内陸盆地都市における気温の日変化と内陸盆地都市における気温の日変化と地形・ 都市の影響

  • 荒井 崇嘉, 2015: 内陸盆地都市における気温の日変化と内陸盆地都市における気温の日変化と地形・ 都市の影響 .

要旨

Diurnal temperature variations in inland basin cities in summer were statistically analyzed using observation data, and the basin and urban effects on the variations are numerically examined with the Weather Research and Forecasting (WRF) model.

Statistical analyses were carried out with observation data (meteorological offices data or Automated Meteorological Data Acquisition System, AMeDAS) in the southern Tohoku area. In sunny summer days, daytime temperature is a few degrees higher in inland basin cities than in coast cities. On the other hand, the urban heat island intensity (UHII) in basin cities is several degrees higher at night than in the daytime. These indicate that UHII might be higher in inland basin cites than in coast cites which have huge population.

Idealised simulations with WRF model were carried out to examine the basin and urban effects on the temperature increase. In sunny summer days, the urban effect was little found in a basin urban case in the daytime; however the increment from 0.5 °C to 1.2 °C appeared in the nighttime. In the nighttime, the urban effect in an inland basin city case was nearly equal to that in an inland city case; however the urban effect in a coast city case into which sea breeze flows is lower than that in the inland city case. Moreover, the increment due to the basin effect in the basin urban case is 1.5 °C in the daytime. Hence, the major reason why the daytime temperature is higher in inland basin urban cities than in inland areas is not the urban effect but the basin effect. Daytime heating in the lower atmosphere of inland basin urban areas could be divided into the following two processes; one is heating in the mixed layer due to turbulent heat transport and surface sensible heat flux, and the other is subsiding heating in the upper mixed layer. These processes are similar to those in rural basin areas; therefore basin heating processes are hardly influenced by surface conditions.

Key Words: Basin, Urban heat island, Local circulations, Statistical analysis, Ideal simulations