著者

HSIEH Min-Ken CHEN Yu-Wen CHEN Yi-Chun WU Chien-Ming

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-028, (Released:2022-03-10)

被引用文献数

3

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We applied tracer transport simulations using Taiwan vector vorticity equation cloud-resolving model (TaiwanVVM) to evaluate the effects of the local circulation associated with the lee vortex and the planetary boundary layer development on the transport and accumulation of the pollutants on a diurnal time scale in central Taiwan. The wind directions of crucial synoptic northeast monsoon are idealized as the initial conditions of the simulations to examine the impact of the lee vortex on the pollutants transport. The primary local non-traffic emission sources are taken as the tracer emission sites so that the experiment results could be a good proxy of the realistic scenarios. With the local circulation over complex topography being resolved explicitly, the impact of the boundary layer development on the tracer transport of the Puli basin is discussed. The simulation results clarify the contribution of the sea breeze and the lee vortex to the tracer transport in central Taiwan. We conclude that high tracer concentration at Puli at night is due to the tracer being trapped by the thinning of the mixed layer depth in the evening. The sensitivity of the local tracer transport to the change of the synoptic wind direction shows that under northeasterly due east (due north) environment, the pollutant transports from the southern source (northern source) of central Taiwan are most likely to induce high concentration in Puli at night. This is the first study to distinguish the contribution of the sea breeze and the lee vortex in pollutants transport in Taiwan. The results obtained from idealized experiments provide the possible mechanism of pollutants transport, which could be taken as an insight to interpret the observations and guide the design of field experiment to further establish the fundamental principles of the pollution transports in central Taiwan.

著者

JIAN Hong-Wen CHEN Wei-Ting CHEN Peng-Jen WU Chien-Ming RASMUSSEN Kristen L.

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-013, (Released:2020-12-02)

被引用文献数

5

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This study investigates the synoptic scale flows associated with extreme rainfall systems over the Asian-Australian monsoon region (90-160°E and 12°S-27°N). Based on statistics of the 17-year Precipitation Radar observations from Tropical Rainfall Measurement Mission, a total of 916 extreme systems with both the horizontal size and maximum rainfall intensity exceeding the 99.9th percentiles of the tropical rainfall systems are identified over this region. The synoptic wind pattern and rainfall distribution surrounding each system are classified into four major types: Vortex, Coastal, Coastal with Vortex, and None of above, with each accounting for 44 %, 29 %, 7 %, and 20 %, respectively. The vortex type occurs mainly over the off-equatorial areas in boreal summer. The coast-related types show significant seasonal variations in their occurrence, with high frequency in the Bay of Bengal in boreal summer and on the west side of Borneo and Sumatra in boreal winter. The None-of-the-above type occurs mostly over the open ocean, and in boreal winter these events are mainly associated with the cold surge events. The environment analysis shows that coast-related extremes in the warm season are found within the areas where high total water vapor and low-level vertical wind shear occur frequently. Despite the different synoptic environments, these extremes show a similar internal structure, with broad stratiform and wide convective core rain. Furthermore, the maximum rain rate locates mostly over convective area, near convective-stratiform boundary in the system. Our results highlight the critical role of the strength and direction of synoptic flows in the generation of extreme rainfall systems near coastal areas. With the enhancement of the low-level vertical wind shear and moisture by the synoptic flow, the coastal convection triggered diurnally has a higher chance to organize into mesoscale convective systems and hence a higher probability to produce extreme rainfall.

著者

KUO Kuan-Ting WU Chien-Ming

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-031, (Released:2019-02-02)

被引用文献数

11

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In this study, the mechanism for precipitation hotspots (PHs) of locally developed afternoon thunderstorms in the Taipei Basin is investigated using a three-dimensional Vector Vorticity equation cloud resolving Model (VVM) with an idealized topography and surface properties. A 500-m horizontal grid resolution is used in all experiments. The results show that the local circulation is a key for PHs at the south of the Taipei Basin. The two valleys guide background southwesterly flow along with the sea breezes to penetrate into the basin. The urban heat island effect enhances the sea breeze convergence at the south of the basin and produces strong convection there. Interactions between cold pools generated by the convection and the sea breezes produce northward propagating new convective cells. Besides, the background wind direction is important in determining the location of sea breeze convergence. If the background wind direction changes from westerly to west-northwesterly, there might be no precipitation at all in the basin. This study suggests that the idealized experiments also provide a useful framework for studying the impacts of future climate change on the PHs in the Taipei Basin by applying the pseudo-global warming approach.