In this study, records from a 3-yr intensified observational experiment at eight stations along the hillside of Seqilashan over the southeastern Tibetan Plateau were analyzed and combined with records at 28 routine ob...In this study, records from a 3-yr intensified observational experiment at eight stations along the hillside of Seqilashan over the southeastern Tibetan Plateau were analyzed and combined with records at 28 routine observation stations in the Chinese National Meteorological Station Network to investigate the influences of station location on the different diurnal rainfall variations between station records and Tropical Rainfall Measuring Mission (TRMM) data products. The results indicate that the diurnal variation of warm season rainfall is closely related to location of stations. The prevailing nocturnal rainfall peak in observations at routine stations can be largely attributed to the relatively lower location of the stations, which are mostly situated in valleys. The records at Seqilashan stations on hillsides revealed an evident diurnal afternoon peak of warm season rainfall, similar to that indicated by TRMM data. The different diurnal phases between valley and hillside stations are closely related to the orographically induced regional circulations caused by the complex topography over the Tibetan Plateau. The results of this study indicate that the prevailing nocturnal rainfall associated with the relatively lower location of routine observation stations can partially explain the diurnal rainfall variations between observation station records and TRMM data.展开更多
Due to uncertainties in initial conditions and parameters, the stability and uncertainty of grassland ecosystem simulations using ecosystem models are issues of concern. Our objective is to determine the types and pat...Due to uncertainties in initial conditions and parameters, the stability and uncertainty of grassland ecosystem simulations using ecosystem models are issues of concern. Our objective is to determine the types and patterns of initial and parameter perturbations that yield the greatest instability and uncertainty in simulated grassland ecosystems using theoretical models. We used a nonlinear optimization approach, i.e., a conditional nonlinear optimal perturbation related to initial and parameter perturbations (CNOP) approach, in our work. Numerical results indicated that the CNOP showed a special and nonlinear optimal pattern when the initial state variables and multiple parameters were considered simultaneously. A visibly different complex optimal pattern characterizing the CNOPs was obtained by choosing different combinations of initial state variables and multiple parameters in different physical processes. We propose that the grassland modeled ecosystem caused by the CNOP-type perturbation is unstable and exhibits two aspects: abrupt change and the time needed for the abrupt change from a grassland equilibrium state to a desert equilibrium state when the initial state variables and multiple parameters are considered simultaneously. We compared these findings with results affected by the CNOPs obtained by considering only uncertainties in initial state variables and in a single parameter. The numerical results imply that the nonlinear optimal pattern of initial perturbations and parameter perturbations, especially for more parameters or when special parameters are involved, plays a key role in determining stabilities and uncertainties associated with a simulated or predicted grassland ecosystem.展开更多
Using the observed daily temperatures from 756 stations in China during the period from 1951 to 2009 extensive and persistent extreme cold events (EPECEs) were defined according to the following three steps:1) a stati...Using the observed daily temperatures from 756 stations in China during the period from 1951 to 2009 extensive and persistent extreme cold events (EPECEs) were defined according to the following three steps:1) a station was defined as an extreme cold station (ECS) if the observed temperature was lower than its 10th percentile threshold;2) an extensive extreme cold event was determined to be present if the approximated area occupied by the ECSs was more than 10% of the total area of China (83rd percentile) on its starting day and the maximum area occupied by the ECSs was at least 20% of the total area of China (96th percentile);and 3) an EPECE was determined to be present if the extensive extreme cold event lasted for at least for eight days.52 EPECEs were identified in this manner,and these identification results were also verified using other reliable data.On the basis of cluster analysis,five types of EPECEs were classified according to the spatial distribution of ECSs at their most extensive time over the course of the EPECE.展开更多
The response of a grassland ecosystem to climate change is discussed within the context of a theoretical model.An optimization approach,a conditional nonlinear optimal perturbation related to parameter(CNOP-P) appro...The response of a grassland ecosystem to climate change is discussed within the context of a theoretical model.An optimization approach,a conditional nonlinear optimal perturbation related to parameter(CNOP-P) approach,was employed in this study.The CNOP-P,a perturbation of moisture index in the theoretical model,represents a nonlinear climate perturbation.Two kinds of linear climate perturbations were also used to study the response of the grassland ecosystem to different types of climate changes.The results show that the extent of grassland ecosystem variation caused by the CNOP-P-type climate change is greater than that caused by the two linear types of climate change.In addition,the grassland ecosystem affected by the CNOP-P-type climate change evolved into a desert ecosystem,and the two linear types of climate changes failed within a specific amplitude range when the moisture index recovered to its reference state.Therefore,the grassland ecosystem response to climate change was nonlinear.This study yielded similar results for a desert ecosystem seeded with both living and wilted biomass litter.The quantitative analysis performed in this study also accounted for the role of soil moisture in the root zone and the shading effect of wilted biomass on the grassland ecosystem through nonlinear interactions between soil and vegetation.The results of this study imply that the CNOP-P approach is a potentially effective tool for assessing the impact of nonlinear climate change on grassland ecosystems.展开更多
Optimal precursor perturbations of El Ni?o in the Zebiak-Cane model were explored for three different cost functions. For the different characteristics of the eastern-Pacific(EP) El Ni?o and the central-Pacific(CP) El...Optimal precursor perturbations of El Ni?o in the Zebiak-Cane model were explored for three different cost functions. For the different characteristics of the eastern-Pacific(EP) El Ni?o and the central-Pacific(CP) El Ni?o, three cost functions were defined as the sea surface temperature anomaly(SSTA) evolutions at prediction time in the whole tropical Pacific, the Ni?o3 area, and the Ni?o4 area. For all three cost functions, there were two optimal precursors that developed into El Ni?o events, called Precursor I and Precursor Ⅱ. For Precursor Ⅰ, the SSTA component consisted of an east-west(positive-negative) dipole spanning the entire tropical Pacific basin and the thermocline depth anomaly pattern exhibited a tendency of deepening for the whole of the equatorial Pacific. Precursor I can develop into an EP-El Ni?o event, with the warmest SSTA occurring in the eastern tropical Pacific or into a mixed El Ni?o event that has features between EP-El Ni?o and CP-El Ni?o events. For Precursor Ⅱ, the thermocline deepened anomalously in the eastern equatorial Pacific and the amplitude of deepening was obviously larger than that of shoaling in the central and western equatorial Pacific. Precursor Ⅱ developed into a mixed El Ni?o event. Both the thermocline depth and wind anomaly played important roles in the development of Precursor Ⅰ and Precursor Ⅱ.展开更多
Characteristics of the total clear-sky greenhouse effect (GA) and cloud radiative forcings (CRFs), along with the radiative-related water vapor and cloud properties simulated by the Spectral Atmospheric Model deve...Characteristics of the total clear-sky greenhouse effect (GA) and cloud radiative forcings (CRFs), along with the radiative-related water vapor and cloud properties simulated by the Spectral Atmospheric Model developed by LASGIAP (SAMIL) are evaluated. Impacts of the convection scheme on the simulation of CRFs are discussed by using two AMIP (Atmospheric Model Inter-comparison Project) type simulations employing different convection schemes: the new Zhang-McFarlane (NZH) and Tiedtke (TDK) convection schemes. It shows that both the climatological GA and its response to El Nio warming are simulated well, both in terms of spatial pattern and magnitude. The impact of the convection scheme on GA is not significant. The climatological longwave CRF (LWCRF) and its response to El Nio warming are simulated well, but with a prominently weaker magnitude. The simulation of the climatology (response) of LWCRF in the NZH (TDK) run is slightly more realistic than in the TDK (NZH) simulation, indicating significant impacts of the convection scheme. The shortwave CRF (SWCRF) shows large biases in both spatial pattern and magnitude, and the results from the TDK run are better than those from the NZH run. A spuriously excessive negative climatological SWCRF over the southeastern Pacific and an insufficient response of SWCRF to El Nio warming over the tropical Pacific are seen in the NZH run. These two biases are alleviated in the TDK run, since it produces vigorous convection, which is related to the low threshold for convection to take place. Also, impacts of the convection scheme on the cloud profile are discussed.展开更多
The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were ac...The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were accompanied by a CCW in the initial stages. From the comparison between the CECs and the CCWs that were independent of any CEC, it is found that a south- west-northeast-oriented tilted ridge at 500 hPa was present around the Europe-Barents Sea regions approximately 10 days prior to the start of the CEC. Consistent with this feature, a high sea level pressure and strong cold air accumulation occurred over a broad extent of northern Eurasia one week prior to the start of the CEC. The tilted ridge and the strong cold air accumulation were the precursory signals that were absent for the CCW, and they provide important clues for the early prediction of whether a CCW event might evolve into a CEC.展开更多
Within the frame of the Zebiak-Cane model,the impact of the uncertainties of the Madden-Julian Oscillation(MJO) on ENSO predictability was studied using a parameterized stochastic representation of intraseasonal for...Within the frame of the Zebiak-Cane model,the impact of the uncertainties of the Madden-Julian Oscillation(MJO) on ENSO predictability was studied using a parameterized stochastic representation of intraseasonal forcing.The results show that the uncertainties of MJO have little effect on the maximum prediction error for ENSO events caused by conditional nonlinear optimal perturbation(CNOP);compared to CNOP-type initial error,the model error caused by the uncertainties of MJO led to a smaller prediction uncertainty of ENSO,and its influence over the ENSO predictability was not significant.This result suggests that the initial error might be the main error source that produces uncertainty in ENSO prediction,which could provide a theoretical foundation for the data assimilation of the ENSO forecast.展开更多
A latent heating peak in the PBL was detected in a simulation by a global GCM that failed to reproduce Madden Julian Oscillation (MJO). The latent heating peak in the PBL was generated by very shallow convection, wh...A latent heating peak in the PBL was detected in a simulation by a global GCM that failed to reproduce Madden Julian Oscillation (MJO). The latent heating peak in the PBL was generated by very shallow convection, which prevented moisture from being transported to the free troposphere. Large amount of moisture was therefore confined to the PBL, leading to a dry bias in the free atmosphere. Suffering from this dry bias, deep convection became lethargic, and MJO signals failed to occur. When the latent heating peak in the PBL was removed in another simulation, reasonable MJO signals, including the eastward propagation and the structure of its large-scale circulation, appeared. We therefore propose that the excessive latent heating peak in the PBL due to hyperactive shallow convection may be a reason for a lack of MJO signals in some simulations by other GCMs as well.展开更多
Using the Regional Ocean Modeling System, this study investigates the simulation uncertainties in the current velocity in the low-latitude North Pacific where the Kuroshio originates [i.e., the beginning of the Kurosh...Using the Regional Ocean Modeling System, this study investigates the simulation uncertainties in the current velocity in the low-latitude North Pacific where the Kuroshio originates [i.e., the beginning of the Kuroshio(BK)]. The results show that the simulation uncertainties largely reflect the contributions of wind stress forcing errors, especially zonal wind stress errors,rather than initial or boundary errors. Using the idea of a nonlinear forcing singular vector, two types of zonal wind stress errors(but sharing one EOF mode) are identified from error samples derived from reanalysis data as having the potential to yield large simulation uncertainties. The type-1 error possesses a pattern with positive anomalies covering the two zonal bands of 0?–15?N and 25?–40?N in the Pacific Ocean, with negative anomalies appearing between these two bands; while the type-2 error is almost opposite to the type-1 error. The simulation uncertainties induced by the type-1 and-2 errors consist of both large-scale circulation errors controlled by a mechanism similar to the Sverdrup relation and mesoscale eddy-like errors generated by baroclinic instability. The type-1 and-2 errors suggest two areas: one is located between the western boundary and the meridional 130?E along 15?–20?N, and the other is located between 140?–150?E and along 15?–20?N. The reduction of errors over these two areas can greatly improve the simulation accuracy of the current velocity at BK. These two areas represent sensitive areas for targeted observations associated with the simulation of the current velocity at BK.展开更多
This paper focuses on the impacts of convective momentum transport(CMT) on simulations of the tropical intraseasonal oscillation(TIO) in SAMIL. Two sets of experiments are performed, which give different reality of th...This paper focuses on the impacts of convective momentum transport(CMT) on simulations of the tropical intraseasonal oscillation(TIO) in SAMIL. Two sets of experiments are performed, which give different reality of the Madden-Julian Oscillation(MJO). The Tiedtke cumulus parameterization scheme is used for all experiments. It is found that simulations of the TIO can be influenced by CMT, and the impacts on the simulated TIO depend on the model capability in simulating the MJO. CMT tends to have large influences to the model that can simulate the eastward propagation of the MJO. CMT can further influence the long-term mean of zonal wind and its vertical shear. Zonal wind suffers from easterlies biases at low level and westerlies biases at upper level when CMT is introduced. Such easterlies biases at low level reduce the reality of the simulated tropical intraseasonal oscillation. When CMT is introduced in the model, MJO signals disappear but the model's mean state improves. Therefore, a more appropriate way is needed to introduce CMT to the model to balance the simulated mean state and TIO signals.展开更多
To compare differences among the Medieval Warm Period (MWP), Little Ice Age (LIA), and 20th century global warming (20CW), six sets of transient and equilibrium simulations were generated using the climate system mode...To compare differences among the Medieval Warm Period (MWP), Little Ice Age (LIA), and 20th century global warming (20CW), six sets of transient and equilibrium simulations were generated using the climate system model FGOALS_gl. This model was developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences. The results indicate that MWP warming is evident on a global scale, except for at mid-latitudes of the North Pacific. However, the magnitude of the warming is weaker than that in the 20th century. The warming in the high latitudes of the Northern Hemisphere is stronger than that in the Southern Hemisphere. The LIA cooling is also evident on a global scale, with a strong cooling over the high Eurasian continent, while the cooling center is over the Arctic domain. Both the MWP and the 20CW experiments exhibit the strongest warming anomalies in the middle troposphere around 200-300 hPa, but the cooling center of the LIA experiment is seen in the polar surface of the Northern Hemisphere. A comparison of model simulation against the reconstruction indicates that model's performance in simulating the surface air temperature changes during the warm periods is better than that during the cold periods. The consistencies between model and reconstruction in lower latitudes are better than those in high latitudes. Comparison of the inter-annual variability mode of East Asian summer monsoon (EASM) rainfall during the MWP, LIA and 20CW reveals a similar rainfall anomalies pattern. However, the time spectra of the principal component during the three typical periods of the last millennium are different, and the quasi-biannual oscillation is more evident during the two warm periods. At a centennial time scale, the external mode of the EASM variability driven by the changes of effective solar radiation is determined by the changes of large scale land-sea thermal contrast. The rainfall anomalies over the east of 110°E exhibit a meridional homogeneous change pattern, which is different from the meridional out-of-phase change of rainfall anomalies associated with the internal mode.展开更多
Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contras...Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contrast between land and ocean and summer precipitation over the East Asian monsoon region during the past millennium; compared the basic characteristics of the East Asian summer monsoon (EASM) circulation and precipitation in the present day, the Little Ice Age (LIA) and the Medieval Warm Period (MWP); and explored their links with solar irradiance and global climate change. The results indicate that over the last 150 years, the EASM circulation and precipitation, indicated by the temperature contrast between the East Asian mainland and adjacent oceans, had a significant decadal perturbation and have been weaker during the period of rapid global warming over the past 50 years. On the centennial time scale, the EASM in the MWP was strongest over the past 1000 years. Over the past 1000 years, the EASM was weakest in 1450-1570. When the EASM circulation was weaker, the monsoon rain belt over eastern China was generally located more southward, with there being less precipitation in North China and more precipitation in the Yangtze River valley; therefore, there was an anomalous pattern of southern flood/northern drought. From the 1900s to 1920s, precipitation had a pat- tern opposite to that of the southern flood/northern drought, with there being less precipitation in the Yangtze River valley and more precipitation in North China. Compared with the case for the MWP, there was a longer-time-scale southern flood/northern drought phenomenon in 1400-1600. Moreover, the EASM circulation and precipitation did not synchronously vary with the trend of global temperature. During the last 150 years, although the annual mean surface temperature around the world and in China has increased, the EASM circulation and precipitation did not have strengthening or weakening trends. Over the past 1000 years, the weakest EASM occurred ahead of the lowest Northern Hemispheric temperature and corresponded to the weakest solar irradiance.展开更多
Two record-breaking rainfalls in late June of2015 led to widespread flooding in Eastern China, especially over the Yangtze River Delta, and this in turn led to huge economic losses. Analysis suggests that the El Nin? ...Two record-breaking rainfalls in late June of2015 led to widespread flooding in Eastern China, especially over the Yangtze River Delta, and this in turn led to huge economic losses. Analysis suggests that the El Nin? olike sea surface temperature pattern during that month facilitated an intensified and southwestward-shifted western Pacific subtropical high and enhanced water vapor convergence along the Meiyu front, which provided a favorable environment for the occurrence of heavy rainfall over Eastern China. Meanwhile, two midlatitude troughs were successively formed over East Asia in the second half of the month as a consequence of the downstream energy dispersions of two midlatitude blockings. These configurations facilitated the southward intrusion of the extratropical high potential vorticity toward the Meiyu front. In this way, the ascent was enhanced along the Meiyu front over Eastern China, and the occurrence of heavy rainfalls was triggered. Moreover, a tropical intraseasonal active convection propagated northward and also contributed constructively to the heavy rainfall.展开更多
Hourly data of 42 rain gauges over South China during 1966–2005 were used to analyze the corresponding relation between precipitation extremes and surface air temperature in the warm season(May to October).The result...Hourly data of 42 rain gauges over South China during 1966–2005 were used to analyze the corresponding relation between precipitation extremes and surface air temperature in the warm season(May to October).The results show that below 25℃,both daily and hourly precipitation extremes in South China increase with rising temperature.More extreme events transit to the two-time Clausius-Clapeyron(CC)relationship at lower temperatures.Daily as well as hourly precipitation extremes have a decreasing tendency nearly above 25℃,among which the decrease of hourly extremes is much more significant.In order to investigate the efects of rainfall durations,hourly precipitation extremes are presented by short duration and long duration precipitation,respectively.Results show that the dramatic decrease of hourly rainfall intensities above 25℃ is mainly caused by short duration precipitation,and long duration precipitation extremes rarely occur in South China when surface air temperature surpasses 28℃.展开更多
The conditional nonlinear optimal perturbation (CNOP), which is a nonlinear generalization of the linear singular vector (LSV), is applied in important problems of atmospheric and oceanic sciences, including ENSO ...The conditional nonlinear optimal perturbation (CNOP), which is a nonlinear generalization of the linear singular vector (LSV), is applied in important problems of atmospheric and oceanic sciences, including ENSO predictability, targeted observations, and ensemble forecast. In this study, we investigate the computational cost of obtaining the CNOP by several methods. Differences and similarities, in terms of the computational error and cost in obtaining the CNOP, are compared among the sequential quadratic programming (SQP) algorithm, the limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm, and the spectral projected gradients (SPG2) algorithm. A theoretical grassland ecosystem model and the classical Lorenz model are used as examples. Numerical results demonstrate that the computational error is acceptable with all three algorithms. The computational cost to obtain the CNOP is reduced by using the SQP algorithm. The experimental results also reveal that the L-BFGS algorithm is the most effective algorithm among the three optimization algorithms for obtaining the CNOP. The numerical results suggest a new approach and algorithm for obtaining the CNOP for a large-scale optimization problem.展开更多
North-south displacements and meridional vacillations of the eddy-driven jet are widely accepted as the dominant cause of variability of the observational zonal-mean zonal wind anomalies(denoted [u]').In this stud...North-south displacements and meridional vacillations of the eddy-driven jet are widely accepted as the dominant cause of variability of the observational zonal-mean zonal wind anomalies(denoted [u]').In this study,a new idea regarding the primary variability of the observational [u]' in the middle latitude troposphere is presented.It is hypothesized that there are two different classes of primary variability of the observational [u]':the poleward propagation of the [u]'(abbreviated as PP) and meridional vacillations.To validate this hypothesis,one-point correlation maps of [u]' at 200-hPa during the boreal cold season(November-April) of every year from 1957-2002 are used as a criterion.Twelve PP years,in which the PP events are dominant in the variability of [u]',and 15 no_PP years,in which the PP events are recessive and the meridional vacillations are dominant in the variability of [u]',are examined.The results show that the variabilities of [u]' are different in the chosen PP and no_PP years.In the PP years,the PP events dominate the variability of [u]';however,the meridional vacillations are prevalent in the no_PP years.展开更多
基金supported by the Major National Basic Research Program of China (973 Program) on Global Change (Grant No.2010CB951902)the National Natural Science Foundation of China (Grant Nos. 40625014,40705025,40921003,and 41005044)
文摘In this study, records from a 3-yr intensified observational experiment at eight stations along the hillside of Seqilashan over the southeastern Tibetan Plateau were analyzed and combined with records at 28 routine observation stations in the Chinese National Meteorological Station Network to investigate the influences of station location on the different diurnal rainfall variations between station records and Tropical Rainfall Measuring Mission (TRMM) data products. The results indicate that the diurnal variation of warm season rainfall is closely related to location of stations. The prevailing nocturnal rainfall peak in observations at routine stations can be largely attributed to the relatively lower location of the stations, which are mostly situated in valleys. The records at Seqilashan stations on hillsides revealed an evident diurnal afternoon peak of warm season rainfall, similar to that indicated by TRMM data. The different diurnal phases between valley and hillside stations are closely related to the orographically induced regional circulations caused by the complex topography over the Tibetan Plateau. The results of this study indicate that the prevailing nocturnal rainfall associated with the relatively lower location of routine observation stations can partially explain the diurnal rainfall variations between observation station records and TRMM data.
基金provided by grants from National Natural Science Foundation of China (Grant Nos. 40905050and 40830955)the Chinese Academy of Sciences (CASGrant No. KZCX3-SW-230)
文摘Due to uncertainties in initial conditions and parameters, the stability and uncertainty of grassland ecosystem simulations using ecosystem models are issues of concern. Our objective is to determine the types and patterns of initial and parameter perturbations that yield the greatest instability and uncertainty in simulated grassland ecosystems using theoretical models. We used a nonlinear optimization approach, i.e., a conditional nonlinear optimal perturbation related to initial and parameter perturbations (CNOP) approach, in our work. Numerical results indicated that the CNOP showed a special and nonlinear optimal pattern when the initial state variables and multiple parameters were considered simultaneously. A visibly different complex optimal pattern characterizing the CNOPs was obtained by choosing different combinations of initial state variables and multiple parameters in different physical processes. We propose that the grassland modeled ecosystem caused by the CNOP-type perturbation is unstable and exhibits two aspects: abrupt change and the time needed for the abrupt change from a grassland equilibrium state to a desert equilibrium state when the initial state variables and multiple parameters are considered simultaneously. We compared these findings with results affected by the CNOPs obtained by considering only uncertainties in initial state variables and in a single parameter. The numerical results imply that the nonlinear optimal pattern of initial perturbations and parameter perturbations, especially for more parameters or when special parameters are involved, plays a key role in determining stabilities and uncertainties associated with a simulated or predicted grassland ecosystem.
基金supportedby the National Key Technologies R&D Program of China (Grant No. 2009BAC51B02)the Special Funds for Meteorology Scientific Research on Public Cause (Grant No. GYHY201106015)
文摘Using the observed daily temperatures from 756 stations in China during the period from 1951 to 2009 extensive and persistent extreme cold events (EPECEs) were defined according to the following three steps:1) a station was defined as an extreme cold station (ECS) if the observed temperature was lower than its 10th percentile threshold;2) an extensive extreme cold event was determined to be present if the approximated area occupied by the ECSs was more than 10% of the total area of China (83rd percentile) on its starting day and the maximum area occupied by the ECSs was at least 20% of the total area of China (96th percentile);and 3) an EPECE was determined to be present if the extensive extreme cold event lasted for at least for eight days.52 EPECEs were identified in this manner,and these identification results were also verified using other reliable data.On the basis of cluster analysis,five types of EPECEs were classified according to the spatial distribution of ECSs at their most extensive time over the course of the EPECE.
基金supported by National Natural Science Foundation of China(Grant Nos. 40905050,40805020,40830955)the Chinese Academy of Sciences (Grants No. KZCX3-SW-230),LASG Free Exploration Fund,and LASG State Key Lab-oratory Special Fund
文摘The response of a grassland ecosystem to climate change is discussed within the context of a theoretical model.An optimization approach,a conditional nonlinear optimal perturbation related to parameter(CNOP-P) approach,was employed in this study.The CNOP-P,a perturbation of moisture index in the theoretical model,represents a nonlinear climate perturbation.Two kinds of linear climate perturbations were also used to study the response of the grassland ecosystem to different types of climate changes.The results show that the extent of grassland ecosystem variation caused by the CNOP-P-type climate change is greater than that caused by the two linear types of climate change.In addition,the grassland ecosystem affected by the CNOP-P-type climate change evolved into a desert ecosystem,and the two linear types of climate changes failed within a specific amplitude range when the moisture index recovered to its reference state.Therefore,the grassland ecosystem response to climate change was nonlinear.This study yielded similar results for a desert ecosystem seeded with both living and wilted biomass litter.The quantitative analysis performed in this study also accounted for the role of soil moisture in the root zone and the shading effect of wilted biomass on the grassland ecosystem through nonlinear interactions between soil and vegetation.The results of this study imply that the CNOP-P approach is a potentially effective tool for assessing the impact of nonlinear climate change on grassland ecosystems.
基金supported by the National Natural Science Foundation of China (Grant No. 41006007)the National Basic Research Program of China (Grant No. 2012CB417404)
文摘Optimal precursor perturbations of El Ni?o in the Zebiak-Cane model were explored for three different cost functions. For the different characteristics of the eastern-Pacific(EP) El Ni?o and the central-Pacific(CP) El Ni?o, three cost functions were defined as the sea surface temperature anomaly(SSTA) evolutions at prediction time in the whole tropical Pacific, the Ni?o3 area, and the Ni?o4 area. For all three cost functions, there were two optimal precursors that developed into El Ni?o events, called Precursor I and Precursor Ⅱ. For Precursor Ⅰ, the SSTA component consisted of an east-west(positive-negative) dipole spanning the entire tropical Pacific basin and the thermocline depth anomaly pattern exhibited a tendency of deepening for the whole of the equatorial Pacific. Precursor I can develop into an EP-El Ni?o event, with the warmest SSTA occurring in the eastern tropical Pacific or into a mixed El Ni?o event that has features between EP-El Ni?o and CP-El Ni?o events. For Precursor Ⅱ, the thermocline deepened anomalously in the eastern equatorial Pacific and the amplitude of deepening was obviously larger than that of shoaling in the central and western equatorial Pacific. Precursor Ⅱ developed into a mixed El Ni?o event. Both the thermocline depth and wind anomaly played important roles in the development of Precursor Ⅰ and Precursor Ⅱ.
基金supported jointly by the National Natural Science Foundation of China (Grant Nos 40890054 and 40821092)the National Basic Research Program of China (Grant No 2010CB951904)National Key Technologies R&D Program (Grant No 2007BAC29B03)
文摘Characteristics of the total clear-sky greenhouse effect (GA) and cloud radiative forcings (CRFs), along with the radiative-related water vapor and cloud properties simulated by the Spectral Atmospheric Model developed by LASGIAP (SAMIL) are evaluated. Impacts of the convection scheme on the simulation of CRFs are discussed by using two AMIP (Atmospheric Model Inter-comparison Project) type simulations employing different convection schemes: the new Zhang-McFarlane (NZH) and Tiedtke (TDK) convection schemes. It shows that both the climatological GA and its response to El Nio warming are simulated well, both in terms of spatial pattern and magnitude. The impact of the convection scheme on GA is not significant. The climatological longwave CRF (LWCRF) and its response to El Nio warming are simulated well, but with a prominently weaker magnitude. The simulation of the climatology (response) of LWCRF in the NZH (TDK) run is slightly more realistic than in the TDK (NZH) simulation, indicating significant impacts of the convection scheme. The shortwave CRF (SWCRF) shows large biases in both spatial pattern and magnitude, and the results from the TDK run are better than those from the NZH run. A spuriously excessive negative climatological SWCRF over the southeastern Pacific and an insufficient response of SWCRF to El Nio warming over the tropical Pacific are seen in the NZH run. These two biases are alleviated in the TDK run, since it produces vigorous convection, which is related to the low threshold for convection to take place. Also, impacts of the convection scheme on the cloud profile are discussed.
基金supported by the National Key Technologies R&D Program of China (Grant No. 2009BAC51B02)
文摘The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were accompanied by a CCW in the initial stages. From the comparison between the CECs and the CCWs that were independent of any CEC, it is found that a south- west-northeast-oriented tilted ridge at 500 hPa was present around the Europe-Barents Sea regions approximately 10 days prior to the start of the CEC. Consistent with this feature, a high sea level pressure and strong cold air accumulation occurred over a broad extent of northern Eurasia one week prior to the start of the CEC. The tilted ridge and the strong cold air accumulation were the precursory signals that were absent for the CCW, and they provide important clues for the early prediction of whether a CCW event might evolve into a CEC.
基金sponsored by the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No. KZCX2-YW-QN203)the National Basic Research Program of China (Grant Nos. 2012CB955202 and 2010CB950402)the National Natural Science Foundation of China (Grant No. 40821092)
文摘Within the frame of the Zebiak-Cane model,the impact of the uncertainties of the Madden-Julian Oscillation(MJO) on ENSO predictability was studied using a parameterized stochastic representation of intraseasonal forcing.The results show that the uncertainties of MJO have little effect on the maximum prediction error for ENSO events caused by conditional nonlinear optimal perturbation(CNOP);compared to CNOP-type initial error,the model error caused by the uncertainties of MJO led to a smaller prediction uncertainty of ENSO,and its influence over the ENSO predictability was not significant.This result suggests that the initial error might be the main error source that produces uncertainty in ENSO prediction,which could provide a theoretical foundation for the data assimilation of the ENSO forecast.
基金jointly supported by the National Basic Research Program of China(973 Program)[grant number 6131270305]the Ministry of Water Resources'special research grant for non-profit public service[grant number 201301062-02]+1 种基金the National Natural Science Foundation of China[grant number61572058]the Strategic Priority Research Program of the Chinese Academy of Sciences[grant number XDA05110304]
基金supported by National Science Foundation of U.S.A.(Grant No. ATM0739402)the National Natural Science Foundation of China (Grant Nos. U0833602 and 40905035)
文摘A latent heating peak in the PBL was detected in a simulation by a global GCM that failed to reproduce Madden Julian Oscillation (MJO). The latent heating peak in the PBL was generated by very shallow convection, which prevented moisture from being transported to the free troposphere. Large amount of moisture was therefore confined to the PBL, leading to a dry bias in the free atmosphere. Suffering from this dry bias, deep convection became lethargic, and MJO signals failed to occur. When the latent heating peak in the PBL was removed in another simulation, reasonable MJO signals, including the eastward propagation and the structure of its large-scale circulation, appeared. We therefore propose that the excessive latent heating peak in the PBL due to hyperactive shallow convection may be a reason for a lack of MJO signals in some simulations by other GCMs as well.
基金jointly sponsored by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA11010303)the National Natural Science Foundation of China (Grant No. 41525017)
文摘Using the Regional Ocean Modeling System, this study investigates the simulation uncertainties in the current velocity in the low-latitude North Pacific where the Kuroshio originates [i.e., the beginning of the Kuroshio(BK)]. The results show that the simulation uncertainties largely reflect the contributions of wind stress forcing errors, especially zonal wind stress errors,rather than initial or boundary errors. Using the idea of a nonlinear forcing singular vector, two types of zonal wind stress errors(but sharing one EOF mode) are identified from error samples derived from reanalysis data as having the potential to yield large simulation uncertainties. The type-1 error possesses a pattern with positive anomalies covering the two zonal bands of 0?–15?N and 25?–40?N in the Pacific Ocean, with negative anomalies appearing between these two bands; while the type-2 error is almost opposite to the type-1 error. The simulation uncertainties induced by the type-1 and-2 errors consist of both large-scale circulation errors controlled by a mechanism similar to the Sverdrup relation and mesoscale eddy-like errors generated by baroclinic instability. The type-1 and-2 errors suggest two areas: one is located between the western boundary and the meridional 130?E along 15?–20?N, and the other is located between 140?–150?E and along 15?–20?N. The reduction of errors over these two areas can greatly improve the simulation accuracy of the current velocity at BK. These two areas represent sensitive areas for targeted observations associated with the simulation of the current velocity at BK.
基金sponsored by the Joint Project of Natural Science Foundation of China and Yunnan Province (U0833602)
文摘This paper focuses on the impacts of convective momentum transport(CMT) on simulations of the tropical intraseasonal oscillation(TIO) in SAMIL. Two sets of experiments are performed, which give different reality of the Madden-Julian Oscillation(MJO). The Tiedtke cumulus parameterization scheme is used for all experiments. It is found that simulations of the TIO can be influenced by CMT, and the impacts on the simulated TIO depend on the model capability in simulating the MJO. CMT tends to have large influences to the model that can simulate the eastward propagation of the MJO. CMT can further influence the long-term mean of zonal wind and its vertical shear. Zonal wind suffers from easterlies biases at low level and westerlies biases at upper level when CMT is introduced. Such easterlies biases at low level reduce the reality of the simulated tropical intraseasonal oscillation. When CMT is introduced in the model, MJO signals disappear but the model's mean state improves. Therefore, a more appropriate way is needed to introduce CMT to the model to balance the simulated mean state and TIO signals.
基金the National Natural Science Foundation of China (40890054)
文摘To compare differences among the Medieval Warm Period (MWP), Little Ice Age (LIA), and 20th century global warming (20CW), six sets of transient and equilibrium simulations were generated using the climate system model FGOALS_gl. This model was developed by the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences. The results indicate that MWP warming is evident on a global scale, except for at mid-latitudes of the North Pacific. However, the magnitude of the warming is weaker than that in the 20th century. The warming in the high latitudes of the Northern Hemisphere is stronger than that in the Southern Hemisphere. The LIA cooling is also evident on a global scale, with a strong cooling over the high Eurasian continent, while the cooling center is over the Arctic domain. Both the MWP and the 20CW experiments exhibit the strongest warming anomalies in the middle troposphere around 200-300 hPa, but the cooling center of the LIA experiment is seen in the polar surface of the Northern Hemisphere. A comparison of model simulation against the reconstruction indicates that model's performance in simulating the surface air temperature changes during the warm periods is better than that during the cold periods. The consistencies between model and reconstruction in lower latitudes are better than those in high latitudes. Comparison of the inter-annual variability mode of East Asian summer monsoon (EASM) rainfall during the MWP, LIA and 20CW reveals a similar rainfall anomalies pattern. However, the time spectra of the principal component during the three typical periods of the last millennium are different, and the quasi-biannual oscillation is more evident during the two warm periods. At a centennial time scale, the external mode of the EASM variability driven by the changes of effective solar radiation is determined by the changes of large scale land-sea thermal contrast. The rainfall anomalies over the east of 110°E exhibit a meridional homogeneous change pattern, which is different from the meridional out-of-phase change of rainfall anomalies associated with the internal mode.
基金the National Natural Science Foundation of China (40890053 and 40890052)the National Basic Research Program of China (2007CB815901)the Special Project of Basic Science and Technology (2011FY120300)
文摘Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contrast between land and ocean and summer precipitation over the East Asian monsoon region during the past millennium; compared the basic characteristics of the East Asian summer monsoon (EASM) circulation and precipitation in the present day, the Little Ice Age (LIA) and the Medieval Warm Period (MWP); and explored their links with solar irradiance and global climate change. The results indicate that over the last 150 years, the EASM circulation and precipitation, indicated by the temperature contrast between the East Asian mainland and adjacent oceans, had a significant decadal perturbation and have been weaker during the period of rapid global warming over the past 50 years. On the centennial time scale, the EASM in the MWP was strongest over the past 1000 years. Over the past 1000 years, the EASM was weakest in 1450-1570. When the EASM circulation was weaker, the monsoon rain belt over eastern China was generally located more southward, with there being less precipitation in North China and more precipitation in the Yangtze River valley; therefore, there was an anomalous pattern of southern flood/northern drought. From the 1900s to 1920s, precipitation had a pat- tern opposite to that of the southern flood/northern drought, with there being less precipitation in the Yangtze River valley and more precipitation in North China. Compared with the case for the MWP, there was a longer-time-scale southern flood/northern drought phenomenon in 1400-1600. Moreover, the EASM circulation and precipitation did not synchronously vary with the trend of global temperature. During the last 150 years, although the annual mean surface temperature around the world and in China has increased, the EASM circulation and precipitation did not have strengthening or weakening trends. Over the past 1000 years, the weakest EASM occurred ahead of the lowest Northern Hemispheric temperature and corresponded to the weakest solar irradiance.
基金supported by the National Basic Research Program of China(2013CB430203)the National Natural Science Foundation of China(4123052741422501)
文摘Two record-breaking rainfalls in late June of2015 led to widespread flooding in Eastern China, especially over the Yangtze River Delta, and this in turn led to huge economic losses. Analysis suggests that the El Nin? olike sea surface temperature pattern during that month facilitated an intensified and southwestward-shifted western Pacific subtropical high and enhanced water vapor convergence along the Meiyu front, which provided a favorable environment for the occurrence of heavy rainfall over Eastern China. Meanwhile, two midlatitude troughs were successively formed over East Asia in the second half of the month as a consequence of the downstream energy dispersions of two midlatitude blockings. These configurations facilitated the southward intrusion of the extratropical high potential vorticity toward the Meiyu front. In this way, the ascent was enhanced along the Meiyu front over Eastern China, and the occurrence of heavy rainfalls was triggered. Moreover, a tropical intraseasonal active convection propagated northward and also contributed constructively to the heavy rainfall.
基金supported by the National Basic Research Program of China[grant number 2012CB955202]the National Natural Science Foundation of China[grant numbers 41005040 and 41023002]the R&D Special Fund for Public Welfare Industry(Meteorology)[grant number GYHY201506012]
基金supported by the project of National Natural Science Foundation of China(No.41221064)
文摘Hourly data of 42 rain gauges over South China during 1966–2005 were used to analyze the corresponding relation between precipitation extremes and surface air temperature in the warm season(May to October).The results show that below 25℃,both daily and hourly precipitation extremes in South China increase with rising temperature.More extreme events transit to the two-time Clausius-Clapeyron(CC)relationship at lower temperatures.Daily as well as hourly precipitation extremes have a decreasing tendency nearly above 25℃,among which the decrease of hourly extremes is much more significant.In order to investigate the efects of rainfall durations,hourly precipitation extremes are presented by short duration and long duration precipitation,respectively.Results show that the dramatic decrease of hourly rainfall intensities above 25℃ is mainly caused by short duration precipitation,and long duration precipitation extremes rarely occur in South China when surface air temperature surpasses 28℃.
基金provided by grants from National Natural Science Foundation of China (Nos.40905050,40805020,40830955)the state Key Development Program for Basic Research (Grant No.2006CB400503)the KZCX3-SW-230 of the Chinese Academy of Sciences (CAS),LASG Free Exploration Fund,and LASG State Key Laboratory Special Fund
文摘The conditional nonlinear optimal perturbation (CNOP), which is a nonlinear generalization of the linear singular vector (LSV), is applied in important problems of atmospheric and oceanic sciences, including ENSO predictability, targeted observations, and ensemble forecast. In this study, we investigate the computational cost of obtaining the CNOP by several methods. Differences and similarities, in terms of the computational error and cost in obtaining the CNOP, are compared among the sequential quadratic programming (SQP) algorithm, the limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm, and the spectral projected gradients (SPG2) algorithm. A theoretical grassland ecosystem model and the classical Lorenz model are used as examples. Numerical results demonstrate that the computational error is acceptable with all three algorithms. The computational cost to obtain the CNOP is reduced by using the SQP algorithm. The experimental results also reveal that the L-BFGS algorithm is the most effective algorithm among the three optimization algorithms for obtaining the CNOP. The numerical results suggest a new approach and algorithm for obtaining the CNOP for a large-scale optimization problem.
基金sponsored by the National Key Technologies R&D Program of China (Grant No. 2009BAC51B02)the National Basic Research Program of China (973 Program,Grant No. 2010CB950401)+1 种基金the National Nature Science Foundation of China (Grant Nos. U0833602 and 40805023)the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Free Exploration Fund
文摘North-south displacements and meridional vacillations of the eddy-driven jet are widely accepted as the dominant cause of variability of the observational zonal-mean zonal wind anomalies(denoted [u]').In this study,a new idea regarding the primary variability of the observational [u]' in the middle latitude troposphere is presented.It is hypothesized that there are two different classes of primary variability of the observational [u]':the poleward propagation of the [u]'(abbreviated as PP) and meridional vacillations.To validate this hypothesis,one-point correlation maps of [u]' at 200-hPa during the boreal cold season(November-April) of every year from 1957-2002 are used as a criterion.Twelve PP years,in which the PP events are dominant in the variability of [u]',and 15 no_PP years,in which the PP events are recessive and the meridional vacillations are dominant in the variability of [u]',are examined.The results show that the variabilities of [u]' are different in the chosen PP and no_PP years.In the PP years,the PP events dominate the variability of [u]';however,the meridional vacillations are prevalent in the no_PP years.