Contrasting frontal and warm-sector heavy rainfalls over South China during the early-summer rainy season

The characteristics of the synoptic situation and the evolution of the organized warm-sector rainfalls (OWSRs) in the coastal region of South China in the pre-summer rainy season were investigated, using a period (2011–2016) of high-resolution observational data and European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-Interim) data. The results show that a strong southwesterly low-level jet (LLJ) ahead of a trough over southwestern China with a marked boundary-layer jet (BLJ) over the northern South China Sea (synoptic situation SWLLJ) or a prominent, low-level anticyclone over the Yangtze River Basin (synoptic situation ACR) is present when the OWSRs occur in the coastal region of South China. The OWSRs are prone to initiate on the windward side of the coastal mountains, owing to the convergence enhanced by the colliding of the BLJ with the mountains and the coupling of double LLJs near the coast (for SWLLJ), or due to the convergence between northerly and southeasterly winds near the coastal mountains (for ACR). The OWSRs present a long extension when the LLJ axis is nearby. The translation of the LLJ itself also promotes the long extension of the OWSRs. In contrast, the OWSRs show a short extension when the LLJ axis is farther away or ACR occurs. Meanwhile, the OWSRs are directed northeastward in Guangxi Province and more eastward in Guangdong Province, probably owing to the orientation difference of the LLJ in these two provinces. The rainfall systems in the ACR situation tend to move eastward, whereas those in the SWLLJ situation are prone to move eastward when equivalently strong or much-stronger upper-level winds overlay the LLJ, but move northeastward when much weaker upper-level winds couple with the LLJ.

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Characteristics of the Marine Boundary Layer Jet over the South China Sea during the Early Summer Rainy Season of Taiwan

Monthly Weather Review ◽

10.1175/mwr-d-18-0230.1 ◽

2019 ◽

Vol 147 (2) ◽

pp. 457-475 ◽

Cited By ~ 3

Author(s):

Chuan-Chi Tu ◽

Yi-Leng Chen ◽

Pay-Liam Lin ◽

Yu Du

Keyword(s):

Boundary Layer ◽

South China Sea ◽

South China ◽

Rainy Season ◽

Marine Boundary Layer ◽

Frontal Zone ◽

Northern South China Sea ◽

Early Summer ◽

Pressure Gradients ◽

China Sea

Abstract The marine boundary layer jets (MBLJs) over the northern South China Sea during the early summer rainy season over Taiwan are analyzed using 5-yr (2008–12) National Centers for Environmental Prediction Climate Forecast System Reanalysis data with a 6-h interval. The MBLJ is distinctly different from the low-level jets associated with the subsynoptic frontal systems. During this period, the MBLJ events over the northern South China Sea mainly occur during the second half of the monsoon rainy season over Taiwan (after 1 June) and have a wind speed maximum around the 925-hPa level. The MBLJs are mainly related to the subsynoptic-scale pressure gradients related to a relatively deep mei-yu trough over southeastern China and a stronger-than-normal west Pacific subtropical high. Within the MBL, there is a three-way balance among pressure gradients, Coriolis force, and surface friction, with cross-isobar ageostrophic winds pointing toward the mei-yu trough throughout the diurnal cycle. At the jet core, the vertical wind profile resembles an Ekman spiral with supergeostrophic winds >12 m s−1 near the top of the MBL. The MBLJs are strongest at night and close to geostrophic flow in the late afternoon/early evening. This is because the friction velocity and ageostrophic wind decrease during daytime in response to mixing in the lowest levels. The MBLJs play an important role in horizontal moisture transport from the northern South China Sea to the Taiwan area. In the frontal zone, the moisture tongue extends vertically upward. The rainfall production is related to vertical motions in the frontal zone or localized lifting due to orographic effects.

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Budgets of rotational and divergent kinetic energy in the warm-sector torrential rains over South China: a case study

Meteorology and Atmospheric Physics ◽

10.1007/s00703-021-00778-1 ◽

2021 ◽

Author(s):

Shui-Xin Zhong ◽

Wei-Guang Meng ◽

Fu-You Tian

Keyword(s):

Kinetic Energy ◽

Energy Budget ◽

South China ◽

Extreme Precipitation ◽

Flux Divergence ◽

Low Level ◽

Warm Sector ◽

Kinetic Energy Budget ◽

Rotational Components ◽

The Pearl River

AbstractThe contributions of divergent and rotational wind components to the kinetic energy budget during a record-breaking rainstorm on 7 May 2017 over South China are examined. This warm-sector extreme precipitation caused historical maximum of 382.6 mm accumulated rainfall in 3 h over the Pearl River Delta (PRD) regions in South China. Results show that there was a high low-level southerly wind-speed tongue stretching into the PRD regions from the northeast of the South China Sea (SCS) during this extreme precipitation. The velocity potential exhibited a low-value center as well as a low-level divergence-center over the SCS. The rotational components of the kinetic energy (KR)-related terms were the main contribution-terms of the kinetic energy budget. The main contribution-terms of KR and the divergent component of kinetic energy (KD) were the barotropical and baroclinic processes-related terms due to cross-contour flow and the vertical flux divergence.

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Prediction model based on the Laplacian eigenmap method combined with a random forest algorithm for rainstorm satellite images during the first annual rainy season in South China

Natural Hazards ◽

10.1007/s11069-021-04585-0 ◽

2021 ◽

Author(s):

Xiao-yan Huang ◽

Li He ◽

Hua-sheng Zhao ◽

Ying Huang ◽

Yu-shuang Wu

Keyword(s):

Random Forest ◽

Prediction Model ◽

South China ◽

Rainy Season ◽

Satellite Images ◽

Random Forest Algorithm ◽

Model Based

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A 7-Year Climatology of Warm-Sector Heavy Rainfall over South China during the Pre-Summer Months

Atmosphere ◽

10.3390/atmos12070914 ◽

2021 ◽

Vol 12 (7) ◽

pp. 914

Author(s):

Tao Chen ◽

Da-Lin Zhang

Keyword(s):

South China ◽

Heavy Rainfall ◽

Large Scale ◽

Convective Available Potential Energy ◽

Potential Temperature ◽

Vertical Wind Shear ◽

Precipitable Water ◽

Atmospheric Parameter ◽

Low Level ◽

Warm Sector

In view of the limited predictability of heavy rainfall (HR) events and the limited understanding of the physical mechanisms governing the initiation and organization of the associated mesoscale convective systems (MCSs), a composite analysis of 58 HR events over the warm sector (i.e., far ahead of the surface cold front), referred to as WSHR events, over South China during the months of April to June 2008~2014 is performed in terms of precipitation, large-scale circulations, pre-storm environmental conditions, and MCS types. Results show that the large-scale circulations of the WSHR events can be categorized into pre-frontal, southwesterly warm and moist ascending airflow, and low-level vortex types, with higher frequency occurrences of the former two types. Their pre-storm environments are characterized by a deep moist layer with >50 mm column-integrated precipitable water, high convective available potential energy with the equivalent potential temperature of ≥340 K at 850 hPa, weak vertical wind shear below 400 hPa, and a low-level jet near 925 hPa with weak warm advection, based on atmospheric parameter composite. Three classes of the corresponding MCSs, exhibiting peak convective activity in the afternoon and the early morning hours, can be identified as linear-shaped, a leading convective line adjoined with trailing stratiform rainfall, and comma-shaped, respectively. It is found that many linear-shaped MCSs in coastal regions are triggered by local topography, enhanced by sea breezes, whereas the latter two classes of MCSs experience isentropic lifting in the southwesterly warm and moist flows. They all develop in large-scale environments with favorable quasi-geostrophic forcing, albeit weak. Conceptual models are finally developed to facilitate our understanding and prediction of the WSHR events over South China.

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Non-invasive assessment of oestrous cycles and evaluation of reproductive seasonality in the female wild black rhinoceros (Diceros bicornis minor)

Reproduction ◽

10.1530/rep.0.1230877 ◽

2002 ◽

pp. 877-889 ◽

Cited By ~ 22

Author(s):

JN Garnier ◽

WV Holt ◽

PF Watson

Keyword(s):

Rainy Season ◽

Total Duration ◽

Reproductive Behaviour ◽

Early Embryo ◽

Early Summer ◽

Normal Cycle ◽

Black Rhinoceros ◽

Non Invasive ◽

Progesterone Metabolite ◽

Suitable Environment

Female wild black rhinoceroses in Zimbabwe were monitored non-invasively using faecal progesterone metabolite analysis and observation of reproductive behaviour. A postpartum period of reproductive inactivity of at least 4 months, followed by a period of 4-7 months of oestrous cyclicity, was detected in six multiparous females. Three-quarters of the oestrous cycles (n = 21) had a total duration (mean +/- SEM) of 26.8 +/- 1 days. Other types of cycle were characterized either by an extended luteal phase, lasting on average twice as long as the normal cycle, or by an extended follicular phase. These extended cycles may have resulted from early embryo loss and heat stress. Female rhinoceroses did not conceive before 8 months after giving birth and some females (n = 2) most likely aborted after 3.0-3.5 months of gestation. The detected period of cyclic oestrus occurred between May and March in females (n = 9), and there was a 3 month extended interoestrous interval in nulliparous females during the period of decreasing daylengths that can be presumed to be the period of poorest fertility for the black rhinoceros under tropical latitudes. In contrast, the period of optimum fertility in the Southern hemisphere coincided with the late spring and early summer, and corresponded to the early rainy season. As a result, a higher incidence of births was detected in the late rainy season, providing the lactating female with the most suitable environment in terms of nutritional requirements.

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Circulation Features Associated with the Record-Breaking Rainfall over South China in June 2017

Journal of Climate ◽

10.1175/jcli-d-17-0903.1 ◽

2018 ◽

Vol 31 (18) ◽

pp. 7209-7224 ◽

Cited By ~ 10

Author(s):

Jianqi Sun ◽

Jing Ming ◽

Mengqi Zhang ◽

Shui Yu

Keyword(s):

East Asia ◽

South China ◽

North Atlantic ◽

Large Scale ◽

Wave Train ◽

Western Pacific Subtropical High ◽

Early Summer ◽

Intense Rainfall ◽

Maritime Continent ◽

Anomalous Anticyclone

In June 2017, south China suffered from intense rainfall that broke the record spanning the previous 70 years. In this study, the large-scale circulations associated with the south China June rainfall are analyzed. The results show that the anomalous Pacific–Japan (PJ) pattern is a direct influence on south China June rainfall or East Asian early summer rainfall. In addition, the Australian high was the strongest in June 2017 during the past 70 years, which can increase the equatorward flow to northern Australia and activate convection over the Maritime Continent. Enhanced convection over the Maritime Continent can further enhance local meridional circulation along East Asia, engendering downward motion over the tropical western North Pacific and enhancing the western Pacific subtropical high (WPSH) and upward motion over south China, which increases the rainfall therein. In addition, a strong wave train pattern associated with North Atlantic air–sea interaction was observed in June 2017 at Northern Hemispheric mid- to high latitudes; it originated from the North Atlantic and propagated eastward to East Asia, resulting in an anomalous anticyclone over the Mongolian–Baikal Lake region. This anomalous anticyclone produced strong northerly winds over East Asia that encountered the southerly associated with the WPSH over south China, thereby favoring intense rainfall over the region. Case studies of June 2017 and climate research based on data during 1979–2017 and 1948–2017 indicate that the extremities of the atmospheric circulation over south Europe and Australian high and their coupling with the PJ pattern could be responsible for the record-breaking south China rainfall in June 2017.

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