著者

LI Zhenghui LUO Yali DU Yu CHAN Johnny C. 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.2020-012, (Released:2019-11-30)

被引用文献数

38

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Climatological characteristics of pre-summer (April-to-June) rainfall over Southern China (SC) and associated synoptic conditions are examined using 1980-2017 hourly rainfall observations and reanalysis data. The rainfall amount, frequency, and intensity show pronounced regional variations and substantial changes between pre- and post-monsoon-onset periods. Owing to more favorable thermodynamic conditions after monsoon onset over South China Sea (SCS), rainfall intensifies generally over entire SC irrespective of the rainfall-event durations. Increased magnitudes of rainfall amount in longer-duration (> 6 h) events are found over a designated west-inland region (west of 111°E), which are partially attributed to enhanced dynamic instability. In addition, rainfall events occur more frequently over the west-inland region, as well as coastal regions west side of 118°E, but less over a designated east-inland region. The inland-region rainfall is closely linked to dynamic lifting driven by subtropical synoptic systems (low pressure and an associated front or shearline). The westward extension of the western North Pacific high and the eastward extension/movement of the front or shearline, interacting with the intra-period intensification of the southwesterly monsoonal flows, play important roles in providing high-θe (equivalent potential temperature) air to the west- and east-inland regions, respectively. The warm-sector, coastal rainfall is closely related to the deceleration of the southerly boundary layer (BL) jet (BLJ) over the northern SCS and associated convergence of BL high-θe air near the coast. Meanwhile the southwesterly synoptic-system-related low-level jet in the lower-to-middle troposphere to the south of the inland cold front can contribute to the coastal rainfall occurrence by providing divergence above the BL convergence near the coast. The BLJ often simultaneously strengthens with the lower-troposphere horizontal winds, suggesting a close association between the BLJ and the synoptic systems. The quantitative statistics provided in this study complement previous case studies or qualitative results and thus advance understanding about pre-summer rainfall over SC.

著者

LUO Yali XIA Rudi CHAN Johnny C. 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.2020-002, (Released:2019-10-16)

被引用文献数

44

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Pre-summer rainy season (April to mid-June) over South China (SC) is characterized by high intensity and frequent occurrence of heavy rainfall in the East Asian monsoon region. This review describes recent progress in the research related to such a phenomenon. The mechanisms responsible for pre-summer rainfall consist of multi-scale processes. Sea surface temperatures over tropical Pacific and Indian Ocean are shown to have a great influence on the interannual variations of pre-summer rainfall over SC. Synoptic disturbances associated with regional extreme rainfall over SC are mainly related to cyclone- and trough-type anomalies. Formation and intensification of such anomalies can be contributed by surface sensible heating and mechanical forcing from the Tibetan Plateau. On a sub-daily scale, double rain belts often co-exist over SC. The northern rain belt is closely linked to dynamic lifting by a subtropical low pressure and its associated front/shear line, while the westward extension of the western North Pacific high and the intensification of the southwesterly monsoonal flows play important roles in providing high-equivalent potential temperature air to the west- and east-inland regions, respectively. The southern rain belt with a smaller horizontal span is in the warm sector over either inland or coastal SC. The warm-sector rainfall over inland SC results from surface heating, local topographic lifting, and urban heat island effect interacting with the sea breeze. The warm-sector rainfall over coastal SC is closely associated with double low-level jets, land-sea-breeze fronts, and coastal mountains. A close relationship is found between convectively-generated quasi-stationary mesoscale outflow boundaries and continuous convective initiation in extreme rainfall events. Active warm-rain microphysical processes can play an important role in some extreme rainfall events, although the relative contributions by warm-rain, riming and ice-phase microphysical processes remain unclear. Moreover, to improve the rainfall prediction, efforts have been made in convection-permitting modeling studies.

著者

CHAN Kelvin T. F. CHAN Johnny C. 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.2018-042, (Released:2018-04-27)

被引用文献数

14

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This paper presents a summary of some of the observational and numerical studies on the climatology and possible change mechanisms of the outer-core wind structure of a tropical cyclone (TC), which has been generally referred to as size, a term also to be used in this review although various definitions have been given in the literature. In all the ocean basins where TCs exist, TC size has been found to vary with season, year, decade, latitude and longitude. Such variations are related to those in the synoptic flow patterns in which the TCs are embedded. Several factors have been identified to be responsible for changes in TC size, which include environmental humidity, vortex structure, sea surface temperature and planetary vorticity. Each of these factors can modify the transport of lower tropospheric angular momentum into the TC and hence cause changes in its size. The paper ends with a discussion of outstanding issues in the study of the outer-core wind structure of a TC.

著者

LI Zhenghui LUO Yali DU Yu CHAN Johnny C. L.

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.98, no.1, pp.213-233, 2020

被引用文献数

38

---

<p>In this study, the climatological characteristics of pre-summer (April to June) rainfall over South China (SC) and the associated synoptic conditions are examined using 1980–2017 hourly rainfall observations and reanalysis data. The amount, frequency, and intensity of rainfall show pronounced regional variations and substantial changes between pre- and post-monsoon-onset periods. Owing to the more favorable thermodynamic conditions after monsoon onset over the South China Sea (SCS), rainfall intensifies generally over SC irrespective of the rainfall-event durations. Increased rainfall amounts in longer-duration (> 6 h) events were found over a designated west-inland region (west of 111°E), which are partially attributed to enhanced dynamic instability. In addition, rainfall events occur more frequently over the west-inland region, as well as coastal regions to the west of 118°E, but less over a designated east-inland region. Inland-region rainfall is closely linked to dynamic lifting driven by subtropical synoptic systems (low pressure and an associated front or shearline). The westward extension of the western North Pacific high and the eastward extension/movement of the front or shearline, interacting with the intra-period intensification of the southwesterly monsoonal flows, play important roles in providing high-<i>θ</i>_e (equivalent potential temperature) air to the west- and east-inland regions, respectively. Warm-sector coastal rainfall is closely related to the deceleration of the southerly boundary layer (BL) air flow over the northern SCS and associated convergence of BL high-<i>θ</i>_e air near the coast. Meanwhile, the southwesterly synoptic-system-related low-level jet in the lower-to-middle troposphere to the south of the inland cold front can contribute to the coastal rainfall occurrence by providing divergence above the BL convergence near the coast. The BL flow often simultaneously strengthens with the lower-troposphere horizontal winds, suggesting a close association between the BL flow and the synoptic systems. The quantitative statistics provided in this study complement previous case studies or qualitative results and, thus, advance our understanding about pre-summer rainfall over SC.</p>