Hiroshi Yoshikado

Influence of Air-Conditioning Waste Heat on Air Temperature in Tokyo during Summer: Numerical Experiments Using an Urban Canopy Model Coupled with a Building Energy Model

Abstract A coupled model consisting of a multilayer urban canopy model and a building energy analysis model has been developed to investigate the diurnal variations of outdoor air temperature in the office areas of Tokyo, Japan. Observations and numerical experiments have been performed for the two office areas in Tokyo. The main results obtained in this study are as follows. The coupled model has accurately simulated the air temperature for a weekday case in which released waste heat has been calculated from the energy consumption and cooling load in the buildings. The model has also simulated the air temperature for a holiday case. However, the waste heat from the buildings has little influence on the outdoor temperatures and can be neglected because of the low working activity in the buildings. The waste heat from the air conditioners has caused a temperature rise of 1°–2°C or more on weekdays in the Tokyo office areas. This heating promotes the heat-island phenomenon in Tokyo on weekdays. Thus, it is ...

Inland penetration of the sea breeze over the suburban area of Tokyo

Observational results of the structure of the sea breeze over the urban and suburban areas of Tokyo for four summer days are presented.On two of these days, the inland penetration of the sea breeze front could be clearly traced. In one case, the sea breeze was first observed along the shores of Tokyo Bay around 0900 JST, and propagated in three hours through the Tokyo City area, the width of which is about 20 km. It then advanced inland at a rate of 16 km h−1. Prior to the arrival of the sea breeze at the suburban site, the mixing height had remained at about 600 m for four hours. With the arrival of the sea breeze front, accompanied by an abrupt change in wind speed and direction, the mixing height increased sharply to 1700 m. It is suggested that this behavior and the structure of the front are intensified due to the urban effect, or the difference in the thermal characteristics between the urban and rural areas.On the days without a sea breeze front, the land breeze system during the early morning was less intense, allowing the sea breeze to develop simultaneously with the inland valley wind and easily form a large-scale local wind system during the morning hours. In both cases, the vertical motion accompanying the local wind system works as a feedback mechanism to control the local winds by modifying the thermal and pressure fields.

On some characteristics of the diurnal variation of O3 observed in Island, urban and rural areas

Some statistical and meteorological analysis on O3 near the ground was carried out using the data obtained at three sites in respectively, island, urban and rural areas, for 9 months from winter to summer. Night-time O3 is usually low but sometimes increases at the three sites almost at the same time. The increase in night-time O3 in winter is often associated with a winter monsoon pressure pattern. In spring, night-time O3 often increases near the passage of a cold front. However, in summer there are no special synoptic weather conditions for increase in night-time O3. Using the stability parameter defined by — Rn/U2 (Rn: net-radiation near the ground, U: surface wind speed), we showed that an increase in O3 at night is due to a decrease in this parameter and NOx concentration, irrespective of the season. Variation of daytime O3 in winter and early spring was found to be well described by the entrainment of background O3 aloft due to the development of mixing layer and the emission of NO near the observation site. On a typical day of high level O3 episode, O3 at the island site sometimes exceeds 140 ppb in the sea breeze. O3 precursors carried by the land breeze in the previous night or early morning was inferred to be a possible cause of this high level O3.

Analysis of the Relationship between Changes in Meteorological Conditions and the Variation in Summer Ozone Levels over the Central Kanto Area

An increasing trend in ground-level ozone (O3) concentrations has recently been recognized in Japan, although concentrations of ozone precursors, nitrogen oxides (NOx), volatile organic compounds (VOCs) and nonmethane hydrocarbons (NMHCs) have decreased. In this paper, the relationship between meteorological factors (temperature and wind speed) and ground-level ozone concentrations in the summer over the central Kanto area of Japan was examined using both statistical analyses and numerical models. The Fifth-Generation NCAR/Penn State Mesoscale Model (MM5) and the Community Multiscale Air Quality (CMAQ) model were employed in this study. It was found that there is a close relationship between meteorological conditions and ground-level ozone concentrations over the central Kanto area. In summer, up to 84% of the long-term variation in peak ozone concentrations may be accounted for by changes in the seasonally averaged daily maximum temperature and seasonally averaged wind speed, while about 70% of the recent short-term variation in peak ozone depends on the daily maximum temperature and the daily averaged wind speed. The results of numerical simulations also indicate that urban heat island (UHI) phenomena can play an important role in the formation of high ozone concentrations in this area.

Development of a low-rise industrial source dispersion model

In Japan, with amendment of the Air Pollution Control Law in May 1996, various substances, including benzene and trichloroethylene, were newly designated as hazardous air pollutants, and environmental standards were established. In this situation, it is necessary to develop a dispersion model that is applicable to environmental impact assessment of industrial areas with a complex of factory buildings. To overcome this problem, modification of the ISC downdraught model was undertaken based on datasets from wind tunnel experiments by the Ministry of International Trade and Industries and Japan Environmental Management Association for Industry. This new model is called the METI-LIS model, and comparison shows that the performance of the model is better than that of the original ISC model.

Intense Summer Heat in Tokyo and Its Suburban Areas Related with Variation in the Synoptic-Scale Pressure Field: A Statistical Analysis

AbstractIntense summer heat in Tokyo, Japan, and its suburban areas between 1990 and 2010 was statistically analyzed. Sample days were selected from among days with a sea breeze and sufficient sunshine duration, because sea breeze is the dominant summertime meteorological system in the region. Excess in the daily maximum temperature of an inland urban site in Tokyo over a site facing the outer sea where the sea breeze originates was selected as a key index. A comparison of a group of days for which the temperature excess was large with an opposing group of days for which it was small revealed a distinct difference in diurnal wind variations: persistent southwesterly winds overwhelmed the sea breeze in areas facing the outer sea in the former case, whereas in the latter case a diurnal sea-breeze cycle was typically observed in those areas as well as in the inland areas. This difference could furthermore be connected to differences in the pressure gradient in the region, that is, differences in the synoptic...

Development of numerical model for dispersion over complicated terrain in the convective boundary layer

Complicated terrain and atmospheric stability are important factors in the predicting the dispersion of air pollutants. The aim of our study is to develop practical dispersion model for unstable conditions for regulatory use. The numerical model we adopted was a combination of the potential flow model and Lagrangian stochastic dispersion model. In this model, time-mean flow field is solved by the potential flow model and concentration field is calculated by Lagrangian stochastic model by using the flow field from potential model. Wind tunnel experiments simulating gas dispersion in the convective boundary layer were also done. The data sets of turbulent properties and concentrations obtained in the wind tunnel were used for the modification of dispersion model and model validation. Based on the developed model, user-friendly software applicable to dispersion over complicated terrain was also developed.

Sea Breeze Blowing into Urban Areas: Mitigation of the Urban Heat Island Phenomenon

Currently, about 50% of the world’s population is living in urban areas, and that figure is predicted to continue to increase (United Nations, Department of Economic and Social Affairs Population Division, Population Estimates and Projections Section (2009) World urbanization prospects: the 2009 revision). On the other hand, many cities are facing problems caused by urbanization. The urban heat island phenomenon, one of the urban climate problems, is a typical environmental problem encountered in dense urban areas in summer. The use of the sea breeze to mitigate the urban heat island phenomenon has attracted attention in coastal cities. Some statistics show that about 40% of the world’s population lives within 100 km of the coast (World Resources Institute, Fisheries (2007) Population within 100 km of coast). Further investigation of the environment in the urban area near the coast is, therefore, important. In this chapter, Tokyo is targeted for investigation. Tokyo is the Japanese capital, and its surrounding region, the Tokyo metropolitan area, comprises a circular area with a radius of 50 km and a population of over 30 million. Within this area, the sea breeze from Tokyo Bay is an important factor mitigating the air temperature rise in summer. However, ongoing urbanization could be changing not only the mechanism of the energy balance on the urban surface but also the sea breeze system in the region. To clarify the effects of urbanization, a mesoscale meteorological model was adopted for analysis. Simulation results suggest that expansion of the Tokyo metropolitan area from the 1970s to the 1990s has induced a temperature rise near the ground and that the difference is largest in inland areas. Moreover, the time of sea breeze penetration is delayed in suburban areas. These results suggest that the ongoing urbanization process could raise the air temperature and change the sea breeze system in the Tokyo metropolitan area.