Yukitaka Ohashi

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 ...

The phenology of cherry blossom (Prunus yedoensis “Somei-yoshino”) and the geographic features contributing to its flowering

We investigated relationships between the flowering phenology of Prunus yedoensis “Somei-yoshino” (cherry blossom) and the local temperatures in Japan. Our observations were carried out across the Okayama Plain, which included Okayama City (about 700,000 inhabitants), from the winter of 2008 to the spring of 2009. Local air temperature (AT) and the globe temperature (GT) were recorded at the tree height. The flowering dates (FDs) of P. yedoensis were earliest in the central commercial area (located at the center of the plain), followed by the north residential area (further inland), and finally the south residential area (seaward). The recorded FDs were related to the period-averaged daily maximum/minimum AT and GT, and the phenologically effective AT and GT defined in this study. Of these parameters, the phenologically effective GTs correlated most with the FDs. Since the GT is determined by AT, solar and infrared radiations, and wind speed, our previous result suggests that a combination of these three components surrounding the tree is more important for budding and flowering than is AT alone. The supposition is supported by the flowering of P. yedoensis being the latest at the coastal region of the Okayama Plain where the AT were higher than at the inland region, excluding the urban area; it is probably caused by stronger winds there than at the other sites.

Effects of Synoptic-Scale Wind under the Typical Summer Pressure Pattern on the Mesoscale High-Temperature Events in the Osaka and Kyoto Urban Areas by the WRF Model

AbstractThe actual conditions of mesoscale summer high temperatures (HTs) recorded in the Osaka–Kyoto urban area of Japan were investigated using an observation network. The daytime temperatures observed on 10 HT events in this area were the highest in the southern area of Kyoto [area with no Automated Meteorological Data Acquisition System (AMeDAS) observation sites]. To quantitatively evaluate the formation mechanisms of HT events, a heat budget analysis on an atmospheric column was conducted using the Weather Research and Forecasting (WRF) model. The results showed that over the HT area the daytime column temperature increased as a result of sensible-heat diffusion generated from the urban surface at the contribution rate of 54% and as a result of the sensible-heat advection and diffusion supplied from the sides and at the top of the column at the rate of 46% of all sensible heat supplied. To clarify previously unreported effects of synoptic-scale winds under typical summer pressure patterns on the HT ...

Numerical Simulations of Outdoor Heat Stress Index and Heat Disorder Risk in the 23 Wards of Tokyo

AbstractIn this study, the summertime outdoor heat stress hazard and heat disorder risks (HDR) were simulated numerically using a mesoscale meteorological model combined with an urban canopy model and a building energy model. Model grid maps including the 23 wards of Tokyo (23 Tokyo), Japan, were produced with a 1-km horizontal resolution for the period of July–September 2010. Model simulations of the daily maximum wet-bulb globe temperature (WBGTmax), which was adopted as a heat stress index, indicated the spatial heterogeneity of the heat stress hazard within 23 Tokyo. The heat stress hazard was greater in the inland western region, particularly for sunny conditions in July and August (based on the monthly mean; the maximum difference exceeded 2°C for both sunny and shaded conditions). This likely occurred as a result of greater spatial heterogeneity in the globe temperature than in the air temperature among model grid cells, with differences in the radiation environment induced by differences in urban ...

In situ observational research of the gap wind “Hijikawa-Arashi” in Japan

The Hijikawa-arashi, a gap wind occurring in Ozu City, Ehime Prefecture, Japan, was investigated through in situ observations of horizontal and vertical directions. Analysis of surface air temperature data revealed that the inland Ozu Basin was radiatively cooled on the days on which the Hijikawa-arashi events occurred. This induced a greater difference in air temperature between the basin and the estuary of the Hijikawa River in comparison to days that no basin cooling occurred. In addition, the wind speeds of the Hijikawa-arashi observed at the estuary of the Hijikawa River were strongly proportional to the sea-level pressure difference between the inland Ozu Basin and the estuary. Theoretical calculations indicated that this pressure gradient force was sufficient for driving the strong wind of the Hijikawa-arashi. Moreover, calculation of the Froude number using vertical meteorological data revealed that the Hijikawa-arashi developed as a supercritical flow. That is, the flow was intensified at the exit of the gap, in accordance with the hydraulic theory. The vertical observations detected the inversion layer over the Hijikawa-arashi and suggested an application of the shallow water theory to this gap wind. The Hijikawa-arashi is an interesting gap flow with a strong wind, despite its small-scale geography relative to other gap winds worldwide. There is an important trigger getting higher basin pressure upstream due to the radiative cooling of the atmosphere and formation of a cold pool at the basin.