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1.
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 Ni?a 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 Ni?a 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 Ni?a 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.  相似文献   

2.
In this study, two possible persistent anomalies of the Madden-Julian Oscillation mode (MJO) are found in the summer season (persistently Pacific active and Indian Ocean active), and an index is set to define the intensity of the two modes. They are proved to have high statistical correlations to the later ENSO events in the autumn and winter seasons: When persistent anomaly of MJO happens in the Pacific Ocean in summer, El Ni?o events are often induced during the autumn and winter seasons of that year. However, during the other MJO mode when the summer persistent anomaly of MJO occurs in the Indian Ocean, La Ni?a events often follow instead. The analysis of the atmospheric circulation field indicates that persistent anomaly of MJO can probably affect the entire Equatorial Pacific circulation, and results in wind stress anomalies. The wind stress anomalies could excite warm or cold water masses which propagate eastwards at the subsurface ocean. The accumulation of warm or cold subsurface water in the Equatorial Eastern Pacific Ocean may eventually lead to the formation of an ENSO.  相似文献   

3.
The Northern Hemisphere(NH) often experiences frequent cold air outbreaks and heavy snowfalls during La Ni?a winters. In 2022, a third-year La Ni?a event has exceeded both the oceanic and atmospheric thresholds since spring and is predicted to reach its mature phase in December 2022. Under such a significant global climate signal, whether the Eurasian Continent will experience a tough cold winter should not be assumed, despite the direct influence of mid-to high-latitude,large-scale atmospheric ...  相似文献   

4.
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 Ni?a 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 Ni?a deserve further investigation.  相似文献   

5.
Although there has been a considerable amount of research conducted on the East Asian winter-mean climate, subseasonal surface air temperature(SAT) variability reversals in the early and late winter remain poorly understood. In this study,we focused on the recent winter of 2014/15, in which warmer anomalies dominated in January and February but colder conditions prevailed in December. Moreover, Arctic sea-ice cover(ASIC) in September–October 2014 was lower than normal,and warmer sea surface temperature(SST) anomalies occurred in the Ni ?no4 region in winter, together with a positive Pacific Decadal Oscillation(PDO|+) phase. Using observational data and CMIP5 historical simulations, we investigated the PDO|+ phase modulation upon the winter warm Ni ?no4 phase(autumn ASIC reduction) influence on the subseasonal SAT variability of East Asian winter. The results show that, under a PDO|+ phase modulation, warm Ni ?no4 SST anomalies are associated with a subseasonal delay of tropical surface heating and subsequent Hadley cell and Ferrel cell intensification in January–February, linking the tropical and midlatitude regions. Consistently, the East Asian jet stream(EAJS) is significantly decelerated in January–February and hence promotes the warm anomalies over East Asia. Under the PDO|+ phase,the decrease in ASIC is related to cold SST anomalies in the western North Pacific, which increase the meridional temperature gradient and generate an accelerated and westward-shifted EAJS in December. The westward extension of the EAJS is responsible for the eastward-propagating Rossby waves triggered by declining ASIC and thereby favors the connection between ASIC and cold conditions over East Asia.  相似文献   

6.
The Atlantic Multidecadal Oscillation （AMO）, the multidecadal variation of North Atlantic sea surface temperature （SST）, exhibits an oscillation with a period of 65-80 years and an amplitude of 0.4℃. Observational composite analyses reveal that the warm phase AMO is linked to warmer winters in East China, with enhanced precipitation in the north of this region and reduced precipitation in the south, on multidecadal time scales. The pattern is reversed during the cold phase AMO. Whether the AMO acts as a forcing of the multidecadal winter climate of East China is explored by investigating the atmospheric response to warm AMO SST anomalies in a large ensemble of atmospheric general circulation model （AGCM） experiments. The results from three AGCMs are consistent and suggest that the AMO warmth favors warmer winters in East China. This influence is realized through inducing negative surface air pressure anomalies in the hemispheric-wide domain extending from the midlatitude North Atlantic to midlatitude Eurasia. These negative surface anomalies favor the weakening of the Mongolian Cold High, and thus induce a weaker East Asian Winter Monsoon.  相似文献   

7.
Based on a linear model, the present study provides analytical solutions for ideal triple forcing sources similar to sea surface temperature anomaly （SSTA） pat- terns associated with El Nino-Southern Oscillation （ENSO） Modoki in winter. The ideal triple pattern is composed of an equatorially symmetric heat source in the middle and equatoriaUy asymmetric cold forcing in the southeast and northwest. The equatorially symmetric heat source excites low-level cyclonic circulation anomalies associated with Rossby waves in both hemispheres, while the northwest- ern and southeastern equatorially asymmetric cold sources induce low-level anomalous anticyclones associated with Rossby waves in the hemisphere where the forcing source is located. Low-level zonal winds converge toward the heat sources associated with Kelvin and Rossby waves. Due to unequal forcing intensity in the northwest and southeast, atmospheric responses around the equatorially symmetric forcing become asymmetric, and low-level cyclonic circulation anomalies in the Southern Hemisphere become greater than those in the Northern Hemisphere. Ascending （descending） flows coincide with heat （cold） sources, resulting in a double-cell structure over the regions of forcing sources. Ideal triple patterns similar to SSTA patterns associated with La Nina Modoki produce opposite atmospheric responses. The theoretical atmospheric responses are consistent with observed circulation anomalies associated with ENSO Modoki. Therefore, the theoretical solutions can explain the dynamics responsible for atmospheric circulation anomalies associated with ENSO Modoki events.  相似文献   

8.
The variation characteristics of precipitation during the winter (between October and the following March, to be referred to as just “the winter” hereafter) in Guangdong province during the past 50 years (from 1957 to 2006) and the relationship with Pacific SST are studied using the methods of Empirical Orthogonal Function (EOF) analysis, wavelet analysis, and correlation analysis. The results show that The Guangdong precipitation during the winter exhibits quasi-periodic significant oscillations of 40 years and 2 years; rainfall is less from the end of the 1950s to the start of the 1970s and from the end of the 1990s to the present than from the mid 1970s to the mid 1990s. The frequency of sustained drought is more than sustained flooding during the winter. The Guangdong precipitation during this time period is in significantly positive correlation to the equatorial central and eastern Pacific SST, but in a significantly negative correlation with the western and northern Pacific SST east of the Philippine Sea. 61.5% of the sustained drought occurred in the phase of negative anomalies of the Ni?o3.4 index and 38.5% in the phase of positive ones. A composite analysis of atmospheric circulation is performed for the positive and negative phases of the Ni?o3.4 region associated with the sustained drought. The results showed that a weak polar vortex, a strong trough in Europe and a ridge near Balkhash Lake, active cold air and consistent northerly wind anomalies controlling Guangdong at low levels, an inactive westerly low disturbance in the low-mid latitude of the Asian continent, and a weak southern branch westerly trough, are all mutual causes for the sustained drought.  相似文献   

9.
Three striking and impactful extreme cold weather events successively occurred across East Asia and North America during the mid-winter of 2020/21.These events open a new window to detect possible underlying physical processes.The analysis here indicates that the occurrences of the three events resulted from integrated effects of a concurrence of anomalous thermal conditions in three oceans and interactive Arctic-lower latitude atmospheric circulation processes,which were linked and influenced by one major sudden stratospheric warming(SSW).The North Atlantic warm blob initiated an increased poleward transient eddy heat flux,reducing the Barents-Kara seas sea ice over a warmed ocean and disrupting the stratospheric polar vortex(SPV)to induce the major SSW.The Rossby wave trains excited by the North Atlantic warm blob and the tropical Pacific La Nina interacted with the Arctic tropospheric circulation anomalies or the tropospheric polar vortex to provide dynamic settings,steering cold polar air outbreaks.The long memory of the retreated sea ice with the underlying warm ocean and the amplified tropospheric blocking highs from the midlatitudes to the Arctic intermittently fueled the increased transient eddy heat flux to sustain the SSW over a long time period.The displaced or split SPV centers associated with the SSW played crucial roles in substantially intensifying the tropospheric circulation anomalies and moving the jet stream to the far south to cause cold air outbreaks to a rarely observed extreme state.The results have significant implications for increasing prediction skill and improving policy decision making to enhance resilience in“One Health,One Future”.  相似文献   

10.
Arctic sea ice and Eurasian climate: A review   总被引：12，自引：0，他引：12  
The Arctic plays a fundamental role in the climate system and has shown significant climate change in recent decades,including the Arctic warming and decline of Arctic sea-ice extent and thickness. In contrast to the Arctic warming and reduction of Arctic sea ice, Europe, East Asia and North America have experienced anomalously cold conditions, with record snowfall during recent years. In this paper, we review current understanding of the sea-ice impacts on the Eurasian climate.Paleo, observational and modelling studies are covered to summarize several major themes, including: the variability of Arctic sea ice and its controls; the likely causes and apparent impacts of the Arctic sea-ice decline during the satellite era,as well as past and projected future impacts and trends; the links and feedback mechanisms between the Arctic sea ice and the Arctic Oscillation/North Atlantic Oscillation, the recent Eurasian cooling, winter atmospheric circulation, summer precipitation in East Asia, spring snowfall over Eurasia, East Asian winter monsoon, and midlatitude extreme weather; and the remote climate response(e.g., atmospheric circulation, air temperature) to changes in Arctic sea ice. We conclude with a brief summary and suggestions for future research.  相似文献   

11.
Using a high-resolution precipitation dataset,the present study detected that the mountainous area of central China(MACA)is a hotspot of ENSO’s impact on the summer rainfall variability.Further analysis suggests that both ENSO and atmospheric forcing make contributions to the summer rainfall variability in MACA.The dominant rainfall-related SST mode features as a seasonal transition from an El Niño-like warming in the preceding winter to a La Nina-like cooling in the following autumn,and it explains about 29%of the total variance of the rainfall during 1951–2018.It indicates that ENSO with a rapid phase transition is responsible for inducing summer rainfall anomalies in MACA.Besides,an upperlevel circumglobal wave mode in the Northern Hemisphere during summer also explains about 29%of the summer rainfall variance.Contributions of both the SST and the atmospheric modes have experienced interdecadal changes.The influence of the SST mode gradually increases and plays a dominant role in the recent decades,suggesting that ENSO with a rapid phase transition becomes more important for rainfall prediction in MACA.  相似文献   

12.
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 Ni?a 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.  相似文献   

13.
In this paper,we discussed the features of atmospheric circulations over Eurasia as a response to sea surface temperature anomalies (SSTAs) over the tropical Indian Ocean,the equatorial Pacific,Kuroshio and the North Atlantic.Our results are shown as follows: (1) CAM3.0,driven by the combined SSTAs over the four oceanic regions,can simulate well the features of anomalous atmospheric circulations over Eurasia in January 2008,indicating that the effects of the SSTAs over these four regions were one of the key causes of the anomalous systems over Eurasia.(2) The SSTAs over each key region contributed to the intensification of blocking over the Urals Mountains and a main East Asian trough.However,the influence of the SSTAs over individual oceanic regions differed from one another in other aspects.The SSTAs over the North Atlantic had an impact on the 500-hPa anomalous height (Z500A) over the middle-high latitudes and had a somewhat smaller effect over the low latitudes.For the warm SSTAs over Kuroshio,the subtropical high was much stronger,spread farther north than usual,and had an anomalous easterly that dominated the northwest Pacific Ocean.The warm SSTAs over the tropical Indian Ocean could have caused a negative Z500A from West Asia to Middle Asia,a remarkably anomalous southwesterly from the Indian Ocean to the south of China and an anomalous anticyclone circulation over the South China Sea-Philippine Sea region.Because of the La Nia event,the winter monsoon was stronger than normal,with an anomalously cooler northerly over the southeastern coastal areas of China.(3) The combined effects of the SSTAs over the four key regions were likely more important to the atmospheric circulation anomalies of January 2008 over Eurasia than the effects of individual or partly combined SSTAs.This unique SSTA distribution possibly led to the circulation anomalies over Eurasia in January 2008,especially the atmospheric circulation anomalies over the subtropics,which were more similar to those of the winter El Ni?o events than to the circulation anomalies following La Nia.  相似文献   

14.
This study uses multiple sea surface temperature(SST) datasets to perform a parallel comparison of three super El Ni os and their effects on the stratosphere. The results show that, different from ordinary El Ni os, warm SST anomalies appear earliest in the western tropical Pacific and precede the super El Ni o peak by more than 18 months. In the previous winter,relative to the mature phase of El Ni o, as a precursor, North Pacific Oscillation-like circulation anomalies are observed. A Pacific–North America(PNA) teleconnection appears in the extratropical troposphere during the mature phase, in spite of the subtle differences between the intensities, as well as the zonal position, of the PNA lobes. Related to the negative rainfall response over the tropical Indian Ocean, the PNA teleconnection in the winter of 1997/98 is the strongest among the three super El Ni os. The northern winter stratosphere shows large anomalies in the polar cap temperature and the circumpolar westerly, if the interferences from other factors are linearly filtered from the circulation data. Associated with the positive PNA response in a super El Ni o winter, positive polar cap temperature anomalies and circumpolar easterly anomalies,though different in timing, are also observed in the mature winters of the three super El Ni os. The stratospheric polar vortex in the next winter relative to the 1982/83 and 1997/98 events is also anomalously weaker and warmer, and the stratospheric circulation conditions remain to be seen in the coming winter following the mature phase of the 2015/16 event.  相似文献   

15.
Using multiple datasets, this paper analyzes the characteristics of winter precipitation over southern China and its association with warm and cold phases of E1 Nifio-Southern Oscillation during 1948 2011. The study proves that E1 Nifio is an important external forcing factor resulting in above-normal winter precipitation in southern China. The study also reveals that the impact ofLa Nifia on the winter precipitation in southern China has a decadal variability. During the winter of La Nifia before 1980, the East Asian winter monsoon is stronger than normal with a deeper trough over East Asia, and the western Pacific subtropical high weakens with its high ridge retreating more eastward. Therefore, anomalous northerly winds dominate over southern China, leading to a cold and dry winter. During La Nifia winter after 1980, however, the East Asian trough is weaker than normal, unfavorable for the southward invasion of the winter monsoon. The India-Burma trough is intensified, and the anomalous low-level cyclone excited by La Nifia is located to the west of the Philippines. Therefore, anomalous easterly winds prevail over southern China, which increases moisture flux from the tropical oceans to southern China. Meanwhile, La Nifia after 1980 may lead to an enhanced and more northward subtropical westerly jet over East Asia in winter. Since southern China is rightly located on the right side of the jet entrance region, anomalous ascending motion dominates there through the secondary vertical circulation, favoring more winter precipitation in southern China. Therefore, a cold and wet winter, sometimes with snowy and icy weathers, would occur in southern China during La Nifia winter after 1980. Further analyses indicate that the change in the spatial distribution of sea surface temperature anomaly during the La Nifia mature phase, as well as the decadal variation of the Northern Hemisphere atmospheric circulation, would be the important reasons for the decadal variability of the La Nifia impact on the atmospheric circulation in East Asia and winter precipitation over southern China after 1980.  相似文献   

16.
The winters of 1997/1998 and 1998/1999,corresponding to El Ni(?)o and La Ni(?)a episodes,respectively, were two typical rain-abundant and-scarce seasons for the southern China.In order to understand the cause of the anomalous precipitation during the two winters,a comparative analysis technique has been employed to investigate the differences in general circulation and moisture transportation between the two seasons. The results show that the abundant rainfall during the winter of 1997/1998 was associated with the ENSO warm episode event,eastward shifted weak westerly trough/ridge,weakened East Asian winter monsoon (EAWM),strengthened subtropical high,and presented two anti-cyclonic circulations over Hokkaido and the Philippine Sea,respectively,as well as one cyclonic circulation over the Yangtze River Basin in the anomalous wind fields of the lower troposphere.During the rain-scarce winter,however,the patterns of equatorial sea surface temperature anomalies and the circulation systems both in upper and lower levels were nearly the opposite of those during the rain-abundant winter.It has also been discovered that the water vapor over southern China during the winters came mainly from the southwesterly flow ahead of troughs in the southern branch of westerlies and the turning flow over the South China Sea-Indo-China Peninsula area;and the moisture transportation channels varied significantly with regard to height.The intensified flow in the southern branch of westerlies and the anti-cyclonic circulation anomaly over the Philippine Sea during the winter of 1997/1998 were favorable for moisture transportation to mainland China,however the two moisture transportation streams were dramatically weakened during the winter of 1998/1999 due to weak westerly flow and the dominance of a cold high system in the lower level over the southeast coast of China.Such a significant inter-annual change of moisture transportation is a key factor resulting in the obvious difference in precipitation between the two winters.  相似文献   

17.
The impact of La Ni?a on the winter Arctic stratosphere has thus far been an ambiguous topic of research. Contradictory results have been reported depending on the La Ni?a events considered. This study shows that this is mainly due to the decadal variation of La Ni?a's impact on the winter Arctic stratosphere since the late 1970 s. Specifically,during the period1951–78,the tropospheric La Ni?a teleconnection exhibits a typical negative Pacific–North America pattern,which strongly inhibits the propagation of the planetary waves from the extratropical troposphere to the stratosphere,and leads to a significantly strengthened stratospheric polar vortex. In contrast,during 1979–2015,the La Ni?a teleconnection shifts eastwards,with an anomalous high concentrated in the northeastern Pacific. The destructive interference of the La Ni?a teleconnection with climatological stationary waves seen in the earlier period reduces greatly,which prevents the drastic reduction of planetary wave activities in the extratropical stratosphere. Correspondingly,the stratospheric response shows a less disturbed stratospheric polar vortex in winter.  相似文献   

18.
Based on Global Ocean Data Assimilation System(GODAS) and NCEP reanalysis data, atmospheric and oceanic processes possibly responsible for the onset of the 2011/12 La Nia event, which followed the 2010/11 La Nia even—referred to as a "double dip" La Nia—are investigated. The key mechanisms involved in activating the 2011/12 La Nia are illustrated by these datasets. Results show that neutral conditions were already evident in the equatorial eastern Pacific during the decaying phase of the 2010/11 La Nia. However, isothermal analyses show obviously cold water still persisting at the surface and at subsurface depths in off-equatorial regions throughout early 2011, being most pronounced in the tropical South Pacific. The negative SST anomalies in the tropical South Pacific acted to strengthen a southern wind across the equator. The subsurface cold water in the tropical South Pacific then spread northward and broke into the equatorial region at the thermocline depth. This incursion process of off-equatorial subsurface cold water successfully interrupted the eastern propagation of warm water along the equator, which had previously accumulated at subsurface depths in the warm pool during the 2010/11 La Nia event. Furthermore, the incursion process strengthened as a result of the off-equatorial effects, mostly in the tropical South Pacific. The negative SST anomalies then reappeared in the central basin in summer 2011, and acted to trigger local coupled air–sea interactions to produce atmospheric–oceanic anomalies that developed and evolved with the second cooling in the fall of 2011.  相似文献   

19.
The region of south China is sometimes subject to major climatic catastrophes in winter. To have a clear understanding, the time in which extremely severe cold months occur in the south China wintertime over the past 45 years are determined and characteristics of the 500-hPa geopotential fields and SST fields are studied for the simultaneous and preceding 6-month periods. Similarity exists in the 500-hPa geopotential fields between each current severely cold month, with the geopotential pattern of being high in the north, but low in the south, of Asian-Pacific region and meridional circulation developing. The work presents anomalies of the months with significant differences in the 500-hPa geopotential field of the previous periods. The SSTA is continuous in the distribution from each extremely severe cold winter month back to the 6 months leading up to it for the region of south China while the SST pattern is of El Ni?o in January and the preceding 1 ~ 6 months for equatorial eastern Pacific but of La Ni?a in February and December. It is concluded that the prediction of severely cold winter months are possible with the use of the geopotential field at 500 hPa and the SST fields for the months ahead of the target time.  相似文献   

20.
The impact of sea surface temperature (SST) on winter haze in Guangdong province (WHDGD) was analyzed on the interannual scale. It was pointed out that the northern Indian Ocean and the northwest Pacific SST play a leading role in the variation of WHDGD. Cold (warm) SST anomalies over the northern Indian Ocean and the Northwest Pacific stimulate the eastward propagation of cold (warm) Kelvin waves through the Gill forced response, causing Ekman convergence (divergence) in the western Pacific, inducing abnormal cyclonic (anticyclonic) circulation. It excites the positive (negative) Western Pacific teleconnection pattern (WP), which results in the temperature and the precipitation decrease (increase) in Guangdong and forms the meteorological variables conditions that are conducive (not conducive) to the formation of haze. ENSO has an asymmetric influence on WHDGD. In El Ni?o (La Ni?a) winters, there are strong (weak) coordinated variations between the northern Indian Ocean, the northwest Pacific, and the eastern Pacific, which stimulate the negative (positive) phase of WP teleconnection. In El Ni?o winters, the enhanced moisture is attributed to the joint effects of the horizontal advection from the surrounding ocean, vertical advection from the moisture convergence, and the increased atmospheric apparent moisture sink (Q2) from soil evaporation. The weakening of the atmospheric apparent heat source (Q1) in the upper layer is not conducive to the formation of inversion stratification. In contrast, in La Ni?a winters, the reduced moisture is attributed to the reduced upward water vapor transport and Q2 loss. Due to the Q1 increase in the upper layer, the temperature inversion forms and suppresses the diffusion of haze.  相似文献   

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