著者
Naveen CHANDRA Prabir K. PATRA Jagat S. H. BISHT 伊藤 昭彦 梅澤 拓 三枝 信子 森本 真司 青木 周司 Greet JANSSENS-MAENHOUT 藤田 遼 滝川 雅之 渡辺 真吾 齋藤 尚子 Josep G. CANADELL
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.99, no.2, pp.309-337, 2021 (Released:2021-04-15)
参考文献数
92
被引用文献数
6 7

メタン(CH4)は主要な温室効果気体の一つであり、対流圏および成層圏における化学過程にも重要な役割を果たしている。気候変動および大気汚染に関するCH4の影響は非常に大きいが、過去30年間のCH4濃度増加率や経年変動の要因については、未だ科学的な確証が得られていない。本研究は、十分に検証された化学輸送モデルを用いて、1988年から2016年の期間を対象に大気中CH4濃度をシミュレートし、逆解析によって地域別CH4排出量を推定した。まず、標準実験としてOHラジカルの季節変動のみを考慮し、大気中CH4濃度の観測データを用いた逆解法モデル、排出インベントリ、湿地モデル、およびδ13C-CH4のボックスモデルを用いた解析を行ったところ、1988年以降におけるヨーロッパとロシアでのCH4排出量の減少が示された。特に、石油・天然ガス採掘と畜産由来の排出量の減少が1990年代のCH4増加率の減少に寄与していることが明らかとなった。その後、2000年代初頭には大気中CH4濃度が準定常状態になった。 2007年からはCH4濃度は再び増加に転じたが、これは主に中国の炭鉱からの排出量の増加と熱帯域での畜産の拡大によるものと推定された。OHラジカルの年々変動を考慮した感度実験を行ったところ、逆解析による中高緯度域からのCH4排出推定量はOHラジカルの年々変動には影響されないことが示された。さらに,我々は全球的なCH4排出量が低緯度側へシフトしたことと熱帯域でのOHラジカルによるCH4消失の増加が相殺したことによって、南半球熱帯域と北半球高緯度域の間のCH4濃度の勾配は1988-2016年の間にわたってほとんど変化していなかったことを明らかにした。このような排出地域の南北方向のシフトは、衛星によるCH4カラム観測の全球分布からも確認された。今回の解析期間には、北極域を含めて地球温暖化によるCH4排出量の増加は確認できなかった。これらの解析結果は、気候変動の緩和へ向けた効果的な排出削減策を行う上で重要な排出部門を特定することに貢献できると思われる。
著者
Seiji YUKIMOTO Yukimasa ADACHI Masahiro HOSAKA Tomonori SAKAMI Hiromasa YOSHIMURA Mikitoshi HIRABARA Taichu Y. TANAKA Eiki SHINDO Hiroyuki TSUJINO Makoto DEUSHI Ryo MIZUTA Shoukichi YABU Atsushi OBATA Hideyuki NAKANO Tsuyoshi KOSHIRO Tomoaki OSE Akio KITOH
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.90A, pp.23-64, 2012 (Released:2012-06-07)
参考文献数
157
被引用文献数
354 500

A new global climate model, MRI-CGCM3, has been developed at the Meteorological Research Institute (MRI). This model is an overall upgrade of MRI’s former climate model MRI-CGCM2 series. MRI-CGCM3 is composed of atmosphere-land, aerosol, and ocean-ice models, and is a subset of the MRI’s earth system model MRI-ESM1. Atmospheric component MRI-AGCM3 is interactively coupled with aerosol model to represent direct and indirect effects of aerosols with a new cloud microphysics scheme. Basic experiments for pre-industrial control, historical and climate sensitivity are performed with MRI-CGCM3. In the pre-industrial control experiment, the model exhibits very stable behavior without climatic drifts, at least in the radiation budget, the temperature near the surface and the major indices of ocean circulations. The sea surface temperature (SST) drift is sufficiently small, while there is a 1 W m-2 heating imbalance at the surface. The model’s climate sensitivity is estimated to be 2.11 K with Gregory’s method. The transient climate response (TCR) to 1 % yr-1 increase of carbon dioxide (CO2) concentration is 1.6 K with doubling of CO2 concentration and 4.1 K with quadrupling of CO2 concentration. The simulated present-day mean climate in the historical experiment is evaluated by comparison with observations, including reanalysis. The model reproduces the overall mean climate, including seasonal variation in various aspects in the atmosphere and the oceans. Variability in the simulated climate is also evaluated and is found to be realistic, including El Niño and Southern Oscillation and the Arctic and Antarctic oscillations. However, some important issues are identified. The simulated SST indicates generally cold bias in the Northern Hemisphere (NH) and warm bias in the Southern Hemisphere (SH), and the simulated sea ice expands excessively in the North Atlantic in winter. A double ITCZ also appears in the tropical Pacific, particularly in the austral summer.
著者
YAMAGUCHI Munehiko MAEDA Shuhei
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.2020-039, (Released:2020-05-21)
被引用文献数
3

Based on observations, the number of tropical cyclones (TCs) approaching the southern coast of Japan, including Tokyo, has increased over the last 40 years, and these TCs are increasing in strength when they approach land. The environmental conditions for TC development have become more favorable, with warmer sea surface temperature, less vertical wind shear and more moisture in the atmosphere. In addition, the translation speed of TCs has decreased, which indicates a longer influence time. Comparison of the synoptic environment during July–October between the first (1980-1999, P1) and second (2000-2019, P2) 20 years shows that the sub-tropical high is strengthened in P2, where the western and northern edge of the high extends further the west and the north, respectively. Also, the westerly jet is weakened in P2 over and south of Japan in the middle to upper troposphere. These changes in the synoptic environment are considered to play a role in increasing the number of TCs approaching Tokyo and also in producing more favorable conditions for TC development. The relationship between the changes in TC characteristics over the last 40 years and global warming is unclear. As the Pacific Decadal Oscillation (PDO) is in a positive phase in P1 and a negative phase in many years of the P2 period, decadal oscillations may have played some role in the increase in the number of approaching TCs and in the changes in the synoptic environment.
著者
村松 照男
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.64, no.2, pp.259-272, 1986 (Released:2007-10-19)
参考文献数
17
被引用文献数
13 14

レーダーと衛星で決定した台風眼(T8019, WYNNE)の移動軌跡上にトロコイダル運動による顕著な周期変動が観測された。周期は5~8時間,最大振幅は23kmであった。周期の減少とともに振幅も減少した。レーダーエコーの解析の結果,台風眼の中心は台風系全体の中心とは一致せず,約20km偏位し系の中心に対し反時計回りに回転していることが明らかとなった。この間,外側と内側の eye wal1の直径が各々260kmと30kmである二重眼構造と,それに対応する風速分布の二重極大が観測された。特に,気圧と風速場で楕円状の循環が見られ,その結果としての矩形状エコー構造が外側 eye wal1の内側で観測された。この矩形と楕円状循環は台風系の中心に対しトロコイダル周期と同周期で,外側 eye wal1に内接しながら回転していた。台風眼は楕円の一方の焦点を追うように移動し,この結果としてトロコイダル軌跡となった。しかしながら,なぜ眼が系の中心から偏れるのかはまだ明らかとなっていない。
著者
ITO Kosuke WU Chun-Chieh CHAN Kelvin T. F. TOUMI Ralf DAVIS Chris
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.2020-001, (Released:2019-10-08)
被引用文献数
4

While the fundamental understanding of the movement of a tropical cyclone (TC) is fairly mature, there are still notable advancements being made. This paper summarizes new concepts and updates on existing fundamental theories on TC movement obtained from simplified barotropic models, full-physics models, and data analysis particularly since 2014. It includes the recent works on the interaction of the TC with its environment and the fundamental aspects of predictability related to TC movement. The conventional concepts of the steering flow, β-gyre, and diabatic heating remain important. Yet, a more complete understanding of mechanisms governing TC movement serves as an important basis toward the further improvement of track forecasts.
著者
CHANDRA Naveen PATRA Prabir K. BISHT Jagat S. H. ITO Akihiko UMEZAWA Taku SAIGUSA Nobuko MORIMOTO Shinji AOKI Shuji JANSSENS-MAENHOUT Greet FUJITA Ryo TAKIGAWA Masayuki WATANABE Shingo SAITOH Naoko CANADELL Josep G.
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.2021-015, (Released:2020-12-04)
被引用文献数
7

Methane (CH4) is an important greenhouse gas and plays a significant role in tropospheric and stratospheric chemistry. Despite the relevance of methane (CH4) in human-induced climate change and air pollution chemistry, there is no scientific consensus on the causes of changes in its growth rates and variability over the past three decades. We use a well-validated chemistry-transport model for simulating CH4 concentration and estimation of regional CH4 emissions by inverse modelling for the period of 1988-2016. The control simulations are performed using a seasonally varying hydroxyl (OH) concentrations and assumed no interannual variability. Using inverse modelling of atmospheric observations, emission inventories, a wetland model, and a δ13C-CH4 box model, we show that reductions in emissions from Europe and Russia since 1988, particularly from oil-gas exploitation and enteric fermentation, led to decreased CH4 growth rates in the 1990s. This period was followed by a quasi-stationary state of CH4 in the atmosphere during the early 2000s. CH4 resumed growth from 2007, which we attribute to increases in emissions from coal mining mainly in China and intensification of ruminant farming in tropical regions. A sensitivity simulation using interannually varying OH shows that regional emission estimates by inversion are unaffected for the mid- and high latitude areas. We show that meridional shift in CH4 emissions toward the lower latitudes and the increase in CH4 loss by hydroxyl (OH) over the tropics finely balance out, which keep the CH4 gradients between the southern hemispheric tropical and polar sites relatively unchanged during 1988-2016. The latitudinal emissions shift is confirmed using the global distributions of the total column CH4 observations by satellite remote sensing. There is no evidence of emission enhancement due to climate warming, including the boreal regions, during our analysis period. These findings highlight key sectors for effective emission reduction strategies toward climate change mitigation.
著者
IWAKIRI Tomoki WATANABE Masahiro
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.2020-064, (Released:2020-08-28)
被引用文献数
1

La Niña is the negative phase of the El Niño-Southern Oscillation (ENSO) cycle. It occurs in the equatorial Pacific, and events known as multiyear La Niña often persist for more than two years. During a conventional La Niña event, the seasonal cycle of surface temperature over Japan is known to be amplified (i.e. hotter summer and colder winter than normal years), but the influence of multiyear events on temperature over Japan has not yet been clarified. In this study, we evaluate the teleconnection associated with multiyear La Niña using composite analyses of observations, reanalysis data, and a large-ensemble of atmospheric general circulation model (AGCM) simulations for 1951-2010 driven by observed boundary conditions, and propose two distinct mechanisms involved in multiyear La Niña causing hot summers over Japan.  Composites of observational data show significant positive temperature anomalies over Japan in the boreal summer season preceding the two consecutive La Niña events reaching their mature phases. This robust summer signal can be reproduced by AGCM large ensemble simulations, which indicates that it is forced by multiyear La Niña. The time evolution of the anomalous summer temperature over Japan differs between the first and second years of multiyear La Niña. In the first summer, warm conditions are found in August–October in the southwestern part of Japan, due to anomalous southwesterly winds in the lower troposphere. This atmospheric circulation anomaly can be explained by a La Niña-induced decrease in precipitation over the equatorial western Pacific. In the second summer, warm anomalies are found in June–August over northeastern Japan, and these are accompanied by an anomalous barotropic high-pressure induced by negative precipitation anomalies over the equatorial Pacific. The seasonal march in atmospheric background states and the delayed effect of a preceding El Niño may explain the distinct teleconnection during multiyear La Niña.
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 1985

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
JUDT Falko KLOCKE Daniel RIOS-BERRIOS Rosimar VANNIERE Benoit ZIEMEN Florian AUGER Ludovic BIERCAMP Joachim BRETHERTON Christopher CHEN Xi DÜBEN Peter HOHENEGGER Cathy KHAIROUTDINOV Marat KODAMA Chihiro KORNBLUEH Luis LIN Shian-Jiann NAKANO Masuo NEUMANN Philipp PUTMAN William RÖBER Niklas ROBERTS Malcolm SATOH Masaki SHIBUYA Ryosuke STEVENS Bjorn VIDALE Pier Luigi WEDI Nils ZHOU Linjiong
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.2021-029, (Released:2021-01-21)

Recent progress in computing and model development has initiated the era of global storm-resolving modeling and with it the potential to transform weather and climate prediction. Within the general theme of vetting this new class of models, the present study evaluates nine global-storm resolving models in their ability to simulate tropical cyclones (TCs). Results show that, broadly speaking, the models produce realistic TCs and remove longstanding issues known from global models such as the deficiency to accurately simulate TC intensity. However, TCs are strongly affected by model formulation, and all models suffer from unique biases regarding the number of TCs, intensity, size, and structure. Some models simulated TCs better than others, but no single model was superior in every way. The overall results indicate that global storm-resolving models are able to open a new chapter in TC prediction, but they need to be improved to unleash their full potential.
著者
YAMADA Hiroyuki ITO Kosuke TSUBOKI Kazuhisa SHINODA Taro OHIGASHI Tadayasu YAMAGUCHI Munehiko NAKAZAWA Tetsuo NAGAHAMA Norio SHIMIZU Kensaku
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.2021-063, (Released:2021-07-01)

Upper-tropospheric aircraft reconnaissance was carried out for Typhoon Lan (2017) using a civil jet with a newly developed dropsonde system. This was the first case of a Japanese research group observing the inner core of an intense typhoon using dropsondes. This paper describes the warm-core structure in the eye and the associated thermodynamic and kinematic features of the eyewall. During two days of reconnaissance, this typhoon preserved its peak intensity in an environment with a strengthening vertical shear. Dropsondes captured a double warm-core structure with a higher perturbation temperature in the middle and upper troposphere, which persisted between the two flight missions. The two warm cores show a difference in the equivalent potential temperature (θe) of more than 10 K, suggesting different air origins. Saturation point analysis suggest that air observed in the upper warm core was entrained from the eyewall. The eyewall updraft in the left-of-shear semicircle had a two-layer structure with a higher θe and lower absolute angular momentum on the inner side of the updraft core. Analyses of the saturation point and parcel method suggest that the warmer air with a θe exceeding 370 K on the inner side of the updrafts originated from the eye boundary layer and was eventually transported into the upper warm core. These results led us to hypothesize that the vertical transport of high-θe air from the eye boundary layer contributed to the continuous eye warming in the upper troposphere against the negative effect of a strengthening environmental wind shear on the storm intensity. This study demonstrates the significance of eyewall-penetrating upper-tropospheric reconnaissance for monitoring the warm-core structure in the present situation where accurate measurements of both humidity and temperature for calculating θe can only be made with dropsonde-type expendables.
著者
STEVENS Bjorn ACQUISTAPACE Claudia HANSEN Akio HEINZE Rieke KLINGER Carolin KLOCKE Daniel RYBKA Harald SCHUBOTZ Wiebke WINDMILLER Julia ADAMIDIS Panagiotis ARKA Ioanna BARLAKAS Vasileios BIERCAMP Joachim BRUECK Matthias BRUNE Sebastian BUEHLER Stefan A. BURKHARDT Ulrike CIONI Guido COSTA-SURÓS Montserrat CREWELL Susanne CRÜGER Traute DENEKE Hartwig FRIEDERICHS Petra HENKEN Cintia Carbajal HOHENEGGER Cathy JACOB Marek JAKUB Fabian KALTHOFF Norbert KÖHLER Martin LAAR Thirza W. van LI Puxi LÖHNERT Ulrich MACKE Andreas MADENACH Nils MAYER Bernhard NAM Christine NAUMANN Ann Kristin PETERS Karsten POLL Stefan QUAAS Johannes RÖBER Niklas ROCHETIN Nicolas SCHECK Leonhard SCHEMANN Vera SCHNITT Sabrina SEIFERT Axel SENF Fabian SHAPKALIJEVSKI Metodija SIMMER Clemens SINGH Shweta SOURDEVAL Odran SPICKERMANN Dela STRANDGREN Johan TESSIOT Octave VERCAUTEREN Nikki VIAL Jessica VOIGT Aiko ZÄNGL Günter
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.2020-021, (Released:2020-01-28)
被引用文献数
32

More than one hundred days were simulated over very large domains with fine (0.156 km to 2.5 km) grid spacing for realistic conditions to test the hypothesis that storm (kilometer) and large-eddy (hectometer) resolving simulations would provide an improved representation of clouds and precipitation in atmospheric simulations. At scales that resolve convective storms (storm-resolving for short) scales, the vertical velocity variance becomes resolved and a better physical basis is achieved for representing clouds and precipitation. Similar to past studies we find an improved representation of precipitation at kilometer scales, as compared to models with parameterised convection. The main precipitation features (location, diurnal cycle and spatial propagation) are well captured already at kilometer scales, and refining resolution to hectometer scales does not substantially change the simulations in these respects. It does, however, lead to a reduction in the precipitation on the time-scales considered – most notably over the Tropical ocean. Changes in the distribution of precipitation, with less frequent extremes are also found in simulations incorporating hecto-meter scales. Hectometer scales appear more important for the representation of clouds, and make it possible to capture many important aspects of the cloud field, from the vertical distribution of cloud cover, to the distribution of cloud sizes, to the diel (daily) cycle. Qualitative improvements, particularly in the ability to differentiate cumulus from stratiform clouds, are seen when reducing the grid spacing from kilometer to hectometer scales. At the hectometer scale new challenges arise, but the similarity of observed and simulated scales, and the more direct connection between the circulation and the unconstrained degrees of freedom make these challenges less daunting. This quality, combined with an already improved simulation as compared to more parameterised models, underpins our conviction that the use and further development of storm-resolving models offers exciting opportunities for advancing understanding of climate and climate change.
著者
KATO Teruyuki
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.2020-029, (Released:2020-03-24)
被引用文献数
9

In Japan, localized heavy rainfall events producing accumulated three-hour precipitation amounts larger than 200 mm are often observed to cause severe landslides and floods. Such events are mainly brought by quasi-stationary band-shaped precipitation systems, named “senjo-kousuitai” in Japanese. Senjo-kousuitai is defined as a band-shaped heavy rainfall area with a length of 50-300 km and a width of 20-50 km, produced by successively formed and developed convective cells, lining up to organize multi-cell clusters, and passing or stagnating at almost the same place for a few hours. The formation processes of senjo-kousuitai are categorized mainly into two types; the broken line type in which convective cells simultaneously form on a quasi-stationary local front by the inflow of warm and humid air, and the back building type in which new convective cells successively forming on the upstream side of low-level winds linearly organize with pre-existing cells. In this study, previous studies of band-shaped precipitation systems are reviewed, and the numerical reproducibility of senjo-kousuitai events and the favorable conditions for their occurrence are examined. In a case of Hiroshima heavy rainfall observed in western Japan on 20 August 2014, the reproduction of the senjo-kousuitai requires a horizontal resolution of at least 2 km, which is sufficient to roughly resolve the formation and development processes of convective cells, while a resolution of 250-500 m is necessary to accurately reproduce their inner core structures. The 2-km model quantitatively reproduced the Hiroshima case when initial conditions 10 hours before the event were used, but the predicted amounts of maximum accumulated precipitation were considerably reduced as the initial time became closer to the occurrence time of the senjo-kousuitai. This reduction was brought from the excessive inflow of low-level dry air that shifted occurrence areas of new multi-cell clusters.  Six favorable occurrence conditions of senjo-kousuitai events for their diagnostic forecasts were statistically constructed from environmental atmospheric fields in previous localized heavy rainfall events. Two conditions of (1) large water vapor flux amounts (> 150 g m−2 s−1) and (2) short distances to the level of free convection (< 1000 m) were chosen representatively for the low-level water vapor field that is judged based on 500-m height data. Four other favorable conditions are selected; (3) high relative humidity at midlevels (> 60 % at 500 hPa and 700 hPa), (4) large vertical shear estimated from the storm relative environmental helicity (> 100 m2 s−2), (5) synoptic-scale ascending areas (400 km mean field at 700 hPa), and (6) the exclusion of warm air advection frequently appearing at 700-850 hPa and inhibiting the development of convection (i.e., an equilibrium level > 3000 m).
著者
SAITO Kazuo KUNII Masaru ARAKI Kentaro
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.2018-027, (Released:2018-02-11)
被引用文献数
5

Local heavy rainfall of about 100 mm h-1 occurred in Tokyo and Kanagawa Prefecture on 26 August 2011. This rain was brought by a mesoscale convective system (MCS) that developed near a stationary front that slowly moved southward. In an analysis using geostationary multi-purpose satellite rapid scan images and dense automated weather station networks, development of the MCS occurred after the merging of sea breezes from the east (Kashima-nada) and the south (Tokyo Bay). Numerical experiments by the Japan Meteorological Agency (JMA) nonhydrostatic model (NHM) with horizontal resolutions of 10 km and 2 km using mesoscale 4D-VAR analysis of JMA for initial conditions tended to predict the position of intense rainfall areas west of observed positions. In the mesoscale ensemble forecast using perturbations from JMA’s one-week global ensemble prediction system (EPS) forecast, some ensemble members showed enhanced precipitation around Tokyo, but false precipitation areas appeared north of the Kanto and Hokuriku Districts. As an attempt to improve the model forecast, we modified the model, reducing the lower limit of subgrid deviation of water vapor condensation to diagnose the cloudiness for radiation. In the modified model simulation, surface temperatures around Tokyo increased by about 1°C and the position of the intense precipitation was improved, but the false precipitation areas in the Hokuriku District were also enhanced in the ensemble member which brought a better forecast than the control run. We also conducted ensemble prediction using a singular vector method based on NHM. One of the ensemble members unstabilized the lower atmosphere on the windward side of the Kanto District and suppressed the false precipitation in the Hokuriku District, and observed characteristics of the local heavy rainfall were well reproduced by NHM with a horizontal resolution of 2 km. A conceptual model of the initiation of deep convection by the formation of a low-level convergence zone succeeding merging of the two sea breezes from the east and south is proposed based on observations, previous studies, and numerical simulation results. In this event, the northerly ambient wind played an important role on the occurrence of the local heavy rainfall around Tokyo by suppressing the northward intrusion of the sea breeze from the south.
著者
KAWABATA Yasuhiro YAMAGUCHI Munehiko
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.2020-042, (Released:2020-05-18)
被引用文献数
2 2

The effectiveness of the probability ellipse for tropical cyclone (TC) track forecasts is investigated with multiple ensembles from the Japan Meteorological Agency (JMA), the European Centre for Medium-Range Weather Forecasts, the U.S. National Centers for Environmental Prediction, and the Met Office in the United Kingdom. All TCs during the 3 years from 2016 to 2018 are included in the verification. We show that the multiple ensembles composed of these four global ensembles are capable of predicting the situation-dependent uncertainties of TC track forecasts appropriately in both the along-track and cross-track directions. The use of a probability circle involves the implicit assumption of an isotropic error distribution, whereas the introduction of the probability ellipse makes it possible to provide information as to which is more uncertain; the direction or the speed of TC movement. Compared to the probability circle adopted operationally at JMA, the probability ellipse can potentially reduce the area by 16, 15, and 24 %, on average, at forecast times of 3, 4, and 5 days, respectively. This indicates that narrowing warning areas of TC track forecasts by the probability ellipse enables us to enhance disaster prevention/mitigation measures.
著者
國富 信一
出版者
Meteorological Society of Japan
雑誌
氣象集誌. 第1輯 (ISSN:00261165)
巻号頁・発行日
vol.40, no.7, pp.en3-en6, 1921-07-10 (Released:2009-02-05)
被引用文献数
2 2
著者
Axel GABRIEL Dieter PETERS
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.86, no.5, pp.613-631, 2008 (Released:2008-11-13)
参考文献数
16
被引用文献数
19 35 26

The long-term behavior of Rossby wave breaking (RWB) events is investigated by a diagnosis separating in different asymmetric types of RWB, i.e., cyclonically sheared waves breaking predominantly pole-ward (P1) or equatorward (LC2) and anticyclonically sheared waves breaking predominantly poleward (P2) or equatorward (LC1). Generally, RWB can be identified by meridional overturning of potential vorticity (PV) on specific isentropes, but a separation in poleward or equatorward asymmetry is too difficult based on PV maps alone. For this paper, we use that northward or southward direction of the meridional wave flux component for quasi-stationary Rossby waves indicates cyclonically or anticyclonically sheared RWB. We demonstrate that the magnitude of the meridional wave fluxes gives a reliable measure of the asymmetric types of RWB when combining with PV diagnostics as well as with the geometry of large-scale diffluent/ confluent flow. Based on 45 winter periods of ECMWF Reanalysis (ERA-40), we found two pronounced regions for P1- and LC2-type events, over the northern North Pacific and the northern North Atlantic, and two extended belts of P2- and LC1-type RWB events, over the North Pacific/North America region and the North Atlantic/European-West Asian region. The results reveal that the long-term mean occurrence of poleward RWB is generally as large as that of equatorward RWB with local differences. Since poleward or equatorward RWB events influence different regions efficiently, e.g., by associated cut-off cyclones or anticyclones, the proposed diagnosis gives an important tool for interpreting long-term general circulation patterns and large-scale weather regimes.
著者
Youichi KAMAE Wei MEI Shang-Ping XIE
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.6, pp.411-431, 2017 (Released:2017-11-14)
参考文献数
76
被引用文献数
25

Eddy transport of atmospheric water vapor from the tropics is important for rainfall and related natural disasters in the middle latitudes. Atmospheric rivers (ARs), intense moisture plumes that are typically associated with extratropical cyclones, often produce heavy precipitation upon encountering topography on the west coasts of mid-latitude North America and Europe. ARs also occur over the northwestern Pacific and sometimes cause floods and landslides over East Asia, but the climatological relationship between ARs and heavy rainfall in this region remains unclear. Here we evaluate the contribution of ARs to the hydrological cycle over East Asia using high-resolution daily rainfall observations and an atmospheric reanalysis during 1958-2007. Despite their low occurrence, ARs account for 14-44 % of the total rainfall and 20-90 % of extreme heavy-rainfall events during spring, summer, and autumn. AR-related extreme rainfall is especially pronounced over western-to-southeastern slopes of terrains over the Korean Peninsula and Japan, owing to strong orographic effects and a stable direction of low-level moisture flows. A strong relationship between warm-season AR heavy rainfall and preceding-winter El Niño is identified since the 1970s, suggesting the potential of predicting heavy-rainfall risk over Korea and Japan at seasonal leads.
著者
YAMAZAKI Akira HONDA Meiji KAWASE Hiroaki
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.2019-012, (Released:2018-11-16)
被引用文献数
6

This study found that regional snowfall distributions in a Japan-Sea side area of Japan are controlled by intraseasonal jet variability, particularly the 10-day-timescale quasi-stationary Rossby waves across the Eurasian continent and the atmospheric blocking over the East Asian region. This study mainly focused on the Niigata area, which is representative of heavy snowfall areas in Japan. Based on previous studies, three types of dominant snowfall distributions were defined: 1) the plain (P) type, which is characterized by heavy snowfall events predominant in coastal regions of the Niigata area, 2) the mountain (M) type, which occurs in the mountainous regions, and 3) the PM type, which occurs across the whole Niigata area. Our results revealed that all distribution types were related to the south-ward shift of the westerly jet over Japan associated with an intensified trough, i.e., cyclonic anomalies, originating from quasi-stationary Rossby waves along westerly jets over Eurasia (Eurasian jets). The cyclonic anomalies were found to be also related to blocking cyclones because the frequency of blocking events considerably increased in the East Siberian region. The mechanisms leading to the trough intensification were different among the events of the three snowfall types. The formation of Siberian blocking with relatively different positions and different paths of quasi-stationary Rossby wave packet propagation along Eurasian jets were evident in the distribution types. Therefore, local-scale snowfall distributions in the Japan-Sea side area are determined by anomalous large-scale circulations, which can be evidently distinguished in the global reanalysis data.