scholarly journals Multiscale Causes of Persistent Heavy Rainfall in the Meiyu Period over the Middle and Lower Reaches of the Yangtze River

2021 ◽  
Vol 9 ◽  
Author(s):  
Yicong Xia ◽  
Qian Huang ◽  
Suxiang Yao ◽  
Tianle Sun
Keyword(s):  
Water Vapor ◽  
Yangtze River ◽  
Heavy Rainfall ◽  
Observation Data ◽  
The Yangtze River ◽  
Synoptic Scale ◽  
Circulation Patterns ◽  
Persistent Heavy Rainfall ◽  
The Difference ◽  
Heavy Rainfall Events

Based on observation data supplied by the Chinese Meteorological Administration (CMA) and reanalysis datasets provided by the ECMWF, the multiscale causes of persistent heavy rainfall events (PHREs) that occurred from 1979 to 2018 during Meiyu periods over the middle and lower reaches of the Yangtze River (MLYR) are investigated. During Meiyu periods, precipitation shows obvious interannual variabilities. In PHRE years, the contribution rate of persistent heavy rainfall to the total precipitation is approximately 57%. Precipitation also shows significant synoptic-scale (less than 10 days) characteristics. Through the quantitative diagnosis of interactions among background-scale (greater than 30 days), quasi-biweekly-scale (10–30-days), and synoptic-scale variables, the possible causes of PHREs are explored. The results reveal that the difference in precipitation intensity between PHRE years and non-PHRE years is determined by the background water vapor, background wind and synoptic-scale wind conditions. In PHRE years, the prevailing background southwesterly winds from lower latitudes provide more background water vapor, and more mean kinetic energy is converted to perturbation energy. Moreover, the active synoptic-scale oscillations from higher latitudes and the convergence of Rossby wave disturbance energy over the MLYR could also cause the occurrence and maintenance of PHREs during Meiyu periods. The multiscale causes and corresponding circulation patterns in 2020 PHREs are similar to PHREs years.

Two Distinct Types of 10-30-day Persistent Heavy Rainfall Events over the Yangtze River Valley

2021 ◽  
pp. 1-44
Author(s):  
Yifeng Cheng ◽  
Lu Wang ◽  
Tim Li
Keyword(s):  
Yangtze River ◽  
Heavy Rainfall ◽  
Yangtze River Valley ◽  
The Yangtze River ◽  
Rainfall Events ◽  
Anticyclonic Circulation ◽  
Persistent Heavy Rainfall ◽  
Circulation Anomalies ◽  
Upper Level ◽  
Heavy Rainfall Events

AbstractLarge-scale circulation anomalies associated with 10-30-day filtered persistent heavy rainfall events (PHREs) over the middle and lower reaches of the Yangtze River Valley (MLYV) in boreal summer for the period of 1961-2017 were investigated. Two distinct types of PHREs were identified based on configurations of anomalies in western Pacific subtropical high (WPSH) and South Asian High (SAH) during the peak wet phase. One type named as PSAH is characterized by eastward extension of the SAH while the other named as NSAH is featured by westward retreat of the SAH, and they both exhibit westward extension of the WPSH. Both types of PHREs are dominated by Mei-yu frontal systems. The lower-level circulation anomalies play a crucial role in initiating rainfall but through different processes. Prior to rainfall occurrence, a strong anticyclonic circulation anomaly is over the western North Pacific (WNP) for the PSAH events and the related southwesterly wind anomaly prevails over the south-eastern China, which advects moisture into the MLYV, moistens the boundary layer, and induces atmospheric convective instability. For the NSAH events, the WNP anticyclonic circulation is weak while a strong northerly wind is observed north of the MLYV. It brings cold air mass southward, favoring initiating frontal rainfall over the MLYV. The formation of upper-level circulation anomalies over the MLYV is primarily due to the shift of anomalous circulations from mid-high latitudes. After the rainfall generation, the precipitation would influence the lower- and upper-level circulation anomalies.

scholarly journals Impact of the Westerly Jet on Rainfall/Runoff in the Source Region of the Yangtze River during the Flood Season

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Xin Lai ◽  
Yuanfa Gong ◽  
Sixian Cen ◽  
Hui Tian ◽  
Heng Zhang
Keyword(s):  
Water Vapor ◽  
Coastal Zone ◽  
Yangtze River ◽  
Source Region ◽  
Observation Data ◽  
The Yangtze River ◽  
Antecedent Rainfall ◽  
Flood Season ◽  
Westerly Jet ◽  
The Impact

Based on runoff data collected at the Zhimenda station, reanalysis data from the National Centers of Environmental Prediction/National Centers of Atmospheric Research (NCEP/NCAR), and observation data from ground stations in China, this study analyzes the characteristics of changes in runoff in the source region of the Yangtze River (SRYR) during the flood season (from July to September), the relationship between runoff and antecedent rainfall, and the impact of the westerly jet (WJ) on rainfall in the coastal zone of the SRYR. The results show the following. The runoff in the SRYR displays a significant interannual and interdecadal variability. The runoff in the SRYR during the flood season is most closely related to 15-day (June 16 to September 15) antecedent rainfall in the coastal zone of the SRYR. In turn, the antecedent rainfall in the coastal zone of the SRYR is mainly affected by the intensity of the simultaneous WJ over a key region (55–85°E, 45–55°N). When the intensity of the WJ over the key region is greater (less) than normal, the jet position moves northward (southward), and the easterly (westerly) wind anomalies over the region to the west of the SRYR become unfavorable (favorable) to the transport of water vapor from high-latitude regions to the SRYR. In addition, the southerly wind over the equatorial region cannot (can) easily advance northward, which is unfavorable (favorable) to the northward transport of water vapor from the low-latitude ocean. Hence, these conditions result in a decrease (increase) in the water vapor content in the SRYR. Furthermore, the convergence (divergence) anomalies in the upper level and the divergence (convergence) anomalies in the lower level result in the descending (ascending) motion over the SRYR. These factors decrease (increase) the rainfall, thereby decreasing (increasing) the runoff in the SRYR during the flood season.

How Were the Eastward-Moving Heavy Rainfall Events from the Tibetan Plateau to the Lower Reaches of the Yangtze River Enhanced?

2021 ◽  
Vol 34 (2) ◽  
pp. 607-620
Author(s):  
Yang Zhao ◽  
Deliang Chen ◽  
Yi Deng ◽  
Seok-Woo Son ◽  
Xiang Wang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Yangtze River ◽  
Heavy Rainfall ◽  
Diabatic Heating ◽  
Convective Motion ◽  
Convective System ◽  
The Tibetan Plateau ◽  
The Yangtze River ◽  
Rainfall Events ◽  
Heavy Rainfall Events

AbstractThis study investigates eastward-moving summer heavy rainfall events in the lower reaches of the Yangtze River (LRYR), which are associated with the Tibetan Plateau (TP) vortices. On the basis of rainfall data from gauges and additional atmospheric data from ERA-Interim, the dynamic and thermodynamic effects of moisture transport and diabatic heating are estimated to determine the physical mechanisms that support the eastward-moving heavy rainfall events. As the rainband moves eastward, it is accompanied by anomalous cyclonic circulation in the upper and middle troposphere and enhanced vertical motion throughout the troposphere. In particular, the rainfall region is located in the fore of the upper-level trough, which is ideal for baroclinic organization of the convective system and further development of the eastward-moving vortex. The large atmospheric apparent heat source (Q1) also contributes for lifting the lower-level air into the upper atmosphere and for enhancing the low-level convective motion and convergence during the heavy rainfall process. Piecewise potential vorticity inversion further verifies the crucial role that the diabatic heating played in developing the anomalous geopotential height favorable for the enhanced rainfall. The combined action of the dynamic and thermodynamic processes, as well as the rich moisture supply from the seas, synergistically sustained and enhanced the eastward-moving rainfall.

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