The formation of spatial patterns is an important issue in reaction–diffusion systems.Previous studies have mainly focused on the spatial patterns in reaction–diffusion models equipped with symmetric diffusion(such ...The formation of spatial patterns is an important issue in reaction–diffusion systems.Previous studies have mainly focused on the spatial patterns in reaction–diffusion models equipped with symmetric diffusion(such as normal or fractional Laplace diffusion),namely,assuming that spatial environments of the systems are homogeneous.However,the complexity and heterogeneity of spatial environments of biochemical reactions in vivo can lead to asymmetric diffusion of reactants.Naturally,there arises an open question of how the asymmetric diffusion affects dynamical behaviors of biochemical reaction systems.To answer this,we build a general asymmetric L´evy diffusion model based on the theory of a continuous time random walk.In addition,we investigate the two-species Brusselator model with asymmetric L´evy diffusion,and obtain a general condition for the formation of Turing and wave patterns.More interestingly,we find that even though the Brusselator model with symmetric diffusion cannot produce steady spatial patterns for some parameters,the asymmetry of L´evy diffusion for this model can produce wave patterns.This is different from the previous result that wave instability requires at least a three-species model.In addition,the asymmetry of L´evy diffusion can significantly affect the amplitude and frequency of the spatial patterns.Our results enrich our knowledge of the mechanisms of pattern formation.展开更多
In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet (JMD) and the Silk Road Pattern (SRP) in summer. The present study reveals that this relati...In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet (JMD) and the Silk Road Pattern (SRP) in summer. The present study reveals that this relationship is robust in northward JMD years but absent in southward JMD years. In other words, the amplitude of the SRP increases with northward displacement of the jet but shows little change with southward displacement. Further analysis indicates that, in northward JMD years, the Rossby wave source (RWS) anomalies, which are primarily contributed by the planetary vortex stretching, are significantly stronger around the entrance of the Asian jet, i.e., the Mediterranean Sea-Caspian Sea area, with the spatial distribution being consistent with that related to the SRP. By contrast, in southward JMD years, the RWS anomalies are much weaker. Therefore, this study suggests that the RWS plays a crucial role in inducing the asymmetry of the JMD-SRP relationship. The results imply that climate anomalies may be stronger in strongly northward-displaced JMD years due to the concurrence of the JMD and SRP, and thus more attention should be paid to these years.展开更多
The influence of summer monsoon on tropical cyclone (TC) genesis over the Bay of Bengal (BoB) is explored using an empirical genesis potential (GP) index. The annual cycle of cyclogenesis frequency over the BoB shows ...The influence of summer monsoon on tropical cyclone (TC) genesis over the Bay of Bengal (BoB) is explored using an empirical genesis potential (GP) index. The annual cycle of cyclogenesis frequency over the BoB shows an asymmetric bimodal pattern with the maximum genesis number appearing in late October and the second largest in early May. The two peaks correspond to the withdrawal and onset of the BoB summer monsoon, respectively. The semimonthly GP index calculated without TC days over the BoB is consistent with TC genesis frequency, indicating that the index captures the monsoon-induced changes in the environment that are responsible for the seasonal variation of TC genesis frequency. Of the four environmental variables (i.e., low-level vorticity, mid-level relative humidity, potential intensity, and vertical wind shear) that enter into the GP index, the potential intensity makes the largest contribution to the bimodal distribution, followed by vertical wind shear due to small wind speed during the summer monsoon onset and withdrawal. The difference in TC genesis frequency between autumn and late spring is mainly owing to the relative humid-ity difference because a divergence (convergence) of horizontal moisture flux associated with cold dry northerlies (warm wet wester-lies) dominates the BoB in late spring (autumn).展开更多
The wind tunnel experiments is conducted to get inspiration for understanding the mechanism of the asymmetric flow pattern and developing an innovative flow control technique for a slender body at high angle of attack...The wind tunnel experiments is conducted to get inspiration for understanding the mechanism of the asymmetric flow pattern and developing an innovative flow control technique for a slender body at high angle of attack. The bi-stable situation of the side forces is observed, which could be easily switched by a tiny disturbances either from coming flow or from artificial disturbances at nose tip (including manufacturing defect). In turbulent flows the side forces switched randomly between positive and negative. There exists a hysteresis loop of side force with the rolling angle. A rod in front of the slender body is used to change the vortex pattern, which could be kept even the rod is moved out from the stream. A miniature strake attached to the nose tip of the model can be moved to different circumferential position. When the strake is stationary, the hysteresis loop disappears and the side force does not change with the turbulent fluctuation of coming flow. The results from dynamic measurements of section side force indicates that when the strake swung at lower frequency the side force can follow the cadence of the swinging strake. With increasing frequency, the magnitude of the side force decreases. At still high frequency, the side force diminishes to zero. If the strake is swinging, while the middle position can be changed to different circumferential angle Фs on either left or right side, the side forces can be changed proportionally with the angle Фs. On the basis of the experimental results, the mechanism of the asymmetry is discussed.展开更多
In this paper,the maximum 1-hour rainfall( rain peak),the maximum 6-hour rainfall and the maximum 24-hour rainfall in the Caojiang River basin from 1967 to 2013 were taken as samples. The typical typhoon rainstorm hyd...In this paper,the maximum 1-hour rainfall( rain peak),the maximum 6-hour rainfall and the maximum 24-hour rainfall in the Caojiang River basin from 1967 to 2013 were taken as samples. The typical typhoon rainstorm hydrograph of joint distribution of rainfall in three periods was constructed based on the asymmetric Archimedean Gumbel-Hougaard extreme value Copula. The main conclusions were as follows:( 1) the design rainstorm value in the Caojiang River basin calculated by using the joint distribution of rainfall in three periods was larger than the design rainstorm value of the joint distribution in two periods and that of a single period. The design rainstorm process hydrograph amplified at the same frequency had the optimal overall effect,which provided a new idea and method for studying the design rainfall patterns.( 2) According to the maximum 24-hour rainfall,the risk rate of the multi-peak rainstorm process that the main peak was in the back was the highest,and the constructed typical design rainstorm process hydrograph was the most representative.( 3) " OR" joint return period of rainfall combination in three periods as the design criteria of a watershed was applicable to responding to the risk of rainfall and flood in this watershed.展开更多
Surface-and subsurface-dwelling planktonic foraminifera from the upper 43 m of Hole A at the Ocean Drilling Program (ODP) Site 807,which was recovered from the western Pacific warm pool during ODP Leg 130,were analyze...Surface-and subsurface-dwelling planktonic foraminifera from the upper 43 m of Hole A at the Ocean Drilling Program (ODP) Site 807,which was recovered from the western Pacific warm pool during ODP Leg 130,were analyzed for stable oxygen and carbon isotopes.By comparing these results with data from ODP Site 851 in the eastern equatorial Pacific,this study has reconstructed the paleoceanographic changes in upper ocean waters in the equatorial Pacific since 2.5 Ma.During the period from 1.6-1.4 Ma,the oxygen isotopes of surface and subsurface waters were found to markedly change in the western and eastern equatorial Pacific,further confirming the final formation of the well-defined asymmetric east-west (E-W) pattern at that time.This feature was similar to the zonal temperature gradient (sea surface temperature is higher in the west and lower in the east) and the asymmetric upper water structure (thermocline depth is deeper in the west and shallower in the east) in the modern equatorial Pacific.The zonal gradient change of subsurface water δ18O was greater than that of surface water δ18O,indicating that the formation of the asymmetric E-W pattern in the equatorial Pacific should be much more related to the shoaled thermocline and markedly decreased subsurface water temperature in the eastern equatorial Pacific.Moreover,since ~1.6 Ma,the carbon isotopic differences between surface and subsurface waters clearly decreased in the equatorial Pacific,and their long-term eccentricity periods changed from 400 ka to ~500 ka,reflecting the reorganization of the ocean carbon reservoir.This probably resulted from the deep water reorganization in the Southern Ocean at that time and its enhanced influence on the tropical Pacific (especially subsurface water).Our study demonstrates that the tropical ocean plays an important role in global climate change.展开更多
The temperature trend near the stratopause is rarely evaluated owing to the limited long-term observations of global temperature. In this study, the spatial patterns of the temperature trends near the northern stratop...The temperature trend near the stratopause is rarely evaluated owing to the limited long-term observations of global temperature. In this study, the spatial patterns of the temperature trends near the northern stratopause are investigated by using satellite and reanalysis datasets. Our analysis reveals a zonally asymmetric temperature trend pattern near the northern mid-to-high latitude stratopause during January, and this pattern underwent an evident transition around the 2000s. From 1980 to 2003, there was a cooling trend in the Western Hemisphere and a warming trend in the Eastern Hemisphere. In contrast, a reversed zonally asymmetric temperature trend pattern existed in the east–west direction from 2003 to 2020. Although the warming trends are statistically insignificant, they contrasted with the overall cooling trend in the upper stratosphere due to ozone depletion and an increase in well-mixed greenhouse gases in recent decades. The zonally asymmetric temperature trends were induced by the transition in the intensity of quasi-stationary planetary wavenumber 1(wave 1) near the stratopause. The increasing(decreasing) trend of the intensity of wave 1 enhanced(weakened) its meridional temperature advection near the stratopause before(after) the 2000s;consequently, a zonally asymmetric temperature trend pattern exists in the east–west direction near the stratopause. The transition in the intensity of the stratospheric wave 1 around the 2000s is most likely caused by the transition in the intensity of wave 1 activity in the troposphere.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.62066026,62363027,and 12071408)PhD program of Entrepreneurship and Innovation of Jiangsu Province,Jiangsu University’Blue Project’,the Natural Science Foundation of Jiangxi Province(Grant No.20224BAB202026)the Science and Technology Research Project of Jiangxi Provincial Department of Education(Grant No.GJJ2203316).
文摘The formation of spatial patterns is an important issue in reaction–diffusion systems.Previous studies have mainly focused on the spatial patterns in reaction–diffusion models equipped with symmetric diffusion(such as normal or fractional Laplace diffusion),namely,assuming that spatial environments of the systems are homogeneous.However,the complexity and heterogeneity of spatial environments of biochemical reactions in vivo can lead to asymmetric diffusion of reactants.Naturally,there arises an open question of how the asymmetric diffusion affects dynamical behaviors of biochemical reaction systems.To answer this,we build a general asymmetric L´evy diffusion model based on the theory of a continuous time random walk.In addition,we investigate the two-species Brusselator model with asymmetric L´evy diffusion,and obtain a general condition for the formation of Turing and wave patterns.More interestingly,we find that even though the Brusselator model with symmetric diffusion cannot produce steady spatial patterns for some parameters,the asymmetry of L´evy diffusion for this model can produce wave patterns.This is different from the previous result that wave instability requires at least a three-species model.In addition,the asymmetry of L´evy diffusion can significantly affect the amplitude and frequency of the spatial patterns.Our results enrich our knowledge of the mechanisms of pattern formation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41320104007, 41421004, and 41731177)
文摘In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet (JMD) and the Silk Road Pattern (SRP) in summer. The present study reveals that this relationship is robust in northward JMD years but absent in southward JMD years. In other words, the amplitude of the SRP increases with northward displacement of the jet but shows little change with southward displacement. Further analysis indicates that, in northward JMD years, the Rossby wave source (RWS) anomalies, which are primarily contributed by the planetary vortex stretching, are significantly stronger around the entrance of the Asian jet, i.e., the Mediterranean Sea-Caspian Sea area, with the spatial distribution being consistent with that related to the SRP. By contrast, in southward JMD years, the RWS anomalies are much weaker. Therefore, this study suggests that the RWS plays a crucial role in inducing the asymmetry of the JMD-SRP relationship. The results imply that climate anomalies may be stronger in strongly northward-displaced JMD years due to the concurrence of the JMD and SRP, and thus more attention should be paid to these years.
基金supported by the National Basic Research Program of China(973Program:2012CB955604)National Natural Science Foundation of China(No.40975038,40830106)the CMA Program(GYHY200906008)
文摘The influence of summer monsoon on tropical cyclone (TC) genesis over the Bay of Bengal (BoB) is explored using an empirical genesis potential (GP) index. The annual cycle of cyclogenesis frequency over the BoB shows an asymmetric bimodal pattern with the maximum genesis number appearing in late October and the second largest in early May. The two peaks correspond to the withdrawal and onset of the BoB summer monsoon, respectively. The semimonthly GP index calculated without TC days over the BoB is consistent with TC genesis frequency, indicating that the index captures the monsoon-induced changes in the environment that are responsible for the seasonal variation of TC genesis frequency. Of the four environmental variables (i.e., low-level vorticity, mid-level relative humidity, potential intensity, and vertical wind shear) that enter into the GP index, the potential intensity makes the largest contribution to the bimodal distribution, followed by vertical wind shear due to small wind speed during the summer monsoon onset and withdrawal. The difference in TC genesis frequency between autumn and late spring is mainly owing to the relative humid-ity difference because a divergence (convergence) of horizontal moisture flux associated with cold dry northerlies (warm wet wester-lies) dominates the BoB in late spring (autumn).
文摘The wind tunnel experiments is conducted to get inspiration for understanding the mechanism of the asymmetric flow pattern and developing an innovative flow control technique for a slender body at high angle of attack. The bi-stable situation of the side forces is observed, which could be easily switched by a tiny disturbances either from coming flow or from artificial disturbances at nose tip (including manufacturing defect). In turbulent flows the side forces switched randomly between positive and negative. There exists a hysteresis loop of side force with the rolling angle. A rod in front of the slender body is used to change the vortex pattern, which could be kept even the rod is moved out from the stream. A miniature strake attached to the nose tip of the model can be moved to different circumferential position. When the strake is stationary, the hysteresis loop disappears and the side force does not change with the turbulent fluctuation of coming flow. The results from dynamic measurements of section side force indicates that when the strake swung at lower frequency the side force can follow the cadence of the swinging strake. With increasing frequency, the magnitude of the side force decreases. At still high frequency, the side force diminishes to zero. If the strake is swinging, while the middle position can be changed to different circumferential angle Фs on either left or right side, the side forces can be changed proportionally with the angle Фs. On the basis of the experimental results, the mechanism of the asymmetry is discussed.
基金Supported by National Natural Science Foundation of China(4177104441371498)。
文摘In this paper,the maximum 1-hour rainfall( rain peak),the maximum 6-hour rainfall and the maximum 24-hour rainfall in the Caojiang River basin from 1967 to 2013 were taken as samples. The typical typhoon rainstorm hydrograph of joint distribution of rainfall in three periods was constructed based on the asymmetric Archimedean Gumbel-Hougaard extreme value Copula. The main conclusions were as follows:( 1) the design rainstorm value in the Caojiang River basin calculated by using the joint distribution of rainfall in three periods was larger than the design rainstorm value of the joint distribution in two periods and that of a single period. The design rainstorm process hydrograph amplified at the same frequency had the optimal overall effect,which provided a new idea and method for studying the design rainfall patterns.( 2) According to the maximum 24-hour rainfall,the risk rate of the multi-peak rainstorm process that the main peak was in the back was the highest,and the constructed typical design rainstorm process hydrograph was the most representative.( 3) " OR" joint return period of rainfall combination in three periods as the design criteria of a watershed was applicable to responding to the risk of rainfall and flood in this watershed.
基金supported by the National Natural Science Foundation of China (40806020)the National Basic Research Program of China (2007CB815901)+1 种基金the Doctoral Program Foundation of Institutions of Higher Education of China (200802471034)the China Ocean Mineral Resources R&D Association (DY115-01-2-3)
文摘Surface-and subsurface-dwelling planktonic foraminifera from the upper 43 m of Hole A at the Ocean Drilling Program (ODP) Site 807,which was recovered from the western Pacific warm pool during ODP Leg 130,were analyzed for stable oxygen and carbon isotopes.By comparing these results with data from ODP Site 851 in the eastern equatorial Pacific,this study has reconstructed the paleoceanographic changes in upper ocean waters in the equatorial Pacific since 2.5 Ma.During the period from 1.6-1.4 Ma,the oxygen isotopes of surface and subsurface waters were found to markedly change in the western and eastern equatorial Pacific,further confirming the final formation of the well-defined asymmetric east-west (E-W) pattern at that time.This feature was similar to the zonal temperature gradient (sea surface temperature is higher in the west and lower in the east) and the asymmetric upper water structure (thermocline depth is deeper in the west and shallower in the east) in the modern equatorial Pacific.The zonal gradient change of subsurface water δ18O was greater than that of surface water δ18O,indicating that the formation of the asymmetric E-W pattern in the equatorial Pacific should be much more related to the shoaled thermocline and markedly decreased subsurface water temperature in the eastern equatorial Pacific.Moreover,since ~1.6 Ma,the carbon isotopic differences between surface and subsurface waters clearly decreased in the equatorial Pacific,and their long-term eccentricity periods changed from 400 ka to ~500 ka,reflecting the reorganization of the ocean carbon reservoir.This probably resulted from the deep water reorganization in the Southern Ocean at that time and its enhanced influence on the tropical Pacific (especially subsurface water).Our study demonstrates that the tropical ocean plays an important role in global climate change.
基金Supported by the National Natural Science Foundation of China (42130601 and 42142038)。
文摘The temperature trend near the stratopause is rarely evaluated owing to the limited long-term observations of global temperature. In this study, the spatial patterns of the temperature trends near the northern stratopause are investigated by using satellite and reanalysis datasets. Our analysis reveals a zonally asymmetric temperature trend pattern near the northern mid-to-high latitude stratopause during January, and this pattern underwent an evident transition around the 2000s. From 1980 to 2003, there was a cooling trend in the Western Hemisphere and a warming trend in the Eastern Hemisphere. In contrast, a reversed zonally asymmetric temperature trend pattern existed in the east–west direction from 2003 to 2020. Although the warming trends are statistically insignificant, they contrasted with the overall cooling trend in the upper stratosphere due to ozone depletion and an increase in well-mixed greenhouse gases in recent decades. The zonally asymmetric temperature trends were induced by the transition in the intensity of quasi-stationary planetary wavenumber 1(wave 1) near the stratopause. The increasing(decreasing) trend of the intensity of wave 1 enhanced(weakened) its meridional temperature advection near the stratopause before(after) the 2000s;consequently, a zonally asymmetric temperature trend pattern exists in the east–west direction near the stratopause. The transition in the intensity of the stratospheric wave 1 around the 2000s is most likely caused by the transition in the intensity of wave 1 activity in the troposphere.