著者

KIM Eun-Hee LEE Eunhee LEE Seung-Woo LEE Yong Hee

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.2019-056, (Released:2019-07-24)

被引用文献数

3

---

In this study, we evaluated the impacts of revised observation error on ground-based global navigation satellite system (GNSS) zenith total delay (ZTD) data in the data assimilation system of the Korea Meteorological Administration 1.5 km convective-scale model. Out of 100 total stations on the Korean Peninsula, 40 ground-based GNSS data stations were assimilated using three-dimensional variational (3D-Var) data assimilation. The ZTD observation errors were diagnosed for each station using a posteriori methods, giving errors with a variety of spatial and temporal characteristics. These station-specific error data were then implemented using the data assimilation system, and their impacts were evaluated for a one-month period in July 2016. The root-mean-square error (RMSE) of the relative humidity in the lower troposphere was found to be improved for the period from T+0 to T+36 hours when using GNSS data. Replacing the errors used in the previous model with the average diagnosed errors also provided better results, but they were not as good as the results obtained using station-specific errors. We found that observation error is closely related to precipitable water vapor (PWV); therefore, correction values reflecting seasonal characteristics should be applied. In addition, the quantitative precipitation forecasts were improved in all experiments using GNSS data, although the effects were small.

著者

Tomoaki OSE

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.97, no.5, pp.1041-1053, 2019 (Released:2019-10-09)

参考文献数

22

被引用文献数

4

---

In order to investigate the dependence of future projections for summertime East Asian precipitation on their present-day model climatology, the models well reproducing the observed climatology over East Asia are focused on in the analysis of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) future projections for the period from 2075 to 2099 under the Representative Concentration Pathway 8.5 global warming scenario. The future projection by these models indicates that summertime monthly climatological precipitation in future East Asia is more likely systematically decreased in some regions rather than evenly increased in every wet region.  The CMIP5 36-model ensemble mean monthly circulation change at 700hPa is characterized through the future summertime by a cyclonic circulation change to the south of Japan and the associated downward motion changes around Japan. The models showing the above features more clearly tend to simulate stronger westerlies over East Asia and more tropical precipitation in the present-day northern summer climatology. Therefore, an ensemble of the models reproducing the observed westerlies over East Asia, which are stronger than the 36-model ensemble mean, tends to simulate a strong downward motion change regionally in the future East Asian summer so that the possibility of a decrease in monthly precipitation is enhanced there against the “wet-getting-wetter” effect.  The future circulation change over East Asia was considered as part of the western North Pacific circulation change that responds to the future reduction of vertical motion in the vertically stabilized tropics. Large future reduction of the tropical vertical motion necessary for the strong downward motion change in East Asia can be attributed to the present-day climatology of much precipitation and large upward motion in the tropics.

著者

Akira T. Noda Hiroshi Niino

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.1, pp.5-8, 2005 (Released:2005-01-25)

参考文献数

17

被引用文献数

9 13

---

A major tornado spawned by a supercell is reproduced by a fine-resolution three-dimensional numerical simulation, and its genesis mechanism and structure are clarified. The tornado, which is associated with a maximum vertical vorticity of 0.85 s-1 and a pressure drop of 27 hPa, originates from one of the small-scale vortices on the gust front that forms between a warm moist environmental air and a rain-cooled air produced by the storm. Only the small-scale vortex that develops into a major tornado is located right under the low-level updraft associated with the low-level mesocyclone; the others that fail to develop are not. Several interesting previously-unexamined characteristics of the threedimensional structure of the simulated tornado vortex are also reported.

著者

LIU Boqi ZHU Congwen SU Jingzhi MA Shuangmei XU Kang

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.2019-047, (Released:2019-04-19)

被引用文献数

33

---

The northward shift of the western North Pacific Subtropical High (WNPSH) in July 2018 broke the historical record since 1958 and resulted in extreme heat waves and casualties across Northeast Asia (NEA). The present work associated this extreme WNPSH anomaly with the anomalies of barotropic anticyclone above NEA originating from the strongest positive tri-pole pattern of sea surface temperature anomaly (SSTA) in the North Atlantic in July. Both data analysis and numerical experiments indicated that the positive tri-pole SSTA pattern could produce an upper-tropospheric wave source over the Europe, which stimulated an eastward propagating wave train along the subpolar westerly jet over the Eurasian continent. When its anticyclonic node reached NEA, the WNPSH started to shift northward. After the cyclonic node in the circulation anomaly encountered the Tibetan Plateau, atmospheric diabatic heating was enhanced over the eastern Tibetan Plateau, initiating another subtropical wave train, which furthered the northward shift of the WNPSH. Therefore, the wave source over Europe was critical for the northward shift of the WNPSH in July, connecting the tri-pole SSTA pattern in the North Atlantic with the WNPSH anomaly and maintaining the downstream effects of thermal forcing over the eastern Tibetan Plateau on the East Asian summer monsoon.

著者

Teruyuki Kato Kohei Aranami

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.1, pp.1-4, 2005 (Released:2005-01-07)

参考文献数

7

被引用文献数

28 37

---

Localized, band-shaped heavy rainfall was observed over the Niigata-Fukushima area on July 13th 2004 and the over Fukui area on July 18th 2004. Both areas are located on the Japan-Sea side of the Japan Islands. These heavy rainfall events were a result of an intensification of convective instability over the Baiu frontal zone, induced by the inflows of low-level humid air and middle-level dry air. The middle-level air was considerably warm, not colder than the surrounding air. This indicates that the formation factors of heavy rainfall should be examined using convective instability, rather than potential instability.Numerical simulations using a cloud-resolving model with a horizontal grid of 1.5 km were carried out in an attempt to reproduce these heavy rainfall events. The Niigata-Fukushima heavy rainfall was reproduced well, while the Fukui heavy rainfall was not. This failure of the Fukui case could be the result of the uncertain analysis of the wind field over the Sea of Japan that determined the movement of low-level humid air. edevelopment of new observation systems over the sea, where upper-air sounding is seldom operated, are required to improve heavy rainfall predictions and to prevent such failures.

著者

Yan Nie Lijuan Li Yanli Tang Bin Wang

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-038, (Released:2019-09-23)

被引用文献数

11

---

External forcings among the different phases of the Coupled Model Intercomparison Project (CMIP) vary considerably, but their impacts have not been extensively investigated yet. This study compares the impacts of CMIP5 and CMIP6 forcings on model stability and the 20th-century global warming and El-Niño Southern Oscillation (ENSO) based on the Pre-Industrial control (PI-control) and historical runs of the Flexible Global Ocean–Atmosphere–Land System Model: Grid-point Version 2 (FGOALS-g2). Results indicate that CMIP6 forcings result in a larger climate drift and a lower climatological global average surface temperature (GAST) than those of CMIP5 in PI-control runs. In historical runs, stronger 20th-century warming trends occur during the periods 1910-1940 and 1970-2005 using CMIP6 forcings, which are closer to the HadCRUT than those of the CMIP5 forcings simulation. A stronger spurious warming trend in the CMIP6 results in an evolution of GAST that is less consistent with the HadCRUT dataset than that in the CMIP5 during 1940-1970. Among all forcings, GHGs and aerosol forcings play the dominant roles in differences in GAST, particularly in the Northern Hemisphere. In both the PI-control and historical runs, a larger ENSO amplitude and smaller seasonality are simulated in CMIP6 than in CMIP5.

著者

Abd. Rahman As-syakur Keiji Imaoka Kakuji Ogawara Manabu D. Yamanaka Tasuku Tanaka Yuji Kashino I Wayan Nuarsa Takahiro Osawa

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-039, (Released:2019-09-24)

被引用文献数

7

---

We analyzed 3-hourly Tropical Rainfall Measuring Mission multi-satellite analysis (TRMM 3B42) version-7 data for the 17-year period 1998-2014 to investigate seasonal and geographic characteristics of the diurnal rainfall cycle (DRC) over Sumatera, Indonesia. Dividing Sumatera into north, central, and south regions approximately perpendicular to the west coast, we point out for the first time early-afternoon initiation of daily rainfall not only in the Barisan Mountains but also in the east-coastal small islands (ECSIs) such as Bangka and Belitung. Westward and eastward migrations of rainfall areas from the Barisan Mountains are varied with seasons and regions, with the most remarkable being westward during September-October-November (SON) in the central region and the least remarkable occurring during June-July-August (JJA) in the southern region. In the central region, the DRC reaches a distance of ∼700 km off the west coast during SON and of only 200 km during March-April-May (MAM). The other westward migrations from the ECSIs in the central and southern regions (except for JJA) have been confirmed by 5-year hourly Multi-functional Transport Satellite-1R (MTSAT-1R) cloud-top data. The results shown in this paper suggest that the rainfall distribution with respect to coastal distance, varying geographically and seasonally.

著者

Kei YOSHIMURA Taikan OKI Nobuhito OHTE Shinjiro KANAE

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.82, no.5, pp.1315-1329, 2004 (Released:2004-12-17)

参考文献数

33

被引用文献数

56 85

---

This study investigated the dynamic motion of atmospheric water advection by an analytic method called colored moisture analysis (CMA), that allows for the estimation and visualization of atmospheric moisture advection from specific source regions. The CMA water transport model includes balance equations with the upstream scheme and, uses external meteorological forcings. The forcings were obtained from the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiments (GAME) reanalysis. A numerical simulation with 79 global sections was run for April to October 1998. The results clearly showed seasonal variations in advection associated with large-scale circulation fields, particularly a difference between rainy and dry seasons associated with the Asian monsoon. The paper also proposes a new definition of southwest Asian monsoon onset and decay, based on the amount of water originating from the Indian Ocean. Earliest onset occurs over southeastern Indochina around 16- 25 May. Subsequent onset occurs in India one month later. These results agree with previous studies on the Asian monsoon onset/end. The CMA provides a clearer, more integrated view of temporal and spatial changes in atmospheric circulation fields, particularly Asian monsoon activities, than previous studies that focused only on one or two distinct circulation features, such as precipitation or wind speed. Furthermore, monsoon transition in a specific year, 1998, first became analyzable, whereas the previous studies used climatologies.

著者

JIN Hao JIN Yi DOYLE James D.

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.2019-011, (Released:2018-11-12)

被引用文献数

2

---

Typhoon Nepartak was a category 5 tropical cyclone of 2016 and had significant societal impacts. It went through a rapid intensification (RI), with an increase of maximum wind speed of 51 m s-1 and a decrease of minimum sea level pressure of 74 hPa in 42 h. The real-time forecast from the Coupled Ocean/Atmosphere Mesoscale Prediction System – Tropical Cyclone (COAMPS-TC), starting from 1200 UTC 3 July, predicted the track and intensity reasonably well for Super Typhoon Nepartak and captured the storm’s RI process. Positive interactions among primary and secondary circulations, surface enthalpy fluxes, and mid-level convective heating are demonstrated to be critical for the RI. The storm structure variations seen from the simulated satellite infrared brightness temperature during RI bear considerable resemblance to the Himawari-8 satellite images, although the forecast inner core is too broad, presumably due to the relatively coarse resolution (5 km) used for the real-time forecasts at the time.

著者

SAITO Izumi GOTOH Toshiyuki WATANABE Takeshi

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.2019-049, (Released:2019-05-17)

被引用文献数

17

---

To consider the growth of cloud droplets by condensation in turbulence, the Fokker-Planck equation is derived for the droplet size distribution (droplet spectrum). This is an extension of the statistical theory proposed by Chandrakar and coauthors in 2016 for explaining the broadening of the droplet spectrum obtained from the ‘Π-chamber', a laboratory cloud chamber. In this Fokker-Planck equation, the diffusion term represents the broadening effect of the supersaturation fluctuation on the droplet spectrum. The aerosol (curvature and solute) effects are introduced into the Fokker-Planck equation as the zero flux boundary condition at R2=0, where R is the droplet radius, which is mathematically equivalent to the case of Brownian motion in the presence of a wall. The analytical expression for the droplet spectrum in the steady state is obtained and shown to be proportional to Rexp(-cR2), where c is a constant. We conduct direct numerical simulations of cloud droplets in turbulence and show that the results agree closely with the theoretical predictions and, when the computational domain is large enough to be comparable to the Π-chamber, agree with the results from the Π-chamber as well. We also show that the diffusion coefficient in the Fokker-Planck equation should be expressed in terms of the Lagrangian autocorrelation time of the supersaturation fluctuation in turbulent flow.

著者

LEE Meng-Tze LIN Pay-Liam CHANG Wei-Yu SEELA Balaji Kumar JANAPATI Jayalakshmi

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.2019-048, (Released:2019-05-10)

被引用文献数

15

---

In the present work, long-term (10 years) raindrop size distribution (RSD) measurements from Joss-Waldvogel Disdrometer (JWD) installed at National Central University (NCU, 24&deg58′6″N 121&deg11′27″E), Taiwan and vertical profile of radar reflectivity were used to analyze the variations in gamma parameters of six seasons (winter, spring, mei-yu, summer, typhoon, and autumn) and types of precipitation. The normalized gamma distribution of RSD revealed that the highest mean Dm (Mass-weighted average diameter) values occurred in summer, whereas the highest mean log10Nw (normalized intercept parameter) values were found in winter. Furthermore, most of the rainfall rate falling at less than 20 mm h-1 occurs in Northern Taiwan. In this study, we used radar reflectivity to differentiate between convective and stratiform systems. It was revealed that the mean Dm values are higher in convective systems, whereas the mean log10Nw values are higher in stratiform systems. The structure of RSD in stratiform systems remains constant in all seasons; however, convection is similar to maritime type. The microphysical characteristics that are responsible for different RSD features in different seasons and types of precipitation are illustrated with the help of contoured frequency by altitude diagrams of radar reflectivity.

著者

SONG Bin ZHI Xiefei PAN Mengting HOU Meiyi HE Chengfei FRAEDRICH Klaus

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.2019-050, (Released:2019-05-24)

被引用文献数

4

---

The turbulent heat flux is the main passageway for air–sea interactions. However, due to lack of long-term observations for the turbulent heat flux, it is difficult to investigate the mechanisms of coupled ocean-atmosphere variabilities, such as the Pacific Decadal Oscillation. We here reconstructed the long-term turbulent heat flux in the North Pacific for the period 1921–2014 based on observations in the International Comprehensive Ocean-Atmosphere Data Set–International Maritime Meteorological Archive. The sea surface temperature, air temperature, wind and humidity were used to reconstruct the turbulent heat flux using the Coupled Ocean–Atmosphere Response Experiment (COARE3.5) algorithm. The modified Fisher–Tippett distribution was employed to calculate the turbulent heat flux at each grid square, and then the missing values were further derived based on data interpolating empirical orthogonal functions (DINEOF). The reconstructed turbulent heat flux was shown to be in accordance with the commonly used short-term heat flux datasets. This reconstruction is further examined by comparison with the long-term data of twentieth century reanalysis from European Center for Medium-range Weather Forecasts twentieth century reanalysis (ERA-20C) and the 20th Century Reanalysis (20CR) dataset from National Oceanic and Atmospheric Administration. It displays a good agreement with the ERA-20C both in spatial and temporal scales, but some differences from the 20CR. By these examinations, the reconstructed turbulent heat flux can well reproduce the main features of the air-sea interaction in the North Pacific, which can be used in studies of the air-sea interaction in the North Pacific on multidecadal timescales.

著者

Suranjith Bandara KORALEGEDARA Chuan-Yao LIN Yang-Fan SHENG

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.97, no.4, pp.821-839, 2019 (Released:2019-08-02)

参考文献数

52

被引用文献数

3

---

In this present study, we analyzed the synoptic and mesoscale dynamics and underlying mechanism of an extreme rainfall and flood event that occurred in Sri Lanka between 14-17 May 2016, using the Weather Research and Forecasting Model simulations with a horizontal grid size of 3 km and observational data. This extreme rainfall event was associated with a low-pressure system (LPS) that originated over the Bay of Bengal in the Indian Ocean and passed over Sri Lanka. The observed maximum accumulation of rainfall during the event exceeded 300 mm at several weather stations on 15-16 May and it resulted in severe flooding and landslides, particularly in the western part of the island. The model closely simulated the timing of the initiation of the LPS and its development along the east coast of Sri Lanka. The model could capture the overall rainfall tendency and pattern of this event. Synoptic and mesoscale analyses indicated that this extreme rainfall event occurred as the cumulative effect of a sustained low-level convergence zone, generated by an enhanced westerly monsoon flow and the circulation of the LPS, alongside a continuous supply of high-magnitude moisture, strong vertical motion, and orographic effects of the Central Mountains of Sri Lanka. Model sensitivity experiments indicated that the rainfall over the western slope area of the mountains was enhanced by mountain lifting, whereas western coastal rainfall was reduced because the mountains blocked the northeasterly flow of the LPS.

著者

Hidekazu Matsueda Rebecca R. Buchholz Kentaro Ishijima Helen M. Worden Dorit Hammerling Toshinobu Machida

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-037, (Released:2019-09-06)

被引用文献数

5

---

We analyzed temporal variations of carbon monoxide (CO) in the upper troposphere from 30°N to 30°S observed using instruments aboard commercial airliner flights between Japan and Australia over the period 1993-2016. Here we focused on the CO variations in the Southern Hemisphere (SH) that showed a unique seasonal cycle with an increased CO around October-November every year. The seasonal CO peaks in the SH showed significant interannual variability (IAV), and are notably enhanced in strong El Niño years, especially 1997. The CO enhancements are proportionally associated with CO emissions from Indonesian fires, when compared to the Global Fire Emissions Database (GFED). The IAV of the CO peak anomalies relative to the mean seasonal cycle was assessed by a statistical regression model that uses a combination of multiple climate indices and their interaction terms. We found that over 80% of the CO IAV observed in the upper troposphere could be explained by the model. The largest anomaly in 1997 showed a different CO-climate relationship than the other periods, which could be due to amplification during synchronized climate modes, or include additional influence from other factors such as human activities.

著者

浅井 富雄

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.48, no.1, pp.18-29, 1970 (Released:2008-05-27)

参考文献数

18

被引用文献数

66 85

---

Boussinesq近似にもとづく摂動方程式を差分近似法により数値的に解いて,不安定成層の平面Couette流中で発現する熱対流の性状を調べた.まつ゜流れの安定性を擾乱の水平波長,Richardson数等について示す.一様なシヤーをもつ流れは一般に擾乱の発達を抑制する効果をもち,その効果は波長の短いほど,又流れに直角な方向の波長が平行な方向の波長に比して長い-transverseモード-ほど著しい。一方流れに平行な方向の波長が直角な方向の波長に比して長く-longitudinalモード-なるにつれシヤー流の抑制作用は減じ,,流れに完全に平行なroll状の対流はシヤーの抑制作用を全く受けず増幅率の最も大きい所謂preferredモードとなる.Rayleigh数が大きくなると,基本流の平均速度で伝播する不安定波の他に波長のより短い前者と違った伝播速度をもつ不安定波が現れるが,その増幅率は前者に比して小さい.これらは異る解法により得られたKuo(1963)その他の結論と一致する.以上の予備的調査にもとついて,平均流で移動する波長の長い不安定波(熱対流にとって主要なモード)の構造やそれに伴うエネルギー変換について考察する.対流による熱の鉛直輸送に伴う位置エネルギーから運動エネルギーへの転換の他に,水平運動量の鉛直輸送に伴い基本流と擾乱の間に運動エネルギーの変換が生ずる.特に運動量の鉛直輸送は擾乱の3次元構造に強く依存する.擾乱がtransverseモードの場合,水平運動量は基本流のシヤーに抗して輸送-counter gradient transfer-され,従って擾乱の運動エネルギーから基本流のそれに転換される.この極端な場合が基本流に平行な鉛直面内の2次元対流で,著者(1964)の数値実験はこの結果を裏づけている.他方3次元運動を伴うlongitudinalモードの擾乱はtransverseモードのそれとは逆に運動量を輸送する.即ち基本流から擾乱へ運動エルギーを転換する.そしてシヤー流中ではこのlongitudinalの3次元対流がpreferredモードである.

著者

SEGUCHI Takafumi IWASAKI Suginori KAMOGAWA Masashi USHIYAMA Tomoki OKAMOTO Hajime

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.2019-033, (Released:2019-02-04)

被引用文献数

1

---

In the summer of 2016, 14 cases of jumping cirrus (JC) were observed around the Kanto region in Japan by ground-based, visible-light cameras. The cameras were set at the summit of Mt. Fuji and National Defense Academy (Kanagawa, Japan), and 15-second time-lapse photography was continually taken for the period. The location and spatial scale of the JC were calculated by measurements using the photometry of background stars in the nighttime and the geostationary meteorological satellite Himawari-8 infrared imagery. The environmental conditions of the JC were also investigated using radiosonde and Himawari-8 visible and infrared measurements. Comparing our cases to the JC in the United States of America (USA) reproduced by a three-dimensional, non-hydrostatic cloud model from previous studies, their motions, morphology, spatial and temporal scales showed similarities, although the horizontal scale of the JC and the magnitude of the underlying convection was relatively smaller in our cases. The sounding by the radiosonde in the vicinity of the storms showed that 3 of the 14 cases reached the stratosphere. However, the hydration of the lower stratosphere was not supported by an analysis of the brightness temperature difference (BTD) between 6.2 and 10.4 µm measured by Himawari-8. The averaged wind shear across the range of the jumping heights above the anvil was -1.1 ms-1 km-1. The maximum value of the convective available potential energy (CAPE) of the 14 cases was 1384 Jkg-1, which is several times smaller than those of the thunderstorm cases observed in the USA in previous numerical JC studies. This indicates that JC occurs from the cumulonimbus anvil top even if the convection is relatively weak. The motion of JC observed by visible-light cameras shows that it can transport moisture above the tops of the anvils of convective clouds regardless of its altitude as cloud ice appears to be sublimated.

著者

ZHAO Haikun WU Liguang WANG Chao KLOTZBACH Philip J.

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.2019-039, (Released:2019-03-11)

被引用文献数

8

---

Most studies have focused on variations of tropical cyclone (TC) frequency, intensity, and track over the western North Pacific (WNP), while variability of WNP TC season onset date (TCSO) has been less studied. Recent research has indicated a close association between WNP TCSO and sea surface temperature (SST) over the tropical Indian Ocean and the tropical central-eastern Pacific. This study finds the relationship between TCSO and SST underwent an interdecadal change in the late 1990s, likely due to a climate shift that occurred around that time. An observed significant correlation between TCSO and SST before the late 1990s and has been insignificant since that time. It was confrimed by the fact that ENSO positively correlates at 0.46 with TCSO from 1965-1999 (significant at the 95 % level), while the correlation becomes insignificant (0.16) during 1998-2016. Further analysis suggests that the close association between TCSO and SST is robust only for major El Niño events, with consistently extreme late TCSO following major El Niños during the satellite era. Accompanying the decay of major El Niños, tropical equatorial easterly anomalies in the WNP are driven by a Matsuno-Gill-type response to the specific SST anomaly pattern over the tropical Indo-Pacific sector. This in turn induces an anomalous anticyclone, anomalous westerly vertical wind shear, reduced mid-level moisture and suppressed convection over the WNP basin – all of which are unfavorable for WNP TCs, resulting in delayed TCSO following major El Niño events. These inter-decadal changes in the inter-annual correlation between TCSO and ENSO are largely due to the changing influence of moderate El Niño events on TCSO before and after the late 1990s. This study improves understanding of the ENSO-TC relationship, which should aid seasonal outlooks of WNP TC activity.

著者

Ryo Onishi Daisuke Sugiyama

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.13, pp.235-239, 2017 (Released:2017-12-21)

参考文献数

15

被引用文献数

1 10

---

We have proposed a deep convolution neural network (CNN) approach for the accurate estimation of the cloud coverage (CC) from images captured by a consumer camera, i.e., snapshot pictures. This CNN can successfully estimate the CC to within the level of the inherent error in the training dataset. A segmentation-based method using a linear support vector machine (SVM) is shown to be unable to distinguish between water surfaces and the sky, while the present CNN can correctly distinguish between them, possibly because the CNN can understand the positioning of components in the images; the sky is over a water surface. The present CNN can also be applied to photo-realistic computer-graphic (CG) images from numerical simulations. Comparisons between the CNN estimates for camera images and for the CG images can provide useful information for data assimilation, and thus contribute to numerical weather forecasting. The CC is a sort of far-field (remote) information. The present CNN has the potential to allow consumer cameras to be used as remote weather sensors.

著者

FUJITA Mikiko SATO Tomonori YAMADA Tomohito J. KAWAZOE Sho NAKANO Masuo ITO Kosuke

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.2019-022, (Released:2018-12-17)

被引用文献数

4

---

We investigated extremely heavy precipitation that occurred around the Kinugawa River, Japan, in September 2015, and the probability of extreme precipitation occurrence, using data from a large ensemble forecast more than 1,000 members that were dynamically downscaled to 1.6 km horizontal grid spacing. The observed event was statistically rare among simulated cases and 3-day accumulated precipitation around the target area was equivalent to the 95th percentile among all simulated ensemble members. Our results show that this extreme precipitation event occurred under specific conditions: two coexisting typhoons at close proximity that produces a high atmospheric instability, and water vapor transport from the Pacific Ocean. We also assessed the probability of extreme precipitation in mountainous areas other than the Kinugawa River case. Heavy precipitation also occurred southwest of the Kinugawa River region due to two typhoons, similar to the Kinugawa River case. The tracks of these typhoons shifted marginally; however, there was a difference in the water vapor supplied to the area, causing heavy precipitation. The large-ensemble downscaled data used in this study hence enable us to evaluate the occurrence probability of a torrential rainfall event that was rarely observed, which may contribute to updating a disaster mitigating plan for possible similar disasters in future.

著者

OSE Tomoaki

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.2019-018, (Released:2018-12-07)

被引用文献数

10

---

Global warming experiments using three different 60 km-mesh atmospheric global circulation models are studied to characterize ensemble mean future changes in monthly East Asian precipitation for June to August. During the summer, wetting and drying effects due to changes in mean vertical motion play a key role in future precipitation changes, as does the “wet-get-wetter” effect due to increased moisture. The former processes are related adiabatically to the projected modification of 500 hPa horizontal atmospheric circulation, which is characterized by two cyclonic circulation anomalies extending over the eastern Eurasian Continent (C1) and the western North Pacific Ocean (C2) for each month. Over Japan, the western edge of C2 shifts from a region south of the Japanese Islands to northern Japan during June–August, representing a delayed northward movement or southward shift of the westerly jet over the western North Pacific in the future compared with the present-day climatology. Most regions of Japan lie within the northeasterly wind and associated downward motion zones of C2, leading to significant uncertainties in the future precipitation over Japan by the offset against the “wet-get-wetter” effect and possibly even a future decrease in precipitation. A wetter future climate is anticipated under weak subsidence or the upward vertical motion zone of C2, such as western Japan in August away from C2, and the Southwest Islands of Japan in June in the C2 southwesterly wind zone. Over the eastern Eurasian Continent, C1 is distributed mainly over northeastern China in June, central and southern China in July and August respectively. During these months, most of the eastern regions are located within the southwesterly-to-southeasterly wind zone of C1, indicating wet future conditions due to enhanced upward motion. This tendency drives a further increase in precipitation in future wetter East Asian climate via the “wet-get-wetter” effect and the increased evaporation.