Yoshinori Shigeta

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 ...

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.