著者

Akira Kuwano-Yoshida

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.10, pp.199-203, 2014 (Released:2014-12-06)

参考文献数

29

被引用文献数

9 18

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The “Local deepening rate (LDR)”, the local surface pressure tendency, which is normalized by the sine of latitude and similar to the definition of an explosive cyclone, is introduced to extratropical cyclone activity analysis. The LDR has the advantage of being much simpler than conventional methods such as cyclone tracking and time filtering. The time average of positive LDR, which implies cyclone deepening, captures not only individual explosive cyclone's deepening but also the mid-latitude storm track climatology. The probability of explosive deepening, defined as LDR ≥ 1 hPa h-1 and based on ensemble forecasts, accurately represents the deepening potential and provides information regarding the influence area of storms—analogous to the strong wind area used in typhoon forecasts. The LDR can also be used to assess the quality of storm tracks in reanalyses products. In the 20th century reanalysis, the storm track activity, calculated from ensemble mean surface pressure, is too weak before 1910 in the North Pacific, and in the South Pacific low activity is observed up to the end of the 20th century, because of large ensemble spread due to few surface pressure observations.

著者

Meiji Honda Akira Yamazaki Akira Kuwano-Yoshida Yusuke Kimura Katsushi Iwamoto

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.12, pp.259-264, 2016 (Released:2016-09-22)

参考文献数

17

被引用文献数

8

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Synoptic conditions causing an extreme snowfall event in the Kanto-Koshin district occurred on 14-15 February 2014 are investigated through a reanalysis data set. Associated with a developing cyclone passing the south coast of Japan, persistent snowfall exceeding more than 24 hours over the Kofu-Basin resulted in 112 cm snowfall at Kofu. Slow progress of the south-coast cyclone also contributed to the long snowfall duration. An anticyclone developed over the northern Japan (∼1032 hPa) also contributed to this extreme snowfall. This anticyclone brought warm and moist air inflow by southeasterlies forming moisture flux convergence over the Kanto-Koshin district on the morning of 14th when snowfall started in the Koshin district in spite that the south-coast cyclone was located to the south of Kyushu. Further, ageostrophic cold northerlies with high pressure extension from the anticyclone by “cold-air damming (CAD)” would suppress warming with the approaching south-coast cyclone and keep snowfall until the morning of 15th. In other four heavy snowfall events at Kofu, snowfall durations were almost 12 hours. Although anticyclone to the north and CAD were identified in each case, the moisture transport from the southeast was not evident and moisture flux convergence was not formed earlier.

著者

Akira Yamazaki Meiji Honda Akira Kuwano-Yoshida

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.11, pp.59-64, 2015 (Released:2015-05-11)

参考文献数

12

被引用文献数

1 16

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The influence of large-scale atmospheric blocking over the northwestern Pacific on heavy snowfall events in the Kanto area and on the Pacific Ocean side of northern Japan (PNJ) within the time scale of ∼10 days was examined through blocking case studies. The past 14 blocking cases over the Pacific, including the blocking during early- to mid-February 2014 that influenced a record-breaking snowfall over the Kanto area, were analyzed using a long-term reanalysis dataset and local meteorological observation station data. Results reveal that blocking over the Pacific causes large precipitation over the Kanto area and the PNJ by shifting cyclone (storm) tracks towards the east coast of Japan from their usual eastward course across the mid-Pacific via the south coast of Japan. Excessive passing of cyclones caused large precipitation in the Kanto area and snowfall in the PNJ. In the blocking cases with heavy snowfall events in the Kanto area, a strong cold-air inflow over Japan also existed in the lower troposphere originating from east Siberia, which initiated synoptic ground cold-air environments in the Kanto area.

著者

Chihiro Kodama Akira Kuwano-Yoshida Shingo Watanabe Takeshi Doi Hiroki Kashimura Tomoe Nasuno

出版者

Japan Agency for Marine-Earth Science and Technology

雑誌

JAMSTEC Report of Research and Development (ISSN:18801153)

巻号頁・発行日

vol.28, pp.5-34, 2019-04-01 (Released:2019-04-03)

参考文献数

133

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The JAMSTEC Model Intercomparison Project (JMIP) provides a first opportunity to systematically compare multiple global models developed and/or used in JAMSTEC with the aim of moving toward better weather and climate predictions. Here, we evaluate climate simulations obtained from atmospheric models (AFES and MIROC5), atmospheric model with slab ocean (NICAM.12), and fully coupled model (SINTEX-F1 and SINTEX-F2). In these simulations, the sea surface temperature is fixed (for AFES and MIROC5) or nudged (NICAM.12, SINTEX-F1, and SINTEX-F2) to the observed historical one. We focus on the climatology and variability of precipitation and its associated phenomena, including the basic state, the energy budget of the atmosphere, extratropical cyclones, teleconnection, and the Asian monsoon. We further discuss the possible causes of similarities and differences among the five JMIP models. Though some or most of the dynamical and physical packages in the JMIP models have been developed independently, common model biases are found among them. The AFES and MIROC5, and the SINTEX-F1 and SINTEX-F2, show strong similarities. In many respects, NICAM.12 shows unique characteristics, such as the distributions of precipitation, shortwave radiation, and explosive extratropical cyclones and the onset of the Asian summer monsoon. To some extent, the similarities and differences among the JMIP models overlap with those among the Coupled Model Intercomparison Project Phase-5 (CMIP5) models, suggesting that JMIP can be used as a simple and in-depth version of CMIP to investigate the mechanisms of model bias. We suggest that this JMIP framework could be expanded to an intercomparison of weekly-to-seasonal scale weather forecasting; here, more fruitful discussion is expected through intensive collaboration among modeling and observation groups.

著者

Yoshimi KAWAI Qoosaku MOTEKI Akira KUWANO-YOSHIDA Takeshi ENOMOTO Atsuyoshi MANDA Hisashi NAKAMURA

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.95, no.2, pp.71-90, 2017 (Released:2017-03-17)

参考文献数

31

被引用文献数

6

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The present study investigated how impacts of the inclusion of radiosonde observations conducted locally in the early summer of 2012 over the Kuroshio and Kuroshio Extension (KE) can spread over time across the North Pacific basin to influence the predictability of synoptic and large-scale tropospheric circulation. For that purpose, observing system experiments (OSEs) were performed where each of two extra sets of radiosonde data, one obtained over the East China Sea in mid-May and the other over the KE in early July, was added to an atmospheric ensemble data assimilation system for comparison with the corresponding analyses without those data. The experiments show that the impact of the extra data assimilated propagates eastward mainly due to advection by the subtropical jet (STJ) in May and July. The strong STJ in May allows the upper-tropospheric impact to travel across the basin only within two days. Under the weaker STJ, the corresponding impact in July tends to remain within the western Pacific, until it eventually reaches the eastern portion of the basin. Assimilation of the extra radiosonde data over the Kuroshio or KE can lead to a decrease of pressure over the Gulf of Alaska in both May and July.  Additional forecast experiments based on the OSEs for May revealed that the pressure decrease over the Gulf of Alaska can be traced back to the west of the Alaska Peninsula and to the east of Japan over three days. The impacts that originate on different dates via different paths merge over the central North Pacific, reinforcing the cyclone over the Gulf of Alaska. This study presents examples where the impacts of atmospheric observations over the western boundary current can propagate across the ocean basin through the westerlies to influence the forecast skill in distant regions.

著者

Akira Yamazaki Takeshi Enomoto Takemasa Miyoshi Akira Kuwano-Yoshida Nobumasa Komori

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.13, pp.41-46, 2017 (Released:2017-03-25)

参考文献数

26

被引用文献数

7

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The observation operators in the local ensemble transform Kalman filter (LETKF) were improved to enable use of observations in the vicinity of the poles in the data assimilation system composed of the atmospheric general circulation model for the Earth Simulator (AFES) and the LETKF. The improved observation operators allow to assimilate the observations located south (north) of southernmost (northernmost) Gaussian grid latitudes. An algorithm for searching the nearest observations from an analyzed grid for error covariance localization was also modified to efficiently assimilate observations near the poles.The new algorithms were incorporated into the LETKF, and the impacts of routine radiosonde observations at the South Pole during the periods of July 2012 and January 2013 were assessed. The radiosonde observations suppressed an artificial expansion of the analysis ensemble spread which occasionally caused numerical instability in the upper troposphere and the lower stratosphere over the Antarctic regions. The analysis was also improved in the Antarctic regions.