Effects of Mountains and Urban Areas on Daytime Local-Circulations in the Osaka and Kyoto Regions

Abstract

In the current study, the effects of topography and urbanization on the daytime local-circulations in the area of the Osaka-Kyoto plain were investigated using a mesoscale atmospheric model. The main results obtained from the numerical and observational data analyses are as follows:1) The stagnation of the inland penetration of the sea-breeze front that occurs in the peripheral portion of the Tokyo urban area does not clearly occur in the peripheral portion of the Osaka urban area. The stagnation is attributed to the heat-island circulation that develops over the peripheral portion of the urban area. Because the northern peripheral portion of the Osaka urban area faces mountains, the valley circulation weakens the heat-island circulation; the about 600-m mountains surrounding the Osaka and Kyoto urban areas are the most suitable to cause the weakening of the heat-island circulation. The valley circulation also induces the surface-air-temperature increase over the plain, through an adiabatic process due to its downward flow; the temperature increase strengthens the horizontal pressure gradient between the sea-breeze circulation and inland areas.2) The surface air over the suburban region between the Osaka and Kyoto urban areas remains drier than that over the Osaka and Kyoto urban areas, until the arrival of the sea-breeze front, even though urban areas were thought to be drier than suburban areas. This dryness results from the fact that the valley circulation transports drier air downward from the upper levels over the suburban area, and transports the surface-air moisture supplied from the ground surface into mountainous areas. The valley circulation also appears to play an important role in the transport of pollutants from the suburban area into mountainous areas.3) A chain flow, which flows downward from the upper levels over the Osaka urban area to the lower levels over the Kyoto urban area, forms ahead of the sea-breeze front. This flow can result in the transport of pollutants emitted from the Osaka urban area into the inland Kyoto area prior to the transport of pollutants by the sea-breeze circulation. Additionally, the chain flow intensifies the downward flow of the valley circulation over the suburban region between the Osaka and Kyoto urban areas.

Progress in Urban Meteorology :A Review

“…Similar threedimensional numerical simulations or data analyses have examined the interaction between UHI and local circulations in other cities: Nagoya (Kitada et al 1998), Hong Kong (Liu et al 2001;Tong et al 2005), and Wroclaw (Szymanowski 2005). Ohashi and Kida (2002a, 2002b used observations and threedimensional numerical simulations to investigate circulations associated with two adjacent urban areas, one coastal (Osaka) and the other inland (Kyoto). These authors showed that a chain-like flow, which connected the two UHI circulations, formed between the two urban areas.…”

Coupling a Single-Layer Urban Canopy Model with a Simple Atmospheric Model: Impact on Urban Heat Island Simulation for an Idealized Case

“…Numerical simulations under idealized or realistic summer synoptic conditions have been conducted using two-or three-dimensional mesoscale models that include a standard surface-layer scheme called slab urban model (e.g., Kimura and Takahashi 1991;Yoshikado 1992Yoshikado , 1994Avissar 1996;Ichinose et al 1999;Kusaka et al 2000;Kanda et al 2001;Ohashi andKida 2002a, 2002b). Their numerical studies have provided us with important and essential idea of the urban weather and climate in summer.…”

Effects of Land Reclamations in Osaka Bay on the Regional Climate

“…Selected days satisfy the following three weather conditions at the Osaka observatory: (1) total sunshine for more than 70% of the day, (2) daily mean surface wind speed of less than 3 m s −1 , and (3) no daily precipitation. These conditions are chosen referred to Kusaka et al (2000) and Ohashi and Kida (2002). These weather conditions are satisfied about 20% of the days in the two years.…”