From the point of view of atmospheric science and oceanography, the author explores the origin of abnormal climatic phenomena of El Nino and La Nina, the interaction between the two and their influence on climatic ano...From the point of view of atmospheric science and oceanography, the author explores the origin of abnormal climatic phenomena of El Nino and La Nina, the interaction between the two and their influence on climatic anomalies in China in general, and on precipitation in the Yangtze River Valley in particular.展开更多
This investigation aims to study the El-Niño-Southern Oscillation (ENSO) events in these three phases: El Niño, La Niña, and neutral. Warm and cold events relate to the Spring/Summer seasons. This paper...This investigation aims to study the El-Niño-Southern Oscillation (ENSO) events in these three phases: El Niño, La Niña, and neutral. Warm and cold events relate to the Spring/Summer seasons. This paper will search for connections between the ENSO events and climate anomalies worldwide. There is some speculation that those events would be necessary for the climate anomalies observed worldwide. After analyzing the data from the reports to the ENSO, it shows almost periodicity from 1950-2023. We emphasized the occurrence of El Niño two years, when it was most prominent, and the climate anomalies (following NOAA maps), 2015 and 2023. The results indicated that the observed climate anomalies couldn’t be linked to the abnormal events observed. The worldwide temperatures in those years enhanced mostly in 2023. It shows an abnormal behavior compared with all the years scrutinized and analyzed since the records began. Therefore, there must be unknown factors beyond ENSO that rule the worldwide temperatures and the climate anomalies observed.展开更多
Using the 1980-2010 winter GODAS oceanic assimilations, study is conducted of the winter heat content(HC) established in the subsurface layer(5 to 366 m in depth) over the western Pacific warm pool(WP), followed by in...Using the 1980-2010 winter GODAS oceanic assimilations, study is conducted of the winter heat content(HC) established in the subsurface layer(5 to 366 m in depth) over the western Pacific warm pool(WP), followed by investigating the HC spatiotemporal characteristics, persistence and the impacts on the climate anomalies of neighboring regions. Results are as follows: 1) the pattern of integral consistency is uncovered by the leading EOF1(PC1) mode of HC interannual variability, the year-to-year fluctuation of the time coefficients being well indicative of the interannual anomaly of the WP winter subsurface-layer thermal regime. The HC variation is bound up with El Ni觡o-Southern Oscillation, keeping pronounced autocorrelation during the following two seasons and more, with the persistence being more stable in comparison to sea surface temperature anomaly in the equatorial middle eastern Pacific; 2) the winter HC anomalies produce lasting effect on the WP thermal state in the following spring and summer and corresponding changes in the warm water volume lead to the meridional transport and vertical exchange of warm water, which exerts greater impacts upon the sea surface temperature/heat flux over the warm pool per se and neighboring regions, especially in the Philippine Sea during the posterior spring and summer; 3) the increase in the winter HC corresponds to the spring outgoing longwave radiation(OLR) decrease and richer precipitation over the waters east to the Philippine Sea and the resultant convective heating anomalies are responsible for the rise of geopotential isobaric surfaces over tropical and subtropical western North Pacific, thereby producing effect on the western Pacific subtropical high(anomaly). Subsequently, the sea-surface heat flux exchange is intensified in the warm pool, a robust anomalous cyclone shows up at lower levels, air-sea interactions are enhanced and abnormal convective heating occurs, together making the winter HC anomalies even more closely associated with the variation in the summer subtropical high. As a result, the WP winter HC can be used as an effective predictor of the variation in spring/summer western Pacific subtropical high and the strength of summer monsoon over the northwestern Pacific.展开更多
Snow cover on the Tibetan Plateau(TP) has been shown to be essential for the East Asian summer monsoon.In this paper, we demonstrate that tropical cyclone(TC) 04B(1999) in the northern Indian Ocean, which made landfal...Snow cover on the Tibetan Plateau(TP) has been shown to be essential for the East Asian summer monsoon.In this paper, we demonstrate that tropical cyclone(TC) 04B(1999) in the northern Indian Ocean, which made landfall during the autumn of 1999, may have contributed to climate anomalies over East Asia during the following spring and summer by increasing snow cover on the TP. Observations indicate that snow cover on the TP increased markedly after TC 04B(1999) made landfall in October of 1999. Sensitivity experiments, in which the TC was removed from a numerical model simulation of the initial field, verified that TC 04B(1999) affected the distribution as well as increased the amount of snow on the TP. In addition, the short-term numerical modeling of the climate over the region showed that the positive snow cover anomaly induced negative surface temperature, negative sensible heat flux, positive latent heat flux, and positive soil temperature anomalies over the central and southern TP during the following spring and summer. These climate anomalies over the TP were associated with positive(negative) summer precipitation anomalies over the Yangtze River valley(along the southeastern coast of China).展开更多
By employing the singular value decomposition(SVD) analysis, we have investigated in the present paper the covariations between circulation changes in the Northern(NH) and Southern Hemispheres(SH) and their associatio...By employing the singular value decomposition(SVD) analysis, we have investigated in the present paper the covariations between circulation changes in the Northern(NH) and Southern Hemispheres(SH) and their associations with ENSO by using the NCEP/NCAR reanalysis, the reconstructed monthly NOAA SST, and CMAP precipitation along with NOAA Climate Prediction Center(CPC) ENSO indices. A bi-hemispheric covariation mode(hereafter BHCM) is explored, which is well represented by the first mode of the SVD analysis of sea surface pressure anomaly(SLPA-SVD1). This SVD mode can explain 57.36% of the total covariance of SLPA. BHCM varies in time with a long-term trend and periodicities of 3—5 years. The long term trend revealed by SVD1 shows that the SLP increases in the equatorial central and eastern Pacific but decreases in the western Pacific and tropical Indian Ocean, which facilitates easterlies in the lower troposphere to be intensified and El Ni觡o events to occur with lower frequency. The spatial pattern of the BHCM looks roughly symmetric about the equator in the tropics, whereas it is characterized by zonal disturbances in the mid-latitude of NH and is highly associated with AAO in the mid-latitude of SH. On inter-annual time scales, the BHCM is highly correlated with ENSO. The atmosphere in both the NH and SH responds to sea surface temperature anomalies in the equatorial region, while the contemporaneous circulation changes in the NH and SH in turn affect the occurrence of El Ni觡o/La Ni觡a. In boreal winter, significant temperature and precipitation anomalies associated with the BHCM are found worldwide. Specifically, in the positive phase of the BHCM,temperature and precipitation are anomalously low in eastern China and some other regions of East Asia. These results are helpful for us to better understand interactions between circulations in the NH and SH and the dynamical mechanisms behind these interactions.展开更多
There are knowledge gaps in our understanding of vegetation responses to multi-scale climate-related variables in tropical/subtropical mountainous islands in the Asia-Pacific region.Therefore, this study investigated ...There are knowledge gaps in our understanding of vegetation responses to multi-scale climate-related variables in tropical/subtropical mountainous islands in the Asia-Pacific region.Therefore, this study investigated inter-annual vegetation dynamics and regular/irregular climate patterns in Taiwan. We applied principal component analysis(PCA) on 11 years(2001~2011) of highdimensional monthly photosynthetically active vegetation cover(PV) derived from the Moderate Resolution Imaging Spectroradiometer(MODIS) and investigated the relationships between spatiotemporal patterns of the eigenvectors and loadings of each component through time and multi-scale climaterelated variations. Results showed that the first five components contributed to 96.4% of the total variance. The first component(PC1, explaining 94.5%of variance) loadings, as expected, were significantly correlated with the temporal dynamics of the PV(r =0.94), which was mainly governed by regional climate The temporal loadings of PC2 and PC3(0.8% and0.6% of variance, respectively) were significantly correlated with the temporal dynamics of the PV of forests(r = 0.72) and the farmlands(r = 0.80),respectively. The low-order components(PC4 and PC5, 0.3% and 0.2% of variance, respectively) were closely related to the occurrence of drought(r = 0.49)and to irregular ENSO associated climate anomalies(r =-0.54), respectively. Pronounced correlations were also observed between PC5 and the Southern Oscillation Index(SOI) with one to three months of time lags(r =-0.35 ^-0.43, respectively), revealing biophysical memory effects on the time-series pattern of the vegetation through ENSO-related rainfall patterns. Our findings reveal that the sensitivity of the ecosystems in this tropical/subtropical mountainous island may not only be regulated by regional climate and human activities but also be susceptible to largescale climate anomalies which are crucial and comparable to previous large scale analyses. This study demonstrates that PCA can be an effective tool for analyzing seasonal and inter-annual variability of vegetation dynamics across this tropical/subtropical mountainous islandin the Pacific Ocean, which provides an opportunity to forecast the responses and feedbacks of terrestrial environments to future climate scenarios.展开更多
A conventional method to define short-term climate anomalies for atmospheric and oceanic variables,recommended by the World Meteorological Organization(WMO),is the departure from a 30-yr climatological mean in the pre...A conventional method to define short-term climate anomalies for atmospheric and oceanic variables,recommended by the World Meteorological Organization(WMO),is the departure from a 30-yr climatological mean in the preceding three decades.Such a method,however,introduces spurious errors such as sudden jumps and artificial trends.A new method,named a trend correctional method,is introduced to eliminate the errors.To demonstrate the capability of this new method,we examine a set of idealized cases first by superposing a"true"interannual or interdecadal signal onto a linear or a nonlinear trend.Comparing to the conventional method,the trend correctional method is able to retain,to a large extent,the"true"anomaly signals.Next,we examined real-time indices.The anomaly time series derived based on the trend correctional method show a better agreement with the observed anomaly series.The rootmean-square error is greatly improved,comparing to that calculated based on the conventional method.Therefore,the results from both the idealized and real cases demonstrate that the new method has a clear advantage to the conventional method in deriving true climate anomalies,in particular under the ongoing global warming circumstance.展开更多
Quantitative assessment of natural internal variability and externally forced responses of Northern Hemisphere(NH)temperatures is necessary for understanding and attributing climate change signals during past warm and...Quantitative assessment of natural internal variability and externally forced responses of Northern Hemisphere(NH)temperatures is necessary for understanding and attributing climate change signals during past warm and cold periods.However,it remains a challenge to distinguish the robust internally generated variability from the observed variability.Here,largeensemble(70 member)simulations,Energy Balance Model simulation,temperature ensemble reconstruction,and three dominant external forcings(volcanic,solar,and greenhouse gas)were combined to estimate the internal variability of NH summer(June–August)temperatures over the past 2000 years(1–2000 CE).Results indicate that the Medieval Climate Anomaly was predominantly attributed to centennial-scale internal oscillation,accounting for an estimated 104%of the warming anomaly.In contrast,the Current Warm Period is influenced mainly by external forcing,contributing up to 90%of the warming anomaly.Internal temperature variability offsets cooling by volcanic eruptions during the Late Antique Little Ice Age.These findings have important implications for the attribution of past climate variability and improvement of future climate projections.展开更多
The Medieval Climate Anomaly(MCA,AD950-1250)is the most recent warm period lasting for several hundred years and is regarded as a reference scenario when studying the impact of and adaptation to global and regional wa...The Medieval Climate Anomaly(MCA,AD950-1250)is the most recent warm period lasting for several hundred years and is regarded as a reference scenario when studying the impact of and adaptation to global and regional warming.In this study,we investigated the characteristics of temperature variations on decadal-centennial scales during the MCA for four regions(Northeast,Northwest,Central-east,and Tibetan Plateau)in China,based on high-resolution temperature reconstructions and related warm-cold records from historical documents.The ensemble empirical mode decomposition method is used to analyze the time series.The results showed that for China as a whole,the longest warm period during the last 2000 years occurred in the 10th-13th centuries,although there were multi-decadal cold intervals in the middle to late 12th century.However,in the beginning and ending decades,warm peaks and phases on the decadal scale of the MCA for different regions were not consistent with each other.On the inter-decadal scale,regional temperature variations were similar from 950 to 1130;moreover,their amplitudes became smaller,and the phases did not agree well from 1130 to 1250.On the multi-decadal to centennial scale,all four regions began to warm in the early 10th century and experienced two cold intervals during the MCA.However,the Northwest and Central-east China were in step with each other while the warm periods in the Northeast China and Tibetan Plateau ended about 40-50 years earlier.On the multi-centennial scale,the mean temperature difference between the MCA and Little Ice Age was significant in Northeast and Central-east China but not in the Northwest China and Tibetan Plateau.Compared to the mean temperature of the 20th century,a comparable warmth in the MCA was found in the Central-east China,but there was a little cooling in Northeast China;meanwhile,there were significantly lower temperatures in Northwest China and Tibetan Plateau.展开更多
Based on the known climatic shift that occurred in 1976, we divide the present study period into two epochs:epoch-Ⅰ, for 1958–1976; and epoch-Ⅱ, for 1977–2002. Using ERA-40 and the 20th century reanalysis data, we...Based on the known climatic shift that occurred in 1976, we divide the present study period into two epochs:epoch-Ⅰ, for 1958–1976; and epoch-Ⅱ, for 1977–2002. Using ERA-40 and the 20th century reanalysis data, we investigate the interdecadal change in the Eurasia–Pacific anti-phase relation(EPAR) pattern of atmospheric mass(AM) during boreal winter before and after 1976. It is found that anomalous AM over lands is highly and negatively correlated with anomalous AM over oceans in the Northern Hemisphere during the winter season. This correlation does not change much from epoch-Ⅰ to epoch-Ⅱ. However, the correlation pattern of surface air pressure anomalies with variations of anomalous AM over lands changes remarkably from epoch-Ⅰ to epoch-Ⅱ; the EPAR pattern emerges evidently in the later period, whereas it is not significant in epoch-Ⅰ. The occurrence of the EPAR pattern in epoch-Ⅱ may be attributable to the Pacific Decadal Oscillation(PDO). The PDO may modulate the EPAR pattern in two ways. Firstly, the interdecadal component of the PDO as a background may modulate the intensities of the Aleutian low, East Asian trough, and westerly flow, acting as a waveguide during the warm phase(epoch-Ⅱ) of the PDO.Secondly, the interannual variations of sea surface temperature anomalies in the North Pacific, in association with the PDO, may affect the interannual variations of AM, which facilitates the existence of the EPAR pattern in epoch-Ⅱ only. With the teleconnection pattern having changed before and after 1976, winter climate anomalies, including rainfall and temperature, are found to be different in many regions in the Northern Hemisphere between epoch-Ⅰ and epoch-Ⅱ. All the results of the present work are meaningful for a better understanding of climate anomalies during boreal winter.展开更多
文摘From the point of view of atmospheric science and oceanography, the author explores the origin of abnormal climatic phenomena of El Nino and La Nina, the interaction between the two and their influence on climatic anomalies in China in general, and on precipitation in the Yangtze River Valley in particular.
文摘This investigation aims to study the El-Niño-Southern Oscillation (ENSO) events in these three phases: El Niño, La Niña, and neutral. Warm and cold events relate to the Spring/Summer seasons. This paper will search for connections between the ENSO events and climate anomalies worldwide. There is some speculation that those events would be necessary for the climate anomalies observed worldwide. After analyzing the data from the reports to the ENSO, it shows almost periodicity from 1950-2023. We emphasized the occurrence of El Niño two years, when it was most prominent, and the climate anomalies (following NOAA maps), 2015 and 2023. The results indicated that the observed climate anomalies couldn’t be linked to the abnormal events observed. The worldwide temperatures in those years enhanced mostly in 2023. It shows an abnormal behavior compared with all the years scrutinized and analyzed since the records began. Therefore, there must be unknown factors beyond ENSO that rule the worldwide temperatures and the climate anomalies observed.
基金National Key Basic Research/Development Project(2012CB417403)Public Sector(Meteorology)Special Research Foundation(GYHY201306022,GYHY201406024)+1 种基金Foundation of National Natural Sciences(41205065)Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutions
文摘Using the 1980-2010 winter GODAS oceanic assimilations, study is conducted of the winter heat content(HC) established in the subsurface layer(5 to 366 m in depth) over the western Pacific warm pool(WP), followed by investigating the HC spatiotemporal characteristics, persistence and the impacts on the climate anomalies of neighboring regions. Results are as follows: 1) the pattern of integral consistency is uncovered by the leading EOF1(PC1) mode of HC interannual variability, the year-to-year fluctuation of the time coefficients being well indicative of the interannual anomaly of the WP winter subsurface-layer thermal regime. The HC variation is bound up with El Ni觡o-Southern Oscillation, keeping pronounced autocorrelation during the following two seasons and more, with the persistence being more stable in comparison to sea surface temperature anomaly in the equatorial middle eastern Pacific; 2) the winter HC anomalies produce lasting effect on the WP thermal state in the following spring and summer and corresponding changes in the warm water volume lead to the meridional transport and vertical exchange of warm water, which exerts greater impacts upon the sea surface temperature/heat flux over the warm pool per se and neighboring regions, especially in the Philippine Sea during the posterior spring and summer; 3) the increase in the winter HC corresponds to the spring outgoing longwave radiation(OLR) decrease and richer precipitation over the waters east to the Philippine Sea and the resultant convective heating anomalies are responsible for the rise of geopotential isobaric surfaces over tropical and subtropical western North Pacific, thereby producing effect on the western Pacific subtropical high(anomaly). Subsequently, the sea-surface heat flux exchange is intensified in the warm pool, a robust anomalous cyclone shows up at lower levels, air-sea interactions are enhanced and abnormal convective heating occurs, together making the winter HC anomalies even more closely associated with the variation in the summer subtropical high. As a result, the WP winter HC can be used as an effective predictor of the variation in spring/summer western Pacific subtropical high and the strength of summer monsoon over the northwestern Pacific.
基金National Natural Science Foundation of China(4127504841461164006+1 种基金9081502891215302)
文摘Snow cover on the Tibetan Plateau(TP) has been shown to be essential for the East Asian summer monsoon.In this paper, we demonstrate that tropical cyclone(TC) 04B(1999) in the northern Indian Ocean, which made landfall during the autumn of 1999, may have contributed to climate anomalies over East Asia during the following spring and summer by increasing snow cover on the TP. Observations indicate that snow cover on the TP increased markedly after TC 04B(1999) made landfall in October of 1999. Sensitivity experiments, in which the TC was removed from a numerical model simulation of the initial field, verified that TC 04B(1999) affected the distribution as well as increased the amount of snow on the TP. In addition, the short-term numerical modeling of the climate over the region showed that the positive snow cover anomaly induced negative surface temperature, negative sensible heat flux, positive latent heat flux, and positive soil temperature anomalies over the central and southern TP during the following spring and summer. These climate anomalies over the TP were associated with positive(negative) summer precipitation anomalies over the Yangtze River valley(along the southeastern coast of China).
基金National Natural Science Foundation of China(4133042541175062)
文摘By employing the singular value decomposition(SVD) analysis, we have investigated in the present paper the covariations between circulation changes in the Northern(NH) and Southern Hemispheres(SH) and their associations with ENSO by using the NCEP/NCAR reanalysis, the reconstructed monthly NOAA SST, and CMAP precipitation along with NOAA Climate Prediction Center(CPC) ENSO indices. A bi-hemispheric covariation mode(hereafter BHCM) is explored, which is well represented by the first mode of the SVD analysis of sea surface pressure anomaly(SLPA-SVD1). This SVD mode can explain 57.36% of the total covariance of SLPA. BHCM varies in time with a long-term trend and periodicities of 3—5 years. The long term trend revealed by SVD1 shows that the SLP increases in the equatorial central and eastern Pacific but decreases in the western Pacific and tropical Indian Ocean, which facilitates easterlies in the lower troposphere to be intensified and El Ni觡o events to occur with lower frequency. The spatial pattern of the BHCM looks roughly symmetric about the equator in the tropics, whereas it is characterized by zonal disturbances in the mid-latitude of NH and is highly associated with AAO in the mid-latitude of SH. On inter-annual time scales, the BHCM is highly correlated with ENSO. The atmosphere in both the NH and SH responds to sea surface temperature anomalies in the equatorial region, while the contemporaneous circulation changes in the NH and SH in turn affect the occurrence of El Ni觡o/La Ni觡a. In boreal winter, significant temperature and precipitation anomalies associated with the BHCM are found worldwide. Specifically, in the positive phase of the BHCM,temperature and precipitation are anomalously low in eastern China and some other regions of East Asia. These results are helpful for us to better understand interactions between circulations in the NH and SH and the dynamical mechanisms behind these interactions.
基金sponsored by the grants of the National Science Council of Taiwan(NSC 98-2221E-002-198-,NSC 98-2313-B-002-062-MY2,NSC 100-2621-B-002-001-MY3)National Taiwan University(EcoNTU:NTU-CESRP-102R7604-2)
文摘There are knowledge gaps in our understanding of vegetation responses to multi-scale climate-related variables in tropical/subtropical mountainous islands in the Asia-Pacific region.Therefore, this study investigated inter-annual vegetation dynamics and regular/irregular climate patterns in Taiwan. We applied principal component analysis(PCA) on 11 years(2001~2011) of highdimensional monthly photosynthetically active vegetation cover(PV) derived from the Moderate Resolution Imaging Spectroradiometer(MODIS) and investigated the relationships between spatiotemporal patterns of the eigenvectors and loadings of each component through time and multi-scale climaterelated variations. Results showed that the first five components contributed to 96.4% of the total variance. The first component(PC1, explaining 94.5%of variance) loadings, as expected, were significantly correlated with the temporal dynamics of the PV(r =0.94), which was mainly governed by regional climate The temporal loadings of PC2 and PC3(0.8% and0.6% of variance, respectively) were significantly correlated with the temporal dynamics of the PV of forests(r = 0.72) and the farmlands(r = 0.80),respectively. The low-order components(PC4 and PC5, 0.3% and 0.2% of variance, respectively) were closely related to the occurrence of drought(r = 0.49)and to irregular ENSO associated climate anomalies(r =-0.54), respectively. Pronounced correlations were also observed between PC5 and the Southern Oscillation Index(SOI) with one to three months of time lags(r =-0.35 ^-0.43, respectively), revealing biophysical memory effects on the time-series pattern of the vegetation through ENSO-related rainfall patterns. Our findings reveal that the sensitivity of the ecosystems in this tropical/subtropical mountainous island may not only be regulated by regional climate and human activities but also be susceptible to largescale climate anomalies which are crucial and comparable to previous large scale analyses. This study demonstrates that PCA can be an effective tool for analyzing seasonal and inter-annual variability of vegetation dynamics across this tropical/subtropical mountainous islandin the Pacific Ocean, which provides an opportunity to forecast the responses and feedbacks of terrestrial environments to future climate scenarios.
基金Supported by the National Natural Science Foundation of China(42088101)NOAA of US(NA18OAR4310298)National Science Foundation of US(AGS-2006553)。
文摘A conventional method to define short-term climate anomalies for atmospheric and oceanic variables,recommended by the World Meteorological Organization(WMO),is the departure from a 30-yr climatological mean in the preceding three decades.Such a method,however,introduces spurious errors such as sudden jumps and artificial trends.A new method,named a trend correctional method,is introduced to eliminate the errors.To demonstrate the capability of this new method,we examine a set of idealized cases first by superposing a"true"interannual or interdecadal signal onto a linear or a nonlinear trend.Comparing to the conventional method,the trend correctional method is able to retain,to a large extent,the"true"anomaly signals.Next,we examined real-time indices.The anomaly time series derived based on the trend correctional method show a better agreement with the observed anomaly series.The rootmean-square error is greatly improved,comparing to that calculated based on the conventional method.Therefore,the results from both the idealized and real cases demonstrate that the new method has a clear advantage to the conventional method in deriving true climate anomalies,in particular under the ongoing global warming circumstance.
基金This work was jointly funded by the National Natural Science Foundation of China(Grant Nos.41888101 and 42077406)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB26020000)+1 种基金the Key Research Program of the Institute of Geology&Geophysics,CAS(No.IGGCAS-201905)Feng Shi is funded by the Youth Innovation Promotion Association CAS.
文摘Quantitative assessment of natural internal variability and externally forced responses of Northern Hemisphere(NH)temperatures is necessary for understanding and attributing climate change signals during past warm and cold periods.However,it remains a challenge to distinguish the robust internally generated variability from the observed variability.Here,largeensemble(70 member)simulations,Energy Balance Model simulation,temperature ensemble reconstruction,and three dominant external forcings(volcanic,solar,and greenhouse gas)were combined to estimate the internal variability of NH summer(June–August)temperatures over the past 2000 years(1–2000 CE).Results indicate that the Medieval Climate Anomaly was predominantly attributed to centennial-scale internal oscillation,accounting for an estimated 104%of the warming anomaly.In contrast,the Current Warm Period is influenced mainly by external forcing,contributing up to 90%of the warming anomaly.Internal temperature variability offsets cooling by volcanic eruptions during the Late Antique Little Ice Age.These findings have important implications for the attribution of past climate variability and improvement of future climate projections.
基金National Key R&D Program of China,No.2017YFA0603300National Natural Science Foundation of China,No.41671036,No.41831174The Strategic Priority Research Program of the Chinese Academy of Sciences,No.XDA 19040101。
文摘The Medieval Climate Anomaly(MCA,AD950-1250)is the most recent warm period lasting for several hundred years and is regarded as a reference scenario when studying the impact of and adaptation to global and regional warming.In this study,we investigated the characteristics of temperature variations on decadal-centennial scales during the MCA for four regions(Northeast,Northwest,Central-east,and Tibetan Plateau)in China,based on high-resolution temperature reconstructions and related warm-cold records from historical documents.The ensemble empirical mode decomposition method is used to analyze the time series.The results showed that for China as a whole,the longest warm period during the last 2000 years occurred in the 10th-13th centuries,although there were multi-decadal cold intervals in the middle to late 12th century.However,in the beginning and ending decades,warm peaks and phases on the decadal scale of the MCA for different regions were not consistent with each other.On the inter-decadal scale,regional temperature variations were similar from 950 to 1130;moreover,their amplitudes became smaller,and the phases did not agree well from 1130 to 1250.On the multi-decadal to centennial scale,all four regions began to warm in the early 10th century and experienced two cold intervals during the MCA.However,the Northwest and Central-east China were in step with each other while the warm periods in the Northeast China and Tibetan Plateau ended about 40-50 years earlier.On the multi-centennial scale,the mean temperature difference between the MCA and Little Ice Age was significant in Northeast and Central-east China but not in the Northwest China and Tibetan Plateau.Compared to the mean temperature of the 20th century,a comparable warmth in the MCA was found in the Central-east China,but there was a little cooling in Northeast China;meanwhile,there were significantly lower temperatures in Northwest China and Tibetan Plateau.
基金Supported by the National Natural Science Foundation of China(41175062)National Basic Research and Development(973)Program of China(2012CB417202)+1 种基金Priority Academic Program Development Project of Jiangsu Provincethe Creative Program of Science&Technology of Jiangsu(KYZZ_0239)
文摘Based on the known climatic shift that occurred in 1976, we divide the present study period into two epochs:epoch-Ⅰ, for 1958–1976; and epoch-Ⅱ, for 1977–2002. Using ERA-40 and the 20th century reanalysis data, we investigate the interdecadal change in the Eurasia–Pacific anti-phase relation(EPAR) pattern of atmospheric mass(AM) during boreal winter before and after 1976. It is found that anomalous AM over lands is highly and negatively correlated with anomalous AM over oceans in the Northern Hemisphere during the winter season. This correlation does not change much from epoch-Ⅰ to epoch-Ⅱ. However, the correlation pattern of surface air pressure anomalies with variations of anomalous AM over lands changes remarkably from epoch-Ⅰ to epoch-Ⅱ; the EPAR pattern emerges evidently in the later period, whereas it is not significant in epoch-Ⅰ. The occurrence of the EPAR pattern in epoch-Ⅱ may be attributable to the Pacific Decadal Oscillation(PDO). The PDO may modulate the EPAR pattern in two ways. Firstly, the interdecadal component of the PDO as a background may modulate the intensities of the Aleutian low, East Asian trough, and westerly flow, acting as a waveguide during the warm phase(epoch-Ⅱ) of the PDO.Secondly, the interannual variations of sea surface temperature anomalies in the North Pacific, in association with the PDO, may affect the interannual variations of AM, which facilitates the existence of the EPAR pattern in epoch-Ⅱ only. With the teleconnection pattern having changed before and after 1976, winter climate anomalies, including rainfall and temperature, are found to be different in many regions in the Northern Hemisphere between epoch-Ⅰ and epoch-Ⅱ. All the results of the present work are meaningful for a better understanding of climate anomalies during boreal winter.
