HR: 0800h
AN: A51B-0359    [Abstracts]
TI: Old and New Mechanisms of the Urban Heat Island: Thermal Inertia and Fractal Surface
AU: * Sakai, S
EM: sakai@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo-ku Yoshida, Kyoto, 606-8501, Japan
AU: Iizawa, I
EM: iizawa@horikawa.edu.city.kyoto.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo-ku Yoshida, Kyoto, 606-8501, Japan
AU: Umetani, K
EM: umetani@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo-ku Yoshida, Kyoto, 606-8501, Japan
AU: Onishi, M
EM: onishi@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo-ku Yoshida, Kyoto, 606-8501, Japan
AU: Ito, A
EM: aya@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo-ku Yoshida, Kyoto, 606-8501, Japan
AU: Ono, K
EM: ono@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo-ku Yoshida, Kyoto, 606-8501, Japan
AU: Yajima, A
EM: yajira@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo-ku Yoshida, Kyoto, 606-8501, Japan
AU: Amemura, N
EM: amemura@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo-ku Yoshida, Kyoto, 606-8501, Japan
AB: The history of the research of the urban heat island was started from the research of Howard in 1833. At first, it was thought that the principal cause of the heat island was the large thermal inertia of the surface at the city comparing with suburbs. However, when it came to be able to measure the surface temperature at the ground level using the remote sensing technique by 1970's, the daily surface temperature fluctuation in the city part was revealed to be larger than that of suburbs. This fact indicated that the surface of the city part had small thermal inertia, and the explanation by the thermal inertia model failed if this was simply interpreted. We have observed the surface air temperature and the radiation balance of the Kyoto city from 2004 to 2006 at more than 30 points. The data showed clear heat island at the central city area in the nighttime, while no temperature differences are observed in the daytime. Using data when the radiation balance was abruptly changed by clouds at night time, the thermal inertia of the ground surface was estimated. The obtained thermal inertia shows very high value at the city area, and small value at the suburb which explains enough the difference of amplitude in the diunal air temperature change between the city area and the suburbs. These results support the original explanation of the heat island several decades ago. A question arises again why the surface of the city area (not the air temperature) becomes so hot at the daytime. The answer lies in the geometry of the ground surface. The suburbs are covered by many small leaves in natural fractal distributions, while the urban areas are covered by artificial large flat surfaces. This difference in the surface geometry causes a large difference in the heat transfer coefficient resulting large differences between the surface and the air temperatures. To confirm this, an experiment was done with a fractal roof (Sierpinskifs tetrahedron) and a flat roof with almost same area under the sun shine. The results show that the fractal roof is heated only by 10K comparing with the air temperature while the flat roof is heated more than 30K emitting uncomfortable heat radiation. Note that this temperature reduction can be done without any water evaporation.
DE: 3307 Boundary layer processes
DE: 3399 General or miscellaneous
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting