Uplift Mechanism of Coastal Extremely Persistent Heavy Rainfall (EPHR): The Key Role of Low‐Level Jets and Ageostrophic Winds in the Boundary Layer

Huang, Xiaogang; Zhang, Chi; Fei, Jianfang; Cheng, Xiaoping; Ding, Juli; Liu, Haisheng

doi:10.1029/2021gl096029

Cited by 10 publications

(17 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This vertical coupling effect of the double low‐level jets can be a vital convection triggering mechanism for EPHR. The latest research confirms this mechanism and finds that the convergence of non‐geostrophic winds near the coast also has an important impact on the occurrence of EPHR (Huang et al., 2022). For Type 2, EPHR frequently occurs in the inland mountain areas of the central and northern Guangxi (marked in Figure 7b).…”

Section: Synoptic Patterns Associated With Ephrmentioning

confidence: 83%

Spatiotemporal Features and Associated Synoptic Patterns of Extremely Persistent Heavy Rainfall Over China

et al. 2022

Self Cite

View full text Add to dashboard Cite

Extreme precipitation, which can rapidly surpass local climatological values, may lead to natural disasters such as torrents, landslides, and debris flows, causing extensive loss of life and property. Strongly affected by the East Asian monsoon, central and east China frequently experience extreme precipitation events (Zhang et al., 2017). Studies have shown that extreme precipitation tends to increase with global warming (Fischer & Knutti, 2016;Wang & Zhou, 2005;Zhai et al., 2005), causing a rise in the number of studies performed on extreme precipitation over China in recent years. Two primary methods define extreme precipitation. The first classifies extreme precipitation according to a threshold, such as the commonly used 95th percentile threshold method (Wu et al., 2019;Xiao et al., 2016;Zhai et al., 2005) and 99.9th percentile threshold method (Luo et al., 2016), as well as the fixed threshold method (Chen & Yu, 1988). The second method involves fitting an empirical function (Wu et al., 2017;Zheng et al., 2016), which is usually utilized to discuss the return period of extreme precipitation events. Before the early 21st century, due to the lack of long-term high-resolution rainfall data, researchers only had access to daily or monthly data to investigate extreme precipitation events. However, it is easy to overestimate the intensity of long-term light precipitation or underestimate the intensity of short-term heavy precipitation, limiting the availability of detailed characteristics of extreme precipitation (Trenberth et al., 2003). With the continuous refinement of observational technology, researchers can use hourly rainfall datasets to determine extreme hourly precipitation event, focusing on extreme precipitation intensity within an hour.Extreme hourly precipitation generally means that the hourly intensity reaches a certain historical threshold (e.g., 95% or 99%), and then an extreme hourly precipitation event is defined as follows: within a period of time when the station continuously observes the occurrence of precipitation (≥0.1 mm hr −1 ), at most 1-hr precipitation interruption is allowed, and at least one extreme hourly precipitation occurs (Li et al., 2013). Studies indicate that the extreme hourly precipitation event typically exhibits an asymmetrical pattern, meaning that the duration from the beginning to the peak of the precipitation is usually faster than the duration from the peak to the end of the Abstract Extremely persistent heavy rainfall (EPHR) is characterized by high rainfall intensity and long durations, which can cause destructive natural disasters. In this study, hourly merged precipitation data for 2009-2019 are used to investigate the spatiotemporal distribution of EPHR over China. Reanalysis data are used to classify synoptic patterns related to EPHR. Observations show that the EPHR process is substantially asymmetrical, occurring mostly in South China, whereas its strongest intensity takes place in North China. There is a tendency for EPHR to occur near coastal and mountainou...

show abstract

Section: Synoptic Patterns Associated With Ephrmentioning

confidence: 83%

Spatiotemporal Features and Associated Synoptic Patterns of Extremely Persistent Heavy Rainfall Over China

et al. 2022

Self Cite

View full text Add to dashboard Cite

show abstract

“…It has been widely used to separate the flow field into synoptic-, meso-, and convective scales (Xu et al, 2017;Wei et al, 2022) and study the physical mechanisms of diurnal variability of low-level ageostrophic winds (Xue et al, 2018). By using the same weight constant settings (g = 0.3 and c = 30,000) as Huang et al (2022), the geopotential height is filtered to damp most of the waves shorter than 500 km and obtain most of the geostrophic motion with wavelengths greater than 1000 km, so the ageostrophic scales are mostly damped.…”

Section: Barnes Filteringmentioning

confidence: 99%

“…In their definition of EPHR, the duration of hourly precipitation exceeding 20 mm at a fixed location should be at least 5 hr (although there can be an interruption of up to 1 hr). Most of the coastal EPHR in South China can be classified as WSHR, and the majority of the cases are accompanied by southwest BLJs (Huang et al, 2022). In addition, in most cases, there is strong convergence in the lower troposphere in the coastal rainfall area, and the ageostrophic winds exhibit obvious confluence patterns (Huang et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

“…Most of the coastal EPHR in South China can be classified as WSHR, and the majority of the cases are accompanied by southwest BLJs (Huang et al, 2022). In addition, in most cases, there is strong convergence in the lower troposphere in the coastal rainfall area, and the ageostrophic winds exhibit obvious confluence patterns (Huang et al, 2022). The intensity and duration of heavy rainfall events vary with different confluence patterns of the ageostrophic wind.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Mechanisms of Ageostrophic Wind Convergence in the Boundary Layer of Coastal Warm-Sector Extreme Heavy Rainfall

Xia

Huang

Fei

et al. 2023

Preprint

View full text Add to dashboard Cite

The South China coast has a high incidence of warm-sector heavy rainfall (WSHR) events. The ageostrophic winds in the boundary layer in most of these events associated with the southwesterly boundary layer jets (BLJs) mainly exhibit strong convergence at rainfall area. In this paper, we analyze two cases of WSHR in May 2013 and May 2015, which occurred in similar synoptic environments but varied in intensity, extent, and duration of rainfall, where the ageostrophic winds are the confrontational confluence and asymptotic confluence pattern, respectively. ERA-5 reanalysis data and the diagnostic equation of ageostrophic wind are used to examine the factors affecting the ageostrophic winds in the northern land region and the southern offshore region of the rainfall. The results suggest that land-sea contrast leads to the convergence of ageostrophic winds in the rainfall area. Boundary layer friction dominates the northeasterly ageostrophic winds on land. The diurnal variation of BLJs dominates the ageostrophic winds and their diurnal variation at sea, contributing southwesterly or southeasterly ageostrophic winds, so the phase difference between the land and sea forms confrontational or asymptotic confluence, respectively. BLJs with different intensities, extents, and diurnal variations can lead to different ageostrophic wind patterns and their confluence modes. The land-sea thermal contrast can directly affect ageostrophic winds, and it can also affect the diurnal variation of BLJs, thus affecting the ageostrophic winds and their confluence mode. It is further verified that the BLJs and thermal forcing are important in warm-sector heavy rainfall processes in South China.

show abstract

“…The results show that EPHR tends to occur near coastal and mountainous areas, basins, and urban agglomerations, with high incidence in early morning. Recently, the relationships between EPHR, ageostrophic winds, and LLJs have been examined, indicating a unique uplift mechanism of EPHR events over coastal southern China (Huang et al., 2022). The results suggest that ageostrophic winds in the boundary layer mainly exhibit confrontational and asymptotic convergence, with the former being accompanied by double LLJ, which transport more vapor and provide favorable uplift conditions, thus producing stronger precipitation and wider rainbands.…”

Section: Introductionmentioning

confidence: 99%

Mechanism Analysis of a Wintertime Extreme Persistent Heavy Rainfall Event in Hainan Island

et al. 2023

Self Cite

View full text Add to dashboard Cite

In recent years, extreme rainfall events and attendant flooding continue to pose significant threats to life and property in China. For example, on July 19-20, 2016, an extensive extreme rainfall event swept across North China, causing 139 human fatalities, 141,000 house collapses, and 718,000 ha of crops damages over the region, leading to a direct economic loss of 10 billion RMB (Xia & Zhang, 2019). More severely, the "21•7" extreme rainfall in Henan caused devastating floods, with a record-breaking hourly rainfall rate of 201.9 mm hr −1 , leaving 398 human fatalities and a direct economic loss of 120.06 billion RMB (Luo et al., 2022;Su et al., 2021;Wei et al., 2022;Yin et al., 2022), which has brought unprecedented attention to extreme rainfall events. Early warning and forecasting are always a crucial part of disaster prevention and mitigation. However, the current meteorological forecasting system is still struggling to accurately predict the location and intensity of extreme precipitation (Fritsch & Carbone, 2004;Novak et al., 2011;Zhang et al., 2016), which urgently requires a deeper understanding of the mechanisms of extreme rainfall events.Previous studies have pointed out that sufficient moisture supply, favorable uplifting, and unstable atmospheric environments are generally the key factors that are conducive to heavy rainfall (Doswell et al., 1996;Lin et al., 2001). Subsequent studies revealed that mesoscale convective systems (MCS) play an important role in extreme rainfall events. Johnson (2005, 2006) found that about 65% of extreme rainfall events in the central and eastern United States were directly caused by MCS (weak synoptic-scale forcing), 27% were caused by synoptic-scale forcing (e.g., frontal, or extratropical cyclone), and the other 8% are caused by tropical cyclones and their remnants. Of importance is the organizational structure of MCS, which primarily controls the intensity, duration, and location of extreme rainfall. The so-called "back-building" and "echo-training" processes are the two major patterns. The back-building process occurs when convective cells repeatedly develop upstream of previous deep convection and pass over the same region (Schumacher & Johnson, 2005, 2009Zheng et al., 2013), forming a quasi-stationary MCS, while the echo training process occurs when a series of convective Abstract Extremely persistent heavy rainfall (EPHR) events frequently occur in southern China, but its mechanisms of initiation and maintenance are not well understood, leading to difficulties in accurately forecasting. Thus, we investigated a typical EPHR case that occurred on Hainan Island on 14 December 2013 (UTC) using convection-resolving WRF simulation and multi-source observations. Results revealed that the intrusion of the cold surge, the formation of the quasi-stationary mesoscale perturbed vortex (MPV) caused by deflected southerly winds and northeasterly winds, and local topographic forcing are three crucial factors for this EPHR event. Firstly, the invasion of cold surge provides a ...

show abstract

Uplift Mechanism of Coastal Extremely Persistent Heavy Rainfall (EPHR): The Key Role of Low‐Level Jets and Ageostrophic Winds in the Boundary Layer

Cited by 10 publications

References 34 publications

Spatiotemporal Features and Associated Synoptic Patterns of Extremely Persistent Heavy Rainfall Over China

Spatiotemporal Features and Associated Synoptic Patterns of Extremely Persistent Heavy Rainfall Over China

Mechanisms of Ageostrophic Wind Convergence in the Boundary Layer of Coastal Warm-Sector Extreme Heavy Rainfall

Mechanism Analysis of a Wintertime Extreme Persistent Heavy Rainfall Event in Hainan Island

Contact Info

Product

Resources

About