著者

HIROSE Hitoshi SHIGE Shoichi YAMAMOTO Munehisa K. HIGUCHI Atsushi

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.2019-040, (Released:2019-03-15)

被引用文献数

23

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We introduce a novel rainfall estimation algorithm with a random-forest machine-learning method only from Infrared (IR) observations. As training data, we use nine-band brightness temperature (BT) observations obtained from IR radiometers on the third-generation geostationary meteorological satellite (GEO) Himawari-8 and precipitation radar observations from the Global Precipitation Measurement core observatory. The Himawari-8 Rainfall estimation Algorithm (HRA) enables us to estimate rain rate with high spatial and temporal resolution (i.e., 0.04° every 10 min), covering the entire Himawari-8 observation area (i.e., 85°E–155°W, 60°S–60°N) based solely on satellite observations. We conducted a case analysis of the Kanto–Tohoku heavy rainfall event to compare rainfall estimation results of HRA and the near-real-time version of the Global Satellite Mapping of Precipitation (GSMaP_NRT), which combines global rainfall estimation products with microwave and IR BT observations obtained from satellites. In this case, HRA could estimate heavy rainfall from warm-type precipitating clouds, although GSMaP_NRT could not estimate heavy rainfall when the microwave satellites were unavailable. Further, a statistical analysis showed that the warm-type heavy rain seen in the Asian monsoon region occurred frequently when the BT differences between the 6.9-μm and 7.3-μm of water vapor (WV) bands (ΔT6.9–7.3) were small. Himawari-8 is the first GEO to include the 6.9-μm band which is sensitive to middle-to-upper tropospheric WV. An analysis for the weighting functions of the WV multibands revealed that ΔT6.9–7.3 became small as WV amount in the middle-to-upper troposphere was small and there were optically thick cloud with the cloud top near the middle troposphere. Statistical analyses during boreal summer (August and September 2015 and July 2016) and boreal winter (December 2015 and January and February 2016) indicate that HRA has higher estimation accuracy for heavy rain from warm-type precipitating clouds than a conventional rain estimation method based on only one IR band.

著者

Akiyoshi WADA Hiroshige TSUGUTI Kozo OKAMOTO Naoko SEINO

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.3, pp.553-575, 2019 (Released:2019-06-05)

参考文献数

62

被引用文献数

4

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The September 2015 Kanto-Tohoku heavy rainfall event occurred in a stationary linear convective system between Typhoons Kilo and Etau. We investigated the influence of sea surface temperature (SST) on the local heavy rainfall event using a regional air-sea strongly coupled data assimilation system based on the local ensemble transform Kalman filter (LETKF) and a nonhydrostatic atmosphere model (NHM) coupled with an ocean-surface wave model and a multilayer ocean model with an Advanced Microwave Scanning Radiometer 2 (AMSR2) level 2 (L2) SST product. From the validation of SST analyzed by the coupled data assimilation system with the Japanese geostationary multi-functional transport satellite 2 hourly SST product and in-situ observations at a moored buoy, we demonstrated that the coupled system with the AMSR2 L2 SST led to an improvement in the SST analysis. Based on the verification using radiosonde observations and radar-rain gauge rainfall analysis, the analysis of the lower-atmospheric components was improved by the air-sea coupled NHM-LETKF. The local torrential rainfall event that occurred around 37°N in the Tochigi prefecture was embedded in a stationary linear convective system. The location of the linear convective system corresponded to the synoptic-scale convergence area between the cyclonic circulation associated with Etau and easterly lower-tropospheric winds. Strong southerly winds associated with Etau caused a periodic enhancement of local convection along the convergence area on the upwind side of the linear convective system and resulted in a wave-like train of the total water content around an altitude of 4-8 km on the leeward side. The improvement of SST analysis could not only change the transition of Etau to the extratropical cyclone but also the lower-tropospheric wind field and thereby the location of the stationary linear convective system with embedded local torrential rain.

著者

SHIN Uju LEE Tae-Young PARK Sang-Hun

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.2019-036, (Released:2019-02-19)

被引用文献数

10

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An investigation has been carried out using rainfall observation data, National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) analysis and forecast data to explain the environment and processes that lead to heavy rainfall in the early morning over the Korean peninsula during episodes of cloud clusters (CCs) associated with mesoscale troughs (CCMTs). For this study, nine episodes with maximum hourly rainfall amount in the early morning (i.e., 0300–0900 LST) are selected from seventeen heavy-rainfall episodes associated with CCMTs during 2001–2011. Case studies on two episodes have revealed that, for both episodes, 1) a low-level trough develops over eastern China and its coastal area during the daytime; 2) the strong southwesterly band (SWB; an area with wind speeds > 12.5 m s-1) on the pressure level 925 hPa over the East China Sea, which is located southeast of the trough, strengthens and expands at nighttime toward the southwestern Korean peninsula; 3) the SWB supplies large amount of moisture and increases convective instability over the southwestern Korean peninsula with a convection trigger mechanism (i.e., strong horizontal convergence); and 4) heavy rainfall occurs in the early morning over the southwestern Korean peninsula, where the exit region of the SWB is located. A mechanism for the SWB growth is presented. Furthermore, generality of the major results from the two case studies is verified using the results obtained for the composite fields of the 9 CCMT episodes.

著者

Yasumitsu Maejima Keita Iga Hiroshi Niino

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.2, pp.80-83, 2006 (Released:2006-06-29)

参考文献数

10

被引用文献数

2

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Upper-tropospheric vortices having a horizontal wavelength of 300-400 km were observed on water vapor images of the Japanese geostationary satellite (MTSAT-1). Grid point values predicted by the Regional Spectral Model of the Japan Meteorological Agency show that the vortices were located along a zonal belt with strong cyclonic shear and horizontal convergence. A quasi-geostrophic linear stability analysis of the basic flow having horizontal and vertical shear shows that the fastest growing mode has a horizontal wavelength, a phase speed and a growth rate that reasonably agree with those of the satellite observation. The amplitude of the fastest growing mode is confined to a region having a meridional width of 2 degrees and a vertical depth of 2 km. An energy budget analysis shows that barotropic instability is the dominant generation mechanism for the growing mode.

著者

SAUNDERS Peter YU Yafan PU Zhaoxia

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.2019-030, (Released:2019-01-25)

被引用文献数

3

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Hurricane Joaquin, a notable hurricane over the Atlantic Ocean in 2015, is studied with emphasis on its unique hairpin turn that occurred between 2100 UTC 1 October and 0600 UTC 2 October 2015. A series of mesoscale high-resolution numerical simulations is performed with an advanced research version of the Weather Research and Forecasting (WRF) model. The sensitivity of numerical simulations to different cumulus, boundary layer, and microphysical parameterization schemes is examined to investigate the most relevant processes influencing the track evolution of Hurricane Joaquin. It is found that the numerical simulation of Hurricane Joaquin’s track is highly sensitive to the choice of cumulus scheme. Large-scale environmental conditions and hurricane inner-core structures are diagnosed. Results indicate that middle- to upper-level steering flows are crucial in influencing Joaquin’s track. Further investigation of the large-scale environment (e.g., middle- and upper-level trough, blocking high, thermal distribution, etc.) shows that middle-level blocking high plays an important role in Joaquin’s movement. The structure of the hurricane core region, including the vertical extent of diabatic heating, vertical velocity, and relative humidity, could also play an important role. Specifically, the asymmetry and local absolute vorticity tendency over the inner-core region and its vicinity has a strong implication for Joaquin’s hairpin turn.

著者

Akifumi Nishi Hiroyuki Kusaka Lidia Lazarova Vitanova Yuma Imai

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-024, (Released:2019-05-27)

被引用文献数

5

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We quantitatively evaluated the contributions of foehn winds and the urban heat island (UHI) effect to an extreme high-temperature nocturnal event at Niigata city on 23-24 August 2018. During this event, southeasterly winds blew continually across the Niigata Plain and temperatures on the plain were higher than those in the windward region of the mountain range. Back-trajectory analysis and numerical simulations with and without topography showed that the southeasterly winds were foehn winds that caused precipitation and latent heating on the windward slope of the mountain range. The foehn winds and UHI contributed about 2.8°C and 1.9°C, respectively, to the extreme high-temperature of 31.0°C at 2100 JST in Niigata city. The combined impact of the foehn winds and the UHI at Niigata was about 4.0°C during the night. The contribution of the foehn winds was greater at around midnight, whereas that of the UHI was greater during the early night.

著者

Takumi Matsunobu Mio Matsueda

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.15A-004, (Released:2019-05-24)

被引用文献数

8

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Extremely heavy rainfall events occurred over western Japan in early July 2018. This study assesses the predictability of these events for the period 5th–7th July using three operational medium-range ensemble forecasts available from the European Centre for Medium-range Weather Forecasts (ECMWF), the Japan Meteorological Agency (JMA), and the National Centers for Environmental Prediction (NCEP), and ensemble simulations conducted with an ECMWF model and NCEP operational ensemble initial conditions. All three operational ensembles predicted extreme rainfall on 5th–6th July at lead times of ≤ 6 days, indicating the high predictability of this event. However, the extreme rainfall event of 6th–7th July was less predictable. The NCEP forecasts, initialised on 30th June, performed better at predicting this event than the other operational forecasts. The JMA forecasts initialised on 1st July showed improved predictability; however, the ECMWF forecasts initialised after 30th June showed only gradual improvements as the initialisation time progressed. The ensemble simulations revealed that the lower predictability of the rainfall in the ECMWF forecasts on 6th–7th July can be attributed to the model rather than to the initial conditions. Accurate prediction of the North Pacific Subtropical High is a prerequisite for accurate prediction of such extreme rainfall events.

著者

Hironori FUDEYASU Ryuji YOSHIDA

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.2, pp.439-451, 2019 (Released:2019-04-04)

参考文献数

33

被引用文献数

9

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This study examined the statistical characteristics of tropical cyclones (TCs) for which the cyclogenesis (TCG) process was modulated by upper tropospheric cold lows (UCLs) over the western North Pacific during the 38 years from 1979 to 2016. Among the 965 TCs, 90 TCs (9 %, 2.4 per year) were defined as having TCG influenced by UCLs in the northwest quadrant of the TC region (UL-TCs). Most UL-TCs occurred in the summer, with large variability in the annual occurrence rate of UL-TCs during June to October, ranging from 0 to approximately 30 %. The annual variation was related to the activity of the Tibetan high and the summer temperature anomaly over Japan. The extremely hot summer of 2016 was partly enhanced by the intense Tibetan high, when 4 UL-TCs also occurred. The average location of UL-TCs at the time of TCG and tropical storm formation (TSF) was significantly farther to the north than the average location of TCs not formed under the influence of UCL (N-UL-TCs). Many UL-TCs occurred in lower tropospheric environments associated with the shear line or confluence regions. The UL-TCs tended to move northward, and the occurrence rate of UL-TCs that made landfall in Japan was approximately double that of other countries. The atmospheric environmental parameters around UL-TCs at the time of TCG were more favorable for the development of TCs than those around N-UL-TCs. In contrast, the atmospheric and oceanic environmental parameters around UL-TCs at the time of TSF were less favorable for the development of TCs, such that UL-TCs tended to remain at weak intensity.

著者

Wan-Ru HUANG Po-Han HUANG Ya-Hui CHANG Chao-Tzuen CHENG Huang-Hsiung HSU Chia-Ying TU Akio KITOH

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.97, no.2, pp.481-499, 2019 (Released:2019-04-03)

参考文献数

58

被引用文献数

9

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By using the Weather Research and Forecasting (denoted as WRF) model driven by two super-high-resolution global models, High Resolution Atmospheric Model (denoted as HiRAM) and Meteorological Research Institute Atmospheric General Circulation Model (denoted as MRI), this study investigates the dynamical downscaling simulation and projection of extreme precipitation activities (including intensity and frequency) in Taiwan during the Mei-Yu seasons (May and June). The analyses focus on two time period simulations: the present-day (1979-2003, historical run) and the future (2075-2099, RCP8.5 scenario). For the present-day simulation, our results show that the bias of HiRAM and MRI in simulating the extreme precipitation activities over Taiwan can be reduced after dynamical downscaling by using the WRF model. For the future projections, both the dynamical downscaling models (i.e., HiRAM-WRF and MRI-WRF) project that extreme precipitation will become more frequent and more intense over western Taiwan but less frequent and less intense over eastern Taiwan. The east-west contrast in the projected changes in extreme precipitation in Taiwan are found to be a local response to the enhancement of southwesterly monsoonal flow over the coastal regions of South China, which leads to an increase in water vapor convergence over the windward side (i.e., western Taiwan) and a decrease in water vapor convergence over the leeward side (i.e., eastern Taiwan). Further examinations of the significance of the projected changes in extreme precipitation that affect the agriculture regions of Taiwan show that the southwestern agriculture regions will be affected by extreme precipitation events more frequently and more intensely than the other subregions. This finding highlights the importance of examining regional differences in the projected changes in extreme precipitation over the complex terrain of East Asia.

著者

Kuan-Ting KUO Chien-Ming WU

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.2, pp.501-517, 2019 (Released:2019-04-03)

参考文献数

21

被引用文献数

11

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In this study, the mechanism for precipitation hotspots (PHs) of locally developed afternoon thunderstorms in the Taipei Basin is investigated using a three-dimensional Vector Vorticity equation cloud-resolving Model (VVM) with an idealized topography and surface properties. A 500 m horizontal grid resolution is used in all experiments. The results show that the local circulation is a key for PHs at the south of the Taipei Basin. The two valleys guide background southwesterly (SW) flow along with the sea breezes to penetrate into the basin. The urban heat island (UHI) effect enhances the sea breeze convergence at the south of the basin and produces strong convection there. The interactions between cold pools generated by the convection and the sea breezes produce northward propagating new convective cells. Besides, the background wind direction is important in determining the location of sea breeze convergence. If the background wind direction changes from westerly (W) to west-northwesterly (WNW), there might be no precipitation at all in the basin. This study suggests that the idealized experiments also provide a useful framework for studying the impacts of future climate changes on the PHs in the Taipei Basin by applying the pseudo–global warming approach.

著者

Kenji Suzuki Rimpei Kamamoto Katsuhiro Nakagawa Michinobu Nonaka Taro Shinoda Tadayasu Ohigashi Yukiya Minami Mamoru Kubo Yuki Kaneko

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-018, (Released:2019-04-10)

被引用文献数

5

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A field observation was carried out along the coast of the Japan Sea in the 2016-2017 and 2017-2018 winter seasons, using the Ground-based Precipitation particle Image and Mass Measurement System (G-PIMMS) to evaluate the Global Precipitation Measurement Mission (GPM) dual-frequency precipitation radar (DPR) precipitation type classification algorithm. The G-PIMMS was installed at Kanazawa University and Ishikawa Prefectural University, which are around 10 km apart from each other. The G-PIMMS observations showed that the major precipitation particle type (graupel or snowflake) was different in the precipitation types classified by the GPM DPR algorithm.

著者

大後 美保 鈴木 雄次

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.21, no.2, pp.52-58, 1943 (Released:2009-02-05)

参考文献数

6

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The coefficients of correlation between the yield of hemp and the weather factors (i. e. monthly mean temperature, monthly amount of rainfall, monthly total number of rainy days and monthly total hours of sunsh ne) have been calculated by the method reported in a previous number of this magazine, for each prefecture in Japan, in each month during the cultivating time. The correlation coefficients calculated are shown in tables 1, 2, 3 and 4.The correlation coefficients are generally small; only, in the north-eastern provinces, air temperature is more closely correlated with the yield than any other weather factor, and that positively, while in the southern part the closest correlation is found between the yield and rainfall. The results of this investigation show that the warm, rainy weather in the cultivation time of hemp is favourable for it in Japan proper.

著者

FANG Yongjie LI Bo LIU Xiangwen

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.2019-019, (Released:2018-12-07)

被引用文献数

4

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The boreal summer intra-seasonal oscillation (BSISO) is the predominant sub-seasonal variability over the East Asia (EA) and western North Pacific (WNP) region and critical for seasonal forecast of the EA summer monsoon. This study examines the theoretically estimated predictability and practical prediction skill of the EAWNP BSISO in the Beijing Climate Center Climate System Model version 2 (BCC_CSM2.0), which is one of participants in the Sub-seasonal to Seasonal Prediction Project. Results from the uninitialized free run of BCC_CSM2.0 show that the model reasonably simulates the EAWNP BSISO in terms of its variance, propagation and structure. Measured by the bivariate correlation (> 0.5) and root mean square error (< √2) between the predicted and observed real-time BSISO index, the prediction skill and predictability of EAWNP BSISO are about 14 and 24-28 days respectively. The initial/target strong BSISO cases have a relatively higher prediction skill compared to the initial/target weak BSISO cases. For the theoretically estimated BSISO predictability, similar dependence on target amplitude occurs in the model, while no significant dependency on initial amplitude is found. Moreover, diagnosis of the phase dependence reveals that BSISO is less skillful for the prediction starting from active or active-to-break transition phases of WNP rainfall, whereas it is more predictable when prediction is targeting extreme dry/wet phases of WNP rainfall. Finally, systematic errors are found in BCC_CSM2.0 such as the underestimation of BSISO amplitude and the faster phase speed.

著者

INATSU Masaru SUZUKI Hayato KAJINO Mizuo

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.2019-010, (Released:2018-11-28)

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A set of atmospheric dispersion-deposition model integrations was conducted with a hypothetical emission of radioactive materials consisting of 137Cs, 131I, and 134Cs from the Tomari Nuclear Power Plant in Hokkaido, Japan, which is a snow climate site. Each integration was driven by Japan Meteorological Agency’s meso-scale model analysis data with 5-km horizontal resolution. The initial conditions were those on each day from January 2010 to December 2016 and the integration period was at most 4 days. The target was the area within 30 km of the plant. Extending a unit-mass emission concept, the measure of relative risk is the probability of exceeding the threshold of the maximum effective dose rate based only on exposure from groundshine. Considering that the measure increased monotonically with the ratio of the total emission amount to the threshold, we evaluated the probabilistic risk with its median. The results suggested that the risk was higher in the eastern part of the target area due to the prevailing westerly. The frequent snowfall in winter drags radioactive materials down in the target region, even under an active turbulent condition with strong vertical shear. The composite analysis for wind direction averaged over the target area revealed that the risk was high in the leeside, but that mountains effectively blocked the inflow of the radioactive materials. The results were insensitive to a wet deposition parameterisation. The risk was reduced when we replaced the emission altitude with a higher one than the standard setting. The snow shielding effect was negligible on the short-term radioactivity just after the emission but was substantial on the seasonal change in radioactivity.

著者

Xue-Song ZHU Hui YU

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.1, pp.153-173, 2019 (Released:2019-02-14)

参考文献数

53

被引用文献数

6

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Using brightness temperature data from passive microwave satellite imagery, this study examines tropical cyclones (TCs) with concentric eyewall (CE) in the western North Pacific between 1997 and 2011. The identified CEs are divided into two types according to the characteristics of the eyewall replacement cycle (ERC) in the microwave imagery: a CE with a typical ERC (T-ERC) and a CE without an ERC (N-ERC). It is indicated that 88% T-ERCs reach peak intensity near (0.2 h after on average) CE formation, whereas 90% N-ERCs reach peak intensity prior to (22.0 h on average) CE formation. In general, N-ERCs tend to occur when there are strong interactions between the environment and the CE, whereas T-ERCs occur in a relatively quiet environment. The three-dimensional conceptual models of the environmental configurations for both CE types are proposed. Specifically, N-ERCs are accompanied by stronger southwesterly and southeasterly inflows, active low-level trough, and stronger subtropical high (SH) and South Asia high (SAH), compared with T-ERCs. For N-ERCs, the stronger inflows may bring in a large amount of moisture, and the active low-level trough may result in a large vertical wind shear (VWS). The stronger SH and SAH may contribute to changes in the intensity and direction of the VWS for N-ERCs, and hence trigger the development of local convection in the outer eyewall. The asymmetries in the convection of the outer eyewall may weaken the ability to cut off the radial inflow to the inner eyewall. Consequently, N-ERCs fail to finish the ERC and weaken rapidly in intensity, even though the moisture remains sufficient after CE formation.

著者

FUKUSHIMA Hirokazu YAZAKI Tomotsugu HIROTA Tomoyoshi IWATA Yukiyoshi WAJIMA Atsushi YOKOTA Ayumi

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.2019-005, (Released:2018-10-29)

被引用文献数

5

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There is an increasing need for accurate winter agrometeorological forecasts, which is facilitated by a better understanding of the evolution process of nighttime air temperature distribution. However, studies on how air temperature distributions evolve in mesoscale plains have been limited. To clarify how the low temperatures in winter nights form, we analyzed the effects of topography and boundary-layer wind on the temperature distribution of the Tokachi region for a winter night using numerical simulations by the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM)with horizontal grid spacing of 2 and 5 km. We also analyzed vertical profiles of boundary-layer atmospheric conditions. The results show that, although boundary-layer wind is expected to affect the temperature distribution over the entire Tokachi region, the effects were generally confined to the northwestern part. Widespread effects over the Tokachi region were found only under strong wind conditions. We found that the mountain pass in the northwestern part of the Tokachi region is an important wind path, and the downslope winds as well as the sensible heat transfer by turbulent mixing in the boundary layer also was important in the evolution of the air temperature distribution. On the night we considered, a moderate boundary-layer wind was maintained throughout the night, but the surface wind speed decreased from the northern and southern parts of the Tokachi region; this can be attributed to the development of an inversion layer. A drainage flow was observed to originate from the southern part of the Tokachi Plain, reaching the central part of the Tokachi region in the night. We find that radiative cooling and sensible heat transfer by turbulent mixing in the surface layer do not adequately explain the temporal change in observed surface air temperatures. The development of an inversion layer and katabatic drainage flow drastically change the temperature distribution, despite a moderately strong wind condition in the boundary layer.

著者

KUO Kuan-Ting WU Chien-Ming

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.2019-031, (Released:2019-02-02)

被引用文献数

11

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In this study, the mechanism for precipitation hotspots (PHs) of locally developed afternoon thunderstorms in the Taipei Basin is investigated using a three-dimensional Vector Vorticity equation cloud resolving Model (VVM) with an idealized topography and surface properties. A 500-m horizontal grid resolution is used in all experiments. The results show that the local circulation is a key for PHs at the south of the Taipei Basin. The two valleys guide background southwesterly flow along with the sea breezes to penetrate into the basin. The urban heat island effect enhances the sea breeze convergence at the south of the basin and produces strong convection there. Interactions between cold pools generated by the convection and the sea breezes produce northward propagating new convective cells. Besides, the background wind direction is important in determining the location of sea breeze convergence. If the background wind direction changes from westerly to west-northwesterly, there might be no precipitation at all in the basin. This study suggests that the idealized experiments also provide a useful framework for studying the impacts of future climate change on the PHs in the Taipei Basin by applying the pseudo-global warming approach.

著者

Akio KITOH Hirokazu ENDO

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.1, pp.141-152, 2019 (Released:2019-02-06)

参考文献数

40

被引用文献数

22

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Future changes in precipitation extremes and role of tropical cyclones are investigated through a large ensemble experiment, considering 6,000 years for the present and 5,400 years under +4 K warming, using a 60-km mesh Meteorological Research Institute atmospheric general circulation model version 3.2. As in the previous findings of the authors, the annual maximum 1-day precipitation total (Rx1d) is projected to increase in the warmer world in the future almost globally, except in the western North Pacific where a projected decrease of tropical cyclone frequency results in only small change or even reduction of Rx1d. Furthermore, a large ensemble size enables us to investigate the changes in the tails of the Rx1d distribution. It is found that 90- and 99-percentile values of the Rx1d associated with tropical cyclones will increase in a region extending from Hawaii to the south of Japan. In this region, the interannual variability of the Rx1d associated with tropical cyclones is also projected to increase, implying an increasing risk of rare heavier rainfall events because of global warming.

著者

Wataru MASHIKO

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.1, pp.39-54, 2019 (Released:2019-02-07)

参考文献数

41

被引用文献数

1

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In this study, the characteristics of wind gusts in Japan in the period from 2002 to 2017 were examined using surface meteorological data recorded at 151 weather observatories throughout Japan. This study does not focus on particular phenomena, such as tornadoes and downbursts, which cause wind gusts. A wind gust is defined on the basis of the gust factor and the amount of increase and decrease of the 3-s mean wind speed from the 10-min mean wind speed. A total of 3,531 events were detected as wind gusts. The frequency of wind gusts with more than 25 m s−1 averaged across all observatories is 0.97 per year, which is four or five orders of magnitude higher than the tornado encounter probability in Japan. The frequency of wind gusts in the coastal region is approximately three times higher than that in the inland area. Wind gusts occur most frequently in September and least frequently in June. Wind gusts have high activities during daytime, especially in the afternoon. Approximately half of the events are the typhoon-associated wind gusts (WGTYs), which occurred within a radius of 800 km from the typhoon center. Most of the WGTYs occur from August to October. Approximately half of the WGTYs occur in the right-front quadrant of a typhoon with respect to the typhoon motion. The frequency of WGTYs is high in western Japan, whereas the northern and eastern parts of Japan are characterized by a high frequency of wind gusts without a typhoon. In addition, persistent strong winds, which meet the same conditions as wind gusts but without a rapid decrease in the wind speed, were investigated. The frequency of such strong winds is high on the Japan Sea coast, especially in December. The effects of the observational environment on the frequency of wind gusts were also discussed.

著者

Shunji Kotsuki Koji Terasaki Kaya Kanemaru Masaki Satoh Takuji Kubota Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15A, pp.1-7, 2019 (Released:2019-01-26)

参考文献数

25

被引用文献数

26

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This paper is the first publication presenting the predictability of the record-breaking rainfall in Japan in July 2018 (RJJ18), the severest flood-related disaster since 1982. Of the three successive precipitation stages in RJJ18, this study investigates synoptic-scale predictability of the third-stage precipitation using the near-real-time global atmospheric data assimilation system named NEXRA. With NEXRA, intense precipitation in western Japan on July 6 was well predicted 3 days in advance. Comparing forecasts at different initial times revealed that the predictability of the intense rains was tied to the generation of a low-pressure system in the middle of the frontal system over the Sea of Japan. Observation impact estimates showed that radiosondes in Kyusyu and off the east coast of China significantly reduced the forecast errors. Since the forecast errors grew more rapidly during RJJ18, data assimilation played a crucial role in improving the predictability.