warming in all seasons, we hypothesize that the former is likely to be a key influence on the latter. We found a weakening of northern-mid-latitude tropospheric warming in a sensitivity experiment in which tropical Pacific sea surface temperatures (SSTs) are nudged to the climatology and enhancement of convective activity in the northern tropics is weakened. These results suggest that SST anomalies in the tropical Pacific, which are well predicted by our reforecast experiment, contribute to the successful prediction of northern-mid-latitude tropospheric warming.
著者
Chiaki Kobayashi Hirokazu Endo Yukinari Ota Shinya Kobayashi Hirokatsu Onoda Yayoi Harada Kazutoshi Onogi Hirotaka Kamahori
出版者
(公社)日本気象学会
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.10, pp.78-82, 2014 (Released:2014-05-14)
参考文献数
11
被引用文献数
6 26

As a subset of the Japanese 55-year Reanalysis (JRA-55) project, the Meteorological Research Institute of the Japan Meteorological Agency is conducting a global atmospheric reanalysis that assimilates only conventional surface and upper air observations, with no use of satellite observations, using the same data assimilation system as the JRA-55. The project, named the JRA-55 Conventional (JRA-55C), aims to produce a more homogeneous dataset over a long period, unaffected by changes in historical satellite observing systems. The dataset is intended to be suitable for studies of climate change or multi-decadal variability. The climatological properties deduced from the early results of the JRA-55C are similar to those of the JRA-55 in the troposphere and lower stratosphere, except for high southern latitudes. On the basis of forecast skill, the quality of the JRA-55C is inferior to that of the JRA-55, but the JRA-55C has better temporal homogeneity than the JRA-55. The skill of the latter changes during the JRA-55 period. We have completed 85% of the entire JRA-55C calculation as of February 2014. We expect that the JRA-55C will contribute to a much better understanding of the impact of changes in observing systems on climate trends and variability estimated from the JRA-55.
著者
Chiaki KOBAYASHI Kiyotaka SHIBATA
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.89, no.4, pp.363-376, 2011-08-25 (Released:2011-08-31)
参考文献数
35
被引用文献数
1 2

Dynamical contributions to past long-term changes in the lower stratospheric ozone over the northern mid-latitudes are evaluated using a chemical transport model (CTM) forced by the horizontal wind of the Japanese 25-year Reanalysis (JRA-25). Two simulations (i.e., one is a simulation that prescribes the time-dependent vertical profile of halogens and the other is a simulation which uses the fixed vertical profile of halogens at 1979.) were conducted to estimate chemical and dynamical contributions to the long-term changes in stratospheric ozone during the last three decades. Different from previous similar studies using meteorological data of ECMWF (European Centre for Medium Weather Forecast) 40-year re-analysis (ERA-40), our current simulation does not show a large positive anomaly of simulated total ozone over northern mid-latitudes in the late 1980s, which is consistent with the observation. Because the trend of the fixed halogen simulation amounts to about two-third of that of the time-dependent halogen simulation during 1980–1993 in the northern mid-latitudes, it is evaluated that about two-thirds of the negative trend in total ozone comes from dynamics in the northern mid-latitudes. Since the increasing ozone from 1994 to 1998 is also represented in the fixed halogen simulation, it is considered that the increase of ozone was mainly due to dynamics as pointed out in previous studies. However the dynamical contribution to the trend after 1994 could not be evaluated in our simulation because of simulated ozone gap in 1998. In the same manner, it is evaluated that about two-thirds of the negative ozone trend in the lower stratosphere comes from dynamics in the northern mid-latitudes from 1980 to the mid-1990s. The simulation results indicate that the effect of transport (dynamical influence) is predominant for the negative ozone trend in the lower stratosphere from 1980 to mid-1990s, while the upper stratospheric ozone trend is strongly influenced by long-term changes in halogens (chemical influence).