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The Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS) began as a Japanese domestic research project in 2010 and aimed to elucidate the mechanisms behind local high-impact weather (LHIW) in urban areas, to improve forecasting techniques for LHIW, and to provide high-resolution weather information to end-users (local governments, private companies, and the general public) through social experiments. Since 2013, the project has been expanded as an international Research and Development Project (RDP) of the World Weather Research Programme (WWRP) of the World Meteorological Organization (WMO). Through this project, the following results were obtained: 1) observation data for LHIW around Tokyo were recorded using a dense network of X-band radars, a C-band polarimetric radar, a Ku-band fast-scanning radar, coherent Doppler lidars, and the Global Navigation Satellite System; 2) quantitative precipitation estimation algorithms for X-band polarimetric radars have been developed as part of an international collaboration; 3) convection initiation by the interaction of sea breezes and urban impacts on the occurrence of heavy precipitation around Tokyo were elucidated by a dense observation network, high-resolution numerical simulations, and different urban surface models; 4) an “imminent” nowcast system based on the vertically integrated liquid water derived from the X-band polarimetric radar network has been developed; 5) assimilation methods for data from advanced observation instruments such as coherent Doppler lidars and polarimetric radars were developed; and 6) public use of high-resolution radar data were promoted through the social experiments.

An extremely heavy rainfall occurred over wide areas of Japan from 28 June to 8 July 2018. Heavily damaged areas were distributed from western Japan to Tokai region. This event was officially named the “Heavy Rain Event of July 2018” by the Japan Meteorological Agency. This paper provides a meteorological overview of the event. A comparison with other heavy rainfall events that have occurred since 1982 showed that the heavy rainfall event of 2018 was characterized by rainfall that was unusually widespread spatially and persistent temporally. Factors primarily responsible for this event included the prolonged concentration of two very moist airstreams over western Japan and persistent upward flow associated with activation of the stationary Baiu front. In some areas, line-shaped precipitation systems led to locally anomalous precipitation totals.

This study explored how heat island intensification affects precipitation in the Tokyo metropolitan area. Numerical experiments were made for the month of August from 2006 to 2013 using the Non-Hydrostatic Model (NHM) with a horizontal grid interval of 2 km and the Square Prism Urban Canopy (SPUC) scheme. We performed the experiments with two different specifications for the Tokyo area: the current highly urbanized surface conditions (CRNT experiment) and less urbanized conditions (MDUB experiment). The simulation results suggest that the mean monthly precipitation in the central Tokyo area was approximately 10% larger in the CRNT experiment than in the MDUB experiment, associated with a mean temperature rise of as much as 1 °C. We also examined the modification of daily precipitation characteristics in the two experiments. The CRNT experiment generally yielded larger amounts of area-maximum precipitation in the urban domain; however, differences between the experiments in daily precipitation varied among cases. Composite analysis was performed to investigate the processes associated with the differences in simulated precipitation. We found that in afternoon rainfall cases without preceding precipitation, a thermally induced change in circulation, particularly enhanced ascending motion, played an important role in the precipitation increase in the CRNT experiment.

The present paper describes background, mission, research topics, and preliminary results of the research project “Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS)”. TOMACS is one of the research projects of “Social System Reformation Program for Adaption to Climate Change” which has been started since July 2010 under the “Special Coordination Funds for Promoting Science and Technology” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT). TOMACS aims to understand the processes and mechanisms of extreme weather, using dense meteorological observation networks designed in the Tokyo metropolitan district, to develop a monitoring and predicting system of extreme phenomena (MPSEP), and to implement social experiments on extreme weather resilient cities in collaboration with related government institutions, local governments, private companies, and residents. More than 25 organizations and over 100 people participate in the present research projects. One of unique features of TOMACS is utilization of dense meteorological instruments in the Tokyo Metropolitan area which is one of the most urbanized areas in the world. The field campaign in the Tokyo metropolitan area, using research instruments and operational meteorological networks is planned by MRI and thirteen groups in the summers of 2011-2013 to target the tropospheric environment, boundary layer, initiation of convections and lifecycle of thunderstorms. Observation on environmental conditions of convections are carried out using radio sonde, wind profiler, GPS network, unmanned air viecle, and network of automated weather stations. Generation and development of convective precipitations are investigated by observations using Doppler lidar, rapid scan geostationary satellite, Kuband polarimetric radar, X-band polarimetric radar network (X-NET) and C-band research polarimetric radar and C-band operational Doppler radars. Several thunderstorms were captured by the dense meteorological network during 2011 campaign observations. The present paper shows preliminary results of the analysis. Social experiments on extreme weather resilient city using radar networks are also presented.

A single-layered square prism urban canopy (SPUC) scheme for the Japan Meteorological Agency nonhydrostatic model (NHM) was developed. This scheme considers the urban canopy layer with square prism–shaped buildings. The basic concept of this scheme is similar to those of the conventional energy balance models for an urban canyon structure. The scheme presented here differs slightly from them in its representation of the bulk resistance circuit and some treatments of radiation processes, however, as well as by considering the water reservoir on building surfaces. A comparison between the SPUC scheme and the existing slab scheme of the NHM was made on summer days in the Tokyo metropolitan area. The SPUC run more accurately reproduced the expected behavior of the urban canopy effect than did the slab run. The effective albedo was smaller in the SPUC run than in the slab run (the upward shortwave radiation of the SPUC run was smaller than that of the slab run). The forecast heat fluxes in the SPUC run, however, showed worse performances. Adequate parameter settings (especially concerning latent heat fluxes) are needed in the SPUC run. The mean bias errors of the surface air temperature during nighttime were less negative and slightly improved in the SPUC run than in the slab run.

気象庁では、火山現象予報の一つとして、2008年3月31日から降灰予報の業務を開始した。この論文では、降灰予報を高度化するために気象庁・気象研究所で開発している降灰予測システムを用いて、降灰量の量的予測を行う方法について論じる。降灰予測の方法は、まず初期値となる噴煙柱モデルを、仮想質量をもつ火山灰トレーサーで構成する。次に、トレーサーの時間発展を移流拡散モデルにより計算する。火山灰移流拡散モデルは、気象場に気象庁メソ数値予報モデル（MSM）を用いたラグランジュ記述のモデルであり、移流・拡散・降下・沈着の各過程を考慮している。そして沈着したトレーサーの仮想質量から、単位面積あたりの重量（面密度）として降灰量を算出する。噴煙柱モデルに気象レーダーで観測された噴煙エコー頂高度を用い、降灰量の算出にMSMより細かい水平格子間隔を用いて、本方法を2009年2月2日浅間山噴火の事例に適用した。観測値と比較して、降灰域の定性的な特徴は概ね予測でき、分布主軸上の降灰量も同じオーダーで予測可能であることが示された。

The Aeolian Dust Experiment on Climate Impact (ADEC) was initiated in April 2000 as a joint five-year Japan–China project. The goal was to understand the impact of aeolian dust on climate via radiative forcing (RF). Field experiments and numerical simulations were conducted from the source regions in northwestern China to the downwind region in Japan in order to understand wind erosion processes temporal and spatial distribution of dust during their long-range transportation chemical, physical, and optical properties of dust and the direct effect of radiative forcing due to dust. For this, three intensive observation periods (IOP) were conducted from April 2002 to April 2004. The in situ and network observation results are summarized as follows: (1) In situ observations of the wind erosion process revealed that the vertical profile of moving sand has a clear size dependency with height and saltation flux and that threshold wind velocity is dependent on soil moisture. Results also demonstrated that saltation flux is strongly dependent on the parent soil size distribution of the desert surface. (2) Both lidar observations and model simulations revealed a multiple dust layer in East Asia. A numerical simulation of a chemical transport model, CFORS, illustrated the elevated dust layer from the Taklimakan Desert and the lower dust layer from the Gobi Desert. The global-scale dust model, MASINGAR, also simulated the dust layer in the middle to upper free troposphere in East Asia, which originated from North Africa and the Middle East during a dust storm in March 2003. Raman lidar observations at Tsukuba, Japan, found the ice cloud associated with the dust layer at an altitude of 6 to 9 km. Analysis from lidar and the radio-sonde observation suggested that the Asian dust acted as ice nuclei at the ice-saturated region. These results suggest the importance of dust's climate impact via the indirect effect of radiative forcing due to the activation of dust into ice nuclei. (3) Studies on the aerosol concentration indicated that size distributions of aerosols in downwind regions have bimodal peaks. One peak was in the submicron range and the other in the supermicron range. The main soluble components of the supermicron peak were Na+, Ca2+, NO3−, and Cl−. In the downwind region in Japan, the dust, sea salt, and a mixture of the two were found to be dominant in coarse particles in the mixed boundary layer. (4) Observation of the optical properties of dust by sky-radiometer, particle shoot absorption photometer (PSAP), and Nephelometer indicated that unpolluted dust at source region has a weaker absorption than originally believed. A sensitivity experiment of direct RF by dust indicated that single scattering albedo is the most important of the optical properties of dust and that the sensitivity of instantaneous RF in the shortwave region at the top of the atmosphere to the refractive index strongly depends on surface albedo. A global scale dust model, MASINGAR, was used for evaluation of direct RF due to dust. The results indicated the global mean RF at the top and the bottom of the atmosphere were − 0.46 and − 2.13 W m− 2 with cloud and were almost half of the RF with cloud-free condition.

Meteorological characteristics and morphology of duststorms and other dust weather phenomena in the arid regions of East Asia were described in order to investigate a possible role of mesoscale cloud disturbances that develop in synoptic-scale mid-latitude cyclones in intensifying dust weather. This study is a statistical examination of conventional surface observational data as well as satellite data obtained during April 2000–2003. In the deserts of Mongolia and northern China (e.g., the Gobi Desert) duststorms and other weaker dust weather (i.e., dust whirls, blowing dust) frequently occur under a strong influence of synoptic-scale cyclones; on the other hand in the Taklamakan Desert (northwestern China), dust weather phenomena occur in a less organized fashion and may be driven mainly by local meteorological and geographical effects. A significant signal was identified, revealing of the intensification of dust weather by the presence of convective cloud disturbances. Meteorological changes such as pressure rise and temperature drop, typically found during the passage of cold fronts, were frequently observed in the cases of duststorms occurring in the analysis region. However, no definite tendency was found for moisture change and wind speed in relation to cloud activity, probably because rainfall amount is generally too low to moisten the boundary-layer air.

The mesoscale atmospheric environment of a dust event in the Tarim Basin, Taklimakan Desert, one of the key sources of aeolian dust in Northeast Asia, is investigated. Dust events in the Taklimakan Desert, including blowing dust and suspended dust, have long-lasting attributes, whereas in the Gobi Desert, dust events occur in phase with the passage of synoptic cyclones. Numerical simulations are conducted for a well-defined dust event on 12-15 April 2002. The Regional Climate Model of the Meteorological Research Institute (MRI-RCM) is employed. The MRI-RCM horizontal grid size is 20 km. The model reasonably well simulates time variations and spatial distributions of the surface wind field. Three types of mesoscale flow are revealed by the simulation. Sequential formation and/or coexistence of these flows can cause wind intensification and active dust emission from various areas across the basin. This gives a possible explanation for the long lasting dust events in the Tarim Basin. A closer examination shows that the development of these mesoscale circulations is closely related to the large-scale flow field behind the surface low-pressure system.

After severe eruptions of the volcano at Miyake Island in August 2000, a large amount of volcanic gas was released into the atmosphere. To simulate flows and dispersion of sulfur dioxide (SO 2 ) over Miyake Island, a set of numerical models was developed. The multi-nesting method was adopted to reflect a realistic meteorological field and to sufficiently resolve the flow over the island with a diameter of 8 km. The outermost model was the Regional Spectral Model (RSM) of the Japan Meteorological Agency (JMA) with a horizontal grid size of 10 km. Finer atmospheric structure was simulated with the nonhydrostatic model jointly developed by the Meteorological Research Institute and the Numerical Prediction Division of JMA (MRI/NPD-NHM) with grid intervals of 2 km, 400 m and 100 m. Realistic topography of the island was represented in the innermost model. The Lagrangian particle method was applied to the dispersion model, which is driven by the meteorological field of the 100 m grid MRI/NPD-NHM. The random walk procedure was used to represent the turbulent diffusion. The model was verified in four cases. Simulated SO 2 concentrations agreed well with observed concentrations at a monitoring station including temporal variation. Under a large synoptic change, however, accurate prediction became difficult. Further numerical experiments have been done to investigate characteristics of the flow and the distribution of SO 2 . Steady inflows, classified according to the surface wind speed and direction, were assumed. Simulated SO 2 distribution on the ground apparently depends on the surface wind. Under relatively weak inflow, there is a large diurnal change in SO 2 distribution, affected by the thermally induced flow. SO 2 gas is widely spread downstream in the nighttime but hardly reaches the coastal area in the daytime. On the other hand, SO 2 gas steadily reached the downstream coast with little diurnal variation under the stronger inflow. Ground temperature, as well as the static stability of the inflow, also influences downstream wind, turbulent diffusivity and SO 2 distribution.

This paper focuses on two cases of a local front that formed ahead of a synoptic cold front under a southwesterly inflow in the Kanto region. Vertical sounding data provided by an observation network of the Tsukuba Area Precipitation Studies (TAPS) enabled a detailed investigation of the mesoscale structure in the vicinity of the local front from its formation through dissipation. Despite some differences in synoptic features, the local front exhibited essential similarities in vertical structure between the two cases, as well as in horizontal structure. The local front, with WSW-ENE orientation, was well defined even in the daytime. A stable layer with a thickness of about 400 m formed on the cold side of the developed local front. As in the upper layer of warm inflow, southwesterly winds prevailed in this stable layer, except for the lowest 50-200 m. The maintenance mechanism of the local front is discussed. The evolution of the local front largely depends on the development of the stable layer on its cold side. In both cases, frontal formation began in the nighttime. A nocturnal cooling on the land surface contributed to forming a cold air mass on the northern side of the local front. In addition, the southwesterly inflow caused warming just above the surface-based cooling layer, which intensified the stratification. Furthermore, the observed vertical structure suggests that the locally modified circulation affected the frontal evolution. Two orographic effects on the circulation, 1) intensification of the inflow over the eastern part, and 2) downslope wind over the western part, both related to the mountains in the west of the Kanto region are expected. Especially, the downslope wind can reasonably explain the daytime persistence of the local front through the enhancement of stratification by adiabatic warming, and resultant influences on the mass transport.

A very fine mesh dispersion model was developed for volcanic gas over Miyake Island. The model consisted of a meteorological prediction part and a dispersion part. The multi-nesting method was used for the meteorological prediction part to express the field, depending on synoptic weather pattern in this study. The grid size of the innermost model was 100 m. The days when the observed SO2 concentration was comparatively high were chosen for the verification of the model. Four cases of 24-hour numerical simulations were conducted. We try to reproduce the SO2 concentration in each situation. Following results were derived. The effect of the advection was dominant as compared with other physics, so the volcanic gas moved leeward. Even the slight change of the wind direction largely varied the concentration. The volcanic gas spread widely, in case of weak wind at night, because of the mountain breeze. Although there were some cases of time-lags of the peaks, and some degrees of overestimation, or underestimation, each situation was almost well reproduced.

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[1] It has been argued that frequent dust storm developments in east Asia in spring are closely related to midlatitude synoptic-scale cyclone activity. This study investigates the relationship of springtime dust storms and other dust-related phenomena in east Asia to the tracks and locations of synoptic-scale cyclones by conducting statistical analyses of surface weather data, cyclone track data, and satellite data. Through these analyses, we discuss the role of cyclone activity on dust weather phenomena in east Asia. In the Gobi Desert and northeast China regions, strong cyclonic winds associated with strong cyclones are responsible for the dust weather developments, and the dust weather preferably occurs in the southwestern sector of the cyclone, where frontal activity and cold air action are significant. Despite the extremely dry climate, the formation of frontal cloud systems is evident particularly over the Gobi Desert, which will contribute to the higher frequency of severer dust weather. On the other hand, in the Taklamakan Desert severe dust weather (i.e., dust storm) is not so much affected by synoptic-scale cyclones, but weaker dust phenomena such as dust haze occur around the centers of cyclones that do not propagate farther eastward out of the Taklamakan region.

Nine species of benthic dinoflagellates collected in subtropical waters were cultured, extracted, and tested for mouse lethality, ichthyotoxicity, and hemolytic activity. Hemolytic activity was detectable in all species, but the activities of Amphidinium carteri, A. klebsi, and Gambierdiscus toxicus were outstanding. G. toxicus showed the most potent mouse lethality. Two hemolytic constituents of A. carteri were determined to be mono- and di-galactoglycerolipids. Maitotoxin, produced by G. toxicus, was suggested to have a molecular weight of 3402 ± 2 (m/z). Two potent toxins against mice were isolated from Prorocentrum lima and identified as okadaic acid and 5-methylene-6-hydroxy-2-hexen-1-okadaate.