著者

SHIBATA Kiyotaka SAI Ayano

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.2021-019, (Released:2021-01-13)

被引用文献数

2

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The surface meteorological data in Japan, beginning around the 1880s, archived by the Japan Meteorological Agency are analyzed focusing on the long–term trends and variations in humidity and temperature. It is found that the annual–mean temperature trend exhibits statistically significant warming of 1.0-2.5°C century−1 for most stations, while the annual–mean relative humidity shows significantly decreasing trend of −2 % to −12 % century−1 for most stations with small seasonality. On the other hand, the annual–mean mixing ratio trend displays a different spatial distribution compared to the temperature or relative humidity trend. In this study, three types of trends exist: significantly positive and negative values, and virtually zero. Significantly negative trends of about −0.2 to −0.3 g kg−1 century−1 are located approximately in the Pacific side of Honshu from the middle Tohoku through Shikoku to the eastern Kyushu. Significantly positive trends of about 0.2 to 0.4 g kg−1 century−1 are observed over Hokkaido, the western Japan along Sea of Japan, the western Kyushu, and the remote islands including Okinawa. The overall pattern is similar for other seasons except for most of the remote islands in winter. Empirical orthogonal function (EOF) analysis indicates that the linear trends in the annual–mean temperature and relative humidity can be almost explained by the nearly uniform persistent warming and drying of EOF–1 components. On the other hand, for the annual–mean mixing ratio, EOF–2 is almost identical with the linear trend component, although the fraction of EOF–2 (14 %) is much smaller than that of EOF–1 (49 %). In recent years from 1960 to 2018 the mixing ratio and temperature trends are very different from those in the longer period from the 1880s. The mixing ratio trend and the temperature trend increase on average from 0.0 to 0.5 g kg−1 century−1 and from 1.5°C to 2.5°C century−1, respectively.

著者

Ginaldi Ari Nugroho Kosei Yamaguchi Eiichi Nakakita Masayuki K. Yamamoto Seiji Kawamura

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.63-68, 2021 (Released:2021-04-13)

参考文献数

17

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High-resolution boundary layer radar (BLR) and wavelet are utilized to observe microscale downdraft-updraft combinations. High-resolution BLR can observe thermal activity that pushed the stable layer. During this thermal, a combination of downdraft-updraft was also observed. A detailed observation of this combination was conducted in this study. Using a 1-dimensional continuous wavelet transform with Paul wavelet, we could quantify this downdraft-updraft combination based on the height and period. Using this quantification and wavelet variance in different weather conditions, we showed the essential period from 0 to 0.25 min, 2 to 4 min, and 4 to 8 min of this microscale downdraft-updraft combination.

著者

Takeshi Horinouchi Yu Kosaka Hiroshi Nakamigawa Hisashi Nakamura Norihisa Fujikawa Yukari N. Takayabu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-019, (Released:2021-04-28)

被引用文献数

14

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A prolonged heavy rainfall event occurred in Kyushu in early July 2020. Its large-scale environmental factors are investigated with observational and reanalysis data. Seven-day precipitation and moisture flux convergence around Kyushu were the greatest among the last 30 years. This pronounced convergence was maintained by nearly steady moisture influx, and the persistent upper-level trough to the northwest enhanced the ratio of moisture convergence to the influx. The magnitude of instantaneous moisture flux, however, was not particularly large among those along the subtropical jet axis or the Meiyu-Baiu rainband. What made this event unique is the persistence of the moisture flux peak anchored around Kyushu under the influence of the Silk-Road teleconnection. In June 2020, three upper-level troughs, whose easternmost one corresponding to the aforementioned trough, tend to form along the subtropical Asian jet. This wave train was persistent in the month and lasted until mid-July, 2020. Our analysis suggests that, prior to the rainfall event, the Silk-Road teleconnection was intensified through an interaction with a wave train at subpolar latitudes, which involves nonlinear processes including trough cut-off.

著者

Takumi Honda Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-018, (Released:2021-04-23)

被引用文献数

1

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In July 2018, record-breaking heavy precipitation caused catastrophic disasters in west Japan. This study investigated the predictability of this precipitation event using a regional ensemble data assimilation system. A series of daily ensemble forecast experiments showed that the forecast ensemble spread during the heavy precipitation event increased in the forecasts initialized on July 1 and July 3. The first peak of the forecast ensemble spread was associated with the uncertain track forecast of Typhoon Prapiroon. Namely, about a half of the ensemble members predicted eastward recurvature of the typhoon, whereas the other members predicted that the typhoon stayed near China. The later peak was associated with the southern convective disturbances near the Ryukyu Islands. Composite analysis and ensemble-based correlations showed that more active convective activities corresponded to a stronger cyclonic circulation and pushed the main precipitation band northward. The results implied that Prapiroon and the southern convective disturbances played important roles in the July 2018 heavy rain event and largely contributed to its predictability.

著者

FENG Lujia ZHANG Tengfei KOH Tieh-Yong HILL Emma M.

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.2021-026, (Released:2021-01-15)

被引用文献数

3

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Using data from the Sumatran GPS Array in Indonesia–a hero network in tectonic and earthquake studies–we study the summer intra-seasonal variability of precipitable water vapor (PWV) over Sumatra in years without strong inter-annual variability. Unlike most other studies that use external meteorological data to derive PWV from GPS (Global Positioning System) signal delays, we use the zenith wet delay (ZWD) time series estimated from a regular geodetic-quality processing routine as a proxy for PWV variations without using auxiliary meteorological data. We decompose the ZWD space-time field into modes of variability using rotated Empirical Orthogonal Function (EOF) analysis, and investigate the mechanisms behind the two most important modes using linear regression analysis both with and without lags. We show that the summer intra-seasonal variability of daily ZWD over Sumatra in 2008, 2016, and 2017 is dominated by the South Asian Summer Monsoon, and further influenced by dry-air intrusions associated with Rossby waves propagating in the Southern Hemisphere midlatitudes. Both active South Asian monsoons and dry-air intrusions contribute to the dryness over Sumatra during northern summer. Our results indicate an intra-seasonal connection between the South Asian and western North Pacific Summer Monsoons: when the South Asian monsoon is strong, it pumps atmospheric water vapor over the eastern Indian Ocean to feed into the western North Pacific monsoon. We also show a tropical-extratropical teleconnection where PWV over the southern Maritime Continent can be modulated by the activity of eastward-traveling Rossby waves in the southern midlatitudes. Our case study demonstrates the use of regional continuously operating GPS (cGPS) networks for investigating atmospheric processes that govern intra-seasonal variability in atmospheric water vapor.

著者

Koichi Watanabe Liu Yang Satoru Nakamura Takuya Otani Kenzaburo Mori

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-017, (Released:2021-04-21)

被引用文献数

3

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Aerosol number concentrations and trace gases (SO2, O3, HCHO, and H2O2) were measured over Imizu City, Toyama Prefecture, Japan on August 5, 2020, from a helicopter. The concentrations of fine particles (0.3-0.5 μm) were high at ground level and at an altitude of approximately 1200 m due to the volcanic plume from Nishinoshima. However, concentrations of aerosol particles were low at an altitude of approximately 2400 m. The volcanic plume did not significantly affect the lower free troposphere. High concentrations of SO2 were also observed. The H2O2 concentrations (0.27-0.56 ppb) were much lower than those during previous observations in the summer (2.0-6.7 ppb) and significantly lower than the SO2 concentrations (1.8-3.3 ppb). The concentrations of HCHO (2.1-2.5 ppb) were higher than those of H2O2. The oxidation of S(IV) to H2SO4 in cloud water might have been suppressed over the studied area.

著者

Yuta Katsuyama Masaru Inatsu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.35-40, 2021 (Released:2021-02-25)

参考文献数

24

被引用文献数

2

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This study developed a volume scan-type disdrometer and investigated the size distribution of solid-precipitation particles observed by flux- and volume-scan type disdrometers, installed in 2016-2017 winter in Sapporo, Japan. The former disdrometer detected particles, by line sensors, of which frequency is proportional to the particle number per area. On the other hand, the latter directly observed the particle number per volume using an image sensor. The flux-scan data are known to have the bias of more frequency in higher-speed (or larger-size) particles, but this bias was hardly corrected due to the error of estimated particles' velocity. It was first validated that the volume scan-type disdrometer could observe particle size between 0.5 mm and 13 mm, consistently with the flux scan-type one. Then, we examined how many events showed the difference of the size distribution between the two disdrometers with the Kolmogorov-Smirnov test. The result showed that 84% of the total events examined fell into the class where they were significantly different, partially due to fast-falling graupels.

著者

Satoshi Iizuka Ryuichi Kawamura Hisashi Nakamura Toru Miyama

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17A, no.Special_Edition, pp.21-28, 2021 (Released:2021-02-23)

参考文献数

19

被引用文献数

11

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Typhoon Hagibis (2019) caused widespread flooding and damage over eastern Japan. The associated rainfall maxima were primarily observed on the windward mountain slopes along with the west of the leading edge of a low-level front. Concomitantly, a significant positive value in sea surface temperature anomalies (SSTAs) was observed in association with an ocean eddy over the Oyashio region, together with anomalous warmth over the entire western North Pacific. The present study examines the role of the SSTAs in the rainfall distribution associated with Hagibis, to deepen our understanding of the influence of the midlatitude ocean on tropical cyclones and associated rainfall. Our sensitivity experiments demonstrate that the observed warm SSTAs had the potential to displace the rainfall caused by Hagibis inland and thereby acted to increase precipitation along the Pacific coast of northeastern Japan. Our results suggest that midlatitude SSTAs on ocean-eddy scales can also influence the synoptic-scale atmospheric front and associated heavy rainfall.

著者

水野 量

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.70, no.1, pp.115-121, 1992 (Released:2007-10-19)

参考文献数

37

被引用文献数

13 13

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日本列島の150地点における地上気象観測データを用いて、あられ降水の統計的特徴を調べた。1971-1986年の全国150地点の地上気象観測によると、あられ日数は冬期の東北•北陸地方の日本海沿岸で卓越している。また、1982-1986年のデータから、この地域の1月のあられによる降水量は少なくとも月降水量の1/4~1/3であると推定された。以上のあられ降水の統計分析から、日本列島におけるシーディングポテンシャルが議論された。

著者

大泉 伝 斉藤 和雄 Le DUC 伊藤 純至

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.98, no.6, pp.1163-1182, 2020 (Released:2020-12-17)

参考文献数

34

被引用文献数

5

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数値気象予測モデルの要素が豪雨のシミュレーションに与える影響を調べるため、広い領域を対象とした超高解像度実験を2014年8月の広島の豪雨事例で行った。本研究はPart 1 の2013年10月伊豆大島での研究に続くものであり同様の実験を行った。これらの研究から豪雨のシミュレーションにおいて広い領域で高解像度モデル(解像度500m以下)を用いる有用性を示した。 広島の事例では降水帯の位置や強度はモデルの解像度に影響を受けることがわかった。解像度2kmの実験では降水帯は再現されたがその位置は北東にずれていた。解像度500mと250mの実験ではこの降水帯の位置ずれは軽減された。最も降水帯の位置と強度をよく再現したのは解像度250mの実験であった。降水帯に対する境界層スキームの影響は小さく、この点は伊豆大島の事例と異なっていた。 本研究では対流コア数のモデル解像度依存性についても調査した。モデルの解像度に対する対流コア数の変化率は解像度500mで小さくなる事がわかった。この結果は、対流コア数は解像度500mより高解像度になると収束する可能性を示す。

著者

Koichi Shiraishi Takashi Shibata

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-005, (Released:2021-01-25)

被引用文献数

2

---

Stratospheric aerosols over the high Arctic at Ny Ålesund, Svalbard (79°N, 12°E) were observed continuously for four years from March 2014 by a lidar system using the second harmonic wavelength (532 nm) of the Nd:YAG laser. Our observations reveal the seasonal features of stratospheric aerosols and the arrival of the smoke at the high Arctic from Canadian forest-fire in August 2017. We estimated the seasonal variation for three years before the Canadian forest-fire when there was no apparent volcanic effect. In the estimation, we removed polar stratospheric clouds by the threshold temperature of their formation. The seasonal variation for the three years is that the vertical profiles of the backscattering ratio take a maximum value of about 1.05-1.06 at altitudes between 13 and 16 km from December to March, and about 1.02-1.04 at altitudes between 17 and 20 km from April to November. These results are compared with the results observed at the low Arctic, northern Norway. We also present the increases in the backscattering ratio and the volume depolarization ratio from September to December 2017 caused by the smoke from the Canadian forest-fire.

著者

Akiyoshi Wada Johnny C. L. Chan

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.17A-005, (Released:2021-01-11)

被引用文献数

9

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In the 2019 tropical cyclone season in the western North Pacific, Typhoons FAXAI and HAGIBIS made landfall in Japan while keeping the intensity, resulting in serious disasters. This study addresses the influences of an increasing trend and variations in the upper ocean heat content above 26°C (tropical cyclone heat potential: TCHP) from January 1982 to June 2020 on FAXAI and HAGIBIS. TCHP underneath FAXAI and HAGIBIS in 2019 was higher than the climatological mean except for a part of mature phase of HAGIBIS due to HAGIBIS-induced sea surface cooling. TCHP significantly increased with the interannual oceanic variations (IOVs) in the subtropical (15-20°N, 140-150°E) and midlatitude (30-35°N, 130-140°E) areas where FAXAI and HAGIBIS intensified or kept the intensity. From an empirical orthogonal function (EOF) analysis of TCHP, we demonstrate that the leading three EOF modes of TCHP explains approximately 76.8% of total variance, but the increase in TCHP along the tracks of FAXAI and HAGIBIS particularly in the early intensification of HAGIBIS cannot be explained only by the IOVs included in the leading three EOF modes but rather by the warming trend irrespective of the IOVs.

著者

NAYAK Sridhara TAKEMI Tetsuya

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.2019-003, (Released:2018-10-29)

被引用文献数

13 27

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Typhoons are considered as one of the most powerful disaster-spawning weather phenomena. Recent studies have revealed that typhoons will be stronger and more powerful in a future warmer climate and be a threat to lives and properties. In this study, we conduct downscaling experiments of an extreme rain-producing typhoon, Typhoon Lionrock (2016) in order to assess the impacts of climate change on resulting hazards by assuming pseudo global warming (PGW) conditions. The downscaled precipitations over the landfall region in the present climate condition agree well with the Radar- Automated Meteorological Data Acquisition System (Radar-AMeDAS) observations. A typhoon track in the future climate similar to that in the present climate is successfully reproduced, with a stronger wind speed (by ~20 knots) and lower central pressure (by ~20 hPa) under the PGW condition. The changes in precipitation amounts associated with the typhoon under PGW condition are analyzed over 7 individual prefectures in the northern part of Japan. The typhoon in the warming climate produces more precipitation over all prefectures. Iwate, Aomori, Akita, Miyagi and Hokkaido are projected to have relatively more precipitation associated with the typhoon in the warming climate. The overall analysis suggests that Typhoon Lionrock under PGW may increase the risk of flooding, damages to infrastructures, and lives staying along the typhoon track.

著者

Kosuke Ito Hana Ichikawa

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17A, no.Special_Edition, pp.1-6, 2021 (Released:2021-01-01)

参考文献数

18

被引用文献数

7

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One of the remarkable environmental characteristics of tropical cyclone (TC) Hagibis (2019) was the positive sea surface temperature (SST) anomaly observed in the western North Pacific Ocean. In this study, an ensemble-based sensitivity experiment was conducted with a nonhydrostatic model, focusing on the impact of SST on TC motion. The TC with the analyzed SST (warm run) moved faster near mainland Japan than with the lowered SST (cold run), as the TC in the warm run was embedded earlier in the mid-latitude westerly jet located to the north than that in the cold run. The TC displacement was consistent with the large decrease of geopotential height at 500-hPa (Z500) in the north of TC Hagibis during the warm run. Further investigation showed that the approach to the westerly jet presumably induced the low local inertial stability as well as the southwesterly vertical wind shear enhancing the upward mass flux in the north of the TC. They led the enhanced upper-tropospheric northward outflow from the TC energized by the warm SST, and it resulted in the decrease of the Z500 in the north. This study suggests that warm SST can affect TC tracks through interaction with mid-latitude westerly jets.

著者

Lusha Wang Ayumi Kotani Takafumi Tanaka Takeshi Ohta

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.259-264, 2020 (Released:2020-12-24)

参考文献数

20

被引用文献数

1

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Based on the drought severity index (DSI), which is derived from the ratio of evapotranspiration (ET) to potential evapotranspiration (PET) and normalized difference vegetation index (NDVI), as measured by remote sensing, we replaced the ET/PET ratio with soil moisture (0-10 cm) to establish an improved index (IDSI) and evaluated the drought situation in Inner Mongolia. The two components in IDSI are independently derived; however, the effects of evapotranspiration are contained in the soil moisture, and even precipitation changes could be reflected. We used monthly IDSI data for Inner Mongolia to evaluate drought throughout the growing season (May–September) during 2001-2010. The IDSI showed that 2001, 2007, and 2009 were years with significant drought. Areas that experienced extreme drought were less extensive than those found by the DSI because we removed the ET/PET component, which already contains the effects of the NDVI. IDSI results not only contained the degree of precipitation change for a given month through soil moisture, but also reflected the influence of water and heat in the previous month through the NDVI. Moreover, IDSI results were generally consistent with agricultural drought disaster records.

著者

Yu Li Shuqing Ma Ling Yang Xiaoqiong Zhen Dan Qiao

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.252-258, 2020 (Released:2020-12-23)

参考文献数

28

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Array weather radar (AWR), a kind of distributed phased array radar, includes at least three Phased Array Front Ends (PAFE). Every three PAFEs are grouped for synchronous scanning to ensure that the Data Time Difference (DTD) at the same point in the fine detection area is less than 2 s. This paper adopts the multiple-Doppler wind synthesis method to synthesize the wind field of the small-DTD AWR data and discusses the sensitivity analysis on the wind fields under the different DTDs. The analysis experiment includes the wind fields under two types of precipitation systems. One is a convective precipitation system with unstable airflow, and the other is a non-convective precipitation system with stable airflow. The statistical analysis showed that, due to the advection effect and intrinsic evolution of the precipitation systems, the bigger the DTD is, the bigger the wind field error is. When the DTD is greater than 24 s, the wind field obtained by the convective precipitation system has more errors. When the DTD is greater than 84 s, the wind field obtained by the non-convective precipitation system has more errors.

著者

Tomoe Nasuno

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-003, (Released:2020-12-23)

被引用文献数

1

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Relationship between diurnal convection and the intraseasonal oscillation (ISO) over the western Maritime Continent (MC) was investigated by a case study of an ISO event that occurred during the Years of the Maritime Continent (YMC)-Sumatra 2017 campaign. Two sets of global cloud-permitting simulations using cloud microphysics settings for ISO prediction (CTL) and for climate simulation (MOD) were performed to clarify their impacts. CTL had biases of weaker diurnal variation and smaller precipitation amounts over land than in observations; these were reduced in MOD by higher probabilities of local intense convection in the middle troposphere and higher precipitation efficiency. The enhanced convection over land coincided with suppressed convection over the surrounding ocean, especially at the diurnal peak time of land convection. Exception is the onset period of the ISO convection, when upward moisture advection and precipitation increased also over ocean in MOD than in CTL at the diurnal peak time of oceanic convection. These results suggest that the enhancement of local convection over the MC by the cloud microphysical processes basically hinder the ISO convection by the activation of land convection, but it also favors the ISO convection development over ocean during the onset period.

著者

Sridhara NAYAK 竹見 哲也

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.98, no.6, pp.1147-1162, 2020 (Released:2020-12-12)

参考文献数

59

被引用文献数

12

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極端降水の振る舞いを説明する上でのクラウジウス-クラペイロン(CC)スケーリングの有用性について、現在気候および疑似地球温暖化(PGW)条件で調べた。日本で発生した最近の2つの極端降水イベント、すなわち2017年7月5~6日の九州北部での豪雨および2018年7月5~8日の四国での豪雨を対象として、格子解像度1 kmでの領域気象シミュレーションにより解析した。数値シミュレーションにはWeather Research and Forecasting(WRF)モデルを用い、モデルデータは1時間間隔で格子点毎の値として出力し、解析に用いた。極端に強い降水の発生頻度とその強度は、時間雨量強度で評価すると、2つのイベントともに、PGW条件下で増大する。極端に強い降水(> 50 mm h-1)は、現在気候条件では気温22℃に上がるまでCCスケーリングにしたがい、PGW条件では24℃の気温に上がるまでCCスケーリングにしたがう。降水と気温の関係において、極端降水のピーク強度は、現在気候条件では25℃で約140 mm h-1であり、一方、PGW条件では 27℃で約160 mm h-1となる。極端降水の気温に対する増加率は、現在気候条件では約3% ℃-1であり、PGW条件では約3.5% ℃-1であることが分かった。将来の温暖化気候におけるピーク降水強度の増加と気温に対する降水量の増加率は、気温減率の減少にもかかわらず、大気中の水蒸気および不安定エネルギーが増加することに起因する。著者の知る限りでは、本研究の結果は、事例解析ではあるものの、極端降水に対するCCスケーリングについて定量的に調べた最初の取り組みであると言える。

著者

Sachie Kanada Hidenori Aiki Kazuhisa Tsuboki Izuru Takayabu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.17A-003, (Released:2020-12-16)

被引用文献数

8

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Numerical experiments on Typhoon Trami (2018) using a regional 1-km-mesh three-dimensional atmosphere–ocean coupled model in current and pseudo-global warming (PGW) climates were conducted to investigate future changes of a slow-moving intense typhoon under the warming climate. Over the warmer sea in the PGW climate, the maximum near-surface wind speed rapidly increased around the large eye of the simulated Trami. The stronger winds in the PGW simulation versus the current simulation caused a 1.5-fold larger decrease of sea surface temperature (SST) in the storm core-region. In the PGW climate, near-surface air temperature increased by 3.1°C. A large SST decrease due to ocean upwelling caused downward heat fluxes from the atmosphere to the ocean. The magnitude of the SST decrease depended strongly on initial ocean conditions. Consideration of the SST decrease induced by an intense typhoon, and a slow-moving storm in particular, indicated that such a typhoon would not always become more intense under the warmer climate conditions. An atmosphere–ocean coupled model should facilitate making more reliable projections of typhoon intensities in a warming climate.

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.