Effective Diffusivity as a Diagnostic of Synoptic Scale Events

• Main Authors: Li-Wei Kuo, 郭力瑋
• Other Authors: Hung-Chi Kuo
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/75676388701441363410

碩士 === 國立臺灣大學 === 大氣科學研究所 === 100 === The effective diffusivity diagnosis is used to obtain a basic insight into the two-dimensional transport and mixing properties of synoptic scale events such as trough thinning processes, wave breaking of Antarctic polar vortex and both a developing and non-developing disturbance during the 2010 Atlantic hurricane season. Effective diffusivity is used as a mixing diagnostic on a passive tracer subject to diffusion and advection by the non-divergent part of observed winds. Large/small effective diffusivity corresponds to strong/weak mixing. For the trough event, the filaments are regions of large effective diffusivity, which suggests strong mixing. For the Antarctic polar vortex, the effective diffusivity shows that strong mixing occurs at the edge of stratospheric polar vortex. This is in good qualitative agreements between effective diffusivity and measurements of chemical tracers taken by the NASA ER-2 aircraft. The tropical cyclone formation has long been recognized to form in regions of approximately circular flow. Recent studies showed that a region of recirculation, also called pouch, along a propagating Easterly wave occurred in all genesis cases. We use effective diffusivity as a diagnosis that can identify the transport and mixing properties around the tropical disturbances. The effective diffusivity diagnosis is used to evaluate the intrusion of dry air into Gaston, which did not re-develop into a tropical cyclone, and the intrusion of dry air into Karl, which did become a tropical cyclone and later a major hurricane. The northwestern region of Gaston shows a strong mixing region at 700hPa and 500hPa, allowing mixing dry air into Gaston to be quite effective. On the other hand, the Karl is in a weak mixing environment where the Karl is slightly affected by the dry air. The results show that the effective diffusivity diagnosis of mixing can be useful in understanding the tropical cyclogenesis.