Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-ran...Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-range time scale.The blocking pattern from the Kara Sea to Lake Baikal characterized the first cold wave,while the large-scale tilted ridge and trough over the Asian continent featured the second cold wave.Prior to the cold waves,both the northwest and hyperpolar paths of cold air contributed to a zonally extensive cold air accumulation in the key region of Siberia.This might be the primary reason why strong and extensive supercold waves occur even under the Arctic amplification background.The two cold waves straddling 2020 and 2021 exhibited distinct features:(1)the blocking circulation occurred to the north or the east of the Ural Mountains and was not confined only to the Ural Mountains as it was for the earlier cold waves;(2)the collocation of the Asian blocking pattern and the polar vortex deflection towards East Asia preferred the hyperpolar path of cold air accumulation and the subsequent southward outburst;and(3)both high-and low-frequency processes worked in concert,leading to the very intense cold waves.The cold air advance along the northwest path,which coincides with the southeastward intrusion of the Siberian High(SH)front edge,is associated with the high-frequency process,while the cold air movement along the hyperpolar path,which is close to the eastern edge of the SH,is controlled by the low-frequency process.展开更多
Concurrence of low temperature,precipitation and freezing weather in an extensive area would cause devastating impacts on local economy and society.We call such a combination of concurrent disastrous weather“extensiv...Concurrence of low temperature,precipitation and freezing weather in an extensive area would cause devastating impacts on local economy and society.We call such a combination of concurrent disastrous weather“extensive coldprecipitation-freezing”events(ECPFEs).In this study,the ECPFEs in southern China(15°−35°N,102°−123°E)are objectively defined by using daily surface observational data for the period 1951−2013.An ECPFE in southern China is defined if the low temperature area,precipitation area and freezing area concurrently exceed their respective thresholds for at least three consecutive days.The identified ECPFEs are shown to be reasonable and reliable,compared with those in previous studies.The circulation anomalies in ECPFEs are characterized by a large-scale tilted ridge and trough pairing over mid-and high-latitude Eurasia,and the intensified subtropical westerlies along the southern foot of the Tibetan Plateau and the anomalous anticyclonic circulation over the subtropical western Pacific.Comparative analysis reveals that the stable cold air from the north and the warm and moist air from the south converge,facilitating a favorable environment for the concurrence of extensive low-temperature,precipitation and freezing weather.展开更多
Using rain-gauge-observation daily precipitation data from the Global Historical Climatology Network(V3.25)and the Chinese Surface Daily Climate Dataset(V3.0),this study investigates the fidelity of the AHPRODITE data...Using rain-gauge-observation daily precipitation data from the Global Historical Climatology Network(V3.25)and the Chinese Surface Daily Climate Dataset(V3.0),this study investigates the fidelity of the AHPRODITE dataset in representing extreme precipitation,in terms of the extreme precipitation threshold value,occurrence number,probability of detection,and extremal dependence index during the cool(October to April)and warm(May to September)seasons in Central Asia during 1961–90.The distribution of extreme precipitation is characterized by large extreme precipitation threshold values and high occurrence numbers over the mountainous areas.The APHRODITE dataset is highly correlated with the gauge-observation precipitation data and can reproduce the spatial distributions of the extreme precipitation threshold value and total occurrence number.However,APHRODITE generally underestimates the extreme precipitation threshold values,while it overestimates the total numbers of extreme precipitation events,particularly over the mountainous areas.These biases can be attributed to the overestimation of light rainfall and the underestimation of heavy rainfall induced by the rainfall distribution–based interpolation.Such deficits are more evident for the warm season than the cool season,and thus the biases are more pronounced in the warm season than in the cool season.The probability of detection and extremal dependence index reveal that APHRODITE has a good capability of detecting extreme precipitation,particularly in the cool season.展开更多
Intense and extensive dust,caused by a strong Mongolian cyclone,hit Mongolia and northern China on 14-15 March 2021.In this study,the development process of this cyclone is analysed from the perspective of highfrequen...Intense and extensive dust,caused by a strong Mongolian cyclone,hit Mongolia and northern China on 14-15 March 2021.In this study,the development process of this cyclone is analysed from the perspective of highfrequency eddy energetics.During the low-frequency circulation field of early March of 2021,an amplified polar vortex intruding towards central Asia and a ridge straddling eastern and northeastern Asia worked in concert to comprise a strong baroclinic zone from central Asia to Lake Baikal.Under these favourable conditions,on 13 March,a migratory trough triggered the Mongolian cyclone by crossing over the Sayan Mountains.The downwards transfer of kinetic energy from the eddy at 850 hPa played a key role in the intensification and mature stage of the cyclone.This mechanism was primarily completed by the cold air sinking behind the cold front.The frontal cyclone wave mechanism became crucial once the cyclone started to rapidly develop.The authors emphasize that the anomalously large growth of high-frequency available potential energy,which characterized this super strong cyclone,was obtained by extracting energy first from the time-mean available potential energy and then from the low-frequency available potential energy.The interannual temperature anomaly pattern of"north cold south warm"facilitated the additional time-mean available potential energy,and the temperature anomaly pattern of"northwest cold southeast warm"conditioned the extra low-frequency available potential energy.The analysis results suggest that the interaction between high-and low-frequency waves was also important in the development of the intense cyclone.展开更多
This study investigates the major patterns of large-scale tilted ridges(LSTRS)over the Eurasian continent and their connections with large-scale surface air temperature during boreal winter.A total number of 134 LSTR ...This study investigates the major patterns of large-scale tilted ridges(LSTRS)over the Eurasian continent and their connections with large-scale surface air temperature during boreal winter.A total number of 134 LSTR events with zonal extent exceeding 90°of longitude on the peak day are identified.Using self-organizing map(SOM),the LSTRs are classified into five clusters that are characterized by different spatial distributions and orientations.The leading two clusters are closely associated with extensive and persistent cold events over different places.Considering the first cluster,LSTRs extend from the Ural Mountains to Northeast Asia and are favorable for the amplification and southeastward extension of the Siberian high.Therefore,this cluster is closely associated with the occurrence of extensive and persistent cold events in china.In comparison with the first cluster,the LSTRs of second group are situated to the west,with starting points from the Kola Peninsula,and cause extensive and persistent cold events over Eastern Europe,central Asia,and central Siberia.The results suggest that the vertical coupling between LSTRs and the corresponding anomalous sea level pressure is crucial for the persistent cold temperature events associated with the leading two SOM clusters.展开更多
This study objectively defined an extreme precipitation event(EPE)over southern China and investigated the associated typical circulation pattern on the intraseasonal time scale.The occurrence of the EPE resulted from...This study objectively defined an extreme precipitation event(EPE)over southern China and investigated the associated typical circulation pattern on the intraseasonal time scale.The occurrence of the EPE resulted from the joint operations of anomalous circulations over the subtropics and mid-high latitudes.During the EPE,simultaneous enhancements of the trough over the Bay of Bengal(BBT)and the Western Pacific subtropical high(WPSH)facilitated the abundant water vapor conditions over southern China,whereas the weakened East Asian major trough(EAT)led to a moderate cold air invasion to that region,producing a persistent convergence zone over southern China.Wave train pattern in North Atlantic and Europe may be viewed as precursory signals for the EPE over southern China,and it contributed to the Rossby wave propagation in association with the EPE.These wave packets propagated toward East Asia mainly along the North African-Asian subtropical westerly jet waveguide.Low-frequency disturbances along this waveguide contributed to the enhancement of the BBT and WPSH and the weakening of the EAT,constituting favorable circulation conditions for the EPE.展开更多
The relationship between the anomalous East Asian winter monsoon (EAWM) activity and the tropical Pacific SST anomalies has been identified using the results of 40-year integration of the IAP CGCM1 model and 10-year o...The relationship between the anomalous East Asian winter monsoon (EAWM) activity and the tropical Pacific SST anomalies has been identified using the results of 40-year integration of the IAP CGCM1 model and 10-year observational data, In the strong EAWM year, the western and central Pacific are dominated by positive SST anomalies while the eastern Pacific is negative ones. In the weak EAWM year, the SSTA pattern is quite different and shows El Nio-like SSTanomalies. The strong EAWM activity tends to create extra easterly flow to the east and extra westerly flow to the west of the warm SSTA region over the equatorial western and central Pacific, thus leading to the enhancement of convergence and convection of the flow in this region and favorable to the maintenance and development of such an SSTA pattern. On the other hand, the warm SST anomaly over the western and central Pacific, as a forcing, may lead to a specific pattern of the northern extratropical atmosphere, which is favorable to the strong展开更多
The Polar/Eurasia(POL) pattern was previously identified based on the empirical orthogonal function method and monthly mean data, in which the positive and negative phases are anti-symmetric in spatial distribution. T...The Polar/Eurasia(POL) pattern was previously identified based on the empirical orthogonal function method and monthly mean data, in which the positive and negative phases are anti-symmetric in spatial distribution. This paper identifies the positive(POL+) and negative(POL-) phases of the POL pattern through applying a novel approach, i.e.,self-organizing maps, to daily 500-h Pa geopotential height fields in May over 1948–2017. The POL+, POL1-, and POL2-patterns defined by this method represent actual physical modes. The POL+ pattern features a wave train from the northeastern Atlantic/northern Europe via the subarctic regions of Eurasia to Lake Baikal. The POL1-pattern is characterized by a planetary-scale dipole pattern with a positive anomaly band over subarctic Eurasia and a negative anomaly band from central Asia to the Sea of Okhotsk. The anomaly centers of the POL2-pattern are basically antisymmetrical to those of the POL+ pattern. The POL+ pattern increases the blocking frequency over the northeastern Atlantic/northern Europe and northeastern Asia, where high-frequency transient eddies are highly recurrent in the north. Accordingly, precipitation increases apparently in the subarctic Asian continent and western Siberia, and decreases around Europe and Lake Baikal. A mimic wave train is also observed in the surface air temperature anomaly field. During the POL1-period, the blocking frequency is abnormally high over Eurasia, whereas high-frequency transient eddies are apparently suppressed over northern Eurasia. Correspondingly, significant precipitation deficits are observed in northern Eurasia. The POL1-pattern also causes a remarkable temperature increase in the subarctic seas of Eurasia and a considerable temperature drop in the midlatitude Asian continent. As the POL2-pattern prevails, the blocking frequency decreases over the North Atlantic/Europe but strengthens over the Asian continent. The POL2-pattern also causes wavelike anomalies of precipitation and surface air temperature over northern Eurasia.展开更多
Cold air outbreaks（CAOs）always hit East Asia during boreal winter and have significant impacts on human health and public transport.The amplitude and route of CAOs are closely associated with blocking circulations o...Cold air outbreaks（CAOs）always hit East Asia during boreal winter and have significant impacts on human health and public transport.The amplitude and route of CAOs are closely associated with blocking circulations over the Eurasian continent.Two categories of CAOs are recognized,namely,the ordinary cold wave events（CWEs）and the extensive and persistent extreme cold events（EPECEs）,with the latter having even stronger impacts.The blocking features associated with these two types of CAOs and their differences are investigated in this study on the intraseasonal timescale.What these two CAOs do have in common is that they are both preceded by the intensification and recurrence of a blocking high over the midlatitude North Atlantic.The difference between these events is primarily reflected on the spatial scale and duration of the corresponding blocking high.During the CWEs,blocking occurs around the Ural Mountains,and exhibits a regional feature.The resulting cold air temperature persists for only up to 8 days.In contrast,during the EPECEs,the blocking region is quite extensive and is not only confined around the Ural Mountains but also extends eastward into Northeast Asia in a southwest–northeast orientation.As a result,the cold air tends to accumulate over a large area and persists for a much longer time.The blocking activity is primarily induced by an increased frequency and eastward extension of the synoptic anticyclonic Rossby wave breaking（AWB）.Compared with the CWEs,characterized by a regional and short-lived synoptic AWB frequency,the EPE-CEs tend to be accompanied by more recurrent and eastward extensions of the synoptic AWB.展开更多
基金jointly supported by the National Key Research and Development Project (Grant No. 2018YFC1505601)the National Natural Science Foundation of China (Grant No. 41975072)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA23090102).
文摘Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-range time scale.The blocking pattern from the Kara Sea to Lake Baikal characterized the first cold wave,while the large-scale tilted ridge and trough over the Asian continent featured the second cold wave.Prior to the cold waves,both the northwest and hyperpolar paths of cold air contributed to a zonally extensive cold air accumulation in the key region of Siberia.This might be the primary reason why strong and extensive supercold waves occur even under the Arctic amplification background.The two cold waves straddling 2020 and 2021 exhibited distinct features:(1)the blocking circulation occurred to the north or the east of the Ural Mountains and was not confined only to the Ural Mountains as it was for the earlier cold waves;(2)the collocation of the Asian blocking pattern and the polar vortex deflection towards East Asia preferred the hyperpolar path of cold air accumulation and the subsequent southward outburst;and(3)both high-and low-frequency processes worked in concert,leading to the very intense cold waves.The cold air advance along the northwest path,which coincides with the southeastward intrusion of the Siberian High(SH)front edge,is associated with the high-frequency process,while the cold air movement along the hyperpolar path,which is close to the eastern edge of the SH,is controlled by the low-frequency process.
基金This research was funded by the National Natural Science Foundation of China(Grant Nos.41975072 and 41675086)the National Science and Technology Support Program of China(Grant No.2015BAC03B03).
文摘Concurrence of low temperature,precipitation and freezing weather in an extensive area would cause devastating impacts on local economy and society.We call such a combination of concurrent disastrous weather“extensive coldprecipitation-freezing”events(ECPFEs).In this study,the ECPFEs in southern China(15°−35°N,102°−123°E)are objectively defined by using daily surface observational data for the period 1951−2013.An ECPFE in southern China is defined if the low temperature area,precipitation area and freezing area concurrently exceed their respective thresholds for at least three consecutive days.The identified ECPFEs are shown to be reasonable and reliable,compared with those in previous studies.The circulation anomalies in ECPFEs are characterized by a large-scale tilted ridge and trough pairing over mid-and high-latitude Eurasia,and the intensified subtropical westerlies along the southern foot of the Tibetan Plateau and the anomalous anticyclonic circulation over the subtropical western Pacific.Comparative analysis reveals that the stable cold air from the north and the warm and moist air from the south converge,facilitating a favorable environment for the concurrence of extensive low-temperature,precipitation and freezing weather.
基金the two anonymous reviewers for their valuable comments and suggestions.This research was funded by the National Key Research and Development Program of China(Grant No.2018YFC1507101)the National Natural Science Foundation of China(Grant Nos.41861144014,41875078 and 41630424)+3 种基金the National Key Research and Development Program of China(Grant No.2016YFA0601501)We acknowledge Hirosaki University for providing the APHRODITE precipitation data(http://aphrodite.st.hirosaki-u.ac.jp/download/)We thank the China Meteorological Data Service Center for providing the Chinese Surface Daily Climate Dataset(V3.0)(https://data.cma.cn/en/?r=data/detail&data-Code=SURF_CLI_CHN_MUL_DAY_CES_V3.0)the National Oceanic and Atmospheric Administration,National Centers for Environmental Information,for providing the GHCN-D dataset(V3.25)(Menne et al.,2012).We convey our gratitude to the contributors of the SciPy ecosystem(Virtanen et al.,2020),which was used for data analysis and visualization.
文摘Using rain-gauge-observation daily precipitation data from the Global Historical Climatology Network(V3.25)and the Chinese Surface Daily Climate Dataset(V3.0),this study investigates the fidelity of the AHPRODITE dataset in representing extreme precipitation,in terms of the extreme precipitation threshold value,occurrence number,probability of detection,and extremal dependence index during the cool(October to April)and warm(May to September)seasons in Central Asia during 1961–90.The distribution of extreme precipitation is characterized by large extreme precipitation threshold values and high occurrence numbers over the mountainous areas.The APHRODITE dataset is highly correlated with the gauge-observation precipitation data and can reproduce the spatial distributions of the extreme precipitation threshold value and total occurrence number.However,APHRODITE generally underestimates the extreme precipitation threshold values,while it overestimates the total numbers of extreme precipitation events,particularly over the mountainous areas.These biases can be attributed to the overestimation of light rainfall and the underestimation of heavy rainfall induced by the rainfall distribution–based interpolation.Such deficits are more evident for the warm season than the cool season,and thus the biases are more pronounced in the warm season than in the cool season.The probability of detection and extremal dependence index reveal that APHRODITE has a good capability of detecting extreme precipitation,particularly in the cool season.
基金This work is supported by the National Natural Science Foundation of China[Grant No.41630424].
文摘Intense and extensive dust,caused by a strong Mongolian cyclone,hit Mongolia and northern China on 14-15 March 2021.In this study,the development process of this cyclone is analysed from the perspective of highfrequency eddy energetics.During the low-frequency circulation field of early March of 2021,an amplified polar vortex intruding towards central Asia and a ridge straddling eastern and northeastern Asia worked in concert to comprise a strong baroclinic zone from central Asia to Lake Baikal.Under these favourable conditions,on 13 March,a migratory trough triggered the Mongolian cyclone by crossing over the Sayan Mountains.The downwards transfer of kinetic energy from the eddy at 850 hPa played a key role in the intensification and mature stage of the cyclone.This mechanism was primarily completed by the cold air sinking behind the cold front.The frontal cyclone wave mechanism became crucial once the cyclone started to rapidly develop.The authors emphasize that the anomalously large growth of high-frequency available potential energy,which characterized this super strong cyclone,was obtained by extracting energy first from the time-mean available potential energy and then from the low-frequency available potential energy.The interannual temperature anomaly pattern of"north cold south warm"facilitated the additional time-mean available potential energy,and the temperature anomaly pattern of"northwest cold southeast warm"conditioned the extra low-frequency available potential energy.The analysis results suggest that the interaction between high-and low-frequency waves was also important in the development of the intense cyclone.
基金jointly supported by the National Natural Science Foundation of China [grant number 41375064 and41675086]the National Key Technology Research and Development Program of the Ministry of Science and Technology of China [grant number 2015BAC03B03]
文摘This study investigates the major patterns of large-scale tilted ridges(LSTRS)over the Eurasian continent and their connections with large-scale surface air temperature during boreal winter.A total number of 134 LSTR events with zonal extent exceeding 90°of longitude on the peak day are identified.Using self-organizing map(SOM),the LSTRs are classified into five clusters that are characterized by different spatial distributions and orientations.The leading two clusters are closely associated with extensive and persistent cold events over different places.Considering the first cluster,LSTRs extend from the Ural Mountains to Northeast Asia and are favorable for the amplification and southeastward extension of the Siberian high.Therefore,this cluster is closely associated with the occurrence of extensive and persistent cold events in china.In comparison with the first cluster,the LSTRs of second group are situated to the west,with starting points from the Kola Peninsula,and cause extensive and persistent cold events over Eastern Europe,central Asia,and central Siberia.The results suggest that the vertical coupling between LSTRs and the corresponding anomalous sea level pressure is crucial for the persistent cold temperature events associated with the leading two SOM clusters.
基金supported by the National Basic Research Program of China(2012CB4172012009CB421401)+2 种基金the National Key Technologies R&D Program of China(2009BAC51B02)the National Natural Science Foundation of China(41375055)the China Meteorological Administration Special Public Welfare Research Fund(GYHY201106015)
文摘This study objectively defined an extreme precipitation event(EPE)over southern China and investigated the associated typical circulation pattern on the intraseasonal time scale.The occurrence of the EPE resulted from the joint operations of anomalous circulations over the subtropics and mid-high latitudes.During the EPE,simultaneous enhancements of the trough over the Bay of Bengal(BBT)and the Western Pacific subtropical high(WPSH)facilitated the abundant water vapor conditions over southern China,whereas the weakened East Asian major trough(EAT)led to a moderate cold air invasion to that region,producing a persistent convergence zone over southern China.Wave train pattern in North Atlantic and Europe may be viewed as precursory signals for the EPE over southern China,and it contributed to the Rossby wave propagation in association with the EPE.These wave packets propagated toward East Asia mainly along the North African-Asian subtropical westerly jet waveguide.Low-frequency disturbances along this waveguide contributed to the enhancement of the BBT and WPSH and the weakening of the EAT,constituting favorable circulation conditions for the EPE.
文摘The relationship between the anomalous East Asian winter monsoon (EAWM) activity and the tropical Pacific SST anomalies has been identified using the results of 40-year integration of the IAP CGCM1 model and 10-year observational data, In the strong EAWM year, the western and central Pacific are dominated by positive SST anomalies while the eastern Pacific is negative ones. In the weak EAWM year, the SSTA pattern is quite different and shows El Nio-like SSTanomalies. The strong EAWM activity tends to create extra easterly flow to the east and extra westerly flow to the west of the warm SSTA region over the equatorial western and central Pacific, thus leading to the enhancement of convergence and convection of the flow in this region and favorable to the maintenance and development of such an SSTA pattern. On the other hand, the warm SST anomaly over the western and central Pacific, as a forcing, may lead to a specific pattern of the northern extratropical atmosphere, which is favorable to the strong
基金Supported by the National Science and Technology Support Program of China(2015BAC03B03)National Natural Science Foundation of China(41630424,41875078,and 41861144014)
文摘The Polar/Eurasia(POL) pattern was previously identified based on the empirical orthogonal function method and monthly mean data, in which the positive and negative phases are anti-symmetric in spatial distribution. This paper identifies the positive(POL+) and negative(POL-) phases of the POL pattern through applying a novel approach, i.e.,self-organizing maps, to daily 500-h Pa geopotential height fields in May over 1948–2017. The POL+, POL1-, and POL2-patterns defined by this method represent actual physical modes. The POL+ pattern features a wave train from the northeastern Atlantic/northern Europe via the subarctic regions of Eurasia to Lake Baikal. The POL1-pattern is characterized by a planetary-scale dipole pattern with a positive anomaly band over subarctic Eurasia and a negative anomaly band from central Asia to the Sea of Okhotsk. The anomaly centers of the POL2-pattern are basically antisymmetrical to those of the POL+ pattern. The POL+ pattern increases the blocking frequency over the northeastern Atlantic/northern Europe and northeastern Asia, where high-frequency transient eddies are highly recurrent in the north. Accordingly, precipitation increases apparently in the subarctic Asian continent and western Siberia, and decreases around Europe and Lake Baikal. A mimic wave train is also observed in the surface air temperature anomaly field. During the POL1-period, the blocking frequency is abnormally high over Eurasia, whereas high-frequency transient eddies are apparently suppressed over northern Eurasia. Correspondingly, significant precipitation deficits are observed in northern Eurasia. The POL1-pattern also causes a remarkable temperature increase in the subarctic seas of Eurasia and a considerable temperature drop in the midlatitude Asian continent. As the POL2-pattern prevails, the blocking frequency decreases over the North Atlantic/Europe but strengthens over the Asian continent. The POL2-pattern also causes wavelike anomalies of precipitation and surface air temperature over northern Eurasia.
基金Supported by the National Natural Science Foundation of China(41305047,41375064,and 41630424)National Science and Technology Support Program of China(2015BAC03B03)
文摘Cold air outbreaks（CAOs）always hit East Asia during boreal winter and have significant impacts on human health and public transport.The amplitude and route of CAOs are closely associated with blocking circulations over the Eurasian continent.Two categories of CAOs are recognized,namely,the ordinary cold wave events（CWEs）and the extensive and persistent extreme cold events（EPECEs）,with the latter having even stronger impacts.The blocking features associated with these two types of CAOs and their differences are investigated in this study on the intraseasonal timescale.What these two CAOs do have in common is that they are both preceded by the intensification and recurrence of a blocking high over the midlatitude North Atlantic.The difference between these events is primarily reflected on the spatial scale and duration of the corresponding blocking high.During the CWEs,blocking occurs around the Ural Mountains,and exhibits a regional feature.The resulting cold air temperature persists for only up to 8 days.In contrast,during the EPECEs,the blocking region is quite extensive and is not only confined around the Ural Mountains but also extends eastward into Northeast Asia in a southwest–northeast orientation.As a result,the cold air tends to accumulate over a large area and persists for a much longer time.The blocking activity is primarily induced by an increased frequency and eastward extension of the synoptic anticyclonic Rossby wave breaking（AWB）.Compared with the CWEs,characterized by a regional and short-lived synoptic AWB frequency,the EPE-CEs tend to be accompanied by more recurrent and eastward extensions of the synoptic AWB.
