著者
WANG Jingyu HOUZE Jr. Robert. A. FAN Jiwen BRODZIK Stacy. R. FENG Zhe HARDIN Joseph C.
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.2019-058, (Released:2019-08-06)

The Global Precipitation Measurement (GPM) core observatory satellite launched in 2014 features more extended latitudinal coverage (65°S-65°N) than its predecessor Tropical Rainfall Measuring Mission (TRMM, 35°S-35°N). The Ku-band radar onboard of the GPM is known to be capable of characterizing the 3D structure of deep convection globally. In this study, GPM’s capability for detecting mesoscale convective systems (MCSs) is evaluated. Extreme convective echoes seen by GPM are compared against an MCS database that tracks convective entities over the contiguous US. The tracking is based on geostationary satellite and ground-based Next Generation Radar (NEXRAD) network data obtained during the 2014-2016 warm seasons. Results show that more than 70 % of the GPM-detected Deep-Wide Convective Core (DWC) and Wide Convective Core (WCC) objects are part of NEXRAD identified MCSs, indicating that GPM-classified DWCs and WCCs correlate well with typical MCSs containing large convective features. By applying this method to the rest of the world, a global view of MCS distribution is obtained. This work reveals GPM’s potential in MCS detection at the global scale, particularly over remote regions without dense observation network.
著者
TAKEMURA Kazuto MUKOUGAWA Hitoshi
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.2020-010, (Released:2019-12-01)

This study investigates a new possible process linking the quasi-stationary Rossby wave propagation (SWP) over Eurasia along the Asian jet and the Pacific-Japan (PJ) pattern through the Rossby wave breaking (RWB) near the jet exit region during boreal summer using a reanalysis dataset. To assess the statistical significance of the process, we conduct a lag composite analysis of the past 44 RWB events east of Japan. The result of the lag composite analysis shows that the SWP along the Asian jet induces the RWB accompanied by an amplified anomalous anticyclone east of Japan. The associated “inverse-S” shaped overturning of the upper-level potential vorticity (PV) distribution causes the southwestward intrusion of the high PV toward the subtropical western North Pacific (WNP). The Q-vector diagnosis and vorticity budget analysis indicate that the upper-level positive vorticity advection associated with the RWB is an important factor dynamically inducing ascent and reinforcing convection over the subtropical WNP, which in turn excites the subsequent PJ pattern. Classification of the cases by RWB strength indicates that the stronger RWB is significantly related to the stronger preceding SWP and subsequent enhanced PJ pattern, and vice versa. A partial correlation analysis of all the cases quantitatively shows the greater contribution of the upper-level positive vorticity advection over the subtropical WNP to the enhanced convection in this area and the formation of the PJ pattern, compared to that of the anomalous warm sea surface temperature condition. These results show that the SWP along the Asian jet can excite the PJ pattern, through the RWB east of Japan and the consequent intrusion of the high PV toward the subtropical WNP.
著者
TOMITA Tomohiko SHIRAI Taiga YAMAURA Tsuyoshi
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.2020-011, (Released:2019-11-30)

In general, La Niña (LN) events are longer than El Niño (EN) events. Using objective analysis data, we herein investigated the effects of the Australian winter monsoon (AWM) on prolonging LN events. Conventionally, EN events are terminated through the eastward shift of the anomalous Walker circulation in the equatorial Pacific during March–August. In contrast, the stronger-than-usual AWM induced by the LN anchors the upflow branch of anomalous Walker circulation in the Indonesian maritime continent (IMC). The strength of the AWM is controlled by the surface temperature difference between the IMC and the northern Australian continent (NAC). The LN has a large impact on the decrease in surface temperature on the NAC through decrease of the downward surface short-wave radiation flux and increase in surface soil moisture on the NAC. In LN events, the strength of the AWM and the anomalous Walker circulation reinforce each other through the common convective ascending in and around the IMC, which may be termed LN–AWM feedback, prolonging the duration of LN events. During EN events, such feedback is weak so that EN events generally end in the period of March–August.
著者
QIN Zhengkun ZOU Xiaolei
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.2019-064, (Released:2019-09-13)

The Tibetan Plateau (TP) and the atmospheric conditions over it strongly affect downstream regional weather. Advanced Microwave Sounding Unit-A (AMSU-A) brightness temperature observations provide temperature sounding information and have been long assimilated successfully for numerical weather prediction. AMSU-A brightness temperatures observed from the polar-orbiting NOAA-15 and -18 satellites in July and August 2016 were collected. During these months, the equator crossing time of these particular satellites was around 0600 local time. Observations collected within the three-hour periods centered at 0000 UTC and 1200 UTC, covering the TP, were assimilated. The weighting coefficients for mid-tropospheric AMSU-A channels 6 and 7 were significantly reduced over areas with terrain heights greater than 2 km and 4 km, respectively, in the National Centers for Environmental Prediction Gridpoint Statistical Interpolation system. The assimilation of AMSU-A observations was improved to better exploit the role of AMSU-A channels 6 and 7 over the TP. This was achieved by not decreasing the weighting coefficients of the two channels over the grassy surface of the TP’s high terrain so that they were consistent with the inverse error variances. This modification produced larger positive impacts of satellite data assimilation on the 48-h forecasts of the mid-tropospheric trough, water vapor, and quantitative precipitation forecasts downstream of the TP. This study also suggests the importance of having AMSU-A observations from early-morning satellite orbits for numerical weather prediction downstream of the TP.
著者
UMEZAWA Taku ANDREWS Stephen J. SAITO Takuya
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.2020-007, (Released:2019-11-10)

Although methane plays an important role in climate change and atmospheric chemistry, its global budget remains quantitatively uncertain due mainly to a wide variety of source types. The stable carbon isotope ratio of atmospheric methane (δ13C-CH4) is useful for separating contributions of different source categories, but due to the complex and laborious analysis, limited measurement data exists. We present a new system for δ13C-CH4 measurement, optimized for the automated analysis of air samples. Although the system is designed in principle similarly to those in previous studies, we successfully set up the system with no use of cryogens (e.g. liquid nitrogen) and attained reproducibility sufficient to analyze atmospheric variations (∼ 0.1 ‰). We performed automated continuous measurements of ambient air outside our laboratory at about hourly intervals for 2 months, which characterized imprint of local methane sources well. Future measurement operation for flask air samples from existing atmospheric monitoring programs will provide a large number of atmospheric δ13C-CH4 data.
著者
HA Kyung-Ja YEO Ji-Hye SEO Ye-Won CHUNG Eui-Seok MOON Ja-Yeon FENG Xuelei LEE Yang-Won HO Chang-Hoi
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.2020-009, (Released:2019-11-16)

In 2018, heatwaves (HWs), which are defined as period of abnormally hot weather with the daily maximum temperature (T_Max) exceeding its 95th percentile threshold for at least three consecutive days, were prevalent during June to August, and temperature records were broken in many countries over East Asia (EA) including China (CH), Japan (JP), and the Korean Peninsula (KP). In particular, extreme HWs through July to August lasted for the longest duration with 21.3 days with T_Max reaching 36.9°C. The highest T_Max, recorded since 1907, exceeded to 41°C in Hongcheon, located east of Seoul in the KP. Here, we examine the factors that influenced the 2018 HW, and how these relate to the 1994 HW, which was second longest HW recorded in the KP. The results show that abnormally strong and northwestward extended anticyclone features observed in July 2018 lasted as a persistent North Pacific anticyclone anomaly until August 2018 centered at the northern KP. These anticyclone features subsequently formed as a modon-like blocking with a cyclonic anomaly in the East China Sea. Meanwhile, in August 1994, the North Pacific High (NPH) extended to eastern EA, which broked the meridional dipole structure and HWs do not persist. The NPH, which persisted till August 2018, was accompanied by a sinking motion, suppression of precipitation, anomalous maximum temperature, weakening of the westerly jet stream, and increased insolation due to clear sky. We find that the prolonged and northwestward-shifted NPH including the KP drove the extraordinarily hot 2018 summer in Korea. In addition, low precipitation and massive evapotranspiration with the persistent insolation in July 2018 influenced the dry condition at the surface. We suggest that the predictions for the location and duration of the NPH associated with the HWs are required to reduce heat-related mortality and the impact on agriculture due to excessive evapotranspiration.
著者
LIN Yu-Feng WU Chun-Chieh YEN Tzu-Hsiung HUANG Yi-Hsuan LIEN Guo-Yuan
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.2020-006, (Released:2019-11-10)

Using special data from the field program of “Impact of Typhoons on the Ocean in the Pacific” (2010) and an ensemble Kalman filter-based vortex initialization method, this study explores the impact of the Taiwan terrain on the uncertainty in forecasting track, intensity and rainfall of Typhoon Fanapi (2010) based on ensemble simulations. The results show that the presence of Taiwan topography leads to rapid growths of the simulation uncertainty in track and intensity during the landfall period, in particular at the earlier landfall period. The fast moving ensemble members show an earlier southward track deflection as well as the weakening of intensity, resulting in a sudden increase of standard deviation in track and intensity. During the period of offshore departure from Taiwan, our analysis suggests that the latitudinal location of the long-lasting and elongated rainband to the south of tropical cyclone (TC) center has a strong dependence on the latitude of the TC center. In addition, the rainfall uncertainty in southern Taiwan is dominated by the uncertainty of simulated TC rainband, and the latitude of TC track can be regarded as a good predictor of the rainband's location at departure time. It is also found that the rainband develop farther to the south as the topography is elevated. Considering the fact that the rainband impinging the high mountains in the southern Central Mountain Range generates the greatest accumulated rainfall, positions where the rainband associated circulation and its interaction with topography appear to offer an explanation on the uncertainty of the simulated rainfall.
著者
永田 雅
出版者
社団法人日本気象学会
雑誌
気象集誌 (ISSN:00261165)
巻号頁・発行日
vol.71, no.1, pp.43-57, 1993-02-25
被引用文献数
11

高解像度3重ネスティングの静力学近似数値モデルによって、日本海寒帯気団収束帯(JPCZ)に沿って発達するメソβスケールの渦列がうまくシミュレートされた。再現された重要な特徴には、直径数1Okmの「目」に似た構造と、それを取り巻くスパイラル状の上昇流の帯が含まれている。再現された渦列は最初、JPCZに沿う1O^<-3>s^<-1>のオーダーの正の渦度が集中した帯の折れ曲がりとして現れる。その折れ曲がりが次第に鋭くなっていき、4-8時間のうちに、ついにはその渦度の帯の谷が巻き込んで、乾いた目とスパイラル状の上昇流の帯を伴った、気圧偏差2-4hPaのメソβスケールの低気圧を形成する。この目および近接した湿った上昇流域は暖気核で特徴づけられる。シミュレートされた渦の、空間スケールと発達の時間スケールの理論との一致、及び、エネルギー論による解析は、渦の主要な発達機構としてバロトロピックシアー不安定を示している。
著者
LUO Yali XIA Rudi CHAN Johnny C. L.
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.2020-002, (Released:2019-10-16)
被引用文献数
1

Pre-summer rainy season (April to mid-June) over South China (SC) is characterized by high intensity and frequent occurrence of heavy rainfall in the East Asian monsoon region. This review describes recent progress in the research related to such a phenomenon. The mechanisms responsible for pre-summer rainfall consist of multi-scale processes. Sea surface temperatures over tropical Pacific and Indian Ocean are shown to have a great influence on the interannual variations of pre-summer rainfall over SC. Synoptic disturbances associated with regional extreme rainfall over SC are mainly related to cyclone- and trough-type anomalies. Formation and intensification of such anomalies can be contributed by surface sensible heating and mechanical forcing from the Tibetan Plateau. On a sub-daily scale, double rain belts often co-exist over SC. The northern rain belt is closely linked to dynamic lifting by a subtropical low pressure and its associated front/shear line, while the westward extension of the western North Pacific high and the intensification of the southwesterly monsoonal flows play important roles in providing high-equivalent potential temperature air to the west- and east-inland regions, respectively. The southern rain belt with a smaller horizontal span is in the warm sector over either inland or coastal SC. The warm-sector rainfall over inland SC results from surface heating, local topographic lifting, and urban heat island effect interacting with the sea breeze. The warm-sector rainfall over coastal SC is closely associated with double low-level jets, land-sea-breeze fronts, and coastal mountains. A close relationship is found between convectively-generated quasi-stationary mesoscale outflow boundaries and continuous convective initiation in extreme rainfall events. Active warm-rain microphysical processes can play an important role in some extreme rainfall events, although the relative contributions by warm-rain, riming and ice-phase microphysical processes remain unclear. Moreover, to improve the rainfall prediction, efforts have been made in convection-permitting modeling studies.
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)

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

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
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
2

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
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 71

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)

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)

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)

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)

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

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
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 82

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)

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.