Dynamics of East Asian Spring Rainband and spring-autumn contrast: Environmental forcings of large-scale circulation

2021 ◽  
pp. 1-59
Author(s):  
Shi-Xin Wang ◽  
Hong-Chao Zuo ◽  
Fen Sun ◽  
Li-Yang Wu ◽  
Yixing Yin ◽  
...  

AbstractDynamics of the East Asian spring rainband are investigated with reanalysis dataset and station observations. Here, it is revealed that the rainband is anchored by external forcings. Midtropospheric jet core stays quasi-stationary around Japan. It has two branches in its entry region, which originate from the south and north flanks of Tibetan Plateau and then run northeastward and southeastward, respectively. The southern branch advects warm air from the Hengduan-Tibetan plateaus northeastwards, forming rainband over southern China through both causing adiabatic ascent motion and triggering diabatic feedback. The rainband is much stronger in spring than in autumn due to the stronger diabatic heating over Hengduan-Tibetan Plateau, more southward-displaced midtropospheric jet and resultant stronger warm advection over southern China. The northern jet branch forms a zonally-elongated cold advection belt, which reaches the maximum around northern China, and then weakens and extends eastwards towards east of Japan. The westerly jet also steers strong disturbance activities roughly collocated with the cold advection belt via baroclinic instability. The high disturbance activities belt causes large cumulative warm advections (CWA) through drastically increasing extremely warm-advection days in its eastern and south flank, where weak cold advection prevails. CWA is more essential for monthly/seasonally rainfall than conventionally-used time-average temperature advection because it is revealed that strengthened warm advection can increase rainfall through positive diabatic feedback, while cold advection cannot cause negative rainfall. Thus, the rainband is collocated with the large CWA belt instead of the 48 warm advection south of it. This rainband is jointed to the rainband over southern China, forming the long southwest-northeast-oriented East Asian spring rainband. Southeastward-increasing moisture slightly displaces the rainband southeastwards.

2016 ◽  
Vol 29 (19) ◽  
pp. 7027-7044 ◽  
Author(s):  
Mingxin Li ◽  
Qinghong Zhang ◽  
Fuqing Zhang

Abstract Based on a comprehensive collection of hail observations and the NCEP–NCAR reanalyses from 1960 to 2012, the long-term trends of hail day frequency in mainland China and the associated changes in atmospheric circulation patterns were analyzed. There was no detectable trend in hail frequency from 1960 to the early 1980s, but a significant decreasing trend was apparent in later periods throughout most of China and in particular over the Tibetan Plateau from the early 1980s and over northern and northwestern China from the early 1990s. Hail frequency in southern China did not decrease as significantly as in other regions over the last couple of decades. An objective classification method, the obliquely rotated T-mode principal component technique, was used to investigate atmospheric circulation patterns. It was found that 51.85% of the hail days occurred during two major circulation types, both of which were associated with cold frontal systems in northern China. More specifically, the synoptic trough in East Asia, signified by the meridional circulation at 850 hPa, became considerably weaker after 1990. This change in the synoptic pattern is consistent with a weakening trend in the East Asian summer monsoon, the primary dynamic forcing of moisture transport that contributes to the generation of severe convection in northern China. The long-term variability of hail day frequency over the Tibetan Plateau was more strongly correlated with the change in mean freezing-level height (FLH) than the strength of the East Asian monsoon.


2020 ◽  
Author(s):  
Julia Curio ◽  
Reinhard Schiemann ◽  
Kevin Hodges ◽  
Andrew Turner ◽  
Nicholas Klingaman

<p>The Tibetan Plateau (TP) and surrounding high mountains constitute an important forcing of the atmospheric circulation due to their height and extent, and thereby impact weather and climate in East Asia. Mesoscale Tibetan Plateau Vortices (TPVs) form over the TP and are one of the major systems generating TP precipitation. The majority of TPVs remain on the TP throughout their lifetime, while a fraction moves east off the TP. These “moving-off” TPVs can trigger extreme precipitation and severe flooding over large parts of eastern and southern China, for example in Sichuan province and the Yangtze River valley. Due to their potentially severe impacts downstream of the TP, it is first important to understand the conditions under which TPVs can move east off the TP.</p><p>In this study, we examine the vertical and horizontal structure of TPVs moving off the TP in contrast to those that do not using reanalysis in order to understand which local and/or large-scale atmospheric conditions lead TPVs to move off the TP. We use composites of atmospheric fields at different stages of the TPV lifecycle (e.g. genesis, maximum intensity, and maximum precipitation) and at different locations over and downstream of the TP, to account for the heterogeneous topography. Preliminary results suggest that the large-scale background flow, characterised by the strength and position of the subtropical westerly jet, is one of the factors determining whether a TPV moves off the TP or not.</p><p>Another important question is how and where moving-off TPVs trigger precipitation. Do TPVs transport moisture from the TP to the downstream regions? Do they move off while already precipitating? Do they trigger precipitation dynamically east of the TP? Results from a case study suggest that the TPV triggers precipitation as it moves over the edge of the TP, which then stays locked to the orography while the system is moving further east. The TPV appears to change the local atmospheric circulation in the Sichuan basin while moving off, thereby directing a flow of moist air towards the eastern slope of the TP.</p><p>Understanding how the combination of the right large-scale atmospheric conditions and a TPV-induced change in the local circulation downstream of the TP can create an impactful TPV may enable improved forecasts of TPVs and their impacts in the densely populated regions downstream of the TP.</p>


2016 ◽  
Author(s):  
Yu Hao Mao ◽  
Hong Liao

Abstract. We applied a global three-dimensional chemical transport model (GEOS-Chem) to examine the impacts of the East Asian monsoon on the interannual variations of mass concentrations and direct radiative forcing (DRF) of black carbon (BC) over eastern China (110–125° E, 20–45° N). With emissions fixed at the year 2010 levels, model simulations were driven by the Goddard Earth Observing System (GEOS-4) meteorological fields for 1986–2006 and the Modern Era Retrospective-analysis for Research and Applications (MERRA) meteorological fields for 1980–2010. During the period of 1986–2006, simulated JJA and DJF surface BC concentrations were higher in MERRA than in GEOS-4 by 0.30 µg m−3 (44 %) and 0.77 µg m−3 (54 %), respectively, because of the generally weaker precipitation in MERRA. We found that the strength of the East Asian summer monsoon (EASM, (East Asian winter monsoon, EAWM)) negatively correlated with simulated JJA (DJF) surface BC concentrations (r = –0.7 (–0.7) in GEOS-4 and –0.4 (–0.7) in MERRA), mainly by the changes in atmospheric circulation. Relative to the five strongest EASM years, simulated JJA surface BC concentrations in the five weakest monsoon years were higher over northern China (110–125° E, 28–45° N) by 0.04–0.09 µg m−3 (3–11 %), but lower over southern China (110–125° E, 20–27° N) by 0.03–0.04 µg m−3 (10–11 %). Compared to the five strongest EAWM years, simulated DJF surface BC concentrations in the five weakest monsoon years were higher by 0.13–0.15 µg m−3 (5–8 %) in northern China and by 0.04–0.10 µg m−3 (3–12 %) in southern China. The resulting JJA (DJF) mean all-sky DRF of BC at the top of the atmosphere were 0.04 W m−2 (3 %, (0.03 W m−2, 2 %)) higher in northern China but 0.06 W m−2 (14 %, (0.03 W m−2, 3 %)) lower in southern China. In the weakest monsoon years, the weaker vertical convection led to the lower BC concentrations above 1–2 km in southern China, and therefore the lower BC DRF in the region. The differences in vertical profiles of BC between the weakest and strongest EASM years (1998–1997) and EAWM years (1990–1996) reached up to –0.09 µg m−3 (–46 %) and –0.08 µg m−3 (–11 %) at 1–2 km in eastern China.


2017 ◽  
Vol 30 (14) ◽  
pp. 5597-5603 ◽  
Author(s):  
Xian Chen ◽  
Zhong Zhong ◽  
Wei Lu

The NCEP–NCAR reanalysis dataset and the tropical cyclone (TC) best-track dataset from the Regional Specialized Meteorological Center (RSMC) Tokyo Typhoon Center were employed in the present study to investigate the possible linkage of the meridional displacement of the East Asian subtropical upper-level jet (EASJ) with the TC activity over the western North Pacific (WNP). Results indicate that summertime frequent TC activities would create the poleward shift of the EASJ through a stimulated Pacific–Japan (PJ) teleconnection pattern as well as the changed large-scale meridional temperature gradient. On the contrary, in the inactive TC years, the EASJ is often located more southward than normal with an enhanced intensity. Therefore, TC activities over the WNP are closely related to the location and intensity of the EASJ in summer at the interannual time scale.


2019 ◽  
Vol 11 (16) ◽  
pp. 1855 ◽  
Author(s):  
Yanan Chen ◽  
Hongfan Gu ◽  
Munan Wang ◽  
Qing Gu ◽  
Zhi Ding ◽  
...  

Precise quantification of terrestrial gross primary production (GPP) has been recognized as one of the most important components in understanding the carbon balance between the biosphere and the atmosphere. In recent years, although many large-scale GPP estimates from satellite data and ecosystem models have been generated, few attempts have been made to compare the different GPP products at national scales, particularly for various climate zones. In this study, two of the most widely-used GPP datasets were systematically compared over the eight climate zones across China’s terrestrial ecosystems from 2001 to 2015, which included the moderate resolution imaging spectroradiometer (MODIS) GPP and the breathing Earth system simulator (BESS) GPP products. Additionally, the coarse (0.05o) GPP estimates from the vegetation photosynthesis model (VPM) at the same time scale were used for auxiliary analysis with the two products. Both MODIS and BESS products exhibited a decreasing trend from the southeast region to the northwest inland. The largest GPP was found in the tropical humid region with 5.49 g C m−2 d−1 and 5.07 g C m−2 d−1 for MODIS and BESS, respectively, while the lowest GPP was distributed in the warm temperate arid region, midtemperate semiarid region and plateau zone. Meanwhile, the work confirmed that all these GPP products showed apparent seasonality with the peaks in the summertime. However, large differences were found in the interannual variations across the three GPP products over different climate regions. Generally, the BESS GPP agreed better than the MODIS GPP when compared to the seasonal and interannual variations of VPM GPP. Furthermore, the spatial correlation analysis between terrestrial GPP and the climatic factors, including temperature and precipitation, indicated that natural rainfall dominated the variability in GPP of Northern China, such as the midtemperate semiarid region, while temperature was a key controlling factor in the Southern China and the Tibet Plateau area.


2007 ◽  
Vol 135 (7) ◽  
pp. 2588-2609 ◽  
Author(s):  
George Tai-Jen Chen ◽  
Chung-Chieh Wang ◽  
An-Hsiang Wang

Abstract During 8–14 June 2000, a 500-hPa blocking event occurred over Mongolia and northern China (near 45°N, 108°E), which was the only case over this region in June since 1981. As the block developed, the initially weak low-level mei-yu front over southern China evolved into a system with strong baroclinity and subsequently moved south. The frontal passage over Taiwan caused temperatures to drop by 10°C, the largest in June over two decades. Using gridded analyses, manually analyzed weather maps, and satellite and surface data, the present study investigates the evolution of this mei-yu front under the influence of the block. The 925-hPa frontogenetical function is computed and effects of different processes are discussed. As the blocking event developed, concurrent ridge–trough amplification in the lower–midtroposphere produced a reversed thermal pattern. The lower-tropospheric high moved southward, and large-scale confluence and deformation were enhanced between the northerly flow and the prefrontal southwesterly flow. The location of the block, to the west-southwest of the Okhotsk Sea area, allowed it to affect the front over southern China and caused it to penetrate inside 20°N, unusual for the month of June. The distribution of the frontogenetical function indicated that the mei-yu frontogenesis and the maintenance of the front were attributed to both deformation and convergence. These two processes together counteracted the strong frontolysis along the frontal zone from diabatic effects, caused by evaporative cooling of frontal precipitation on the warm side and stronger sensible heat transfer (and daytime heating over less cloudy areas) on the cold side of the front. When deformation, convergence, and diabatic effects were all combined, the net total frontogenesis peaked slightly ahead of the frontal zone, thus contributing to the southward propagation of the front in addition to the advection by postfrontal cold air in the present case. When the front moved into the South China Sea, the cross-frontal thermal gradient diminished rapidly, mainly due to the frontolytic effect from sensible heat flux over warm waters.


2017 ◽  
Vol 17 (7) ◽  
pp. 4799-4816 ◽  
Author(s):  
Yu-Hao Mao ◽  
Hong Liao ◽  
Hai-Shan Chen

Abstract. We applied a global three-dimensional chemical transport model (GEOS-Chem) to examine the impacts of the East Asian monsoon on the interannual variations of mass concentrations and direct radiative forcing (DRF) of black carbon (BC) over eastern China (110–125° E, 20–45° N). With emissions fixed at the year 2010 levels, model simulations were driven by the Goddard Earth Observing System (GEOS-4) meteorological fields for 1986–2006 and the Modern Era Retrospective-analysis for Research and Applications (MERRA) meteorological fields for 1980–2010. During the period of 1986–2006, simulated June–July–August (JJA) and December–January–February (DJF) surface BC concentrations were higher in MERRA than in GEOS-4 by 0.30 µg m−3 (44 %) and 0.77 µg m−3 (54 %), respectively, because of the generally weaker precipitation in MERRA. We found that the strength of the East Asian summer monsoon (EASM; East Asian winter monsoon, EAWM) negatively correlated with simulated JJA (DJF) surface BC concentrations (r = −0. 7 (−0.7) in GEOS-4 and −0.4 (−0.7) in MERRA), mainly by the changes in atmospheric circulation. Relative to the 5 strongest EASM years, simulated JJA surface BC concentrations in the 5 weakest monsoon years were higher over northern China (110–125° E, 28–45° N) by 0.04–0.09 µg m−3 (3–11 %), but lower over southern China (110–125° E, 20–27° N) by 0.03–0.04 µg m−3 (10–11 %). Compared to the 5 strongest EAWM years, simulated DJF surface BC concentrations in the 5 weakest monsoon years were higher by 0.13–0.15 µg m−3 (5–8 %) in northern China and by 0.04–0.10 µg m−3 (3–12 %) in southern China. The resulting JJA (DJF) mean all-sky DRF of BC at the top of the atmosphere was 0.04 W m−2 (3 %; 0.03 W m−2, 2 %) higher in northern China but 0.06 W m−2 (14 %; 0.03 W m−2, 3 %) lower in southern China. In the weakest monsoon years, the weaker vertical convection at the elevated altitudes led to the lower BC concentrations above 1–2 km in southern China, and therefore the lower BC DRF in the region. The differences in vertical profiles of BC between the weakest and strongest EASM years (1998–1997) and EAWM years (1990–1996) reached up to −0.09 µg m−3 (−46 %) and −0.08 µg m−3 (−11 %) at 1–2 km in eastern China.


2021 ◽  
Vol 9 ◽  
Author(s):  
Zhibiao Wang ◽  
Renguang Wu ◽  
Zhang Chen ◽  
Lihua Zhu ◽  
Kai Yang ◽  
...  

In recent years, some studies emphasized the influence of western Tibetan Plateau summer snow on the East Asian summer precipitation. With the temperature rise in the past decades, the snow cover over the western Tibetan Plateau in summer has significantly decreased. This raises the question whether the impact of the Tibetan Plateau snow has changed. The present study identifies a prominent change in the influence of the western Tibetan Plateau snow cover on the East Asian summer precipitation. Before the early 2000’s, positive precipitation anomalies extend from the southeastern Tibetan Plateau through the Yangtze River to Japan and Korea and negative anomalies cover southeast China corresponding to more Tibetan Plateau snow cover. After the early 2000’s, with the reduction of snow cover variability, below-normal and above-normal summer precipitation occurs over northern China-Mongolia and northeast Asia, respectively, corresponding to more Tibetan Plateau snow cover. The change in the influence of the Tibetan Plateau snow on the East Asian summer precipitation is associated with an obvious change in the atmospheric circulation anomaly pattern. Before the early 2000’s, the wind anomalies display a south-north contrast pattern with anomalous convergence along the Yangtze River. After the early 2000’s, an anomalous cyclone occupies Northeast China with anomalous southerlies and northerlies over northeast Asia and northern China, respectively. The Tibetan Plateau snow cover variation after the early 2000’s is associated with the northeast Indian summer precipitation. The model experiments confirm that the weakened influence of summer western Tibetan Plateau snow cover on the East Asian atmospheric circulation and precipitation with the reduced snow cover anomalies.


2021 ◽  
Vol 12 ◽  
Author(s):  
Yihui Wang ◽  
Hongkun Quan ◽  
Xiaohui Li ◽  
Qiang Li ◽  
Md Atiqul Haque ◽  
...  

Fumonisin B (FB) and other fumonisins, deoxynivalenol (DON), and zearalenone (ZEN) are mycotoxins (secondary metabolites of fungi) present at high levels of contamination in poultry diets and threatening the sustainability of the poultry industry and egg safety for consumers. However, residual mycotoxins in breeder eggs and their effects on chicken progeny and gizzard ulcerations remain unclear. To unveil mycotoxin contaminations from daily diets to breeder eggs, 293 poultry feed samples were collected from three large-scale poultry provinces across Northern China to Southern China. Average levels of 1,628 ± 4.36 μg/kg of FB1, 593 ± 11.16 μg/kg of DON, 69 ± 9.21 μg/kg of ZEN, 52 ± 7.33 μg/kg of OTA, and 24 ± 5.85 μg/kg of AFB1 were found in feedstuffs and poultry diets using commercial ELISA kits. In terms of residual mycotoxins in breeder eggs, FB1 and DON contaminations dominated residues in egg albumen and yolk samples. Out of 221 breeder eggs, the average residual of FB1 in albumen were 320.6 ± 10.12 μg/kg (Hebei), 420.2 ± 10.98 μg/kg (Guangdong), and 549.4 ± 10.27 (Guangxi). Moreover, higher residual of DONs were determined in Guangdong and Guangxi provinces compared to Hebei province. ZEN, ochratoxins A (OTA), and aflatoxin B1 (AFB1) contamination at low levels were found in the above samples collected from afronmentioned three provinces. Based on residual mycotoxins in breeder eggs, SPF embryonated eggs aged 11 days were inoculated into albumen with different doses of FB1, FB2 or DON, or a combination of FB1 and DON, or a combination of FB1 with FB2 and FB3. A lower hatching rate was observed in the chicken progenies with the combination of 24 μg of FB1 and 0.1 μg of DON compared to other treatments. Moreover, typical gizzard ulcerations with hemorrhagic lungs were observed in the progeny of breeder eggs post-inoculation of 24 μg of FB1 and synergetic inoculation of FB1 and DON. Finally, residual FB mycotoxins were detected in the gizzards and in the lungs of the progenies. Based on the above evidence, feed-borne FB1 and DON are dominant mycotoxins in breeder eggs and threatening food security using breeder eggs as a Trojan horse. More importantly, the residual of FB1 alone and in combination with of DON contamination are associated with low hatching rate and gizzard ulcerations in chicken progenies, hampering sustainable development perspectives of the poultry industry.


2021 ◽  
Vol 9 ◽  
Author(s):  
Ruxi Dou ◽  
Jianjun Zou ◽  
Xuefa Shi ◽  
Aimei Zhu ◽  
Zhi Dong ◽  
...  

The Sea of Japan (JS) is a unique marginal sea in the western North Pacific that is characterized by four shallow straits. It can provide information about the paleoenvironment, for instance indicating variations in the East Asian Monsoon, Tsushima Warm Current, sea ice coverage, and Westerly Jet. Compared with other marginal seas in the western North Pacific, the JS is currently the only marginal sea without influx from large rivers. It is, therefore, of interest to determine the source of terrigenous sediments over time, particularly in the western JS, which has been less investigated in previous reports. In this study, a suite of multi-proxies including Sr and Nd isotopes and minor elements were measured for fine fractions (<63 μm) of core LV53-18-2 that were recovered from the western JS over the last 30 ka. Our results show that the sediments are rich in volcanic detritus and that the provenance of terrigenous sediments in the western JS is mainly derived from the arid region in northern China and coastal areas in the Far East. During the Last Glacial Maximum, the increased coverage of sea ice may have contributed to the accumulation of terrigenous debris. Meanwhile, the stronger East Asian Winter Monsoon and expansion of the Westerly Jet over northern China also carried more dust to the study area. However, the weakened atmospheric circulation and rise in sea level, induced by the ascending boreal insolation during the last deglaciation and early Holocene, remarkably reduced input of terrigenous debris, and the intense melting of sea ice delivered an amount of detritus from coastal areas to the research area. After 8 ka, the high stand sea level and opening of the Tatar Strait may have led to the development of the Liman Cold Current, which transports large quantities of volcanic materials to the study area continuously and produces more positive Eu anomalies, radiogenic εNd, and depleted ΣREE.


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