Persistent(5-day or longer)extreme cold events(ECEs)over northeastern China during the boreal winter of 1979–2020 are investigated using daily minimum temperature(Tmin)from the China Meteorological Data Network.The e...Persistent(5-day or longer)extreme cold events(ECEs)over northeastern China during the boreal winter of 1979–2020 are investigated using daily minimum temperature(Tmin)from the China Meteorological Data Network.The extreme cooling area and intensity indices associated with the ECEs exhibit a dominant 10–40-day periodicity,indicating a close link with atmospheric intraseasonal oscillations(ISOs).The ECEs are categorized into W-and N-type.In the former,the low-frequency cooling associated with the ISO first penetrates into the western boundary of the northeastern China domain and later occupies the entire domain at its peak phase.The upper-tropospheric circulation associated with this type is characterized by a northwest–southeast-oriented Rossby wave train,expanding from the Ural Mountains to the western Pacific Ocean.In the latter,the cooling invades the northern boundary first and then penetrates into the entire domain.The upper tropospheric precursory signal associated with this type is a zonally oriented negative geopotential height anomaly,which slowly moves southward.A downward-propagating signal is observed in the stratospheric potential vorticity field prior to the peak cooling,implying a possible stratospheric impact.In addition to the W-and N-types,ECEs can also occur in a localized region near either at the northern or southern boundary of the domain.展开更多
Subseasonal forecasting of extreme events is crucial for early warning systems.However,the forecast skills for extreme events are limited.Taking the extreme cold events in January 2018 as a specific example,and analyz...Subseasonal forecasting of extreme events is crucial for early warning systems.However,the forecast skills for extreme events are limited.Taking the extreme cold events in January 2018 as a specific example,and analyzing the 34 extreme cold events in East Asia from 1998 to 2020,the authors evaluated the forecast skills of the ECMWF model ensemble members on subseasonal time scales.The results show that while the ensemble mean has limited skills for forecasting extreme cold events at the 3-week lead time,some individual members demonstrate high forecast skills.For most extreme cold events,there are>10%of members among the total ensembles that can well predict the rapid temperature transitions at the 14-day lead time.This highlights the untapped potential of the ECMWF model to forecast extreme cold events on subseasonal time scales.High-skill ensemble members rely on accurate predictions of atmospheric circulation patterns(500-hPa geopotential height,mean sea level pressure)and key weather systems,including the Ural Blocking and Siberian High,that influence extreme cold events.展开更多
Long-term regional extreme cold events(ECEs)garner significant attention due to their widespread impact and prolonged duration,posing critical threats to human society and ecosystems.Previous studies have examined ECE...Long-term regional extreme cold events(ECEs)garner significant attention due to their widespread impact and prolonged duration,posing critical threats to human society and ecosystems.Previous studies have examined ECE characteristics at single sites or grid points,however,it is crucial to recognize that such events generally manifest as spatiotemporally continuous regional phenomena.Here,we proposed an objective methodology based on spatiotemporal continuity to identify ECEs in the China-Pakistan Economic Corridor(CPEC)during the winters of 1961-2015.This approach successfully reproduced the dynamic evolution of ECEs,encompassing their initiation,development,and dissipation.We further analyzed the changes of ECE intensity,frequency,and duration,and assessed ECE trends within varying return periods by employing the generalized Pareto distribution(GPD).Our findings reveal a decline in the frequency and duration of ECEs in CPEC over the study period,while their intensity has increased by 50%.ECEs predominantly occur in the northern regions of Azad Kashmir and Balochistan’s Quetta in Pakistan,and Kashgar in China.High recurrence levels are associated with an expansion of ECE-prone areas,particularly in the northern Pamir Plateau,which emerges as a regional hotspot.These results highlight the critical need to remain vigilant to potential future surges in ECEs under global warming,underscoring their implications for regional climate resilience.展开更多
We investigate the characteristics and mechanisms of persistent wet–cold events(PWCEs)with different types of coldair paths.Results show that the cumulative single-station frequency of the PWCEs in the western part o...We investigate the characteristics and mechanisms of persistent wet–cold events(PWCEs)with different types of coldair paths.Results show that the cumulative single-station frequency of the PWCEs in the western part of South China is higher than that in the eastern part.The pattern of single-station frequency of the PWCEs are“Yangtze River(YR)uniform”and“east–west inverse”.The YR uniform pattern is the dominant mode,so we focus on this pattern.The cold-air paths for PWCEs of the YR uniform pattern are divided into three types—namely,the west,northwest and north types—among which the west type accounts for the largest proportion.The differences in atmospheric circulation of the PWCEs under the three types of paths are obvious.The thermal inversion layer in the lower troposphere is favorable for precipitation during the PWCEs.The positive water vapor budget for the three types of PWCEs mainly appears at the southern boundary.展开更多
The components of the primary elements in the dune sands for the MGS1 subsection of the Milanggouwan section in the Salawusu River valley, compared with those of modern dune sands, show that they were caused by East A...The components of the primary elements in the dune sands for the MGS1 subsection of the Milanggouwan section in the Salawusu River valley, compared with those of modern dune sands, show that they were caused by East Asian winter monsoon in the Mu Us desert during Holocene. The examined ages for the 11 layers of dune sands, based on the average sedimentary rate, are： 0 to 960, 1350-2240, 2470 to 3530, 4000 to 4180, 4290 to 4350, 4380 to 4760, 5040 to 5920, 6570 to 8270, 9020 to 9700, 9880 to 10160 and 10580 to 11080 a BP, respectively. The climatic events indicated by these dune sands are consistent with those records in the Huguangyan volcanic lake, Zoige peat bog, Hulu cave and Dunde ice core, particularly with the climatic fluctuations of the North Atlantic since 11 000 a BP. Among them, patterns from B0 to B8 correspond to the peak values of 0MD, 2D, 4D, 6D＋8D＋10D, 12D, 14D, 16D, 18D and 20D respectively. It might be caused by the North Atlantic ice age induced by the heat circulation, which strengthened the polar high pressure and Siberian-Mongolian high pressure and further led to the dominance of the winter monsoon over China＇s desert area.展开更多
Starting in mid-November,China was hit by several cold events during the early winter of 2020/21.The lowest temperature observed at Beijing station on 7 January reached−19.6°C.In this paper,we show that the outbr...Starting in mid-November,China was hit by several cold events during the early winter of 2020/21.The lowest temperature observed at Beijing station on 7 January reached−19.6°C.In this paper,we show that the outbreak of the record-breaking extreme cold event can be attributed to a huge merging Ural blocking(UB)ridge over the Eurasian region.The sea-ice cover in the Kara and East Siberia Seas(KESS)in autumn was at its lowest value since 1979,which could have served as a precursor signal.Further analysis shows that several successive UB episodes occurred from 1 September 2020 to 10 January 2021.The persistent UB that occurred in late September/early October 2020 may have made an important contribution to the October historical minimum of sea ice in the KESS region.Our results also show that,after each UB episode in winter,significant upward propagation of wave activity occurred around 60°E,which resulted in weakening the stratospheric vortex.Meanwhile,each UB episode also caused a significant reduction in sea-ice extent in KESS and a significant weakening of the westerly jet in mid-high-latitude Eurasia.Results suggest that the Arctic vortex,which is supposed to enhance seasonally,became weaker and more unstable than the climatic mean under the seasonal cumulative effects of UB episodes,KESS warming,and long-lasting negative-phase North Atlantic Oscillation(NAO-).Those seasonal cumulative effects,combined with the impact of La Niña winter,led to the frequent occurrence of extreme cold events.展开更多
Three extreme cold events invaded China during the early winter period between December 2020 to mid-January 2021 and caused drastic temperature drops,setting new low-temperature records at many stations during 6−8 Jan...Three extreme cold events invaded China during the early winter period between December 2020 to mid-January 2021 and caused drastic temperature drops,setting new low-temperature records at many stations during 6−8 January 2021.These cold events occurred under background conditions of low Arctic sea ice extent and a La Niña event.This is somewhat expected since the coupled effect of large Arctic sea ice loss in autumn and sea surface temperature cooling in the tropical Pacific usually favors cold event occurrences in Eurasia.Further diagnosis reveals that the first cold event is related to the southward movement of the polar vortex and the second one is related to a continent-wide ridge,while both the southward polar vortex and the Asian blocking are crucial for the third event.Here,we evaluate the forecast skill for these three events utilizing the operational forecasts from the ECMWF model.We find that the third event had the highest predictability since it achieves the best skill in forecasting the East Asian cooling among the three events.Therefore,the predictability of these cold events,as well as their relationships with the atmospheric initial conditions,Arctic sea ice,and La Niña deserve further investigation.展开更多
A 700-year record （1.0-1.5 a resolution） of the East Asian winter monsoon （EAWM）, based on grain-size analysis and AMSI4C dating of Core EC2005 from the inner-shelf mud wedge of the East China Sea （ECS）, was com...A 700-year record （1.0-1.5 a resolution） of the East Asian winter monsoon （EAWM）, based on grain-size analysis and AMSI4C dating of Core EC2005 from the inner-shelf mud wedge of the East China Sea （ECS）, was compared with the Dongge stalagmite 8180 record during the mid-Holocene. The upper muddy section of Core EC2005 has been formed mainly by suspended sediments derived from the Changjiang （Yangtze） River mouth since 7.3 ka BP. High precipitation and a strengthened EAWM might have played key roles in the high sedimentation rate （1 324-1 986 crn/ka） between 5.9-5.2 ka BP. The EAWM strengthened when the Asian summer monsoon weakened, especially around 5 500 a BE which corresponded to a worldwide cold event. The EAWM during the mid-Holocene shows statistically significant solar periodicities at 62 and 11 a. The 5 500 a BP cold event might be resulted from orbital forcing and changes in solar activity.展开更多
Several consecutive extreme cold events impacted China during the first half of winter 2020/21,breaking the low-temperature records in many cities.How to make accurate climate predictions of extreme cold events is sti...Several consecutive extreme cold events impacted China during the first half of winter 2020/21,breaking the low-temperature records in many cities.How to make accurate climate predictions of extreme cold events is still an urgent issue.The synergistic effect of the warm Arctic and cold tropical Pacific has been demonstrated to intensify the intrusions of cold air from polar regions into middle-high latitudes,further influencing the cold conditions in China.However,climate models failed to predict these two ocean environments at expected lead times.Most seasonal climate forecasts only predicted the 2020/21 La Niña after the signal had already become apparent and significantly underestimated the observed Arctic sea ice loss in autumn 2020 with a 1-2 month advancement.In this work,the corresponding physical factors that may help improve the accuracy of seasonal climate predictions are further explored.For the 2020/21 La Niña prediction,through sensitivity experiments involving different atmospheric-oceanic initial conditions,the predominant southeasterly wind anomalies over the equatorial Pacific in spring of 2020 are diagnosed to play an irreplaceable role in triggering this cold event.A reasonable inclusion of atmospheric surface winds into the initialization will help the model predict La Niña development from the early spring of 2020.For predicting the Arctic sea ice loss in autumn 2020,an anomalously cyclonic circulation from the central Arctic Ocean predicted by the model,which swept abnormally hot air over Siberia into the Arctic Ocean,is recognized as an important contributor to successfully predicting the minimum Arctic sea ice extent.展开更多
The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were ac...The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were accompanied by a CCW in the initial stages. From the comparison between the CECs and the CCWs that were independent of any CEC, it is found that a south- west-northeast-oriented tilted ridge at 500 hPa was present around the Europe-Barents Sea regions approximately 10 days prior to the start of the CEC. Consistent with this feature, a high sea level pressure and strong cold air accumulation occurred over a broad extent of northern Eurasia one week prior to the start of the CEC. The tilted ridge and the strong cold air accumulation were the precursory signals that were absent for the CCW, and they provide important clues for the early prediction of whether a CCW event might evolve into a CEC.展开更多
Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isent...Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isentropic mass circulation(IMC)perspective.Results show that the midlatitude cold surface temperature anomalies always co-occurred with the high-latitude warm anomalies,and this was closely related to the strengthening of the low-level equatorward cold air branch of the IMC,particularly along the climatological cold air routes over East Asia and North America.Specifically,the two cold surges over East Asia in early winter were results of intensification of cold air transport there,influenced by the Arctic sea ice loss in autumn.The weakened cold air transport over North America associated with warmer northeastern Pacific sea surface temperatures(SSTs)explained the concurrent anomalous warmth there.This enhanced a wavenumber-1 pattern and upward wave propagation,inducing a simultaneous and long-lasting stronger poleward warm air branch(WB)of the IMC in the stratosphere and hence a displacement-type Stratospheric Sudden Warming(SSW)event on 4 January.The WB-induced increase in the air mass transported into the polar stratosphere was followed by intensification of the equatorward cold branch,hence promoting the occurrence of two extreme cold events respectively over East Asia in the beginning of January and over North America in February.Results do not yield a robust direct linkage from La Niña to the SSW event,IMC changes,and cold events,though the extratropical warm SSTs are found to contribute to the February cold surge in North America.展开更多
This study investigates whether and how the Madden-Julian Oscillation(MJO)influences persistent extreme cold events(PECEs),a major type of natural disaster in boreal winter,over Northeast China.Significantly increased...This study investigates whether and how the Madden-Julian Oscillation(MJO)influences persistent extreme cold events(PECEs),a major type of natural disaster in boreal winter,over Northeast China.Significantly increased occurrence probabilities of PECEs over Northeast China are observed in phases 3 and 5 of the MJO,when MJOrelated convection is located over the eastern Indian Ocean and the western Pacific,respectively.Using the temperature tendency equation,it is found that the physical processes resulting in the cooling effects required for the occurrence of PECEs are distinct in the two phases of the MJO when MJO-related convection is consistently located over the warm pool area.The PECEs in phase 3 of the MJO mainly occur as a result of adiabatic cooling associated with ascending motion of the low-pressure anomaly over Northeast Asia.The cooling effect associated with phase 5 is stronger and longer than that in phase 3.The PECEs associated with phase 5 of the MJO are linked with the northwesterly cold advection of a cyclonic anomaly,which is part of the subtropical Rossby wave train induced by MJO-related convection in the tropical western Pacific.展开更多
Utilizing the Community Atmosphere Model,version 4,the influence of Arctic sea-ice concentration(SIC)on the extended-range prediction of three simulated cold events(CEs)in East Asia is investigated.Numerical results s...Utilizing the Community Atmosphere Model,version 4,the influence of Arctic sea-ice concentration(SIC)on the extended-range prediction of three simulated cold events(CEs)in East Asia is investigated.Numerical results show that the Arctic SIC is crucial for the extended-range prediction of CEs in East Asia.The conditional nonlinear optimal perturbation approach is adopted to identify the optimal Arctic SIC perturbations with the largest influence on CE prediction on the extended-range time scale.It shows that the optimal SIC perturbations are more inclined to weaken the CEs and cause large prediction errors in the fourth pentad,as compared with random SIC perturbations under the same constraint.Further diagnosis reveals that the optimal SIC perturbations first modulate the local temperature through the diabatic process,and then influence the remote temperature by horizontal advection and vertical convection terms.Consequently,the optimal SIC perturbations trigger a warming center in East Asia through the propagation of Rossby wave trains,leading to the largest prediction uncertainty of the CEs in the fourth pentad.These results may provide scientific support for targeted observation of Arctic SIC to improve the extended-range CE prediction skill.展开更多
Under the background of global warming, extreme cold events occur frequently. It is important to enhance the understanding of cold air patterns for forecasting cold air and reducing cold air-induced meteorological dis...Under the background of global warming, extreme cold events occur frequently. It is important to enhance the understanding of cold air patterns for forecasting cold air and reducing cold air-induced meteorological disasters. The study used the daily minimum temperatures from the National Climate Centre to classify the cold events affecting China into five different grades and the characteristics of different intensity cold events in China during the winter from 1960 to 2020 were analyzed. The results showed that there is little difference in the distribution of the frequency of general cold events from north to south, with duration longer in the north than in the south and an increase in frequency in the north in the last 60 years. The frequency of strong cold events is more in the north of China than in the south of China, and the duration is longer in the south than in the north China, with the frequency decreasing in most parts of the country. In addition to latitude, cold events frequency is closely linked to topography, with basins surrounded by high mountains being difficult to be affected by cold events, especially extreme cold events. In terms of month distribution, December was subject to the highest frequency of cold events and the longest duration of a single cold events process.展开更多
Introduction:Understanding how mangroves respond to rare cold events has implications for both restoration and conservation under climate change scenarios.This study investigated the responses of photosynthesis and ac...Introduction:Understanding how mangroves respond to rare cold events has implications for both restoration and conservation under climate change scenarios.This study investigated the responses of photosynthesis and activities of key enzymes involving carbon and nitrogen metabolism at different ages of Kandelia obovata to a rare cold event in the winter of 2010.Methods:This study took place on Ximen Island,Zhejiang Province,China.We measured the physiological recovery of 2-3-,5-6-,9-10-and 54-55-year-old K.obovata trees after freezing injury in February and March in 2011 and 2012,respectively.Results:Chilling injury index and electrolyte leakage of K.obovata increased with increasing tree age in the winter of 2010,and electrolyte leakage in K.obovata at different ages in the winter of 2010 was far higher than that in the winter of 2011.The rare cold events significantly changed the recoveries of the leaf net photosynthetic rate(Pn)and stomatal conductance(Gs);ratios of chlorophyll a/chlorophyll b(Chl a/Chl b);contents of total soluble sugar(TSS),sucrose,free amino acid(FAA),and soluble protein;and activities of sucrose phosphate synthase(SPS),endopeptidase,and carboxypeptidase in K.obovata at different ages.These effects were mainly due to changes in the physiological mechanism in the 2-year-old trees.A clear decrease in Pn of the 2-year-old trees was observed in February 2011,as exemplified by reductions in ratios of Chl a/Chl b and chlorophyll/carotenoid(Chl/Car),as well as inhibition of the levels of TSS and FAA(osmotic substances).During recovery in 2011 and 2012,the activities of SPS and sucrose synthase(SS)were responsible for sucrose synthesis after the rare cold events in 2011,but only SPS activity was one of the main factors contributing to the metabolism of stachyose to sucrose without cold damage in 2012.Carboxypeptidase played a more important role than endopeptidase during protein hydrolysis after the rare cold events.Conclusions:The results suggest that the recovery of photosynthetic capacity in K.obovata was changed after a rare cold event,which is associated with pigment components and activities of SS,SPS,and carboxypeptidase,especially the seedlings.展开更多
The number of days with occurrence of winter regional extreme cold events(RECEs) in China was found more during 1960/1961–1985/1986(period 1), less during 1986/1987–2005/2006(period 2), but more again during2006/200...The number of days with occurrence of winter regional extreme cold events(RECEs) in China was found more during 1960/1961–1985/1986(period 1), less during 1986/1987–2005/2006(period 2), but more again during2006/2007–2017/2018(period 3). So far, the differences in the atmospheric circulation favoring RECEs among these three periods are unclear. In this paper, changes in atmospheric circulation during the RECEs over China are examined by using composite analysis based on the station observed temperature data and NCEP–NCAR reanalysis data in winters of 1960/1961–2017/2018. The results show:(1) the stratospheric polar vortex was more active and tended to split before the outbreak of RECEs in period 3 than that in other two periods. The shift of the stratospheric polar vortex to Eurasia helped the upper Arctic cold air to affect the lower latitudes.(2) The troposphere was characterized by a typical or significant three-wave pattern before the outbreak of RECEs in period 2, in contrast to a weakened three-wave pattern in period 1. Compared to periods 1 and 2, the Okhotsk blocking high was stronger in period 3, contributing to the inverted omega-shaped circulation pattern in East Asia–North Pacific section and a shift of global pattern from three-wave to two-wave. The weakened three-wave or two-wave circulation pattern was manifested by the stronger Ural/Okhotsk blocking high, conducive to the strengthening of the meridional circulation and the occurrence of RECEs in East Asia.(3) The Siberian high was the strongest in period 3, followed by period 1, and it was the weakest in period 2. Before the outbreak of RECEs, the Siberian high in period 3 began to intensify one week earlier than that in periods 1 and 2. Thus, the accumulation time of cold air mass in period 3 was the longest. In summary, the synergism of atmospheric circulation at high and low levels in periods 1 and 3 was more conducive to more and strong RECEs than that in period 2. Moreover, the split of the stratospheric polar vortex may have played an important role on the formation of tropospheric two-wave pattern in period 3. The results obtained herein may provide a better understanding of the mechanisms for occurrences of RECEs in China.展开更多
In this study,the mechanism for the sea ice decline over the Bering Sea and its relationship with cold events over North America are investigated based on the daily ERA-Interim data during the winter(December-February...In this study,the mechanism for the sea ice decline over the Bering Sea and its relationship with cold events over North America are investigated based on the daily ERA-Interim data during the winter(December-February)of1979-2016.The results show that the sea ice decline over western(eastern)Bering Sea is mainly contributed by(1)the strengthened southerly(southeasterly)wind near the surface,which possibly pushes the sea ice to move northward,and(2)the intensified downward infrared radiation(IR),which is closely related to the local increasing surface air temperature(SAT)and the intensified moisture convergence mostly induced by the anomalous southeasterly wind associated with an anticyclonic anomaly over the Alaska Bay.During the sea ice decline over the Bering Sea,a cold SAT anomaly is simultaneously found over North America.It is proved that the occurrence of such a cold event is driven by the atmospheric internal variation,but not the forcing of sea ice decline over the Bering Sea.This study deepens our understanding of sea ice decline and its relationship with contemporary cold events in winter.展开更多
Arctic sea ice loss and the associated enhanced warming has been related to midlatitude weather and climate changes through modulate meridional temperature gradients linked to circulation. However, contrasting lines o...Arctic sea ice loss and the associated enhanced warming has been related to midlatitude weather and climate changes through modulate meridional temperature gradients linked to circulation. However, contrasting lines of evidence result in low confidence in the influence of Arctic warming on midlatitude climate. This study examines the additional perspectives that palaeoclimate evidence provides on the decadal relationship between autumn sea ice extent (SIE) in the Barents-Kara (B-K) Seas and extreme cold wave events (ECWEs) in southern China. Reconstruction of the winter Cold Index and SIE in the B-K Seas from 1289 to 2017 shows that a significant anti-phase relationship occurred during most periods of decreasing SIE, indicating that cold winters are more likely in low SIE years due to the “bridge” role of the North Atlantic Oscillation and Siberian High. It is confirmed that the recent increase in ECWEs in southern China is closely related to the sea ice decline in the B-K Seas. However, our results show that the linkage is unstable, especially in high SIE periods, and it is probably modulated by atmospheric internal variability.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.42088101 and 42075032).
文摘Persistent(5-day or longer)extreme cold events(ECEs)over northeastern China during the boreal winter of 1979–2020 are investigated using daily minimum temperature(Tmin)from the China Meteorological Data Network.The extreme cooling area and intensity indices associated with the ECEs exhibit a dominant 10–40-day periodicity,indicating a close link with atmospheric intraseasonal oscillations(ISOs).The ECEs are categorized into W-and N-type.In the former,the low-frequency cooling associated with the ISO first penetrates into the western boundary of the northeastern China domain and later occupies the entire domain at its peak phase.The upper-tropospheric circulation associated with this type is characterized by a northwest–southeast-oriented Rossby wave train,expanding from the Ural Mountains to the western Pacific Ocean.In the latter,the cooling invades the northern boundary first and then penetrates into the entire domain.The upper tropospheric precursory signal associated with this type is a zonally oriented negative geopotential height anomaly,which slowly moves southward.A downward-propagating signal is observed in the stratospheric potential vorticity field prior to the peak cooling,implying a possible stratospheric impact.In addition to the W-and N-types,ECEs can also occur in a localized region near either at the northern or southern boundary of the domain.
基金supported by the National Key Research and Development Program[grant number 2022YFC3004203]the S&T Development Fund of CAMS(Chinese Academy of Meteorological Sciences)[grant numbers 2023KJ040 and 2024KJ013].
文摘Subseasonal forecasting of extreme events is crucial for early warning systems.However,the forecast skills for extreme events are limited.Taking the extreme cold events in January 2018 as a specific example,and analyzing the 34 extreme cold events in East Asia from 1998 to 2020,the authors evaluated the forecast skills of the ECMWF model ensemble members on subseasonal time scales.The results show that while the ensemble mean has limited skills for forecasting extreme cold events at the 3-week lead time,some individual members demonstrate high forecast skills.For most extreme cold events,there are>10%of members among the total ensembles that can well predict the rapid temperature transitions at the 14-day lead time.This highlights the untapped potential of the ECMWF model to forecast extreme cold events on subseasonal time scales.High-skill ensemble members rely on accurate predictions of atmospheric circulation patterns(500-hPa geopotential height,mean sea level pressure)and key weather systems,including the Ural Blocking and Siberian High,that influence extreme cold events.
基金Under the auspices of the Key R&D Program of Xinjiang Uygur Autonomous Region(No.2022B03021)Tianshan Talent Training Program of Xinjiang Uygur Autonomous Region(No.2022TSYCLJ0011)+2 种基金Transformation of Scientific and Technological Achievements from the Qinghai Province(No.2020-SF-145)the 2020 Qinghai Kunlun Talents-leading Scientists Project(No.2020-LCJ-02)Key Program of International Cooperation,Bureau of International Cooperation,Chinese Academy of Sciences(No.131551KYSB20210030)。
文摘Long-term regional extreme cold events(ECEs)garner significant attention due to their widespread impact and prolonged duration,posing critical threats to human society and ecosystems.Previous studies have examined ECE characteristics at single sites or grid points,however,it is crucial to recognize that such events generally manifest as spatiotemporally continuous regional phenomena.Here,we proposed an objective methodology based on spatiotemporal continuity to identify ECEs in the China-Pakistan Economic Corridor(CPEC)during the winters of 1961-2015.This approach successfully reproduced the dynamic evolution of ECEs,encompassing their initiation,development,and dissipation.We further analyzed the changes of ECE intensity,frequency,and duration,and assessed ECE trends within varying return periods by employing the generalized Pareto distribution(GPD).Our findings reveal a decline in the frequency and duration of ECEs in CPEC over the study period,while their intensity has increased by 50%.ECEs predominantly occur in the northern regions of Azad Kashmir and Balochistan’s Quetta in Pakistan,and Kashgar in China.High recurrence levels are associated with an expansion of ECE-prone areas,particularly in the northern Pamir Plateau,which emerges as a regional hotspot.These results highlight the critical need to remain vigilant to potential future surges in ECEs under global warming,underscoring their implications for regional climate resilience.
基金supported by the National Key Research and Development Program of China (Grant No. 2018YFC1505602)the National Natural Science Foundation of China (Grant No. 41705055)+2 种基金the Graduate Innovation Project of Jiangsu Province (Grant No. CXZZ11_0485)the Creative Teams of Jiangsu Qinglan Projectthe Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘We investigate the characteristics and mechanisms of persistent wet–cold events(PWCEs)with different types of coldair paths.Results show that the cumulative single-station frequency of the PWCEs in the western part of South China is higher than that in the eastern part.The pattern of single-station frequency of the PWCEs are“Yangtze River(YR)uniform”and“east–west inverse”.The YR uniform pattern is the dominant mode,so we focus on this pattern.The cold-air paths for PWCEs of the YR uniform pattern are divided into three types—namely,the west,northwest and north types—among which the west type accounts for the largest proportion.The differences in atmospheric circulation of the PWCEs under the three types of paths are obvious.The thermal inversion layer in the lower troposphere is favorable for precipitation during the PWCEs.The positive water vapor budget for the three types of PWCEs mainly appears at the southern boundary.
基金supported by the National Natural Science Foundation of China [grant number 41991281]the National Key R&D Program of China [grant number 2018YFA0606403]the National Natural Science Foundation of China [grant number 41790472]。
基金National Basic Research Program of China, No.2004CB720206 National Natural Science Foundation of China, No.40772118+1 种基金 No.49971009 Knowledge Innovation Project of CAS, No.KZCX2-SW-118
文摘The components of the primary elements in the dune sands for the MGS1 subsection of the Milanggouwan section in the Salawusu River valley, compared with those of modern dune sands, show that they were caused by East Asian winter monsoon in the Mu Us desert during Holocene. The examined ages for the 11 layers of dune sands, based on the average sedimentary rate, are： 0 to 960, 1350-2240, 2470 to 3530, 4000 to 4180, 4290 to 4350, 4380 to 4760, 5040 to 5920, 6570 to 8270, 9020 to 9700, 9880 to 10160 and 10580 to 11080 a BP, respectively. The climatic events indicated by these dune sands are consistent with those records in the Huguangyan volcanic lake, Zoige peat bog, Hulu cave and Dunde ice core, particularly with the climatic fluctuations of the North Atlantic since 11 000 a BP. Among them, patterns from B0 to B8 correspond to the peak values of 0MD, 2D, 4D, 6D＋8D＋10D, 12D, 14D, 16D, 18D and 20D respectively. It might be caused by the North Atlantic ice age induced by the heat circulation, which strengthened the polar high pressure and Siberian-Mongolian high pressure and further led to the dominance of the winter monsoon over China＇s desert area.
基金the financial support from the National Natural Science Foundation of China(Grants Nos. 41975068, 41790473, and 41975099)the Chinese Academy of Sciences Strategic Priority Research Program (Grant No. XDA19070403).
文摘Starting in mid-November,China was hit by several cold events during the early winter of 2020/21.The lowest temperature observed at Beijing station on 7 January reached−19.6°C.In this paper,we show that the outbreak of the record-breaking extreme cold event can be attributed to a huge merging Ural blocking(UB)ridge over the Eurasian region.The sea-ice cover in the Kara and East Siberia Seas(KESS)in autumn was at its lowest value since 1979,which could have served as a precursor signal.Further analysis shows that several successive UB episodes occurred from 1 September 2020 to 10 January 2021.The persistent UB that occurred in late September/early October 2020 may have made an important contribution to the October historical minimum of sea ice in the KESS region.Our results also show that,after each UB episode in winter,significant upward propagation of wave activity occurred around 60°E,which resulted in weakening the stratospheric vortex.Meanwhile,each UB episode also caused a significant reduction in sea-ice extent in KESS and a significant weakening of the westerly jet in mid-high-latitude Eurasia.Results suggest that the Arctic vortex,which is supposed to enhance seasonally,became weaker and more unstable than the climatic mean under the seasonal cumulative effects of UB episodes,KESS warming,and long-lasting negative-phase North Atlantic Oscillation(NAO-).Those seasonal cumulative effects,combined with the impact of La Niña winter,led to the frequent occurrence of extreme cold events.
基金support from the National Natural Science Foundation of China(Grant Nos:41790475,42005046,and 41790473)。
文摘Three extreme cold events invaded China during the early winter period between December 2020 to mid-January 2021 and caused drastic temperature drops,setting new low-temperature records at many stations during 6−8 January 2021.These cold events occurred under background conditions of low Arctic sea ice extent and a La Niña event.This is somewhat expected since the coupled effect of large Arctic sea ice loss in autumn and sea surface temperature cooling in the tropical Pacific usually favors cold event occurrences in Eurasia.Further diagnosis reveals that the first cold event is related to the southward movement of the polar vortex and the second one is related to a continent-wide ridge,while both the southward polar vortex and the Asian blocking are crucial for the third event.Here,we evaluate the forecast skill for these three events utilizing the operational forecasts from the ECMWF model.We find that the third event had the highest predictability since it achieves the best skill in forecasting the East Asian cooling among the three events.Therefore,the predictability of these cold events,as well as their relationships with the atmospheric initial conditions,Arctic sea ice,and La Niña deserve further investigation.
基金Supported by the National Natural Science Foundation of China (Nos. 40576032 and 40776030)Doctor Foundation of China University of Petroleum
文摘A 700-year record （1.0-1.5 a resolution） of the East Asian winter monsoon （EAWM）, based on grain-size analysis and AMSI4C dating of Core EC2005 from the inner-shelf mud wedge of the East China Sea （ECS）, was compared with the Dongge stalagmite 8180 record during the mid-Holocene. The upper muddy section of Core EC2005 has been formed mainly by suspended sediments derived from the Changjiang （Yangtze） River mouth since 7.3 ka BP. High precipitation and a strengthened EAWM might have played key roles in the high sedimentation rate （1 324-1 986 crn/ka） between 5.9-5.2 ka BP. The EAWM strengthened when the Asian summer monsoon weakened, especially around 5 500 a BE which corresponded to a worldwide cold event. The EAWM during the mid-Holocene shows statistically significant solar periodicities at 62 and 11 a. The 5 500 a BP cold event might be resulted from orbital forcing and changes in solar activity.
基金supported by the Key Research Program of Frontier Sciences,CAS (Grant No. ZDBS-LY-DQC010)the National Natural Science Foundation of China (Grant Nos. 41876012 and 41861144015,42175045)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDB42000000).
文摘Several consecutive extreme cold events impacted China during the first half of winter 2020/21,breaking the low-temperature records in many cities.How to make accurate climate predictions of extreme cold events is still an urgent issue.The synergistic effect of the warm Arctic and cold tropical Pacific has been demonstrated to intensify the intrusions of cold air from polar regions into middle-high latitudes,further influencing the cold conditions in China.However,climate models failed to predict these two ocean environments at expected lead times.Most seasonal climate forecasts only predicted the 2020/21 La Niña after the signal had already become apparent and significantly underestimated the observed Arctic sea ice loss in autumn 2020 with a 1-2 month advancement.In this work,the corresponding physical factors that may help improve the accuracy of seasonal climate predictions are further explored.For the 2020/21 La Niña prediction,through sensitivity experiments involving different atmospheric-oceanic initial conditions,the predominant southeasterly wind anomalies over the equatorial Pacific in spring of 2020 are diagnosed to play an irreplaceable role in triggering this cold event.A reasonable inclusion of atmospheric surface winds into the initialization will help the model predict La Niña development from the early spring of 2020.For predicting the Arctic sea ice loss in autumn 2020,an anomalously cyclonic circulation from the central Arctic Ocean predicted by the model,which swept abnormally hot air over Siberia into the Arctic Ocean,is recognized as an important contributor to successfully predicting the minimum Arctic sea ice extent.
基金supported by the National Key Technologies R&D Program of China (Grant No. 2009BAC51B02)
文摘The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were accompanied by a CCW in the initial stages. From the comparison between the CECs and the CCWs that were independent of any CEC, it is found that a south- west-northeast-oriented tilted ridge at 500 hPa was present around the Europe-Barents Sea regions approximately 10 days prior to the start of the CEC. Consistent with this feature, a high sea level pressure and strong cold air accumulation occurred over a broad extent of northern Eurasia one week prior to the start of the CEC. The tilted ridge and the strong cold air accumulation were the precursory signals that were absent for the CCW, and they provide important clues for the early prediction of whether a CCW event might evolve into a CEC.
基金supported by grants from the National Key R&D Program of China(Grant No.2019YFC1510201)National Natural Science Foundation of China(Grant Nos.42075052 and 42088101)the Natural Science Foundation of Jiangsu Province(Grants No.BK20211288).
文摘Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isentropic mass circulation(IMC)perspective.Results show that the midlatitude cold surface temperature anomalies always co-occurred with the high-latitude warm anomalies,and this was closely related to the strengthening of the low-level equatorward cold air branch of the IMC,particularly along the climatological cold air routes over East Asia and North America.Specifically,the two cold surges over East Asia in early winter were results of intensification of cold air transport there,influenced by the Arctic sea ice loss in autumn.The weakened cold air transport over North America associated with warmer northeastern Pacific sea surface temperatures(SSTs)explained the concurrent anomalous warmth there.This enhanced a wavenumber-1 pattern and upward wave propagation,inducing a simultaneous and long-lasting stronger poleward warm air branch(WB)of the IMC in the stratosphere and hence a displacement-type Stratospheric Sudden Warming(SSW)event on 4 January.The WB-induced increase in the air mass transported into the polar stratosphere was followed by intensification of the equatorward cold branch,hence promoting the occurrence of two extreme cold events respectively over East Asia in the beginning of January and over North America in February.Results do not yield a robust direct linkage from La Niña to the SSW event,IMC changes,and cold events,though the extratropical warm SSTs are found to contribute to the February cold surge in North America.
基金supported by the National Natural Science Foundation of China[grant number 42088101]the National Postdoctoral Program for Innovative Talent of China[grant number BX2021133]the China Postdoctoral Science Foundation of No.70 General Fund[grant number 2021M701753]。
文摘This study investigates whether and how the Madden-Julian Oscillation(MJO)influences persistent extreme cold events(PECEs),a major type of natural disaster in boreal winter,over Northeast China.Significantly increased occurrence probabilities of PECEs over Northeast China are observed in phases 3 and 5 of the MJO,when MJOrelated convection is located over the eastern Indian Ocean and the western Pacific,respectively.Using the temperature tendency equation,it is found that the physical processes resulting in the cooling effects required for the occurrence of PECEs are distinct in the two phases of the MJO when MJO-related convection is consistently located over the warm pool area.The PECEs in phase 3 of the MJO mainly occur as a result of adiabatic cooling associated with ascending motion of the low-pressure anomaly over Northeast Asia.The cooling effect associated with phase 5 is stronger and longer than that in phase 3.The PECEs associated with phase 5 of the MJO are linked with the northwesterly cold advection of a cyclonic anomaly,which is part of the subtropical Rossby wave train induced by MJO-related convection in the tropical western Pacific.
基金the National Natural Science Foundation of China(Grant Nos.42288101,41790475,42175051,and 42005046)the State Key Laboratory of Tropical Oceanography(South China Sea Institute of Oceanology,Chinese Academy of Sciences+1 种基金Grant No.LTO2109)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2021A1515011868).
文摘Utilizing the Community Atmosphere Model,version 4,the influence of Arctic sea-ice concentration(SIC)on the extended-range prediction of three simulated cold events(CEs)in East Asia is investigated.Numerical results show that the Arctic SIC is crucial for the extended-range prediction of CEs in East Asia.The conditional nonlinear optimal perturbation approach is adopted to identify the optimal Arctic SIC perturbations with the largest influence on CE prediction on the extended-range time scale.It shows that the optimal SIC perturbations are more inclined to weaken the CEs and cause large prediction errors in the fourth pentad,as compared with random SIC perturbations under the same constraint.Further diagnosis reveals that the optimal SIC perturbations first modulate the local temperature through the diabatic process,and then influence the remote temperature by horizontal advection and vertical convection terms.Consequently,the optimal SIC perturbations trigger a warming center in East Asia through the propagation of Rossby wave trains,leading to the largest prediction uncertainty of the CEs in the fourth pentad.These results may provide scientific support for targeted observation of Arctic SIC to improve the extended-range CE prediction skill.
文摘Under the background of global warming, extreme cold events occur frequently. It is important to enhance the understanding of cold air patterns for forecasting cold air and reducing cold air-induced meteorological disasters. The study used the daily minimum temperatures from the National Climate Centre to classify the cold events affecting China into five different grades and the characteristics of different intensity cold events in China during the winter from 1960 to 2020 were analyzed. The results showed that there is little difference in the distribution of the frequency of general cold events from north to south, with duration longer in the north than in the south and an increase in frequency in the north in the last 60 years. The frequency of strong cold events is more in the north of China than in the south of China, and the duration is longer in the south than in the north China, with the frequency decreasing in most parts of the country. In addition to latitude, cold events frequency is closely linked to topography, with basins surrounded by high mountains being difficult to be affected by cold events, especially extreme cold events. In terms of month distribution, December was subject to the highest frequency of cold events and the longest duration of a single cold events process.
基金funded by projects of special Funding for Research of National Oceanic Public Service Industry(201505028)Zhejiang Provincial Natural Science Foundation(LQ13C030002)+1 种基金Science and Technology Plan Zhejiang Province(2012C12017-3,2013C25096,2014F50003)Zhejiang Province pelagic fishery(2015)“Cooperation and exchange of aquaculture technology between China and Israel based on the level of ecological system,”and Wenzhou Municipal Science。
文摘Introduction:Understanding how mangroves respond to rare cold events has implications for both restoration and conservation under climate change scenarios.This study investigated the responses of photosynthesis and activities of key enzymes involving carbon and nitrogen metabolism at different ages of Kandelia obovata to a rare cold event in the winter of 2010.Methods:This study took place on Ximen Island,Zhejiang Province,China.We measured the physiological recovery of 2-3-,5-6-,9-10-and 54-55-year-old K.obovata trees after freezing injury in February and March in 2011 and 2012,respectively.Results:Chilling injury index and electrolyte leakage of K.obovata increased with increasing tree age in the winter of 2010,and electrolyte leakage in K.obovata at different ages in the winter of 2010 was far higher than that in the winter of 2011.The rare cold events significantly changed the recoveries of the leaf net photosynthetic rate(Pn)and stomatal conductance(Gs);ratios of chlorophyll a/chlorophyll b(Chl a/Chl b);contents of total soluble sugar(TSS),sucrose,free amino acid(FAA),and soluble protein;and activities of sucrose phosphate synthase(SPS),endopeptidase,and carboxypeptidase in K.obovata at different ages.These effects were mainly due to changes in the physiological mechanism in the 2-year-old trees.A clear decrease in Pn of the 2-year-old trees was observed in February 2011,as exemplified by reductions in ratios of Chl a/Chl b and chlorophyll/carotenoid(Chl/Car),as well as inhibition of the levels of TSS and FAA(osmotic substances).During recovery in 2011 and 2012,the activities of SPS and sucrose synthase(SS)were responsible for sucrose synthesis after the rare cold events in 2011,but only SPS activity was one of the main factors contributing to the metabolism of stachyose to sucrose without cold damage in 2012.Carboxypeptidase played a more important role than endopeptidase during protein hydrolysis after the rare cold events.Conclusions:The results suggest that the recovery of photosynthetic capacity in K.obovata was changed after a rare cold event,which is associated with pigment components and activities of SS,SPS,and carboxypeptidase,especially the seedlings.
基金Supported by the National Natural Science Foundation of China (41790471)Strategic Priority Research Program of Chinese Academy of Sciences (XDA20100304)。
文摘The number of days with occurrence of winter regional extreme cold events(RECEs) in China was found more during 1960/1961–1985/1986(period 1), less during 1986/1987–2005/2006(period 2), but more again during2006/2007–2017/2018(period 3). So far, the differences in the atmospheric circulation favoring RECEs among these three periods are unclear. In this paper, changes in atmospheric circulation during the RECEs over China are examined by using composite analysis based on the station observed temperature data and NCEP–NCAR reanalysis data in winters of 1960/1961–2017/2018. The results show:(1) the stratospheric polar vortex was more active and tended to split before the outbreak of RECEs in period 3 than that in other two periods. The shift of the stratospheric polar vortex to Eurasia helped the upper Arctic cold air to affect the lower latitudes.(2) The troposphere was characterized by a typical or significant three-wave pattern before the outbreak of RECEs in period 2, in contrast to a weakened three-wave pattern in period 1. Compared to periods 1 and 2, the Okhotsk blocking high was stronger in period 3, contributing to the inverted omega-shaped circulation pattern in East Asia–North Pacific section and a shift of global pattern from three-wave to two-wave. The weakened three-wave or two-wave circulation pattern was manifested by the stronger Ural/Okhotsk blocking high, conducive to the strengthening of the meridional circulation and the occurrence of RECEs in East Asia.(3) The Siberian high was the strongest in period 3, followed by period 1, and it was the weakest in period 2. Before the outbreak of RECEs, the Siberian high in period 3 began to intensify one week earlier than that in periods 1 and 2. Thus, the accumulation time of cold air mass in period 3 was the longest. In summary, the synergism of atmospheric circulation at high and low levels in periods 1 and 3 was more conducive to more and strong RECEs than that in period 2. Moreover, the split of the stratospheric polar vortex may have played an important role on the formation of tropospheric two-wave pattern in period 3. The results obtained herein may provide a better understanding of the mechanisms for occurrences of RECEs in China.
基金Supported by the National Natural Science Foundation of China(41775001)Technology Development Fund of the Chinese Academy of Meteorological Sciences(2018KJ036).
文摘In this study,the mechanism for the sea ice decline over the Bering Sea and its relationship with cold events over North America are investigated based on the daily ERA-Interim data during the winter(December-February)of1979-2016.The results show that the sea ice decline over western(eastern)Bering Sea is mainly contributed by(1)the strengthened southerly(southeasterly)wind near the surface,which possibly pushes the sea ice to move northward,and(2)the intensified downward infrared radiation(IR),which is closely related to the local increasing surface air temperature(SAT)and the intensified moisture convergence mostly induced by the anomalous southeasterly wind associated with an anticyclonic anomaly over the Alaska Bay.During the sea ice decline over the Bering Sea,a cold SAT anomaly is simultaneously found over North America.It is proved that the occurrence of such a cold event is driven by the atmospheric internal variation,but not the forcing of sea ice decline over the Bering Sea.This study deepens our understanding of sea ice decline and its relationship with contemporary cold events in winter.
基金the National Natural Science Foundation of China(Grant No.42101142)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA19070103)the Young Elite Scientists Sponsorship Program by CAST(Grant No.2022QNRC001).
文摘Arctic sea ice loss and the associated enhanced warming has been related to midlatitude weather and climate changes through modulate meridional temperature gradients linked to circulation. However, contrasting lines of evidence result in low confidence in the influence of Arctic warming on midlatitude climate. This study examines the additional perspectives that palaeoclimate evidence provides on the decadal relationship between autumn sea ice extent (SIE) in the Barents-Kara (B-K) Seas and extreme cold wave events (ECWEs) in southern China. Reconstruction of the winter Cold Index and SIE in the B-K Seas from 1289 to 2017 shows that a significant anti-phase relationship occurred during most periods of decreasing SIE, indicating that cold winters are more likely in low SIE years due to the “bridge” role of the North Atlantic Oscillation and Siberian High. It is confirmed that the recent increase in ECWEs in southern China is closely related to the sea ice decline in the B-K Seas. However, our results show that the linkage is unstable, especially in high SIE periods, and it is probably modulated by atmospheric internal variability.
