著者
Kosuke Ito Hiroyuki Yamada Munehiko Yamaguchi Tetsuo Nakazawa Norio Nagahama Kensaku Shimizu Tadayasu Ohigashi Taro Shinoda Kazuhisa Tsuboki
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.14, pp.105-110, 2018 (Released:2018-07-28)
参考文献数
30
被引用文献数
1 2

The inner core of Tropical Cyclone Lan was observed on 21-22 October 2017 by GPS dropsondes during the first aircraft missions of the Tropical Cyclones-Pacific Asian Research Campaign for the Improvement of Intensity Estimations/Forecasts (T-PARCII). To evaluate the impact of dropsondes on forecast skill, 12 36-h forecasts were conducted using a Japan Meteorological Agency non-hydrostatic model (JMA-NHM) with a JMA-NHM-based mesoscale four-dimensional data assimilation (DA) system. Track forecast skill improved over all forecast times with the assimilation of the dropsonde data. The improvement rate was 8-16% for 27-36-h forecasts. Minimum sea level pressure (Pmin) forecasts were generally degenerated (improved) for relatively short-term (long-term) forecasts by adding the dropsonde data, and maximum wind speed (Vmax) forecasts were degenerated. Some of the changes in the track and Vmax forecasts were statistically significant at the 95% confidence level. It is notable that the dropsonde-derived estimate of Pmin was closer to the real-time analysis by the Regional Specialized Meteorological Center (RSMC) Tokyo than the RSMC Tokyo best track analysis. The degeneration in intensity forecast skill due to uncertainties in the best track data is discussed.
著者
Kosuke Ito
出版者
(公社)日本気象学会
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.12, pp.247-252, 2016 (Released:2016-09-16)
参考文献数
18
被引用文献数
11

Tropical cyclone (TC) intensity forecasts issued by the Regional Specialized Meteorological Centre (RSMC) Tokyo - Typhoon Center are systematically compiled to analyze the long-term behavior of errors and to explore the potential for improvement in the forecast accuracy using a statistical correction approach. In this study, a dataset is constructed from annual statistics and every single forecast listed on annual reports on the activities of the RSMC Tokyo. This study found that (1) the accuracy of annual mean forecast has not improved over 26 years and that (2) forecast errors tend to be larger in the rapidly developing TCs. Further analysis reveals that recent forecast output (2008-2014) contains biases associated with the magnitude of the vertical shear of horizontal wind, convective available potential energy, upper ocean temperature, maximum potential intensity (MPI) and ocean coupling potential intensity (OC_PI). To evaluate the adverse effect of such biases in the current forecast system, a simple statistical correction is applied. It improved TC intensity forecast by 7.8-16.9% when an OC_PI is employed.
著者
Yukiko Imada Masahiro Watanabe Hiroaki Kawase Hideo Shiogama Miki Arai
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.15A-002, (Released:2019-05-22)
被引用文献数
2

The high temperature event in July 2018 caused record-breaking human damage throughout Japan. Large-ensemble historical simulations with a high-resolution atmospheric general circulation model showed that the occurrence rate of this event under the condition of external forcings in July 2018 was approximately 20%. This high probability was a result of the high-pressure systems both in the upper and lower troposphere in July 2018. The event attribution approach based on the large-ensemble simulations with and without human-induced climate change indicated the following: (1) The event would never have happened without anthropogenic global warming. (2) The strength of the two-tiered high-pressure systems was also at an extreme level and at least doubled the level of event probability, which was independent of global warming. Moreover, a set of the large-ensemble dynamically downscaled outputs revealed that the mean annual occurrence of extremely hot days in Japan will be expected to increase by 1.8 times under a global warming level of 2°C above pre-industrial levels.
著者
Shion Sekizawa Takafumi Miyasaka Hisashi Nakamura Akihiko Shimpo Kazuto Takemura Shuhei Maeda
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.15A-005, (Released:2019-05-22)
被引用文献数
3

During a torrential rainfall event in early July 2018, profound enhancement of moisture influx from the south and its convergence occurred over western Japan, which is investigated in this study on the basis of objective analysis and forecast data from the Japan Meteorological Agency Meso-Scale Model. The heavy rainfall over western Japan is found to accompany enhanced oceanic evaporation extensively around Japan, especially around the Kuroshio and entirely over the Sea of Japan. Linear decompositions of the anomalous moisture flux and surface latent heat flux anomalies applied to the high-resolution data reveals that the intensified speed of the low-level southerlies was the primary factor for the pronounced enhancement of both the moisture transport into the heavy rainfall region, especially in its western portion, and evaporation around the Kuroshio into the southerlies. An additional contribution is found from positive sea-surface temperature anomalies to the enhanced southerly moisture inflow into the eastern portion of the rainfall region. These findings have been confirmed through a backward trajectory analysis, which suggests that anomalous moisture supply to air parcels into the rainfall region primarily through the enhanced wind-forced evaporation roughly corresponds to about 10% of the precipitable water anomaly over western Japan.
著者
Tetsuya Takemi Takashi Unuma
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.60-65, 2019 (Released:2019-09-19)
参考文献数
32

This study documented the environmental properties of precipitation systems that produced the July 2018 Heavy Rainfall event in Japan. The gridded analysis data were used to diagnose the potential for the development of convective systems in terms of thermodynamic environmental indices. Precipitable water vapor was extremely larger than that seen in the climatology of warm-season quasi-stationary convective clusters (QSCCs). Such an extreme moisture content was realized by very humid conditions at the middle-levels. In contrast, temperature lapse rate in a convectively unstable layer was not so significant in comparison to the QSCC climatology. Among the environmental indices, K Index was shown to describe the potential for the rainfall development. Based on the analysis, the roles of moisture content and profile on the convection development were discussed. It was suggested that the middle-level high humidity contributes to the occurrence of the present heavy rainfall by minimizing negative effects of environmental mixing and by decreasing vertical displacements to reach levels of free convection. In regions where heavy rainfall occurred, an automated algorithm detected the development of QSCCs, which were mostly categorized as a linear type.
著者
Akihiko Shimpo Kazuto Takemura Shunya Wakamatsu Hiroki Togawa Yasushi Mochizuki Motoaki Takekawa Shotaro Tanaka Kazuya Yamashita Shuhei Maeda Ryuta Kurora Hirokazu Murai Naoko Kitabatake Hiroshige Tsuguti Hitoshi Mukougawa Toshiki Iwasaki Ryuichi Kawamura Masahide Kimoto Izuru Takayabu Yukari N. Takayabu Youichi Tanimoto Toshihiko Hirooka Yukio Masumoto Masahiro Watanabe Kazuhisa Tsuboki Hisashi Nakamura
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.13-18, 2019 (Released:2019-06-15)
参考文献数
22
被引用文献数
7

An extreme rainfall event occurred over western Japan and the adjacent Tokai region mainly in early July, named “the Heavy Rain Event of July 2018”, which caused widespread havoc. It was followed by heat wave that persisted in many regions over Japan in setting the highest temperature on record since 1946 over eastern Japan as the July and summertime means. The rain event was attributable to two extremely moist airflows of tropical origins confluent persistently into western Japan and large-scale ascent along the stationary Baiu front. The heat wave was attributable to the enhanced surface North Pacific Subtropical High and upper-tropospheric Tibetan High, with a prominent barotropic anticyclonic anomaly around the Korean Peninsula. The consecutive occurrence of these extreme events was related to persistent meandering of the upper-level subtropical jet, indicating remote influence from the upstream. The heat wave can also be influenced by enhanced summertime convective activity around the Philippines and possibly by extremely anomalous warmth over the Northern Hemisphere midlatitude in July 2018. The global warming can also influence not only the heat wave but also the rain event, consistent with a long-term increasing trend in intensity of extreme precipitation observed over Japan.
著者
Seiji Yukimoto Kunihiko Kodera Rémi Thiéblemont
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.13, pp.53-58, 2017 (Released:2017-04-04)
参考文献数
29
被引用文献数
1

A delayed response of the winter North Atlantic oscillation (NAO) to the 11-year solar cycle has been observed and modeled in recent studies. However, the mechanisms creating this 2-4-year delay to the solar cycle have still not been well-understood. This study examines the effects of the 11-year solar cycle and the resulting modulation in the strength of the winter stratospheric polar vortex. A coupled atmosphere–ocean general circulation model is used to simulate these effects by introducing a mechanistic forcing in the stratosphere. The intensified stratospheric polar vortex is shown to induce positive and negative ocean temperature anomalies in the North Atlantic Ocean. The positive ocean temperature anomaly migrated northward and was amplified when it approached an oceanic frontal zone approximately 3 years after the forcing became maximum. This delayed ocean response is similar to that observed. The result of this study supports a previous hypothesis that suggests that the 11-year solar cycle signals on the Earth's surface are produced through a downward penetration of the changes in the stratospheric circulation. Furthermore, the spatial structure of the signal is modulated by its interaction with the ocean circulation.
著者
Meiji Honda Akira Yamazaki Akira Kuwano-Yoshida Yusuke Kimura Katsushi Iwamoto
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.12, pp.259-264, 2016 (Released:2016-09-22)
参考文献数
17
被引用文献数
2

Synoptic conditions causing an extreme snowfall event in the Kanto-Koshin district occurred on 14-15 February 2014 are investigated through a reanalysis data set. Associated with a developing cyclone passing the south coast of Japan, persistent snowfall exceeding more than 24 hours over the Kofu-Basin resulted in 112 cm snowfall at Kofu. Slow progress of the south-coast cyclone also contributed to the long snowfall duration. An anticyclone developed over the northern Japan (∼1032 hPa) also contributed to this extreme snowfall. This anticyclone brought warm and moist air inflow by southeasterlies forming moisture flux convergence over the Kanto-Koshin district on the morning of 14th when snowfall started in the Koshin district in spite that the south-coast cyclone was located to the south of Kyushu. Further, ageostrophic cold northerlies with high pressure extension from the anticyclone by “cold-air damming (CAD)” would suppress warming with the approaching south-coast cyclone and keep snowfall until the morning of 15th. In other four heavy snowfall events at Kofu, snowfall durations were almost 12 hours. Although anticyclone to the north and CAD were identified in each case, the moisture transport from the southeast was not evident and moisture flux convergence was not formed earlier.
著者
Takeshi Enomoto
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.66-71, 2019 (Released:2019-11-27)
参考文献数
20

The predictability of the Heavy Rain Event in July 2018 is examined by forecast experiments with an operational global atmospheric forecast model. Experiments from different initial times show that the overall rainfall distribution at the peak on 6 July can be predicted from 12 UTC, June 30, and later. In the successful forecasts, the track error of Typhoon Prapiroon against the best track is small. In the experiments with longer lead times, by contrast, the Baiu frontal zone has a northwared bias with less precipitation, and Prapiroon hardly develop and migrates westward. Poor track forecasts seem to be related to the limited vertical development of the vortex. Near surface equivalent potential tempeature and Q-vector analysis show that Prapiroon act to intensify the Baiu frontal zone. In conclusion, the correct track forecast is essential for Baiu frontogenesis and the formation of heavy precipitation in western Japan.
著者
Akira Kuwano-Yoshida
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.10, pp.199-203, 2014 (Released:2014-12-06)
参考文献数
29
被引用文献数
9 9

The “Local deepening rate (LDR)”, the local surface pressure tendency, which is normalized by the sine of latitude and similar to the definition of an explosive cyclone, is introduced to extratropical cyclone activity analysis. The LDR has the advantage of being much simpler than conventional methods such as cyclone tracking and time filtering. The time average of positive LDR, which implies cyclone deepening, captures not only individual explosive cyclone's deepening but also the mid-latitude storm track climatology. The probability of explosive deepening, defined as LDR ≥ 1 hPa h-1 and based on ensemble forecasts, accurately represents the deepening potential and provides information regarding the influence area of storms—analogous to the strong wind area used in typhoon forecasts. The LDR can also be used to assess the quality of storm tracks in reanalyses products. In the 20th century reanalysis, the storm track activity, calculated from ensemble mean surface pressure, is too weak before 1910 in the North Pacific, and in the South Pacific low activity is observed up to the end of the 20th century, because of large ensemble spread due to few surface pressure observations.
著者
Takeshi Enomoto
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.15A-012, (Released:2019-10-25)

The predictability of the Heavy Rain Event in July 2018 is examined by forecast experiments with an operational global atmospheric forecast model. Experiments from different initial times show that the overall rainfall distribution at the peak on 6 July can be predicted from 12 UTC, June 30, and later. In the successful forecasts, the track error of Typhoon Prapiroon against the best track is small. In the experiments with longer lead times, by contrast, the Baiu frontal zone has a northwared bias with less precipitation, and Prapiroon hardly develop and migrates westward. Poor track forecasts seem to be related to the limited vertical development of the vortex. Near surface equivalent potential tempeature and Q-vector analysis show that Prapiroon act to intensify the Baiu frontal zone. In conclusion, the correct track forecast is essential for Baiu frontogenesis and the formation of heavy precipitation in western Japan.
著者
Tetsuya Takemi Toshiya Yoshida Shota Yamasaki Kentaro Hase
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15, pp.22-27, 2019 (Released:2019-02-06)
参考文献数
27
被引用文献数
5

An intense tropical cyclone, Typhoon Jebi (2018), landed the central part of Japan and caused severe damages. Quantitative assessment of strong winds in urban districts under typhoon conditions is important to understand the underlying risks. As a preliminary study, we investigate the influences of densely built urban environments on the occurrence of wind gusts in an urban district of Osaka City during Typhoon Jebi by merging mesoscale meteorological and building-resolving large-eddy simulations (LES). With the successful reproduction of the track and intensity of the typhoon in meteorological simulations, the simulated winds at the boundary-layer top of the LES model are used to quantitatively estimate the wind gusts in the urban district. The maximum wind gust in the analysis area of Osaka was estimated as 60-70 m s−1, which is comparable to the wind speed at the height of about 300 m.
著者
Qoosaku Moteki
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
pp.15A-007, (Released:2019-06-19)

Heavy rain in western Japan was broadly induced by the stagnation of the Baiu front during 5-7 July 2018. This study hypothesizes that cold air advection over the Sea of Japan intensified by Typhoon Prapiroon (Typhoon No. 7) was one of the triggering factors for the formation process of the Baiu front over western Japan. Typhoon Prapiroon passed over the Sea of Japan on 4 July and became extratropical at approximately 40°N on 5 July. During its passage, the strong southward pressure gradient force to the north of Typhoon Prapiroon broke down the convergence line of the Baiu front that remained at approximately 45°N before 4 July and thick cold air from the Okhotsk High flowed over the Sea of Japan. The Okhotsk High expanded toward the Sea of Japan and enhanced cold air advection to the north of western Japan. As a result, the Baiu front was stationary at approximately 35°N after 5 July. In addition, the westerly jet in the east of an upper-level trough deepened along the typhoon track was associated with the adiabatic component of the ascending motion over the isentropic upslope and was suggested to contribute to the maintenance of Baiu frontal convection.
著者
Yuhei Yamamoto Hirohiko Ishikawa
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.14, pp.179-184, 2018 (Released:2018-11-20)
参考文献数
22
被引用文献数
1

This paper provides the first attempt to investigate the spatial variability of diurnal change patterns of land surface temperature (LST) in urban areas of Japan by applying principal component analysis on LST data retrieved from Himawari-8 geostationary satellite data. The Tokyo and Osaka metropolitan areas were the focus of the analysis, and the target days were days with zero cloud cover in summer and winter. The results of the analysis showed that diurnal cycles of LST are mainly formed by two temporal change patterns in both seasons. For the summer case, the first two principal components (PCs) represented the temporal change patterns related to the amplitude and phase, respectively. For the winter case, the first two PCs represented the temporal change patterns related to the amplitude and gradual change in LST throughout the day, respectively. Results suggest that these temporal change patterns in both seasons have spatial variability partially dictated by land use and wind speed/direction.
著者
Nawo Eguchi Kunihiko Kodera
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.6, pp.137-140, 2010 (Released:2010-10-22)
参考文献数
18
被引用文献数
10 15

The impact of stratospheric sudden warming event in September 2007 on the tropics was investigated based on satellite data (CALIOP, MLS and TRMM PR). Equatorial temperature and water vapor at 100 hPa decreased by about 1 K and 1 ppmv within 10 days, respectively. Changes in tropical clouds are observed together with the occurrence of the SSW as i) frequent formation of higher-level cirrus clouds over the Maritime Continent, to where water vapor was transported from Asian Monsoon and where the lowest temperature occurred, ii) intensification of deep convective activity in the TTL over African continent, and iii) southward shift of the convective clouds over South American continent.
著者
Hirotaka Kamahori Osamu Arakawa
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.14, pp.165-169, 2018 (Released:2018-11-09)
参考文献数
18
被引用文献数
2 2

Tropical cyclone (TC) induced precipitation (TCP) over Japan is evaluated with the rain gauge observation based gridded dataset APHRO_JP. The TC–influenced frequency reaches a maximum in the Nansei Islands and decreases monotonically with latitude. On the other hand, the distribution of TCP indicates different characteristics from the one of TC–influenced frequency. The largest annual TCP, 500 mm yr−1 or more, occurs over eastern Kyushu (E-Kyushu), southern Shikoku (S-Shikoku), and the eastern Kii peninsula (E-Kii), where it accounts for 15% or more of the total precipitation. The maximum daily TCP amounts to 200 mm d−1 in those three areas, which are all located on the eastern side of Japan and correspond to eastward or southeastward topographic inclines. A significant relationship is found between the amount of annual TCP and topographic incline, and the large amount of TCP concentrates in the eastward or the southeastward inclines. The extreme daily TCP once every 50 years is also evaluated. The extreme daily TCP is estimated to be 500 mm d−1 comparable to the climatological annual TCP in E-Kyushu, S-Shikoku, and E-Kii. These three areas appear to be the most hazardous part of Japan in terms of TCP.
著者
Takumi Matsunobu Mio Matsueda
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.19-24, 2019 (Released:2019-06-22)
参考文献数
27

Extremely heavy rainfall events occurred over western Japan in early July 2018. This study assesses the predictability of these events for the period 5-7 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 5-6 July at lead times of ≤ 6 days, indicating the high predictability of this event. However, the extreme rainfall event of 6-7 July was less predictable. The NCEP forecasts, initialised on 30 June, performed better at predicting this event than the other operational forecasts. The JMA forecasts initialised on 1 July showed improved predictability; however, the ECMWF forecasts initialised after 30 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 6-7 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
Toshiya Yoshida Tetsuya Takemi
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.14, pp.174-178, 2018 (Released:2018-11-18)
参考文献数
17
被引用文献数
2

Effects of obstacle-height variability on mixing length and dispersive stress are investigated by conducting large-eddy simulations of airflows over arrays of roughness obstacles with variable height. We evaluate differences among three simulations of flows over obstacles with no, moderate, and high obstacle-height variability. Within the canopies, effective mixing length shows one local maximum and minimum in the simulation with no obstacle-height variability but two maxima and minima in the simulations with obstacle-height variability. The number of the local maxima and minima corresponds to that of the shear layers seen at the heights of obstacle tops. Enhanced dispersive stress appears within the canopy between the heights of the lower- and higher-obstacle tops in the simulations with obstacle-height variability. Particularly in the simulations with high obstacle-height variability, the magnitude of dispersive stress becomes comparable to that of the Reynolds stress at the height of the lower-obstacle top. These results suggest that actual urban areas with high building-height variability should significantly affect properties of mixing length and dispersive stress.
著者
Kazuto Takemura Shunya Wakamatsu Hiroki Togawa Akihiko Shimpo Chiaki Kobayashi Shuhei Maeda Hisashi Nakamura
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15A, pp.49-54, 2019 (Released:2019-08-09)
参考文献数
21
被引用文献数
1 1

This study investigates the influence of strong southerly moisture flux on an extreme rainfall event over western Japan in early July 2018, by using a global atmospheric reanalysis dataset. During its peak period from 5 to 7 July, extensive and unprecedented rainfall observed along the well-defined quasi-stationary Baiu front was attributed to two branches of extremely moist inflow from the southern confluence into western Japan. One was a shallow southerly airstream enhanced by the surface North Pacific Subtropical High, and the other was a deeper southwesterly airstream accompanying enhanced convection over the East China Sea. Both the vertically integrated moisture flux from the south and its convergence into western Japan reached the highest levels for 60 years due to an overwhelming contribution from the intensified southerlies. Anomalous diabatic heating associated with the active convection over the East China Sea acted to maintain the southwesterly moisture flux by inducing low-level cyclonic potential vorticity anomalies. During the rainfall event, a strong meander of the upper-level subtropical jet associated with the intensified surface North Pacific Subtropical High accompanied an amplified upper-level trough over the Korean Peninsula, which acted to induce ascent dynamically along the Baiu front.
著者
Akifumi Nishi Hiroyuki Kusaka
出版者
Meteorological Society of Japan
雑誌
SOLA (ISSN:13496476)
巻号頁・発行日
vol.15, pp.17-21, 2019 (Released:2019-02-05)
参考文献数
34
被引用文献数
2

In this study, we use observational data and numerical models to reveal whether foehn wind affects the record-breaking high-temperature event (41.1°C) at Kumagaya on July 23, 2018. On this day, the weather conditions at Kumagaya satisfied the conditions described in Takane et al. (2014) for a likely extreme high temperature (EHT) day: a “whale-tail” pressure pattern, no precipitation for 6 days, a high potential temperature at 850 hPa, and northerly surface winds. Our back-trajectory analysis shows that the air parcels came to Kumagaya from heights up to 3.0 km above sea level over the Sea of Japan. The Lagrangian energy budget analysis shows that adiabatic heating accounts for about 87.5% of the increase of the thermal energy given to the air parcel, with the rest from diabatic heating. The diabatic heating is caused by heating associated with surface sensible heat flux and the mixing by turbulent diffusion. The adiabatic and diabatic heating are calculated to have raised the temperature of air parcel by 14 and 2.0 K, respectively, for this EHT event. We conclude that the dynamic foehn effect and diabatic heating from the surface, together with mixing in the atmospheric boundary layer, affected the formation of this EHT event.