Energy Budget Analysis for the Urban Effect on the Initiation of Heavy Rainfall Based on Meso-scale Simulation

摘要

Urbanization greatly affects regional climates; one aspect that is affected is convective precipitation, which can cause serious damage to urban infrastructure. This study improves our understanding of urbanization effects on trigger mechanisms for local heavy rainfall. Convective clouds can develop during unstable conditions if the low moist air parcel is lifted to the free convection level. An energy budget analysis was performed to assess how urbanization contributes to the lifting of low-level moist air and triggers the development of a convective cloud. Energy budget equations for the kinematic, potential, and internal energies are presented, including terms for the energy exchange between the three energy types. Fine-scale simulations with a horizontal grid resolution of 1 km using the fifth-generation meso-scale model were used to examine the energy budget during the atmospheric destabilization process in the Tokyo metropolitan region. Numerical simulations successfully reproduced the local heavy rainfall observed in Tokyo on August 15, 2005. Before the heavy rain event occurred, the lower atmosphere was under latent instability conditions because of heating from the land surface. This study also discusses the energy transport from the surface to the lifted air parcels and clarifies the roles of the surface flux and low-level convergence kinematic energy in the trigger process, in which low-level air was lifted and merged with the convective cloud.