Quantitative attribution of vertical motion responsible for summer heavy rainfall over North China

Abstract Based on daily rainfall observations and Japanese 25-year Reanalysis Project data during ~1981–2010, a three-dimensional circulation structure that formed before heavy summer rainfall in central north China (CNC) is revealed in this study. Composite analyses of circulation in advance of 225 heavy rain days show that the circulation structure is characterized by a remarkable upper-tropospheric warm anomaly (UTWA), which covers most of northern China with a center at ~300 hPa. Under hydrostatic and geostrophic equilibriums, the UTWA contributes to the generation of an anticyclonic (cyclonic) anomaly above (below). The anticyclonic anomaly strengthens (weakens) westerly winds to the north (south) of the warm center and pushes the high-level westerly jet to the north. The cyclonic anomaly deepens the trough upstream of CNC and intensifies lower southwesterly winds to the mideast of the warm center. As a result, the northerly stretched high-level jet produces upper divergence in its right-front side and the intensified southwesterly winds induce lower moisture convergence in its left-front side, causing heavy rainfall in CNC. Correlation analyses further confirm the close connections between UTWA and circulation in the upper and lower troposphere. The correlation coefficients between UTWA and the upper geopotential height, upper westerly jet, and lower southerly flow reach 0.95, 0.70, and 0.39, implying that the two critical factors leading to intense rainfall in CNC, the high-level jet and the low-level southerly flow, are closely connected with the UTWA. Consequently, in the future analyses and forecasts of heavy rainfall over northern China, more attention should be paid to the temperature in the upper troposphere.

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A seven-year climatology of the initiation, decay and morphology of severe convective storms during the warm season over North China

Monthly Weather Review ◽

10.1175/mwr-d-20-0087.1 ◽

2021 ◽

Author(s):

Ruoyun Ma ◽

Jianhua Sun ◽

Xinlin Yang

Keyword(s):

Nonlinear Systems ◽

Short Duration ◽

Heavy Rainfall ◽

North China ◽

Doppler Radar ◽

Warm Season ◽

High Wind ◽

Convective Storms ◽

Reflectivity Data ◽

Convective Weather

AbstractThe present work established a 7-year climatology of the initiation, decay, and morphology of severe convective storms (SCSs) during the warm seasons (May–September) of 2011–2018 (except 2014) over North China. This was achieved by using severe weather reports, precipitation observations, and composite Doppler radar reflectivity data. A total of 371 SCSs were identified. SCSs primarily initiated around noon with the highest frequency over the high terrain of Mount Taihang, and they mostly decayed over the plains at night. The storm morphologies were classified into three types of cellular storms (individual cells, clusters of cells, and broken lines), six types of linear systems (convective lines with no stratiform, with trailing stratiform, leading stratiform, parallel stratiform, embedded lines, and bow echoes), and nonlinear systems. Three types of severe convective weather, namely, short-duration heavy rainfall, hail, and thunderstorm high winds associated with these morphologies were investigated. Nonlinear systems were the most frequent morphology, followed by clusters of cells. Convective lines with trailing stratiform were the most frequent linear morphology. A total of 1,429 morphology samples from the 371 SCSs were found to be responsible for 15,966 severe convective weather reports. Linear (nonlinear) systems produced the most short-duration heavy rainfall (hail and thunderstorm high wind) reports. Bow echos were most efficient in producing both short-duration heavy rainfall and thunderstorm high wind reports whereas broken lines had the highest efficiency for hail production. The results in the present study are helpful for local forecasters to better anticipate the storm types and associated hazardous weather.

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An Analysis on the Heavy Rainfall over North China from 18 to 20 July 2016

Climate Change Research Letters ◽

10.12677/ccrl.2020.94029 ◽

2020 ◽

Vol 09 (04) ◽

pp. 254-263

Author(s):

洁田

Keyword(s):

Heavy Rainfall ◽

North China

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Role of baroclinic trough in triggering vertical motion during summertime heavy rainfall events in Korea

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0216.1 ◽

2021 ◽

Cited By ~ 1

Author(s):

Chanil Park ◽

Seok-Woo Son ◽

Jung-Hoon Kim

Keyword(s):

Heavy Rainfall ◽

Vertical Motion ◽

The West ◽

Rainfall Events ◽

Synoptic Conditions ◽

Upper Level ◽

Diabatic Forcing ◽

Upper Level Jet ◽

Q Vector ◽

Heavy Rainfall Events

AbstractThe nature of the vertical motion responsible for the summertime (June–September) heavy rainfall events (HREs) in Korea is quantitatively examined. By compositing 318 HREs in 1979–2018, it is found that the synoptic conditions of the HREs are typically characterized by a developing surface cyclone with a southwesterly low-level jet on its southeastern flank and an upper-level trough to the west of the HREs. This baroclinic environment allows for well-organized vertical motion over Korea at the equatorward side of the upper-level jet entrance. The relative importance of dynamic and diabatic forcings in driving the vertical motion is further quantified by solving the quasi-geostrophic omega equation. It turns out that the dynamic forcing, defined as Q-vector convergence, is comparable to the diabatic forcing in the developing stage of the HREs. The diabatic forcing, however, becomes more important in the mature stage as latent heating rapidly increases. The decomposition of Q-vector into the transverse and shearwise components reveals that the dynamic uplift is largely caused by the shearwise Q-vector convergence which is closely related to the developing trough in the upper-to-middle troposphere on the west of the HREs. This result indicates that the HREs in Korea are organized by the baroclinic trough coupled to moist processes, with a minor contribution of the thermally-direct secondary circulation at the entrance region of the upper-level jet.

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Typhoon Nina and the August 1975 Flood over Central China

Journal of Hydrometeorology ◽

10.1175/jhm-d-16-0152.1 ◽

2017 ◽

Vol 18 (2) ◽

pp. 451-472 ◽

Cited By ~ 15

Author(s):

Long Yang ◽

Maofeng Liu ◽

James A. Smith ◽

Fuqiang Tian

Keyword(s):

Water Vapor ◽

Heavy Rainfall ◽

Flood Control ◽

Vertical Motion ◽

Extreme Rainfall ◽

Vapor Transport ◽

Central China ◽

Water Vapor Transport ◽

Back Trajectory ◽

Central Feature

Abstract The August 1975 flood in central China was one of the most destructive floods in history. Catastrophic flooding was the product of extreme rainfall from Typhoon Nina over a 3-day period from 5 to 7 August 1975. Despite the prominence of the August 1975 flood, relatively little is known about the evolution of rainfall responsible for the flood. Details of extreme rainfall and flooding for the August 1975 event in central China are examined based on empirical analyses of rainfall and streamflow measurements and based on downscaling simulations using the Weather Research and Forecasting (WRF) Model, driven by Twentieth Century Reanalysis (20CR) fields. Key hydrometeorological features of the flood event are placed in a climatological context through hydroclimatological analyses of 20CR fields. Results point to the complex evolution of rainfall over the 3-day period with distinctive periods of storm structure controlling rainfall distribution in the flood region. Blocking plays a central role in controlling anomalous storm motion of Typhoon Nina and extreme duration of heavy rainfall. Interaction of Typhoon Nina with a second tropical depression played a central role in creating a zone of anomalously large water vapor transport, a central feature of heavy rainfall during the critical storm period on 7 August. Analyses based on the quasigeostrophic omega equation identified the predominant role of warm air advection for synoptic-scale vertical motion. Back-trajectory analyses using a Lagrangian parcel tracking algorithm are used to assess and quantify water vapor transport for the flood. The analytical framework developed in this study is designed to improve hydrometeorological approaches for flood-control design.

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The Remote Effect of Typhoon Megi (2010) on the Heavy Rainfall over Northeastern Taiwan

Monthly Weather Review ◽

10.1175/mwr-d-15-0269.1 ◽

2016 ◽

Vol 144 (9) ◽

pp. 3109-3131 ◽

Cited By ~ 6

Author(s):

Ting-Chen Chen ◽

Chun-Chieh Wu

Keyword(s):

Heavy Rainfall ◽

Asian Monsoon ◽

Storm Track ◽

Vertical Motion ◽

Rainfall Event ◽

Rainfall Simulation ◽

Heavy Rainfall Event ◽

Ensemble Simulation ◽

Torrential Rainfall ◽

Upstream Flow

The goal of this work is to improve understanding of the mechanisms leading to a heavy rainfall event under the combined influences of the outer circulation of Typhoon Megi (2010), the Asian monsoon, and the topography of Taiwan. Megi is a case featuring high forecast uncertainty associated with its sudden recurvature, along with remote heavy rainfall over northeastern Taiwan (especially at Yilan) and its adjacent seas during 19–23 October 2010. An ensemble simulation is conducted, and characteristic ensemble members are separated into subgroups based on either track accuracy or rainfall forecast skill. Comparisons between different subgroups are made to investigate favorable processes for precipitation and how the differences between these subgroups affect the rainfall simulation. Several mechanisms leading to this remote rainfall event are shown. The northward transport of water vapor by Megi’s outer circulation provides a moisture-laden environment over the coastal area of eastern Taiwan. Meanwhile, the outer circulation of Megi (with high [Formula: see text]) encounters the northeasterly monsoon (with low [Formula: see text]), and strong vertical motion is triggered through isentropic lifting in association with low-level frontogenesis over the ocean northeast of Yilan. Most importantly, the northeasterly flow advects the moisture inland to the steep mountains in south-southwestern Yilan, where strong orographic lifting further induces torrential rainfall. In addition, the analyses further attribute the uncertainty in simulating Megi’s remote rainfall to several factors, including variations of storm track, strength and extension of the northeasterly monsoon, and, above all, the impinging angle of the upstream flow on the topography.

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