Changes of air temperatures and atmosphere circulation at three high mountainous stations in Bulgaria are investigated for the period of 1941-2008.The three stations are located on peaks Musala,Cherni vrah and Botev,w...Changes of air temperatures and atmosphere circulation at three high mountainous stations in Bulgaria are investigated for the period of 1941-2008.The three stations are located on peaks Musala,Cherni vrah and Botev,where air temperature data have good quality.Some missing data were recovered using the method of differences. A significant mean annual air temperature rise happened in high mountainous parts of Bulgaria- the warming is in the order of 0.7°C for the entire period.The increase is very prominent particularly in the last 30 years.Main contributors to this overall tendency are summer months-June,July and August.To some degree,January also could be included in this group.November trend shows temperature rise at the beginning of the investigated period.One of the causes for such a tendency is atmosphere circulation in respective months.It also shows signs of considerable reorganization in both winter and summer.There is an increase of the cases of warm atmosphere patterns typical for winter, summer and autumn seasons in Bulgaria.Meridional circulation has essential significance for air temperatures during the cold half of the year.In January and June atmosphere circulation has a substantial influence on the thermal regime of air in high mountains of Bulgaria.In July,August and November this influence is reduced.There are no cycles in air temperatures for the investigated period.展开更多
Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both g...Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both global and regional climates.This study assesses the performance of models participating in phase 6 of the Coupled Model Intercomparison Project in simulating interannual variability modes of Northern Hemisphere 500-hPa geopotential height during winter and summer,distinguishing predictable(potentially predictable on seasonal or longer timescales)and unpredictable(intraseasonal and essentially unpredictable at long range)components,using reanalysis data and a variance decomposition method.Although most models effectively capture unpredictable modes in reanalysis,their ability to reproduce dominant predictable modes-specifically the Pacific-North American pattern,Arctic Oscillation,and Western Pacific Oscillation in winter,and the East Atlantic and North Atlantic Oscillations in summer-varies notably.An optimal ensemble is identified to distinguish(a)predictable-external modes,dominated by external forcing,and(b)predictable-internal modes,associated with slow internal variability,during the historical period(1950-2014)and the SSP5-8.5 scenario(2036-2100).Under increased radiative forcing,the leading winter/summer predictable-external mode exhibits a more uniform spatial distribution,remarkably larger trend and annual variance,and enhanced height-sea surface temperature(SST)covariance under SSP5-8.5 compared to historical conditions.The dominant winter/summer predictable-internal modes also exhibit increased variance and height-SST covariance under SSP5-8.5,along with localized changes in spatial configuration.Minimal changes are observed in spatial distribution or variance for dominant winter/summer unpredictable modes under SSP5-8.5.This study,from a predictive perspective,deepens our understanding of model uncertainties and projected changes in circulations.展开更多
Subseasonal-to-seasonal(S2S)forecasting for East Asian atmospheric circulation poses significant challenges for conventional numerical weather prediction(NWP)models.Recently,deep learning(DL)models have demonstrated s...Subseasonal-to-seasonal(S2S)forecasting for East Asian atmospheric circulation poses significant challenges for conventional numerical weather prediction(NWP)models.Recently,deep learning(DL)models have demonstrated significant potential in further enhancing S2S forecasts beyond the capabilities of NWP models.However,most current DLbased S2S forecasting models largely overlook the role of global predictors from multiple spheres,such as ocean,land,and atmosphere domains,that are crucial for effective S2S forecasting.In this study,we introduce EAAC-S2S,a tailored DL model for S2S forecasting of East Asian atmospheric circulation.EAAC-S2S employs the cross-attention mechanism to couple atmospheric circulations over East Asia with representative multi-sphere(i.e.,atmosphere,land,and ocean)variables,providing pentad-averaged circulation forecasts up to 12 pentads ahead throughout all seasons.Experimental results demonstrate,on the S2S time scale,that EAAC-S2S consistently outperforms the European Centre for MediumRange Weather Forecasts(ECMWF)Ensemble Prediction System by decreasing the root-mean-square error(RMSE)by3.8%and increasing the anomaly correlation coefficient(ACC)by 8.6%,averaged across all 17 predictands.Our system also shows good skill for examples of heatwaves and the South China Sea Subtropical High Intensity Index(SCSSHII).Moreover,quantitative interpretability analysis including multi-sphere attribution and attention visualization are conducted for the first time in a DL S2S model,where the traced predictability aligns well with prior meteorological knowledge.We hope that our results have the potential to advance research in data-driven S2S forecasting.展开更多
[Objective] This study aimed to establish models based on atmospheric cir- culation indices for forecasting the area attacked by rice planthopper every year, and to provide guide for preventing and controlling plantho...[Objective] This study aimed to establish models based on atmospheric cir- culation indices for forecasting the area attacked by rice planthopper every year, and to provide guide for preventing and controlling planthopper damage. [Method] The data related to rice planthopper occurrence and atmospheric circulation were collected and analyzed with the method of stepwise regression to establish the prediction models. [Result] The factors significantly related to the area attacked by rice plan-thopper were selected. Two types of prediction models were established. One was for Sogatella furcifera （Horvath）, based on Atlantic-Europe circulation pattern W in October in that year, Pacific polar vortex area index in October in that year, North America subtropical high index in August in that year, Atlantic-Europe circulation pattern W in June in that year, northern boundary of North America subtropical high in February in that year, Atlantic-Europe polar vortex intensity index in October in that year and Asia polar vortex intensity index in November in the last year; the other type of prediction models were for Nilaparvata lugens （Stal）, based on the Eastern Pacific subtropical high intensity index in July in that year, northern hemi- sphere polar vortex area index in October in the last year, Asia polar vortex strength index in November in the last year, north boundary of North America-At- lantic subtropical high in September in that year, north boundary of North Africa-At- lantic-North America subtropical high in January in that year, sunspot in September of the last year and eastern Pacific subtropical high area index in September in that year. [Conclusion] With the stepwise regression, the forecasting equations of the rice planthopper occurrence established based on the atmospheric circulation indices could be used for actual forecast.展开更多
The dynamical framework of the nine-level version of the IAP AGCM is presented in this paper. The emphasis of the model's description is put on the following two aspects:(1) A model's standard atmosphere, whic...The dynamical framework of the nine-level version of the IAP AGCM is presented in this paper. The emphasis of the model's description is put on the following two aspects:(1) A model's standard atmosphere, which is a satisfactory approximation to the observed troposphere and lower stratosphere standard atmosphere, is introduced into the equations of the model to permit a more accurate calculation of the vertical transport terms, especially near the tropopause; (2) The vertical levels of the model are carefully selected to guarantee a smooth dependence of layer thickness upon pressure in order to reduce the truncation error involved in the unequal interval vertical finite-differencing. For testing the model, two kinds of linear baroclinic Rossby-Haurwitz waves, one of which has a dynamically stable vertical structure and the other has a relatively unstable one, are constructed to provide initial conditions for numerical experiments. The two waves have been integrated for more than 300 days and 100 days respectively by using the model and both of them are propagating westward with almost identical phase-speed during the time period of the integrations. No obvious change of the wave patterns is found at the levels in the model's troposphere. The amplitudes of both two waves at the uppermost level, however, exhibit rather significant oscillation with time, of which the periods are exactly 20 days and 25 days espectively.The explanation of this interesting phenomena is still under investigation.展开更多
A comparative study between the output of the Flexible Global Climate Model Version 1.0 （FGCM- 1.0） and the observations is performed. At 500 hPa, the geopotential height of FGCM is similar to the observations, but ...A comparative study between the output of the Flexible Global Climate Model Version 1.0 （FGCM- 1.0） and the observations is performed. At 500 hPa, the geopotential height of FGCM is similar to the observations, but in the North Pacific the model gives lower values, and the differences are most significant over the northern boundary of the Pacific. In a net heat flux comparison, the spatial patterns of the two are similar in winter, but more heat loss appears to the east of Japan in FGCM than in COADS. On the interannual timescale, strong （weak） Kuroshio transports to the east of Taiwan lead the increasing （decreasing） net heat flux, which is centered over the Kuroshio Extension region, by 1-2 months, with low （high） pressure anomaly responses appearing at 500 hPa over the North Pacific （north of 25°N） in winter. The northward heat transport of the Kuroshio is one of the important heat sources to support the warming of the atmosphere by the ocean and the formation of the low pressure anomaly at 500 hPa over the North Pacific in winter.展开更多
The East Asian summer monsoon (EASM) underwent an interdecadal variation with interannual variations during the period from 1958 to 1997, its index tended to decline from a higher stage in the mid-1960,s until it rea...The East Asian summer monsoon (EASM) underwent an interdecadal variation with interannual variations during the period from 1958 to 1997, its index tended to decline from a higher stage in the mid-1960,s until it reached a lower stage after 1980/s. Correlation analysis reveals that EASM is closely related with the global atmospheric circulation and sea surface temperature (SST). The differences between the weak and strong stage of EASM shows that, the summer monsoon circulation over East Asia and North Africa is sharply weakened, in the meantime, the westerlies in high latitudes and the trade-wind over the tropical ocean are also changed significantly. Over the most regions south of the northern subtropics, both air temperature in the lower troposphere and SST tended to rise compared with the strong stage of EASM. It is also revealed that the ocean-atmosphere interaction over the western Pacific and Indian Ocean plays a key role in interannual to interdecadal variation of EASM, most probably, the subtropical indian Ocean is more important. On the other hand, the ENSO event is less related to EASM at least during the concerned period.展开更多
An analysis of time variations of the earth’s length of day (LOD) versus atmospheric geopotential height fields and lunar phase is presented. A strong correlation is found between LOD and geopotential height from whi...An analysis of time variations of the earth’s length of day (LOD) versus atmospheric geopotential height fields and lunar phase is presented. A strong correlation is found between LOD and geopotential height from which a close relationship is inferred and found between atmospheric circulation and the lunar cycle around the earth. It is found that there is a 27.3-day and 13.6-day east-west oscillation in the atmospheric circulation following the lunar phase change. The lunar revolution around the earth strongly influences the atmospheric circulation. During each lunar cycle around the earth there is, on average, an alternating change of 6.8-day-decrease, 6.8-day-increase, 6.8-day-decrease and 6.8-day-increase in atmospheric zonal wind, atmospheric angular momentum and LOD. The dominant factor producing such an oscillation in atmospheric circulation is the periodic change of lunar declination during the lunar revolution around the earth. The 27.3- day and 13.6-day atmospheric oscillatory phenomenon is akin展开更多
The direct radiative forcing （DRF） of sulfate aerosols depends highly on the atmospheric sulfate loading and the meteorology, both of which undergo strong regional and seasonal variations. Because the optical proper...The direct radiative forcing （DRF） of sulfate aerosols depends highly on the atmospheric sulfate loading and the meteorology, both of which undergo strong regional and seasonal variations. Because the optical properties of sulfate aerosols are also sensitive to atmospheric relative humidity, in this study we first examine the scheme for optical properties that considers hydroscopic growth. Next, we investigate the seasonal and regional distributions of sulfate DRF using the sulfate loading simulated from NCAR CAM-Chem together with the meteorology modeled from a spectral atmospheric general circulation model （AGCM） developed by LASG-IAP. The global annual-mean sulfate loading of 3.44 mg m-2 is calculated to yield the DRF of -1.03 and -0.57 W m-2 for clear-sky and all-sky conditions, respectively. However, much larger values occur on regional bases. For example, the maximum all-sky sulfate DRF over Europe, East Asia, and North America can be up to -4.0 W m-2. The strongest all-sky sulfate DRF occurs in the Northern Hemispheric July, with a hemispheric average of -1.26 W m-2. The study results also indicate that the regional DRF are strongly affected by cloud and relative humidity, which vary considerably among the regions during different seasons. This certainly raises the issue that the biases in model-sinmlated regional meteorology can introduce biases into the sulfate DRF. Hence, the model processes associated with atmospheric humidity and cloud physics should be modified in great depth to improve the simulations of the LASG-IAP AGCM and to reduce the uncertainty of sulfate direct effects on global and regional climate in these simulations.展开更多
This study investigates the seasonal evolution of the dominant modes of the Eurasian snowpack and atmospheric circulation from autumn to the subsequent spring using snow water equivalent （SWE）, snow cover frequency ...This study investigates the seasonal evolution of the dominant modes of the Eurasian snowpack and atmospheric circulation from autumn to the subsequent spring using snow water equivalent （SWE）, snow cover frequency （SCF）, and 500 hPa geopotential height data. It is found that the Eurasian SWE/SCF and circulation dominant modes are stably coupled from autumn to the subsequent spring.The temporal coherence of the seasonal evolution of the dominant modes is examined.The seasonal evolution of the Eurasian circulation and SWE dominant modes exhibit good coherence, whereas the evolution of the Eurasian SCF dominant mode is incoherent during the autumn-winter transition season. This incoherence is associated with a sign-change in the SCF anomalies in Europe during the autumn-winter transition season, which is related to the wind anomalies over Europe. In addition, the surface heat budget associated with the Eurasian SWE/SCF and circulation dominant modes is analyzed. The sensible heat flux （SHF） related to the wind-induced thermal advection dominates the surface heat budget from autumn to the subsequent spring, with the largest effect during winter. The surface net shortwave radiation is mainly modulated by snow cover rather than cloud cover, which is estimated to be as important as, or likely superior to, the SHF for the surface heat budget during spring.The NCEP-NCAR surface heat flux reanalysis data demonstrate a consistency with the SWE/SCF and air temperature observational data, indicating a good capability for snow-atmosphere interaction analysis.展开更多
In this study, regional persistent haze events（RPHEs） in the Beijing–Tianjin–Hebei（BTH） region were identified based on the Objective Identification Technique for Regional Extreme Events for the period 1980–201...In this study, regional persistent haze events（RPHEs） in the Beijing–Tianjin–Hebei（BTH） region were identified based on the Objective Identification Technique for Regional Extreme Events for the period 1980–2013. The formation mechanisms of the severe RPHEs were investigated with focus on the atmospheric circulation and dynamic mechanisms. Results indicated that：（1） 49 RPHEs occurred during the past 34 years.（2） The severe RPHEs could be categorized into two types according to the large-scale circulation, i.e. the zonal westerly airflow（ZWA） type and the high-pressure ridge（HPR） type. When the ZWA-type RPHEs occurred, the BTH region was controlled by near zonal westerly airflow in the mid–upper troposphere.Southwesterly winds prevailed in the lower troposphere, and near-surface wind speeds were only 1–2 ms^-1. Warm and humid air originating from the northwestern Pacific was transported into the region, where the relative humidity was 70% to 80%, creating favorable moisture conditions. When the HPR-type RPHEs appeared, northwesterly airflow in the mid–upper troposphere controlled the region. Westerly winds prevailed in the lower troposphere and the moisture conditions were relatively weak.（3） Descending motion in the mid-lower troposphere caused by the above two circulation types provided a crucial dynamic mechanism for the formation of the two types of RPHEs. The descending motion contributed to a reduction in the height of the planetary boundary layer（PBL）, which generated an inversion in the lower troposphere. This inversion trapped the abundant pollution and moisture in the lower PBL, leading to high concentrations of pollutants.展开更多
Possible influences of the Barents Sea ice anomalies on the Eurasian atmospheric circulation and the East China precipitation distribution in the late spring and early summer (May-June) are investigated by analyzing t...Possible influences of the Barents Sea ice anomalies on the Eurasian atmospheric circulation and the East China precipitation distribution in the late spring and early summer (May-June) are investigated by analyzing the observational data and the output of an atmospheric general circulation model (AGCM). The study indicates that the sea ice condition of the Barents Sea from May to July may be interrelated with the atmospheric circulation of June. When there is more than average sea ice in the Barents Sea, the local geopotential height of the 500-hPa level will decrease, and the same height in the Lake Baikal and Okhotsk regions will increase and decrease respectively to form a wave-chain structure over North Eurasia. This kind of anomalous height pattern is beneficial to more precipitation in the south part of East China and less in the north.展开更多
An extraordinary and unprecedented heatwave swept across western North America(i.e.,the Pacific Northwest)in late June of 2021,resulting in hundreds of deaths,a massive die-off of sea creatures off the coast,and horri...An extraordinary and unprecedented heatwave swept across western North America(i.e.,the Pacific Northwest)in late June of 2021,resulting in hundreds of deaths,a massive die-off of sea creatures off the coast,and horrific wildfires.Here,we use observational data to find the atmospheric circulation variabilities of the North Pacific and Arctic-Pacific-Canada patterns that co-occurred with the development and mature phases of the heatwave,as well as the North America pattern,which coincided with the decaying and eastward movement of the heatwave.Climate models from the Coupled Model Intercomparison Project(Phase 6)are not designed to simulate a particular heatwave event like this one.Still,models show that greenhouse gases are the main reason for the long-term increase of average daily maximum temperature in western North America in the past and future.展开更多
Using the summer (June to August) monthly mean data of the National Centers for Environmental Predictions (NCEP) - National Center for Atmospheric Research (NCAR) reanalysis from 1980 to 1997, atmospheric heat sources...Using the summer (June to August) monthly mean data of the National Centers for Environmental Predictions (NCEP) - National Center for Atmospheric Research (NCAR) reanalysis from 1980 to 1997, atmospheric heat sources and moisture sinks are calculated. Anomalous circulation and the vertically integrated heat source with the vertical integrated moisture sink and outgoing longwave radiation (OLR) flux are examined based upon monthly composites for 16 great wet-spells and 8 great dry-spells over the middle-lower reaches of the Yangtze River. The wind anomaly exhibits prominent differences between the great wet-spell and the great dry-spell over the Yangtze River Valley. For the great wet-spell, the anomalous southerly from the Bay of Bengal and the South China Sea and the anomalous northerly over North China enhanced low-level convergence toward a narrow latitudinal belt area (the middle-lower reaches of the Yangtze River). The southerly anomaly is connected with an anticyclonic anomalous circulation system centered at 22 degreesN, 140 degreesE and the northerly anomaly is associated with a cyclonic anomalous circulation system centered at the Japan Sea. In the upper level, the anomalous northwesterly between an anticyclonic anomalous system with the center at 23 degreesN, 105 degreesE and a cyclonic anomalous system with the center at Korea diverged over the middle-lower reaches of the Yangtze River. On the contrary, for the great dry-spell, the anomalous northerly over South China and the anomalous southerly over North China diverged from the Yangtze River Valley in the low level. The former formed in the western part of a cyclonic anomalous system centered at 23 degreesN, 135 degreesE. The latter was located in the western ridge of an anticyclonic anomalous system in the northwestern Pacific. The upper troposphere showed easterly anomaly that converged over the middle-lower reaches of the Yangtze River. A cyclonic anomalous system in South China and an anticyclonic system centered in the Japan Sea enhanced the easterly. Large atmospheric heat source anomalies of opposite signs existed over the western Pacific - the South China Sea, with negative in the great wet-spell and positive in the great dry-spell. The analysis of heat source also revealed positive anomalous heat sources during the great wet-spell and negative anomalous heat sources during the great dry-spell over the Yangtze River valley. The changes of the moisture sink and OLR were correspondingly altered, implying the change of heat source anomaly is due to the latent heat releasing of convective activity. Over the southeastern Tibetan Plateau- the Bay of Bengal, the analysis of heat source shows positive anomalous heat sources during the great wet-spell and negative anomalous heat sources during the great dry-spell because of latent heating change. The change of divergent wind coexisted with the change of heat source. In the great wet-spell, southerly divergent wind anomaly in the low level and northerly divergent wind anomaly in high-level are seen over South China. These divergent wind anomalies are helpful to the low-level convergence anomaly and high-level divergence anomaly over the Yangtze River valley. The low-level northerly divergent wind anomaly and high-level southerly divergent wind anomaly over South China reduced the low-level convergence and high-level divergence over the Yangtze River valley during the great dry-spell.展开更多
The interannual variability of wintertime snow depth over the Tibetan Plateau(TP) and related atmospheric circulation anomalies were investigated based on observed snow depth measurements and NCEP/NCAR reanalysis data...The interannual variability of wintertime snow depth over the Tibetan Plateau(TP) and related atmospheric circulation anomalies were investigated based on observed snow depth measurements and NCEP/NCAR reanalysis data.Empirical orthogonal function(EOF) analysis was applied to identify the spatio-temporal variability of wintertime TP snow depth.Snow depth anomalies were dominated by a monopole pattern over the TP and a dipole structure with opposite anomalies over the southeastern and northwestern TP.The atmospheric circulation conditions responsible for the interannual variability of TP snow depth were examined via regression analyses against the principal component of the most dominant EOF mode.In the upper troposphere,negative zonal wind anomalies over the TP with extensively positive anomalies to the south indicated that the southwestward shift of the westerly jet may favor the development of surface cyclones over the TP.An anomalous cyclone centered over the southeastern TP was associated with the anomalous westerly jet,which is conducive to heavier snowfall and results in positive snow depth anomalies.An anomalous cyclone was observed at 500 hPa over the TP,with an anomalous anticyclone immediately to the north,suggesting that the TP is frequently affected by surface cyclones.Regression analyses revealed that significant negative thickness anomalies exist around the TP from March to May,with a meridional dipole anomaly in March.The persistent negative anomalies due to more winter TP snow are not conducive to earlier reversal of the meridional temperature gradient,leading to a possible delay in the onset of the Asian summer monsoon.展开更多
Evaluation of the mean climate and climate variability in the Southern Hemisphere （SH） in the Twentieth Century Reanalysis data version 2 （20CRv2） is conducted and the results are compared with the NCEP/NCAR versi...Evaluation of the mean climate and climate variability in the Southern Hemisphere （SH） in the Twentieth Century Reanalysis data version 2 （20CRv2） is conducted and the results are compared with the NCEP/NCAR version 2 Reanalysis data （NCEPv2） and the Hadley Center sea-level pressure data （HadSLPv2）.The results show that SH polar High,SH subtropical High,upper level split jet,cross-equatorial flow,Antarctic Oscillation （AAO）,and the pattem of Pacific-South-America （PSA） has been effectively captured by 20CRv2 during 1979-2010,with an apparent zonal asymmetry of AAO in the austral winter （June-July-August,JJA）.The notable upward linear trend of AAO in the entire period of 1871-2010 is represented in both 20CRv2 and HadS1Pv2.The most remarkable discrepancy of the SH climate variability between 20CRv2 and HadSLPv2 occurred in 1897-1920 and was partly caused by such factors as the paucity of meteorological and oceanographic data in the SH to be assimilated,the handling of the specified sea-ice concentration in South Pole,and imperfect climate models.The consistency of these reanalysis data is increased with the use of a large amount of satellite observation and radiosonde data,particularly after 1979.展开更多
This study analyzes the variability of northern Eurasian snow cover(SC)in autumn and the impacts of atmospheric circulation changes.The region of large SC variability displays a southward shift from September to Novem...This study analyzes the variability of northern Eurasian snow cover(SC)in autumn and the impacts of atmospheric circulation changes.The region of large SC variability displays a southward shift from September to November,following the seasonal progression of the transition zones of surface air temperature(SAT).The dominant pattern of SC variability in September and October features a zonal distribution,and that in November displays an obvious west-east contrast.Surface air cooling and snowfall increase are two factors for larger SC.The relative contribution of SAT and snowfall changes to SC,however,varies with the region and depends upon the season.The downward longwave radiation and atmospheric heat advection play important roles in SAT changes.Anomalous convergence of water vapor flux contributes to enhanced snowfall.The changes in downward longwave radiation are associated with those in atmospheric water content and column thickness.Changes in snowfall and the transport of atmospheric moisture determine the atmospheric moisture content in September and October,and the snowfall appears to be a main factor for atmospheric moisture change in November.These results indicate that atmospheric circulation changes play an important role in snow variability over northern Eurasia in autumn.Overall,the coupling between autumn Eurasian snow and atmospheric circulation may not be driven by external forcing.展开更多
The late Ediacaran Shuram-Wonoka excursion, with δ^(13)C_(carb) values as low as-12‰(PDB) in marineshelf deposits and spanning up to 10 Myr, is the deepest and most protracted δ^(13)C_(carb) negative anomaly recogn...The late Ediacaran Shuram-Wonoka excursion, with δ^(13)C_(carb) values as low as-12‰(PDB) in marineshelf deposits and spanning up to 10 Myr, is the deepest and most protracted δ^(13)C_(carb) negative anomaly recognised in Earth history. The excursion formed on at least four continents in low(≤32°) palaeolatitudes, and in China is associated with a major phosphogenic event. Global and intrabasinal correlation, magnetostratigraphy, isotope conglomerate tests and further geochemical data are consistent with a primary or syn-depositional origin for the excursion. Continental-margin phosphorites are generated by oceanic upwelling driven by surface winds, and δ^(13)C_(carb) negative anomalies are explicable by oceanic upwelling of 13 C-depleted deep oceanic waters, arguing that a feature common to these exceptional Ediacaran events was unprecedented perturbation of the world ocean. These events occurred during the transition from an alien Proterozoic world marked by low-palaeolatitude glaciation near sea level and strong seasonality to the familiar Phanerozoic Earth with circum-polar glaciation and temperate climate, suggesting that the Shuram-Wonoka excursion is related to this profound change in Earth's climate system. Of various hypotheses for Proterozoic low-palaeolatitude glaciation, only the high obliquity(>54°) hypothesis, which posits secular decrease in obliquity to near the present-day value(23.5°) during the Ediacaran, predicts an unparalleled revolution in the Ediacaran world ocean. The obliquity controls the sense of the world ocean's meridional overturning circulation, which today is driven by the sinking of cold, dense water at the poles and upwelling driven by zonal surface winds.When the decreasing obliquity passed the critical value of 54° during the Ediacaran the meridional temperature gradient reversed, with the equator becoming warmer than the poles and Hadley lowlatitude(<30°-35°) atmospheric zonal circulation reversing. This reversal of the temperature gradient is unique to the Ediacaran Period and caused reversal of the oceanic meridional overturning circulation,with upwelling of anoxic, 13 C-depleted deep oceanic waters producing a deeply negative and protractedδ^(13)C_(carb) signature on late Ediacaran marine-shelf deposits.展开更多
Experimental outputs of 11 Atmospheric Model Intercomparison Project （AMIP） models from phase 5 of the Coupled Model Intercomparison Project （CMIP5） are analyzed to assess the atmospheric circulation anomaly over ...Experimental outputs of 11 Atmospheric Model Intercomparison Project （AMIP） models from phase 5 of the Coupled Model Intercomparison Project （CMIP5） are analyzed to assess the atmospheric circulation anomaly over Northern Hemisphere induced by the anomalous rainfall over tropical Pacific and Indian Ocean during boreal winter.The analysis shows that the main features of the interannual variation of tropical rainfall anomalies,especially over the Central Pacific （CP） （5°S-5°N,175°E-135°W） and Indo-western Pacific （IWP） （20°S-20°N,110°-150°E） are well captured in all the CMIP5/AMIP models.For the IWP and western Indian Ocean （WIO） （10°S-10°N,45°-75°E）,the anomalous rainfall is weaker in the 11 CMIP5/AMIP models than in the observation.During El Ni（n）o/La Ni（n）a mature phases in boreal winter,consistent with observations,there are geopotential height anomalies known as the Pacific North American （PNA） pattern and Indo-western Pacific and East Asia （IWPEA） pattern in the upper troposphere,and the northwestern Pacific anticyclone （cyclone） （NWPA） in the lower troposphere in the models.Comparison between the models and observations shows that the ability to simulate the PNA and NWPA pattern depends on the ability to simulate the anomalous rainfall over the CP,while the ability to simulate the IWPEA pattern is related to the ability to simulate the rainfall anomaly in the IWP and WIO,as the SST anomaly is same in AMIP experiments.It is found that the tropical rainfall anomaly is important in modeling the impact of the tropical Indo-Pacific Ocean on the extratropical atmospheric circulation anomaly.展开更多
文摘Changes of air temperatures and atmosphere circulation at three high mountainous stations in Bulgaria are investigated for the period of 1941-2008.The three stations are located on peaks Musala,Cherni vrah and Botev,where air temperature data have good quality.Some missing data were recovered using the method of differences. A significant mean annual air temperature rise happened in high mountainous parts of Bulgaria- the warming is in the order of 0.7°C for the entire period.The increase is very prominent particularly in the last 30 years.Main contributors to this overall tendency are summer months-June,July and August.To some degree,January also could be included in this group.November trend shows temperature rise at the beginning of the investigated period.One of the causes for such a tendency is atmosphere circulation in respective months.It also shows signs of considerable reorganization in both winter and summer.There is an increase of the cases of warm atmosphere patterns typical for winter, summer and autumn seasons in Bulgaria.Meridional circulation has essential significance for air temperatures during the cold half of the year.In January and June atmosphere circulation has a substantial influence on the thermal regime of air in high mountains of Bulgaria.In July,August and November this influence is reduced.There are no cycles in air temperatures for the investigated period.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2342210 and 42275043)the National Institute of Natural Hazards,Ministry of Emergency Management of China(Grant Nos.J2223806,ZDJ2024-25 and ZDJ2025-34)。
文摘Climate models are essential for understanding past,present,and future changes in atmospheric circulation,with circulation modes providing key sources of seasonal predictability and prediction uncertainties for both global and regional climates.This study assesses the performance of models participating in phase 6 of the Coupled Model Intercomparison Project in simulating interannual variability modes of Northern Hemisphere 500-hPa geopotential height during winter and summer,distinguishing predictable(potentially predictable on seasonal or longer timescales)and unpredictable(intraseasonal and essentially unpredictable at long range)components,using reanalysis data and a variance decomposition method.Although most models effectively capture unpredictable modes in reanalysis,their ability to reproduce dominant predictable modes-specifically the Pacific-North American pattern,Arctic Oscillation,and Western Pacific Oscillation in winter,and the East Atlantic and North Atlantic Oscillations in summer-varies notably.An optimal ensemble is identified to distinguish(a)predictable-external modes,dominated by external forcing,and(b)predictable-internal modes,associated with slow internal variability,during the historical period(1950-2014)and the SSP5-8.5 scenario(2036-2100).Under increased radiative forcing,the leading winter/summer predictable-external mode exhibits a more uniform spatial distribution,remarkably larger trend and annual variance,and enhanced height-sea surface temperature(SST)covariance under SSP5-8.5 compared to historical conditions.The dominant winter/summer predictable-internal modes also exhibit increased variance and height-SST covariance under SSP5-8.5,along with localized changes in spatial configuration.Minimal changes are observed in spatial distribution or variance for dominant winter/summer unpredictable modes under SSP5-8.5.This study,from a predictive perspective,deepens our understanding of model uncertainties and projected changes in circulations.
基金supported in part by the Meteorological Joint Funds of the National Natural Science Foundation of China(Grant No.U2142211)by the National Key Research and Development Program of China(Grant No.2020YFA0608002)+4 种基金by the National Natural Science Foundation of China(Grant Nos.42075141 and 42341202)by the China National Postdoctoral Program for Innovative Talents(Grant No.BX20230071)by the National Natural Science Foundation of China for Youth(Grant No.42205191)by the Shanghai Municipal Science and Technology Major Project(Grant No.2021SHZDZX0100)the Fundamental Research Funds for the Central Universities。
文摘Subseasonal-to-seasonal(S2S)forecasting for East Asian atmospheric circulation poses significant challenges for conventional numerical weather prediction(NWP)models.Recently,deep learning(DL)models have demonstrated significant potential in further enhancing S2S forecasts beyond the capabilities of NWP models.However,most current DLbased S2S forecasting models largely overlook the role of global predictors from multiple spheres,such as ocean,land,and atmosphere domains,that are crucial for effective S2S forecasting.In this study,we introduce EAAC-S2S,a tailored DL model for S2S forecasting of East Asian atmospheric circulation.EAAC-S2S employs the cross-attention mechanism to couple atmospheric circulations over East Asia with representative multi-sphere(i.e.,atmosphere,land,and ocean)variables,providing pentad-averaged circulation forecasts up to 12 pentads ahead throughout all seasons.Experimental results demonstrate,on the S2S time scale,that EAAC-S2S consistently outperforms the European Centre for MediumRange Weather Forecasts(ECMWF)Ensemble Prediction System by decreasing the root-mean-square error(RMSE)by3.8%and increasing the anomaly correlation coefficient(ACC)by 8.6%,averaged across all 17 predictands.Our system also shows good skill for examples of heatwaves and the South China Sea Subtropical High Intensity Index(SCSSHII).Moreover,quantitative interpretability analysis including multi-sphere attribution and attention visualization are conducted for the first time in a DL S2S model,where the traced predictability aligns well with prior meteorological knowledge.We hope that our results have the potential to advance research in data-driven S2S forecasting.
基金Supported by Special Fund for Agro-scientific Research in the Public Interest(200903051)~~
文摘[Objective] This study aimed to establish models based on atmospheric cir- culation indices for forecasting the area attacked by rice planthopper every year, and to provide guide for preventing and controlling planthopper damage. [Method] The data related to rice planthopper occurrence and atmospheric circulation were collected and analyzed with the method of stepwise regression to establish the prediction models. [Result] The factors significantly related to the area attacked by rice plan-thopper were selected. Two types of prediction models were established. One was for Sogatella furcifera （Horvath）, based on Atlantic-Europe circulation pattern W in October in that year, Pacific polar vortex area index in October in that year, North America subtropical high index in August in that year, Atlantic-Europe circulation pattern W in June in that year, northern boundary of North America subtropical high in February in that year, Atlantic-Europe polar vortex intensity index in October in that year and Asia polar vortex intensity index in November in the last year; the other type of prediction models were for Nilaparvata lugens （Stal）, based on the Eastern Pacific subtropical high intensity index in July in that year, northern hemi- sphere polar vortex area index in October in the last year, Asia polar vortex strength index in November in the last year, north boundary of North America-At- lantic subtropical high in September in that year, north boundary of North Africa-At- lantic-North America subtropical high in January in that year, sunspot in September of the last year and eastern Pacific subtropical high area index in September in that year. [Conclusion] With the stepwise regression, the forecasting equations of the rice planthopper occurrence established based on the atmospheric circulation indices could be used for actual forecast.
文摘The dynamical framework of the nine-level version of the IAP AGCM is presented in this paper. The emphasis of the model's description is put on the following two aspects:(1) A model's standard atmosphere, which is a satisfactory approximation to the observed troposphere and lower stratosphere standard atmosphere, is introduced into the equations of the model to permit a more accurate calculation of the vertical transport terms, especially near the tropopause; (2) The vertical levels of the model are carefully selected to guarantee a smooth dependence of layer thickness upon pressure in order to reduce the truncation error involved in the unequal interval vertical finite-differencing. For testing the model, two kinds of linear baroclinic Rossby-Haurwitz waves, one of which has a dynamically stable vertical structure and the other has a relatively unstable one, are constructed to provide initial conditions for numerical experiments. The two waves have been integrated for more than 300 days and 100 days respectively by using the model and both of them are propagating westward with almost identical phase-speed during the time period of the integrations. No obvious change of the wave patterns is found at the levels in the model's troposphere. The amplitudes of both two waves at the uppermost level, however, exhibit rather significant oscillation with time, of which the periods are exactly 20 days and 25 days espectively.The explanation of this interesting phenomena is still under investigation.
基金The authors would like to thank Prof.Zhengyu Liu,Mr.Wei Liu and Mr.Wu Shu for giving good suggestions and comments.This work was jointly supported by an open project of LASG,the Natural Science Foundation of China(Grant Nos.40333030 and 40231004)the National Key Programme(G2000078502).
文摘A comparative study between the output of the Flexible Global Climate Model Version 1.0 （FGCM- 1.0） and the observations is performed. At 500 hPa, the geopotential height of FGCM is similar to the observations, but in the North Pacific the model gives lower values, and the differences are most significant over the northern boundary of the Pacific. In a net heat flux comparison, the spatial patterns of the two are similar in winter, but more heat loss appears to the east of Japan in FGCM than in COADS. On the interannual timescale, strong （weak） Kuroshio transports to the east of Taiwan lead the increasing （decreasing） net heat flux, which is centered over the Kuroshio Extension region, by 1-2 months, with low （high） pressure anomaly responses appearing at 500 hPa over the North Pacific （north of 25°N） in winter. The northward heat transport of the Kuroshio is one of the important heat sources to support the warming of the atmosphere by the ocean and the formation of the low pressure anomaly at 500 hPa over the North Pacific in winter.
基金the CAS Key Project (KZCXZ-203)the NSFC Project (No. 49735160 and No.40075020)IAP Innovation Fund (No. 8-1307).
文摘The East Asian summer monsoon (EASM) underwent an interdecadal variation with interannual variations during the period from 1958 to 1997, its index tended to decline from a higher stage in the mid-1960,s until it reached a lower stage after 1980/s. Correlation analysis reveals that EASM is closely related with the global atmospheric circulation and sea surface temperature (SST). The differences between the weak and strong stage of EASM shows that, the summer monsoon circulation over East Asia and North Africa is sharply weakened, in the meantime, the westerlies in high latitudes and the trade-wind over the tropical ocean are also changed significantly. Over the most regions south of the northern subtropics, both air temperature in the lower troposphere and SST tended to rise compared with the strong stage of EASM. It is also revealed that the ocean-atmosphere interaction over the western Pacific and Indian Ocean plays a key role in interannual to interdecadal variation of EASM, most probably, the subtropical indian Ocean is more important. On the other hand, the ENSO event is less related to EASM at least during the concerned period.
文摘An analysis of time variations of the earth’s length of day (LOD) versus atmospheric geopotential height fields and lunar phase is presented. A strong correlation is found between LOD and geopotential height from which a close relationship is inferred and found between atmospheric circulation and the lunar cycle around the earth. It is found that there is a 27.3-day and 13.6-day east-west oscillation in the atmospheric circulation following the lunar phase change. The lunar revolution around the earth strongly influences the atmospheric circulation. During each lunar cycle around the earth there is, on average, an alternating change of 6.8-day-decrease, 6.8-day-increase, 6.8-day-decrease and 6.8-day-increase in atmospheric zonal wind, atmospheric angular momentum and LOD. The dominant factor producing such an oscillation in atmospheric circulation is the periodic change of lunar declination during the lunar revolution around the earth. The 27.3- day and 13.6-day atmospheric oscillatory phenomenon is akin
基金supported jointly by the grant from National Basic Research Program of China(Grant No.2012CB955303)and from the Office of Biological and Environmental Sciences,US Department of Energy
文摘The direct radiative forcing （DRF） of sulfate aerosols depends highly on the atmospheric sulfate loading and the meteorology, both of which undergo strong regional and seasonal variations. Because the optical properties of sulfate aerosols are also sensitive to atmospheric relative humidity, in this study we first examine the scheme for optical properties that considers hydroscopic growth. Next, we investigate the seasonal and regional distributions of sulfate DRF using the sulfate loading simulated from NCAR CAM-Chem together with the meteorology modeled from a spectral atmospheric general circulation model （AGCM） developed by LASG-IAP. The global annual-mean sulfate loading of 3.44 mg m-2 is calculated to yield the DRF of -1.03 and -0.57 W m-2 for clear-sky and all-sky conditions, respectively. However, much larger values occur on regional bases. For example, the maximum all-sky sulfate DRF over Europe, East Asia, and North America can be up to -4.0 W m-2. The strongest all-sky sulfate DRF occurs in the Northern Hemispheric July, with a hemispheric average of -1.26 W m-2. The study results also indicate that the regional DRF are strongly affected by cloud and relative humidity, which vary considerably among the regions during different seasons. This certainly raises the issue that the biases in model-sinmlated regional meteorology can introduce biases into the sulfate DRF. Hence, the model processes associated with atmospheric humidity and cloud physics should be modified in great depth to improve the simulations of the LASG-IAP AGCM and to reduce the uncertainty of sulfate direct effects on global and regional climate in these simulations.
基金supported by the National Natural Science Foundation of China[grant numbers 4142100441210007]+1 种基金the Chinese Academy of Sciences(CAS)-Peking University(PKU)Partnership Programthe Atmosphere-Ocean Research Center(AORC)and International Pacific Research Center(IPRC)at University of Hawaii
文摘This study investigates the seasonal evolution of the dominant modes of the Eurasian snowpack and atmospheric circulation from autumn to the subsequent spring using snow water equivalent （SWE）, snow cover frequency （SCF）, and 500 hPa geopotential height data. It is found that the Eurasian SWE/SCF and circulation dominant modes are stably coupled from autumn to the subsequent spring.The temporal coherence of the seasonal evolution of the dominant modes is examined.The seasonal evolution of the Eurasian circulation and SWE dominant modes exhibit good coherence, whereas the evolution of the Eurasian SCF dominant mode is incoherent during the autumn-winter transition season. This incoherence is associated with a sign-change in the SCF anomalies in Europe during the autumn-winter transition season, which is related to the wind anomalies over Europe. In addition, the surface heat budget associated with the Eurasian SWE/SCF and circulation dominant modes is analyzed. The sensible heat flux （SHF） related to the wind-induced thermal advection dominates the surface heat budget from autumn to the subsequent spring, with the largest effect during winter. The surface net shortwave radiation is mainly modulated by snow cover rather than cloud cover, which is estimated to be as important as, or likely superior to, the SHF for the surface heat budget during spring.The NCEP-NCAR surface heat flux reanalysis data demonstrate a consistency with the SWE/SCF and air temperature observational data, indicating a good capability for snow-atmosphere interaction analysis.
基金supported by the National Natural Science Foundation of China(Grants No.51979071,51779073,and 51809073)the Jiangsu Provincial Natural Science Fund for Distinguished Young Scholars(Grant No.BK20180021)the National Ten Thousand Talent Program for Young Top-Notch Talents,and the Six Talent Peaks Project of Jiangsu Province.
基金jointly sponsored by the National Basic Research Program of China(973 Program)(Grant No.2013CB430202)the National Natural Science Foundation of China(Grant No.41401056)+1 种基金the China Meteorological Administration Special Public Welfare Research Fund(Grant No.GYHY201406001)the Research Innovation Program for College Graduates of Jiangsu Province(Grant No.KYLX15 0858)
文摘In this study, regional persistent haze events（RPHEs） in the Beijing–Tianjin–Hebei（BTH） region were identified based on the Objective Identification Technique for Regional Extreme Events for the period 1980–2013. The formation mechanisms of the severe RPHEs were investigated with focus on the atmospheric circulation and dynamic mechanisms. Results indicated that：（1） 49 RPHEs occurred during the past 34 years.（2） The severe RPHEs could be categorized into two types according to the large-scale circulation, i.e. the zonal westerly airflow（ZWA） type and the high-pressure ridge（HPR） type. When the ZWA-type RPHEs occurred, the BTH region was controlled by near zonal westerly airflow in the mid–upper troposphere.Southwesterly winds prevailed in the lower troposphere, and near-surface wind speeds were only 1–2 ms^-1. Warm and humid air originating from the northwestern Pacific was transported into the region, where the relative humidity was 70% to 80%, creating favorable moisture conditions. When the HPR-type RPHEs appeared, northwesterly airflow in the mid–upper troposphere controlled the region. Westerly winds prevailed in the lower troposphere and the moisture conditions were relatively weak.（3） Descending motion in the mid-lower troposphere caused by the above two circulation types provided a crucial dynamic mechanism for the formation of the two types of RPHEs. The descending motion contributed to a reduction in the height of the planetary boundary layer（PBL）, which generated an inversion in the lower troposphere. This inversion trapped the abundant pollution and moisture in the lower PBL, leading to high concentrations of pollutants.
基金This study was supported jointly by the Project ZKCX2-SW-210the"National Key Programme for Developing Basic Sciences of China"(G1998040900)the National Natural Science Foundation of China under Grant No.40135020.
文摘Possible influences of the Barents Sea ice anomalies on the Eurasian atmospheric circulation and the East China precipitation distribution in the late spring and early summer (May-June) are investigated by analyzing the observational data and the output of an atmospheric general circulation model (AGCM). The study indicates that the sea ice condition of the Barents Sea from May to July may be interrelated with the atmospheric circulation of June. When there is more than average sea ice in the Barents Sea, the local geopotential height of the 500-hPa level will decrease, and the same height in the Lake Baikal and Okhotsk regions will increase and decrease respectively to form a wave-chain structure over North Eurasia. This kind of anomalous height pattern is beneficial to more precipitation in the south part of East China and less in the north.
基金supported by the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0306)National Natural Science Foundation of China (Grant Nos. 41731173 and 42192564)+5 种基金National Key R&D Program of China (2019YFA0606701)Strategic Priority Research Program of Chinese Academy of Sciences (XDB42000000 and XDA20060502)Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences (ISEE2021ZD01)Independent Research Project Program of State Key Laboratory of Tropical Oceanography (Grand No. LTOZZ2004)Leading Talents of Guangdong Province Programsupported by the High Performance Computing Division in the South China Sea Institute of Oceanology
文摘An extraordinary and unprecedented heatwave swept across western North America(i.e.,the Pacific Northwest)in late June of 2021,resulting in hundreds of deaths,a massive die-off of sea creatures off the coast,and horrific wildfires.Here,we use observational data to find the atmospheric circulation variabilities of the North Pacific and Arctic-Pacific-Canada patterns that co-occurred with the development and mature phases of the heatwave,as well as the North America pattern,which coincided with the decaying and eastward movement of the heatwave.Climate models from the Coupled Model Intercomparison Project(Phase 6)are not designed to simulate a particular heatwave event like this one.Still,models show that greenhouse gases are the main reason for the long-term increase of average daily maximum temperature in western North America in the past and future.
基金Supported by National Key Programme for Developing Basic Sciences G1998040900 Part 1 and IAPInnovation Foundation 8-1308.
文摘Using the summer (June to August) monthly mean data of the National Centers for Environmental Predictions (NCEP) - National Center for Atmospheric Research (NCAR) reanalysis from 1980 to 1997, atmospheric heat sources and moisture sinks are calculated. Anomalous circulation and the vertically integrated heat source with the vertical integrated moisture sink and outgoing longwave radiation (OLR) flux are examined based upon monthly composites for 16 great wet-spells and 8 great dry-spells over the middle-lower reaches of the Yangtze River. The wind anomaly exhibits prominent differences between the great wet-spell and the great dry-spell over the Yangtze River Valley. For the great wet-spell, the anomalous southerly from the Bay of Bengal and the South China Sea and the anomalous northerly over North China enhanced low-level convergence toward a narrow latitudinal belt area (the middle-lower reaches of the Yangtze River). The southerly anomaly is connected with an anticyclonic anomalous circulation system centered at 22 degreesN, 140 degreesE and the northerly anomaly is associated with a cyclonic anomalous circulation system centered at the Japan Sea. In the upper level, the anomalous northwesterly between an anticyclonic anomalous system with the center at 23 degreesN, 105 degreesE and a cyclonic anomalous system with the center at Korea diverged over the middle-lower reaches of the Yangtze River. On the contrary, for the great dry-spell, the anomalous northerly over South China and the anomalous southerly over North China diverged from the Yangtze River Valley in the low level. The former formed in the western part of a cyclonic anomalous system centered at 23 degreesN, 135 degreesE. The latter was located in the western ridge of an anticyclonic anomalous system in the northwestern Pacific. The upper troposphere showed easterly anomaly that converged over the middle-lower reaches of the Yangtze River. A cyclonic anomalous system in South China and an anticyclonic system centered in the Japan Sea enhanced the easterly. Large atmospheric heat source anomalies of opposite signs existed over the western Pacific - the South China Sea, with negative in the great wet-spell and positive in the great dry-spell. The analysis of heat source also revealed positive anomalous heat sources during the great wet-spell and negative anomalous heat sources during the great dry-spell over the Yangtze River valley. The changes of the moisture sink and OLR were correspondingly altered, implying the change of heat source anomaly is due to the latent heat releasing of convective activity. Over the southeastern Tibetan Plateau- the Bay of Bengal, the analysis of heat source shows positive anomalous heat sources during the great wet-spell and negative anomalous heat sources during the great dry-spell because of latent heating change. The change of divergent wind coexisted with the change of heat source. In the great wet-spell, southerly divergent wind anomaly in the low level and northerly divergent wind anomaly in high-level are seen over South China. These divergent wind anomalies are helpful to the low-level convergence anomaly and high-level divergence anomaly over the Yangtze River valley. The low-level northerly divergent wind anomaly and high-level southerly divergent wind anomaly over South China reduced the low-level convergence and high-level divergence over the Yangtze River valley during the great dry-spell.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW- Q11-04)the National Basic Research Program of China (Grant No. 2010CB950402)the National Natural Science Foundation of China (Grant No. 40975052)
文摘The interannual variability of wintertime snow depth over the Tibetan Plateau(TP) and related atmospheric circulation anomalies were investigated based on observed snow depth measurements and NCEP/NCAR reanalysis data.Empirical orthogonal function(EOF) analysis was applied to identify the spatio-temporal variability of wintertime TP snow depth.Snow depth anomalies were dominated by a monopole pattern over the TP and a dipole structure with opposite anomalies over the southeastern and northwestern TP.The atmospheric circulation conditions responsible for the interannual variability of TP snow depth were examined via regression analyses against the principal component of the most dominant EOF mode.In the upper troposphere,negative zonal wind anomalies over the TP with extensively positive anomalies to the south indicated that the southwestward shift of the westerly jet may favor the development of surface cyclones over the TP.An anomalous cyclone centered over the southeastern TP was associated with the anomalous westerly jet,which is conducive to heavier snowfall and results in positive snow depth anomalies.An anomalous cyclone was observed at 500 hPa over the TP,with an anomalous anticyclone immediately to the north,suggesting that the TP is frequently affected by surface cyclones.Regression analyses revealed that significant negative thickness anomalies exist around the TP from March to May,with a meridional dipole anomaly in March.The persistent negative anomalies due to more winter TP snow are not conducive to earlier reversal of the meridional temperature gradient,leading to a possible delay in the onset of the Asian summer monsoon.
基金supported by the Strategic Technological Program of the Chinese Academy of Sciences(Grant No.XDA05090426)the National Basic Research Program of China(Grant No.2010CB950304)the Key Program of the Chinese Academy of Sciences(Grant KZCX2-YW-QN202)
文摘Evaluation of the mean climate and climate variability in the Southern Hemisphere （SH） in the Twentieth Century Reanalysis data version 2 （20CRv2） is conducted and the results are compared with the NCEP/NCAR version 2 Reanalysis data （NCEPv2） and the Hadley Center sea-level pressure data （HadSLPv2）.The results show that SH polar High,SH subtropical High,upper level split jet,cross-equatorial flow,Antarctic Oscillation （AAO）,and the pattem of Pacific-South-America （PSA） has been effectively captured by 20CRv2 during 1979-2010,with an apparent zonal asymmetry of AAO in the austral winter （June-July-August,JJA）.The notable upward linear trend of AAO in the entire period of 1871-2010 is represented in both 20CRv2 and HadS1Pv2.The most remarkable discrepancy of the SH climate variability between 20CRv2 and HadSLPv2 occurred in 1897-1920 and was partly caused by such factors as the paucity of meteorological and oceanographic data in the SH to be assimilated,the handling of the specified sea-ice concentration in South Pole,and imperfect climate models.The consistency of these reanalysis data is increased with the use of a large amount of satellite observation and radiosonde data,particularly after 1979.
基金supported by the National Key Basic Research Program of China(Grant No.2014CB953902)the National Natural Science Foundation of China(Grant Nos.41530425,41275081 and 41475081)
文摘This study analyzes the variability of northern Eurasian snow cover(SC)in autumn and the impacts of atmospheric circulation changes.The region of large SC variability displays a southward shift from September to November,following the seasonal progression of the transition zones of surface air temperature(SAT).The dominant pattern of SC variability in September and October features a zonal distribution,and that in November displays an obvious west-east contrast.Surface air cooling and snowfall increase are two factors for larger SC.The relative contribution of SAT and snowfall changes to SC,however,varies with the region and depends upon the season.The downward longwave radiation and atmospheric heat advection play important roles in SAT changes.Anomalous convergence of water vapor flux contributes to enhanced snowfall.The changes in downward longwave radiation are associated with those in atmospheric water content and column thickness.Changes in snowfall and the transport of atmospheric moisture determine the atmospheric moisture content in September and October,and the snowfall appears to be a main factor for atmospheric moisture change in November.These results indicate that atmospheric circulation changes play an important role in snow variability over northern Eurasia in autumn.Overall,the coupling between autumn Eurasian snow and atmospheric circulation may not be driven by external forcing.
文摘The late Ediacaran Shuram-Wonoka excursion, with δ^(13)C_(carb) values as low as-12‰(PDB) in marineshelf deposits and spanning up to 10 Myr, is the deepest and most protracted δ^(13)C_(carb) negative anomaly recognised in Earth history. The excursion formed on at least four continents in low(≤32°) palaeolatitudes, and in China is associated with a major phosphogenic event. Global and intrabasinal correlation, magnetostratigraphy, isotope conglomerate tests and further geochemical data are consistent with a primary or syn-depositional origin for the excursion. Continental-margin phosphorites are generated by oceanic upwelling driven by surface winds, and δ^(13)C_(carb) negative anomalies are explicable by oceanic upwelling of 13 C-depleted deep oceanic waters, arguing that a feature common to these exceptional Ediacaran events was unprecedented perturbation of the world ocean. These events occurred during the transition from an alien Proterozoic world marked by low-palaeolatitude glaciation near sea level and strong seasonality to the familiar Phanerozoic Earth with circum-polar glaciation and temperate climate, suggesting that the Shuram-Wonoka excursion is related to this profound change in Earth's climate system. Of various hypotheses for Proterozoic low-palaeolatitude glaciation, only the high obliquity(>54°) hypothesis, which posits secular decrease in obliquity to near the present-day value(23.5°) during the Ediacaran, predicts an unparalleled revolution in the Ediacaran world ocean. The obliquity controls the sense of the world ocean's meridional overturning circulation, which today is driven by the sinking of cold, dense water at the poles and upwelling driven by zonal surface winds.When the decreasing obliquity passed the critical value of 54° during the Ediacaran the meridional temperature gradient reversed, with the equator becoming warmer than the poles and Hadley lowlatitude(<30°-35°) atmospheric zonal circulation reversing. This reversal of the temperature gradient is unique to the Ediacaran Period and caused reversal of the oceanic meridional overturning circulation,with upwelling of anoxic, 13 C-depleted deep oceanic waters producing a deeply negative and protractedδ^(13)C_(carb) signature on late Ediacaran marine-shelf deposits.
基金supported by the Ministry of Science and Technology of China (National Basic Research Program of China Grant No. 2012CB955602)the National Natural Science Foundation of China (Grant Nos. 41176006 and 41221063)
文摘Experimental outputs of 11 Atmospheric Model Intercomparison Project （AMIP） models from phase 5 of the Coupled Model Intercomparison Project （CMIP5） are analyzed to assess the atmospheric circulation anomaly over Northern Hemisphere induced by the anomalous rainfall over tropical Pacific and Indian Ocean during boreal winter.The analysis shows that the main features of the interannual variation of tropical rainfall anomalies,especially over the Central Pacific （CP） （5°S-5°N,175°E-135°W） and Indo-western Pacific （IWP） （20°S-20°N,110°-150°E） are well captured in all the CMIP5/AMIP models.For the IWP and western Indian Ocean （WIO） （10°S-10°N,45°-75°E）,the anomalous rainfall is weaker in the 11 CMIP5/AMIP models than in the observation.During El Ni（n）o/La Ni（n）a mature phases in boreal winter,consistent with observations,there are geopotential height anomalies known as the Pacific North American （PNA） pattern and Indo-western Pacific and East Asia （IWPEA） pattern in the upper troposphere,and the northwestern Pacific anticyclone （cyclone） （NWPA） in the lower troposphere in the models.Comparison between the models and observations shows that the ability to simulate the PNA and NWPA pattern depends on the ability to simulate the anomalous rainfall over the CP,while the ability to simulate the IWPEA pattern is related to the ability to simulate the rainfall anomaly in the IWP and WIO,as the SST anomaly is same in AMIP experiments.It is found that the tropical rainfall anomaly is important in modeling the impact of the tropical Indo-Pacific Ocean on the extratropical atmospheric circulation anomaly.
