Numerical Study On Cloud Lines Over An Urban Street In Tokyo
Numerical Study On Cloud Lines Over An Urban Street In Tokyo
复制标题
东京城市街道上空云线的数值研究
DOI：
10.1023/a:1026504904902
复制
发表时间：
2001
影响因子：
4.3
通讯作者：
I. Uno
中科院分区：
文献类型：
--
作者：
M. Kanda;Yushi Inoue;I. Uno
“Kanpachi Street Cloud（KSC）”是一条不寻常的小尺度积云线，在东京大都市区的一条主要街道上，在平静的夏季条件下可见。为了了解这条云线的形成机制，利用区域大气模式系统进行了数值模拟，模拟的KSC的一般特征与观测结果吻合较好。在大尺度上，KSC可以被描述为在东京湾西侧两股海风的辐合线上产生的积云线，而在小尺度上，KSC则是由风切变纵向修正的Benard型热对流，导致KSC形成的辐合线位置与Kanpachi街位置一致，尽管街道本身并不对KSC的形成产生任何直接影响。通过改变城市化进程中的热影响、地表覆盖和网格分辨率，对KSC的形成进行了数值试验，证实了KSC的形成同时需要两个气象过程：（1）来自东京湾的本地东南海风和来自太平洋的延伸的南部海风的辐合;（2）城市热岛的强迫。结果表明，城市化可以通过增强局地上升运动和改变城市与郊区近地面水平气压梯度来改变KSC的强度和位置。此外，需要精细的水平网格分辨率来解决这些局部热对流问题。
`Kanpachi Street Cloud (KSC)' is an unusual small-scalecumulus cloud line visible during calm summer conditions over a major street in the Tokyo metropolitanarea. In order to understand the mechanism leading to the formation of this cloud line,numerical simulations have been performed using the Regional Atmospheric Modelling System.The general characteristics of the simulated KSC agree well with observations. On alarge-scale view, the KSC can be characterized as a cumulus cloud line generated at the convergenceline of two sea breezes on the western side of Tokyo Bay, while on the microscale view, it resemblesBenard-type thermal convection modified longitudinally by wind shear.The location of the convergence line leading to the KSCformation coincides withthe Kanpachi street location, although the street itself does notmake any direct effect on the KSC formation. Additional numerical experiments were performed toidentify causes of the KSC formation in accordance with urbanization, by changing anthropogenicheat impact, land-cover and grid resolution.They confirmed that the formation of the KSC requirestwo meteorological processes at the same time:(1) the convergence of two sea breezes – the localsouth-eastern sea breeze from Tokyo Bay andan extended southern sea breeze from thePacific Ocean, respectively; (2) Forcing due to an urban heat island. It is shown that urbanization couldchange the intensity and position of the KSC through enhancement of local upward motions and changesin the near-surface horizontal pressure gradient between urban and sub-urban areas. Further,fine horizontal grid resolution is needed to be able to resolve these local thermal convection issues.