Why Nocturnal Long-Duration Rainfall Presents an Eastward-Delayed Diurnal Phase of Rainfall down the Yangtze River Valley

2010 ◽  
Vol 23 (4) ◽  
pp. 905-917 ◽  
Author(s):  
Haoming Chen ◽  
Rucong Yu ◽  
Jian Li ◽  
Weihua Yuan ◽  
Tianjun Zhou
Keyword(s):  
Yangtze River ◽  
Large Scale ◽  
Southern China ◽  
Summer Rainfall ◽  
Early Morning ◽  
The Tibetan Plateau ◽  
The Yangtze River ◽  
Rainfall Events ◽  
Low Level ◽  
Long Duration

Abstract Hourly observational records and 6-hourly reanalysis data were used to investigate the influences of large-scale forcings on the diurnal variation of summer rainfall along the Yangtze River (YR). The results show that long-duration (more than six hours) rainfall events dominate the summer rainfall along the YR. These events tend to start during the night and to peak after several hours of development. The eastward-delayed initiation of the nocturnal long-duration rainfall events is thought to be due to the diurnal clockwise rotation of the low-tropospheric circulation, especially the accelerated nocturnal southwesterlies. In the early evening, the anomalous easterly flow toward the Tibetan Plateau (TP) causes low-level convergence over the Plateau’s eastern slope that induces the formation of rainfall in the upper YR valley. The anomalous wind sequentially rotates clockwise to a southerly flow at midnight and accelerates the meridional wind in the middle valley, resulting in the initiation of rainfall between 2300 and 0300 LST. In the early morning, the accelerated southwesterlies in southern China, when combined with decelerated winds in the north of the YR, causes a strong convergence along the YR and contributes to the early morning rainfall in the lower valley. Furthermore, the development of the convection systems is suppressed in the afternoon by the mid- and low-level warm advection downstream from the TP. This helps explain why long-duration events do not typically start in the afternoon in the upper YR valley.

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.

Formation of Nocturnal Offshore Rainfall near the West Coast of Sumatra: Land Breeze or Gravity Wave?

2021 ◽  
Vol 149 (3) ◽  
pp. 715-731
Author(s):  
Hedanqiu Bai ◽  
Gumilang Deranadyan ◽  
Courtney Schumacher ◽  
Aaron Funk ◽  
Craig Epifanio ◽  
...  
Keyword(s):  
West Coast ◽  
Large Scale ◽  
Deep Convection ◽  
Propagation Speed ◽  
Early Morning ◽  
Land Breeze ◽  
Maritime Continent ◽  
The West ◽  
Rainfall Events ◽  
Low Level

AbstractAfternoon deep convection over the Maritime Continent islands propagates offshore in the evening to early morning hours, leading to a nocturnal rainfall maximum over the nearby ocean. This work investigates the formation of the seaward precipitation migration off western Sumatra and its intraseasonal and seasonal characteristics using BMKG C-band radar observations from Padang and ERA5 reanalysis. A total of 117 nocturnal offshore rainfall events were identified in 2018, with an average propagation speed of 4.5 m s−1 within 180 km of Sumatra. Most offshore propagation events occur when the Madden–Julian oscillation (MJO) is either weak (real-time multivariate MJO index < 1) or active over the Indian Ocean (phases 1–3), whereas very few occur when the MJO is active over the Maritime Continent and western Pacific Ocean (phases 4–6). The occurrence of offshore rainfall events also varies on the basis of the seasonal evolution of the large-scale circulation associated with the Asian–Australian monsoons, with fewer events during the monsoon seasons of December–February and June–August and more during the transition seasons of March–May and September–November. Low-level convergence, resulting from the interaction of the land breeze and background low-level westerlies, is found to be the primary driver for producing offshore convective rain propagation from the west coast of Sumatra. Stratiform rain propagation speeds are further increased by upper-level easterlies, which explains the faster migration speed of high reflective clouds observed by satellite. However, temperature anomalies associated with daytime convective latent heating over Sumatra indicate that gravity waves may also modulate the offshore environment to be conducive to seaward convection migration.

The Effects of Midlatitude Waves over and around the Tibetan Plateau on Submonthly Variability of the East Asian Summer Monsoon

2009 ◽  
Vol 137 (7) ◽  
pp. 2286-2304 ◽  
Author(s):  
Hatsuki Fujinami ◽  
Tetsuzo Yasunari
Keyword(s):  
Tibetan Plateau ◽  
Rossby Wave ◽  
Large Scale ◽  
Southern China ◽  
Phase Speed ◽  
The Tibetan Plateau ◽  
Low Level ◽  
Zonal Wavenumber ◽  
Upper Level ◽  
Southward Migration

Convective variability at submonthly time scales (7–25 days) over the Yangtze and Huaihe River basins (YHRBs) and associated large-scale atmospheric circulation during the mei-yu season were examined using interpolated outgoing longwave radiation (OLR) and NCEP–NCAR reanalysis data for 12 yr having active submonthly convective fluctuation over the YHRBs within the period 1979–2004. Correlations between convection anomalies over the YHRBs and upper-level streamfunction anomalies at every grid point show two contrasting patterns. One pattern exhibits high correlations along the northern to eastern peripheries of the Tibetan Plateau (defined as the NET pattern), whereas the other has high correlations across the Tibetan Plateau (defined as the AT pattern). Composite analysis of the NET pattern shows slow southward migration of convection anomalies from the northeastern periphery of the Tibetan Plateau to southern China, in relation to southward migration of the mei-yu front caused by simultaneous amplification of upper- and low-level waves north of the YHRBs. In the AT pattern, convection anomalies migrate eastward from the western Tibetan Plateau to the YHRBs. A low-level vortex is created at the lee of the plateau by eastward-moving upper-level wave packets and associated convection from the plateau. Rossby wave trains along the Asian jet characterize the upper-level circulation anomalies in the two patterns. The basic state of the Asian jet during the mei-yu season differs between the two patterns, especially around the Tibetan Plateau. The Asian jet has a northward arclike structure in NET years, while a zonal jet dominates in AT years. These differences could alter the Rossby wave train propagation route. Furthermore, the larger zonal wavenumber of AT waves (∼7–8) than of NET waves (∼6) means faster zonal phase speed relative to the ground in the AT pattern than in the NET pattern. These differences likely explain the meridional amplification of waves north of the YHRBs in the NET pattern and the eastward wave movement across the plateau in the AT pattern.

scholarly journals Large-Scale Background and the Role of Quasi-Biweekly Moisture Transport in the Extreme Yangtze River Rainfall in Summer 2020

2022 ◽  
Author(s):  
Yanjun Qi ◽  
Renhe Zhang ◽  
Zhuo Wang
Keyword(s):  
Boundary Layer ◽  
Moisture Transport ◽  
Yangtze River ◽  
Large Scale ◽  
Summer Rainfall ◽  
Moisture Convergence ◽  
Specific Humidity ◽  
The Yangtze River ◽  
Air Mass ◽  
Cold Air

Abstract A severe flooding hit southern China along the Yangtze River in summer 2020. The floods were induced by heavy rains, and the associated dynamic and thermodynamic conditions are investigated using daily gridded rainfall data of China and NCEP-NCAR reanalysis. It is found that the summer rainfall over the Yangtze River Basin (YRB) experienced pronounced subseasonal variation in 2020, dominated by a quasi-biweekly oscillation (QBWO) mode. The southwestward-moving anomalous QBWO circulation was essentially the fluctuation of cold air mass related to the tropospheric polar vortex or trough-ridge activities over the mid-high latitude Eurasian in boreal summer. The large-scale southwestward-transport of cold air mass from mid-high latitudes and the northeastward-transport of warm and moist air by the strong anomalous anticyclone over the western North Pacific provided important circulation support for the heavy rainfall in the YRB. The quasi-biweekly anomalies of potential and divergent component of vertically integrated water vapor flux played a major role in maintaining the moisture during summer 2020. The diagnosis of moisture budget shows that the enhanced moisture associated with the quasi-biweekly fluctuation rainfall was primarily attributed to the moisture convergence. The convergence of QBWO specific humidity by the background mean flow and convergence of mean specific humidity by QBWO flow played dominant roles in contributing to the positive moisture tendency. In combination with an adiabatic ascent induced by the warm temperature advection, the boundary layer moisture convergence strengthens the upward transport of moisture from lower troposphere. The vertical moisture transport associated with boundary layer convergence was of critical importance in causing low-level tropospheric moistening, whereas the horizontal advection of moisture showed a negative effect during the anomalous quasi-biweekly summer rainfall in 2020.

scholarly journals Potential Predictability of Seasonal Extreme Precipitation Accumulation in China

2017 ◽  
Vol 18 (4) ◽  
pp. 1071-1080 ◽  
Author(s):  
Wenguang Wei ◽  
Zhongwei Yan ◽  
P. D. Jones
Keyword(s):  
Extreme Precipitation ◽  
Yangtze River ◽  
Large Scale ◽  
Southern China ◽  
Yangtze River Valley ◽  
River Valley ◽  
Northwestern China ◽  
Chain Model ◽  
The Yangtze River ◽  
Potential Predictability

Abstract The potential predictability of seasonal extreme precipitation accumulation (SEPA) across mainland China is evaluated, based on daily precipitation observations during 1960–2013 at 675 stations. The potential predictability value (PPV) of SEPA is calculated for each station by decomposing the observed SEPA variance into a part associated with stochastic daily rainfall variability and another part associated with longer-time-scale climate processes. A Markov chain model is constructed for each station and a Monte Carlo simulation is applied to estimate the stochastic part of the variance. The results suggest that there are more potentially predictable regions for summer than for the other seasons, especially over southern China, the Yangtze River valley, the north China plain, and northwestern China. There are also regions of large PPVs in southern China for autumn and winter and in northwestern China for spring. The SEPA series for the regions of large PPVs are deemed not entirely stochastic, either with long-term trends (e.g., increasing trends in inland northwestern China) or significant correlation with well-known large-scale climate processes (e.g., East Asian winter monsoon for southern China in winter and El Niño for the Yangtze River valley in summer). This fact not only verifies the claim that the regions have potential predictability but also facilitates predictive studies of the regional extreme precipitation associated with large-scale climate processes.

scholarly journals Using the Global Hydrodynamic Model and GRACE Follow-On Data to Access the 2020 Catastrophic Flood in Yangtze River Basin

2021 ◽  
Vol 13 (15) ◽  
pp. 3023
Author(s):  
Jinghua Xiong ◽  
Shenglian Guo ◽  
Jiabo Yin ◽  
Lei Gu ◽  
Feng Xiong
Keyword(s):  
River Basin ◽  
Hydrodynamic Model ◽  
Yangtze River ◽  
Large Scale ◽  
Yangtze River Basin ◽  
The Yangtze River ◽  
Ecosystem Monitoring ◽  
Catastrophic Flood ◽  
Basin Scale ◽  
The Yangtze River Basin

Flooding is one of the most widespread and frequent weather-related hazards that has devastating impacts on the society and ecosystem. Monitoring flooding is a vital issue for water resources management, socioeconomic sustainable development, and maintaining life safety. By integrating multiple precipitation, evapotranspiration, and GRACE-Follow On (GRAFO) terrestrial water storage anomaly (TWSA) datasets, this study uses the water balance principle coupled with the CaMa-Flood hydrodynamic model to access the spatiotemporal discharge variations in the Yangtze River basin during the 2020 catastrophic flood. The results show that: (1) TWSA bias dominates the overall uncertainty in runoff at the basin scale, which is spatially governed by uncertainty in TWSA and precipitation; (2) spatially, a field significance at the 5% level is discovered for the correlations between GRAFO-based runoff and GLDAS results. The GRAFO-derived discharge series has a high correlation coefficient with either in situ observations and hydrological simulations for the Yangtze River basin, at the 0.01 significance level; (3) the GRAFO-derived discharge observes the flood peaks in July and August and the recession process in October 2020. Our developed approach provides an alternative way of monitoring large-scale extreme hydrological events with the latest GRAFO release and CaMa-Flood model.

scholarly journals Seasonal Variation of the Diurnal Cycle of Rainfall in Southern Contiguous China

2008 ◽  
Vol 21 (22) ◽  
pp. 6036-6043 ◽  
Author(s):  
Jian Li ◽  
Rucong Yu ◽  
Tianjun Zhou
Keyword(s):  
Seasonal Variation ◽  
Diurnal Cycle ◽  
Radiative Forcing ◽  
Early Morning ◽  
Rain Gauge ◽  
Rainfall Events ◽  
Late Afternoon ◽  
Long Duration ◽  
China Region ◽  
Afternoon Peak

Abstract Hourly station rain gauge data are employed to study the seasonal variation of the diurnal cycle of rainfall in southern contiguous China. The results show a robust seasonal variation of the rainfall diurnal cycle, which is dependent both on region and duration. Difference in the diurnal cycle of rainfall is found in the following two neighboring regions: southwestern China (region A) and southeastern contiguous China (region B). The diurnal cycle of annual mean precipitation in region A tends to reach the maximum in either midnight or early morning, while precipitation in region B has a late-afternoon peak. In contrast with the weak seasonal variation of the diurnal phases of precipitation in region A, the rainfall peak in region B shifts sharply from late afternoon in warm seasons to early morning in cold seasons. Rainfall events in south China are classified into short- (1–3 h) and long-duration (more than 6 h) events. Short-duration precipitation in both regions reaches the maximum in late afternoon in warm seasons and peaks in either midnight or early morning in cold seasons, but the late-afternoon peak in region B exists during February–October, while that in region A only exists during May–September. More distinct differences between regions A and B are found in the long-duration rainfall events. The long-duration events in region A show dominant midnight or early morning peaks in all seasons. But in region B, the late-afternoon peak exists during July–September. Possible reasons for the difference in the diurnal cycle of rainfall between the two regions are discussed. The different cloud radiative forcing over regions A and B might contribute to this difference.

Dynamic and Thermodynamic Relations of Distinctive Stratus Clouds on the Lee Side of the Tibetan Plateau in the Cold Season

2013 ◽  
Vol 26 (21) ◽  
pp. 8378-8391 ◽  
Author(s):  
Yi Zhang ◽  
Rucong Yu ◽  
Jian Li ◽  
Weihua Yuan ◽  
Minghua Zhang
Keyword(s):  
Tibetan Plateau ◽  
Large Scale ◽  
Eastern China ◽  
Cold Season ◽  
Water Vapor Transport ◽  
The Tibetan Plateau ◽  
Primary Role ◽  
Moist Air ◽  
Low Level ◽  
Stratus Clouds

Abstract Given the large discrepancies that exist in climate models for shortwave cloud forcing over eastern China (EC), the dynamic (vertical motion and horizontal circulation) and thermodynamic (stability) relations of stratus clouds and the associated cloud radiative forcing in the cold season are examined. Unlike the stratus clouds over the southeastern Pacific Ocean (as a representative of marine boundary stratus), where thermodynamic forcing plays a primary role, the stratus clouds over EC are affected by both dynamic and thermodynamic factors. The Tibetan Plateau (TP)-forced low-level large-scale lifting and high stability over EC favor the accumulation of abundant saturated moist air, which contributes to the formation of stratus clouds. The TP slows down the westerly overflow through a frictional effect, resulting in midlevel divergence, and forces the low-level surrounding flows, resulting in convergence. Both midlevel divergence and low-level convergence sustain a rising motion and vertical water vapor transport over EC. The surface cold air is advected from the Siberian high by the surrounding northerly flow, causing low-level cooling. The cooling effect is enhanced by the blocking of the YunGui Plateau. The southwesterly wind carrying warm, moist air from the east Bay of Bengal is uplifted by the HengDuan Mountains via topographical forcing; the midtropospheric westerly flow further advects the warm air downstream of the TP, moistening and warming the middle troposphere on the lee side of the TP. The low-level cooling and midlevel warming together increase the stability. The favorable dynamic and thermodynamic large-scale environment allows for the formation of stratus clouds over EC during the cold season.

Sign in / Sign up

Export Citation Format

Share Document