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JMSJ, 2018, Vol. 96A

Special issue on Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS)

Articles

Iwai et al. (2018)

Iwai, H., S. Ishii, S. Kawamura, E. Sato, and K. Kusunoki, 2018: Case study on convection initiation associated with an isolated convective storm developed over flat terrain during TOMACS. J. Meteor. Soc. Japan, 96A, 3-23.
https://doi.org/10.2151/jmsj.2017-014   Graphical Abstract

Highlights:

• Many isolated convective storms developed in the southern Kanto Plain on August 17, 2012. We clarify the dynamics leading to the convection initiation of one of them using different remote sensing instruments.
• A convergence line in the form of a sea breeze front moved inland from Tokyo Bay. A near-surface air parcel was lifted to its lifting condensation level (LCL) by an updraft in a convergence zone with a 3 km horizontal scale, which formed the west edge of the convergence line (Fig. 1).
• The saturated air parcel at the LCL was then lifted to its level of free convection (LFC; Fig. 2) by the updrafts associated with thermals below the cumulus cloud base.

Suzuki et al. (2018)

Suzuki, S.-I., T. Maesaka, K. Iwanami, S. Shimizu, and K. Kieda, 2018: X-band dual-polarization radar observations of the supercell storm that generated an F3 tornado on 6 May 2012 in Ibaraki Prefecture, Japan. J. Meteor. Soc. Japan, 96A, 25-33.
https://doi.org/10.2151/jmsj.2017-019   Graphical Abstract

Highlights:

• X-band dual-polarization (multi-parameter) radars were used to observe a supercell storm that generated an F3 tornado in Ibaraki Prefecture, Japan on 6 May 2012. The observed data collected for this storm clearly exhibited the typical polarimetric features of a supercell storm, such as the Z_DR (differential reflectivity) arc, Z_DR column, and the K_DP (specific differential phase) column, as well as their time evolution.
• The Z_DR arc emerged at 10 to 15 min before the tornadogenesis. The Z_DR column appeared approximately 1 h before the formation of the Z_DR arc and was intermittent until tornadogenesis. As the Z_DR arc appeared, the column became tall and stable and lasted until the dissipation of the tornado. These Z_DR signatures of the supercell storm persisted for approximately half an hour.

Seto et al. (2018)

Seto, Y., H. Yokoyama, T. Nakatani, H. Ando, N. Tsunematsu, Y. Shoji, K. Kusunoki, M. Nakayama, Y. Saitoh, and H. Takahashi, 2018: Relationships among rainfall distribution, surface wind, and precipitable water vapor during heavy rainfall in central Tokyo in summer. J. Meteor. Soc. Japan, 96A, 35-49.
https://doi.org/10.2151/jmsj.2017-020   Graphical Abstract

Highlights:

• The relationships between the occurrence of intense rainfall and the convergence of surface winds and water vapor concentration for typical heavy-rainfall cases were examined using data from July to August in 2011–2013, obtained from high-density meteorological observations in Tokyo, Japan.
• Corresponding to heavy-rainfall areas, the convergence of surface winds tended to increase for several tens of minutes prior to the heavy rainfall (Fig. 1). The peak time of wind convergence was 10–30 min before the heavy-rainfall occurrence, and the increasing convergence continued for approximately 30 min until the convergence peak time.
• Around the heavy-rainfall area, the increase in the water vapor concentration (WVC) index coincided with the increase in convergence (Fig. 2).
• From these results, by monitoring the temporal variations and distributions of these parameters using a high-density observation network, it should be possible to predict the occurrence of heavy rainfall rapidly and accurately.

Misumi et al. (2018)

Misumi, R., N. Sakurai, T. Maesaka, S.-I. Suzuki, S. Shimizu, and K. Iwanami, 2018: Transition process from non-precipitating cumuli to precipitating convective clouds over mountains: Observation by Ka-band Doppler radar and stereo photogrammetry. J. Meteor. Soc. Japan, 96A, 51-66.
https://doi.org/10.2151/jmsj.2017-021   Graphical Abstract

Highlights:

• Convective storms are frequently initiated over mountains under weak synoptic forcing conditions. However, the initiation process of such convective storms is not well understood due to a lack of observations, especially of the transition process from non-precipitating cumuli to precipitating convective clouds.
• During the transition process, weak radar echoes observed by the Ka-band radar rose to the higher level and radar reflectivity rapidly increased (E7 in Fig. 13). This phenomenon suggests that drizzle particles produced in a pre-existing convective cloud were lifted by a newly developed updraft, and raindrops were formed rapidly by coalescence of the drizzle particles and cloud droplets.

Sugawara et al. (2018)

Sugawara, H., R. Oda, and N. Seino, 2018: Urban thermal influence on the background environment of convective precipitation. J. Meteor. Soc. Japan, 96A, 67-76.
https://doi.org/10.2151/jmsj.2018-010   Graphical Abstract

Highlights:

• Influence of urban heat excess on atmospheric stability leading to convective precipitation was investigated in Tokyo.
• Convective Available Potential Energy (CAPE) was evaluated in an idealized situation. Although its ideality, the reality of our analysis was achieved by using the observed results in Tokyo for the model inputs.
• Urban heat excess of 200 Wm^-2 increased CAPE by 75%. The anthropogenic vapor flux also increased CAPE, but was near negligible (1% in CAPE).
• The neutral stratification in the urban area in the morning increased CAPE by five times its rural value.

Bélair et al. (2018)

Bélair, S., S. Leroyer, N. Seino, L. Spacek, V. Souvanlasy, and D. Paquin-Ricard, 2018: Role and impact of the urban environment in a numerical forecast of an intense summertime precipitation event over Tokyo. J. Meteor. Soc. Japan, 96A, 77-94.
https://doi.org/10.2151/jmsj.2018-011   Graphical Abstract

Highlights:

• The impact of urbanized surfaces on the development of an intense precipitation event over Tokyo is investigated in this study by comparing two numerical forecasts produced with a 250-m version of the Canadian Global Environmental Multiscale atmospheric model, including a control run with full physics and another without the effect of urban surfaces.
• Results from the two simulations indicate that for this specific case urban areas could lead to an increase of precipitation intensity over Tokyo although they do not appear to have a substantial impact on the timing and overall area of precipitation (Figure on the left).
• Several hypotheses were tested as part of this study. Results show that the precipitation intensification over Tokyo seems to be linked with a strengthening of the horizontal flow of thermodynamic energy at low levels from Tokyo Bay. Another contributing aspect could be linked with the production of low-level waves first propagating away from the Tokyo Bay coast and then in the orthogonal direction (towards the southwest) during the most intense phase of the precipitation event (Figure on the right).

Sano et al. (2018)

Sano, T., and S. Oishi, 2018: Observational study on formation of a localized rainfall on a basin with heat and aridity on days of weak synoptic disturbance in summer. J. Meteor. Soc. Japan, 96A, 95-117.
https://doi.org/10.2151/jmsj.2018-012   Graphical Abstract

Highlights:

• To elucidate the formation of a localized rainfall on a basin with heat and aridity under weak synoptic disturbance in summer, the characteristics of atmospheric conditions on the Kofu Basin preceding the appearance of almost primary precipitating cells were described from localized rainfall events on the Kofu Basin on days of weak synoptic disturbance at the surface.
• According to 23 localized rainfall events on the Kofu Basin on days of weak synoptic disturbance at the surface from 1 June to 30 September in 2012 to 2014, the appearance positions of the almost primary cellular echoes, which is corresponded to precipitating cells, observed by the X-band multi-parameter radar at the Kofu Campus of University of Yamanashi (UYR) were concentrated in the central to eastern regions on the Kofu Basin (Fig.1).
• According to the observation case on 25 July 2014, owing to the thermal contrast between the Kofu Basin with heat and aridity and the outside environment, the south-component wind blowing in the valley connecting it to the coastal region of Suruga Bay and the east-component wind blowing in the valley connecting it to the Kanto Plain entered the Kofu Basin, which caused an increase in the water vapor mixing ratio and the equivalent potential temperature at the surface in the Kofu Basin (Fig.2). After that, through the abrupt increase in precipitable water vapor in the central region of the Kofu Basin, the precipitating cells appeared over the local region between the southern-component wind and the eastern-component wind.

Chandrasekar et al. (2018)

Chandrasekar, V., H. Chen, and B. Philips, 2018: Principles of high-resolution radar network for hazard mitigation and disaster management in an urban environment. J. Meteor. Soc. Japan, 96A, 119-139.
https://doi.org/10.2151/jmsj.2018-015  Graphical Abstract

Highlights:

• Due to the Earth’s curvature, complex terrain and urban deployment challenges, the physically large, high-power, long-range (i.e., S- or C-band) radars in the current operational network have severe limitations in observing the lower part of troposphere where many hazardous weather phenomena occur, such as tornadoes and flash floods.
• This paper presents the principles and applications of high-resolution X-band radar network for urban weather hazards detection and disaster mitigation. A technical summary of the Dallas-Fort Worth (DFW) dense urban radar network is presented from the perspective of tracking and warning of hails, tornadoes, and floods.
• The architecture and associated algorithms of various product systems for the DFW network are detailed, including the real-time hail detection system, the multiple Doppler wind retrieval system, and the high-resolution quantitative precipitation estimation system. The application products in the presence of high wind, tornado, hail, and flash flood are investigated, and the product performance is demonstrated through cross-validation with ground observations and weather reports.

Cifelli et al. (2018)

Cifelli, R., V. Chandrasekar, H. Chen, and L. E. Johnson, 2018: High resolution radar quantitative precipitation estimation in the San Francisco Bay Area: Rainfall monitoring for the urban environment. J. Meteor. Soc. Japan, 96A, 141-155.
https://doi.org/10.2151/jmsj.2018-016   Graphical Abstract

Highlights:

• Radar quantitative precipitation estimation (QPE) over complex terrain such as the San Francisco Bay Area remains a challenge due to the complex spatial and temporal variability of precipitation microphysics.
• The NEXRAD operational radar network is insufficient to provide accurate, short-term near surface rainfall estimates in the Bay Area for urban hydrometeorological applications. This paper describes the deployment of X-band radar system to augment NEXRAD coverage and aid in monitoring precipitation for local forecasters and water managers as well as to better understand precipitation processes occurring in this region.
• The X-band radar can provide high quality rainfall estimates that perform better than NEXRAD-based operational products. The high resolution rainfall monitoring system based on gap-filling radars in this urban region also provides a host of benefits across different sectors of the economy.

Kawabata et al. (2018)

Kawabata, T., H.-S. Bauer, T. Schwitalla, V. Wulfmeyer, and A. Adachi, 2018: Evaluation of forward operators for polarimetric radars aiming for data assimilation. J. Meteor. Soc. Japan, 96A, 157-174.
https://doi.org/10.2151/jmsj.2018-017   Graphical Abstract

Highlights:

• Four forward operators for C-band dual polarimetric radar data are compared with both each other and actual observations from the view point of utilization in data assimilation.
• The first operator derives polarimetric parameters from the models and the other three converters estimate the mixing ratio of rainwater from the measured polarimetric parameters. The second converter uses both the horizontal reflectivity (Z_H) and the differential reflectivity (Z_DR), the third uses the specific differential phase (K_DP), and the fourth uses both K_DP and Z_DR, respectively.
• Comparisons with modeled measurements show that the accuracy of the third converter is superior to the other two (Table 1). Another evaluation with actual observations shows that the first converter has slightly higher fractions skill scores than the other three.
• Considering the attenuation effect (Fig. 1), the first operator and the third converter only with K_DP are found to be the most suitable for data assimilation at C-band.

Saito et al. (2018)

Saito, K., M. Kunii, and K. Araki, 2018: Cloud resolving simulation of a local heavy rainfall event on 26 August 2011 observed in TOMACS. J. Meteor. Soc. Japan, 96A, 175-199.
https://doi.org/10.2151/jmsj.2018-027   Graphical Abstract

Highlights:

• A local heavy rainfall of about 100 mm h^-1 occurred in Tokyo and Kanagawa Prefecture on 26 August 2011. In an analysis using geostationary multi-purpose satellite rapid scan images (Fig. 1) and dense automated weather station networks, development of deep convection occurred after the merging of sea breezes from the east and the south.
• We conducted an ensemble prediction using a singular vector method based on the JMA nonhydrostatic model (NHM). Observed characteristics of the local heavy rainfall were well reproduced by one of the ensemble members with a horizontal resolution of 2 km (Fig. 2).
• A conceptual model of the initiation of deep convection by the formation of a low-level convergence zone succeeding merging of the two sea breezes from the east and south is proposed based on observations and numerical simulation results. In this event, the northerly ambient wind played an important role on the occurrence of the local heavy rainfall around Tokyo by suppressing the northward intrusion of the sea breeze from the south.

Hirano et al. (2018)

Hirano, K., and M. Maki, 2018: Imminent nowcasting for severe rainfall using vertically integrated liquid water content derived from X-band polarimetric radar. J. Meteor. Soc. Japan, 96A, 201-220.
https://doi.org/10.2151/jmsj.2018-028   Graphical Abstract

Highlights:

• A very-short-range nowcast system (VIL_NC) using vertically integrated liquid water content, which is estimated from the X-band polarimetric radar, is developed to increase the skill in forecasting imminent localized heavy rainfall (LHR).
• During the three case studies, VIL_NC performs significantly better than rainfall rate nowcast system (RR_NC) by correctly capturing the time at which rainfall thresholds are first exceed at a majority of grid points from a nowcast made 10 minutes previously, whereas RR_NC produces a much greater number of delays and misses.
• The reduced time lag associated with VIL_NC was achieved partly because VIL_NC successfully captured “eggs” of rain formed aloft and “cores” brought in by verticaly wind shear during the precipitation events. This shows a possible application of using VIL_NC as an indicator or alarm system for heavy rainfall that might affect daily public activities.

Seino et al. (2018)

Seino, N., R. Oda, H. Sugawara, and T. Aoyagi, 2018: Observations and simulations of the mesoscale environment in TOMACS urban heavy rain events. J. Meteor. Soc. Japan, 96A, 221-245.
https://doi.org/10.2151/jmsj.2018-029   Graphical Abstract

Highlights:

• We investigated the formation and development processes of an extremely developed thunderstorm (Case 1 on August 26, 2011) and a moderately developed thunderstorm (Case 2 on July 18, 2013). Radiosonde sounding data showed that, compared to Case 2, the mesoscale environment of the severe storm in Case 1 featured a lower level of free convection and a deeper layer of easterly flow.
• Numerical simulation results fairly represented the spatial distribution and amounts of the rainfall in both cases. In Case 1, the formation of a distinct convergence zone between easterly and southerly flows was the likely trigger of active convective systems around Tokyo.
• To further examine the urban impact on precipitation, we performed two comparative simulations: one using realistic current urban surface conditions (CRNT experiment) and the other using less-urbanized surface conditions (LURB experiment). The CRNT experiment yielded more rainfall than the LURB experiment in the central urban area (Fig. 1). It appears that the higher temperatures caused by urbanization can lead to increased rainfall in Tokyo, not by the change in the static stability, but by intensifying convergence, ascending motion, and the upward transport of the low-level moisture (Fig.2).

Pereira Filho et al. (2018)

Pereira Filho, A. J., F. Vemado, K. Saito, H. Seko, J. L. Flores Rojas, and H. A. Karam, 2018: ARPS simulations of convection during TOMACS. J. Meteor. Soc. Japan, 96A, 247-263.
https://doi.org/10.2151/jmsj.2018-030   Graphical Abstract

Highlights:

• Deep convection over TMA is induced by the heat island (Fig. 1) and sea breeze (Fig. 2) during weak synoptic forcing simulated with the ARPS/T-TEB system and JMA global model inputs.
• The ARPS/T-TEB simulations of three deep convection episodes are similar to previous studies.
• Dissipation (phase) errors on hourly precipitation forecasts tend to dominate, though scores improved up to 300% within the advective time scale with JMA boundary and initial conditions.
• The goal of the study was to test the T-TEB scheme, recently implemented in the ARPS system.
• The T-TEB includes momentum transfer by buildings and constructions.
• Similar ARPS simulations for the Metropolitan Area of São Paulo (MASP) also include wind acceleration by buildings and structures.