scholarly journals Anomalous Atmospheric Circulation Associated with the Extremely Persistent Dense Fog Events over Eastern China in the Late Autumn of 2018

Atmosphere ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 111
Author(s):  
Shengjie Chen ◽  
Duanyang Liu ◽  
Zhiming Kang ◽  
Yan Shi ◽  
Mei Liu
Keyword(s):  
East Asian ◽  
Eastern China ◽  
Lower Troposphere ◽  
Circulation Pattern ◽  
Near Surface ◽  
Late Autumn ◽  
Asian Winter Monsoon ◽  
Long Duration ◽  
Strong Inversion ◽  
Fog Days

Under a declining trend of fog days in China, the duration of fog events since the 1990s reached a significant peak in the late autumn of 2018 over Eastern China. The average anomalous fog days were 4.74 d in November 2018 over Jiangsu Province in Eastern China, with a 1.73 standard deviation departure from climatology. Those fogs can thus be identified as a significantly abnormal climatic event with long duration, strong intensity, and extensive coverage. Based on the daily evolutions and correlations of atmospheric parameters, the dense fogs are revealed to be well configured by favorable metrological conditions such as weak dynamic progress, strong inversion in the lower troposphere and saturated air near the surface. If not disturbed, the intensification or duration of these conditions will further promote and maintain the development of fogs. The anomalous atmospheric background associated with those favorable meteorological conditions is revealed by composing the standardized anomalies of circulation fields during the fog days. Over the fog areas, vortex activities or cold air invasion is effectively hampered and the atmosphere inclines to be stable, due to the anomalous circulation pattern composed of the broadened jet stream, weakened jet core over Eastern China, undermined East Asian trough, declined East Asian winter monsoon, and enhanced anomalous southerly flows that transport abnormal warm and wet air to Eastern China. The vapor supplement is intensified by both sustained anomalous northward wind at the lower troposphere and anomalous westward wind in the near-surface. Overall, the numbers of standardized anomalies of 1000–200-hPa height, temperature, wind, and moisture fields during these fog days all significantly depart from climatology for that locale and time of the season, further demonstrating that the persistent dense fogs over Eastern China in the late autumn of 2018 is an unusual weather event with extreme synoptic-scale departures from normal.

Impact of atmospheric quasi-biweekly oscillation on the persistent heavy PM2.5 pollution over Beijing-Tianjin-Hebei region, China during winter

2020 ◽  
Author(s):  
Libo Gao ◽  
Tijian Wang ◽  
Xuejuan Ren ◽  
Bingliang Zhuang ◽  
Shu Li ◽  
...  
Keyword(s):  
Time Scale ◽  
Wave Train ◽  
Fine Particulate Matter ◽  
East Asian ◽  
Eastern China ◽  
Lower Troposphere ◽  
Stable Stratification ◽  
East Asian Trough ◽  
Asian Winter Monsoon ◽  
Bth Region

<p>In recent years, persistent heavy air pollution (PHP) events occurred frequently over the Beijing-Tianjin-Hebei (BTH) region in China, which posed a great threat to human health. The pollution was characterized by fine particulate matter smaller than 2.5 μm in diameter (PM<sub>2.5</sub>). This study investigates the evolution of PHP over the BTH region and its relation to the atmospheric quasi-biweekly oscillation in winters of 2013–2017. A PHP event is defined as three or more consecutive days with daily mean PM<sub>2.5</sub> concentration exceeding 150 μg m<sup>-3</sup>. We observed a significant periodicity of 10–16 days of the PM<sub>2.5</sub> concentration, which notably contributes to the occurrence of PHP. According to the quasi-biweekly variation of PM<sub>2.5</sub>, the life cycle of PHP events are divided into eight phases. The phase composites of circulation anomalies show that the atmospheric quasi-biweekly oscillation provides favorable conditions for the persistence of wintertime PM<sub>2.5</sub> pollution. During the PHP events, the quasi-biweekly southerly anomalies prevail persistently over eastern China. The East Asian winter monsoon is weakened and more moisture is transported to the BTH region continuously. The anomalous warming in the lower troposphere indicates a stable stratification on the quasi-biweekly time scale. In the mid-troposphere, the oscillation of East Asian trough’s intensity is significantly correlated with the PHP events. Further lead-lag correlation analysis suggested that the quasi-biweekly oscillation of East Asian trough can be traced back to a precursor signal over northwestern Eurasia about 11 days earlier, through a southeastward wave train propagation. Therefore, the meteorological conditions conducive to PHP over the BTH region can be predicted on the quasi-biweekly time scale.</p>

scholarly journals Comparisons of the Circulation Anomalies Associated with Extreme Heat in Different Regions of Eastern China

2015 ◽  
Vol 28 (14) ◽  
pp. 5830-5844 ◽  
Author(s):  
Ruidan Chen ◽  
Riyu Lu
Keyword(s):  
Air Temperature ◽  
North China ◽  
Eastern China ◽  
Lower Troposphere ◽  
Circulation Pattern ◽  
Extreme Heat ◽  
Typical Pattern ◽  
Upper Troposphere ◽  
Anomalous Anticyclone ◽  
The Many

Abstract The circulation associated with extreme heat (EH) typically shows an anomalous anticyclone that enhances temperature through adiabatic heating, but this study indicates obvious spatial variation in eastern China. The EH-related circulation pattern in eastern China can be classified into three categories: typical extratropical pattern, monsoonal pattern, and foehn pattern. EH over northeastern China and eastern north China is characterized by a typical pattern involving an anomalous anticyclone and subsidence, and the air temperature increases throughout almost the entire troposphere. In contrast, EH over the Yangtze River valley and south China is associated with the monsoonal pattern. Over these regions, the air temperature only increases in the lower troposphere as a result of anomalous subsidence and lower humidity that has resulted from a farther north transportation of water vapor by a stronger monsoonal southwesterly. Meanwhile, the air temperature decreases in the upper troposphere because of the decrease of latent heat caused by suppressed precipitation. On the other hand, western north China, with most of its stations located on the eastern leeside of mountains, is obviously influenced by the foehn effect on EH days. The foehn-related northwesterly anomalies bring drier and warmer air from the mountains to sink on the leeside and greatly increase the air temperature in the lower troposphere, particularly near the surface. Therefore, the impacts of monsoon and topography should be taken into consideration when EH-related circulations are discussed over the many regions of eastern China. As a result, the reliable projection of air temperature in these regions under global warming is a challenging problem.

scholarly journals Inter-annual variation of aerosol pollution in East Asia and its relation with strong/weak East Asian winter monsoon

2017 ◽  
Author(s):  
Min Xie ◽  
Lei Shu ◽  
Tijian Wang ◽  
Da Gao ◽  
Shu Li ◽  
...  
Keyword(s):  
East Asia ◽  
Annual Variation ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Lower Troposphere ◽  
Northerly Wind ◽  
Asian Winter Monsoon ◽  
The North ◽  
Change Pattern ◽  
Aerosol Pollution

Abstract. Aerosol has become one of the major air pollutants in East Asia, and its spatial distribution can be affected by the East Asian monsoon circulation. By means of the observational analysis and the numerical simulation, the inter-annual variation of wintertime aerosol pollution in East Asia and its association with strong/weak East Asian winter monsoon (EAWM) are investigated in this study. Firstly, the Moderate Resolution Imaging Spectroradiometer/Aerosol Optical Depth (MODIS/AOD) records during 2000–2013 are analyzed to reveal the inter-annual variation characteristics of aerosols. It is found that there is an increasing trend of AOD in East Asia over the last decade, implying the increasing aerosol loading in this region. The areas with obvious increasing AOD cover the Sichuan Basin (SCB), the North China Plain, and most of the Middle-Lower Yangtze River Plain in China. Secondly, the EAWM index (EAWMI) based on the characteristic of circulation are calculated to investigate the inter-annual variations of EAWM. The National Centers for Environmental Prediction (NCEP) reanalysis data are used in EAWMI calculation and meteorological analysis. Nine strong and thirteen weak EAWM years are identified from 1979 to 2014. In these strong EAWM years, the sea-land pressure contrast increases, the East Asian trough strengthens, and the northerly wind gets anomalous over East Asia. More cold air masses are forced to move southward by strengthened wind field and make cool. In the weak EAWM years, however, the situation is totally on the opposite. Finally, the effects of strong/weak EAWM on the distribution of aerosols in East Asia are discussed. It is found that the northerly wind strengthens (weakens) and transports more (less) aerosols southward in strong (weak) EAWM years, resulting in higher (lower) AOD in the north and lower (higher) AOD in the south. The long-term weakening trend of EAWM may potentially increase the aerosol loading. Apart from the changes in aerosol emissions, the weakening of EAWM should be another cause that results in the increase of AOD over the Yangtze River Delta (YRD) region, the Beijing-Tianjin-Hebei (BTH) region and SCB but the decrease of AOD over the Pearl River Delta (PRD) region. Using the Regional Climate-Chemistry coupled Model System (RegCCMS), we further prove that the intensity of EAWM has great impacts on the spatial distribution of aerosols. In strong (weak) EAWM years, there is a negative (positive) anomaly in the air column content of aerosol, with a reduction (increment) of −80 (25) mg m−2. The change pattern of aerosol concentrations in lower troposphere is different from that at 500 hPa, which is related with the different change pattern of meteorological fields in EAWM circulation at different altitude. More obvious changes occur in lower atmosphere, the change pattern of aerosol column content in different EAWM years is mainly decided by the change of aerosols in lower troposphere.

scholarly journals On the Strengthened Relationship between the East Asian Winter Monsoon and Arctic Oscillation: A Comparison of 1950–70 and 1983–2012

2014 ◽  
Vol 27 (13) ◽  
pp. 5075-5091 ◽  
Author(s):  
Fei Li ◽  
Huijun Wang ◽  
Yongqi Gao
Keyword(s):  
Arctic Oscillation ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
Arctic Sea Ice ◽  
Northern Eurasia ◽  
Tropical Region ◽  
Horizontal Structure ◽  
Near Surface ◽  
Asian Winter Monsoon

In this paper, the authors use NCEP reanalysis and 40-yr ECMWF Re-Analysis (ERA-40) data to document the strengthened relationship between the East Asian winter monsoon (EAWM) and winter Arctic Oscillation (AO) on the interannual time scale with a comparison of 1950–70 and 1983–2012. Their connection was statistically insignificant during 1950–70, whereas it was statistically significant during 1983–2012. The latter significant connection might be attributed to the East Asian jet stream (EAJS) upstream extension: the EAJS signal is relatively confined to the western North Pacific before the 1970s, whereas it extends westward toward East Asia after the 1980s. This upstream extension leads to the rearrangement of eastward-propagating Rossby waves with a much wider horizontal structure, thereby bonding the EAWM and the AO. Furthermore, the authors present observational evidence and model simulations demonstrating that the reduction of autumn Arctic sea ice cover (ASIC) is responsible for the strengthened EAWM–AO relationship after the 1980s by producing the EAJS upstream extension. After the 1980s, a strong anticyclonic anomaly over the polar ocean and anomalous easterly advection over northern Eurasia are generated by the near-surface heating over the Barents–Kara (B–K) Seas caused by the reduction of ASIC. This further induces cold anomalies over northern Eurasia, altering the meridional temperature gradient between the midlatitude and tropical region and consequently leading to westward penetration of the EAJS.

A reconstruction of the East Asian summer monsoon index over the half past millennium

2020 ◽  
Author(s):  
Feng Shi ◽  
Hugues Goosse ◽  
Jianping Li ◽  
Fredrik Charpentier Ljungqvist ◽  
Sen Zhao ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Yangtze River ◽  
East Asian Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Eastern China ◽  
Lower Troposphere ◽  
The Yangtze River ◽  
Asian Summer

<p>The EASM largely determines variations in summer precipitation in the East Asian monsoon region where approximately one-quarter of the world’s population live. A reliable East Asian summer monsoon (EASM) index covering several centuries is important in order to understand EASM dynamics. The wind-field is frequently used to calculate the EASM index during the instrumental period. However, available climate proxy data rather respond to direct precipitation changes. A gridded extended summer (May–September, MJJAS) precipitation reconstruction for China covering AD 1470–2000 is used to indirectly reconstruct two types of EASM indices (defined by the strength of the 850hPa southwesterly winds and a north-south gradient of the zonal winds), using the negative correlation between the EASM index and summer (June–August, JJA) rainfall in the middle and lower reaches of the Yangtze River of China. The two EASM indices are validated by independent historical documentary data for eastern China. The physical processes ruling the EASM variability are explored, highlighting a baroclinic structure over the middle and lower reaches of the Yangtze River. It includes an anticyclonic circulation accompanied by high pressure anomalies in the lower troposphere and a cyclonic circulation with low pressure anomaly in the upper troposphere. This is associated with a decrease in atmospheric water vapor content (due to divergence), which will decrease summer rainfall in the region, and contribute to the strengthen of the EASM variability. The dominated and inter-annual component of the EASM variation is possibly linked to the ‘ENSO-like’ sea surface temperature according to a data assimilation experiment performed with the Community Earth System Model-Last Millennium Ensemble (CESM-LME) simulation.</p>

scholarly journals Comparison of East Asian winter monsoon indices

2007 ◽  
Vol 10 ◽  
pp. 31-37 ◽  
Author(s):  
Keyword(s):  
East Asia ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Summer Precipitation ◽  
Circulation Pattern ◽  
Winter Monsoon ◽  
Significance Level ◽  
Asian Winter Monsoon ◽  
Westerly Jet ◽  
Northwesterly Wind

Abstract. Four East Asian winter monsoon (EAWM) indices are compared in this paper. In the research periods, all the indices show similar interannual and decadal-interdecadal variations, with predominant periods centering in 3–4 years, 6.5 years and 9–15 years, respectively. Besides, all the indices show remarkable weakening trends since the 1980s. The correlation coefficient of each two indices is positive with a significance level of 99%. Both the correlation analyses and the composites indicate that in stronger EAWM years, the Siberian high and the higher-level subtropical westerly jet are stronger, and the Aleutian low and the East Asia trough are deeper. This circulation pattern is favorable for much stronger northwesterly wind and lower air temperature in the subtropical regions of East Asia, while it is on the opposite in weaker EAWM years. Besides, EAWM can also exert a remarkable leading effect on the summer monsoon. After stronger (weaker) EAWM, less (more) summer precipitation is seen over the regions from the Yangtze River valley of China to southern Japan, while more (less) from South China Sea to the tropical western Pacific.

scholarly journals Effects of Large Volcanic Eruptions on Global Summer Climate and East Asian Monsoon Changes during the Last Millennium: Analysis of MPI-ESM Simulations

2014 ◽  
Vol 27 (19) ◽  
pp. 7394-7409 ◽  
Author(s):  
Wenmin Man ◽  
Tianjun Zhou ◽  
Johann H. Jungclaus
Keyword(s):  
East Asia ◽  
East Asian Monsoon ◽  
East Asian ◽  
Eastern China ◽  
Lower Troposphere ◽  
Volcanic Eruptions ◽  
Shortwave Radiation ◽  
Radiative Energy ◽  
Tropical Ocean ◽  
Large Volcanic Eruptions

Abstract Responses of summer [June–August (JJA)] temperature and precipitation to large volcanic eruptions are analyzed using the millennial simulations of the earth system model developed at the Max Planck Institute for Meteorology. The model was driven by up-to-date reconstructions of external forcing, including natural forcing (solar and volcanic) and anthropogenic forcing (land-cover change and greenhouse gases). Cooling anomalies after large volcanic eruptions are seen on a nearly global scale. The cooling in the Northern Hemisphere (NH) is stronger than in the Southern Hemisphere (SH), and cooling is stronger over the continents than over the oceans. The precipitation decreases in the tropical and subtropical regions in the first summer after large volcanic eruptions. The cooling, with amplitudes of up to −0.6°C, is also seen over eastern China. East Asia is dominated by northerly wind anomalies, and the corresponding summer rainfall exhibits a coherent reduction over the entirety of eastern China. The tropospheric mean temperature anomalies indicate that there is coherent cooling over East Asia and the tropical ocean after large volcanic eruptions. The cooling over the middle-to-high latitudes of East Asia is stronger than over the tropical ocean. This temperature anomaly pattern suggests a reduced land–sea thermal contrast and favors a weaker East Asian summer monsoon (EASM) circulation. Analysis of the radiative fluxes at the top of the atmosphere (TOA) suggests that the reduction in shortwave radiation after large volcanic eruptions is nearly twice as large as the reduction in emitted longwave radiation, a net loss of radiative energy that cools the surface and lower troposphere.

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