In this study, based on daily gage precipitation data of 2480 stations from 1961 to 2016, the summer （JuneeAugust） extreme precipitationevent was defined using the 95th percentile, and the changes in persistent （la...In this study, based on daily gage precipitation data of 2480 stations from 1961 to 2016, the summer （JuneeAugust） extreme precipitationevent was defined using the 95th percentile, and the changes in persistent （last for at least 2 d） and non-persistent （1 d） extreme precipitation inChina were analyzed. The results indicate that under global warming, the contribution of extreme precipitation to total summer precipitationincreased in most areas of China, but it decreased in the central part of Inner Mongolia and the Sichuan Basin. In North and Southwest China,both persistent and non-persistent extreme precipitation decreased; the decreasing trend of persistent extreme precipitation was more prominent;thus, extreme precipitation event occurred more as non-persistent event. Meanwhile, in the Yangtze River Basin and South China, both types ofextreme precipitation increased particularly the persistent extreme precipitation; persistent extreme precipitation occurred more compared withnon-persistent events.展开更多
In early 2008, a persistent cold and snowy weather process occurred in South China. Severe freezing rain （FR） and blizzards hit the region, which was not seen in the past 50 years. This work studied the disaster at ...In early 2008, a persistent cold and snowy weather process occurred in South China. Severe freezing rain （FR） and blizzards hit the region, which was not seen in the past 50 years. This work studied the disaster at its most severe stage （25 January 2 February 2008） and addressed the reason for the occurrence of three rainfall types and particularly the FR that resulted from the temperature inversion and low sur- face temperature. Evidence suggests that the south-to-north distribution of rainfall, FR, and snowfall was determined by the surface temperature conditions and the stratification features of the northward-tilting front in the mid-lower troposphere over different parts of South China. Under the above frontal conditions, the temperature inversion in the mid-lower troposphere and the cold ground temperature took place and the FR formed. The temperature layer （〉 0℃） inside the inversion in this region depended on necessary intensity, depth, and height of the inversion, i.e., the depth of the inversion can be neither too thick or low nor too thin or high. For those too thick and low （too thin and high） inversions, the precipitation fell as rain （snow and ice pellets）. In the early 2008 case, the 0 6℃ layer occupied 650-850 hPa, below which was the sub-freezing level with temperature 〈 0℃. With the presence of the low sub-freezing level, FR or ice damage could occur even at the 0-1℃ surface temperature condition. Besides, even in the absence of a suitable inversion, a low ground temperature might have made ice-covered water and supercooled drops or water from melted ice freeze rapidly into ice at the surface, and the ground ice maintained and accumulated, which resulted in the severe disaster.展开更多
A predator-prey system with independent harvesting in either species and BeddingtonDeAngelis functional response is investigated. By analyzing characteristic equations and using an iterative technique,we obtain a set ...A predator-prey system with independent harvesting in either species and BeddingtonDeAngelis functional response is investigated. By analyzing characteristic equations and using an iterative technique,we obtain a set of easily verifiable sufficient conditions,which ensure the local and global stability of the nonnegative equilibria of the system. It is also shown that the time delay can cause a stable equilibrium to become unstable and even a switching of stabilities. Numerical simulations are carried out to illustrate the validity of our results.展开更多
A delayed biological system of predator-prey interaction with stage structure and density dependent juvenile birth rate is investigated. It is assumed that the prey population has two stages: immature and mature. The ...A delayed biological system of predator-prey interaction with stage structure and density dependent juvenile birth rate is investigated. It is assumed that the prey population has two stages: immature and mature. The growth of the immature prey is density dependent and is a function of the density of adult prey. Such phenomenon has been reported for beetles, tribolium, copepods, scorpions, several fish species and even crows. The growth of the predator is affected by the time delay due to gestation. By some Lemmas and methods of delay differential equation, the conditions for the uniform persistence and extinction of the system are obtained. Numerical simulations illustrate the feasibility of the main results and demonstrate that the density dependent coefficient has influence on the system populations’ densities though it has no effect on uniform persistence and extinction of the system.展开更多
In this paper, a two-species nonautonomous competitive model with stage structure and harvesting is considered. Sufficient conditions for the existence, uniqueness, global attractivity of positive periodic solution an...In this paper, a two-species nonautonomous competitive model with stage structure and harvesting is considered. Sufficient conditions for the existence, uniqueness, global attractivity of positive periodic solution and the existence, uniform asymptotic stability of almost periodic solution are obtained.展开更多
文摘In this study, based on daily gage precipitation data of 2480 stations from 1961 to 2016, the summer （JuneeAugust） extreme precipitationevent was defined using the 95th percentile, and the changes in persistent （last for at least 2 d） and non-persistent （1 d） extreme precipitation inChina were analyzed. The results indicate that under global warming, the contribution of extreme precipitation to total summer precipitationincreased in most areas of China, but it decreased in the central part of Inner Mongolia and the Sichuan Basin. In North and Southwest China,both persistent and non-persistent extreme precipitation decreased; the decreasing trend of persistent extreme precipitation was more prominent;thus, extreme precipitation event occurred more as non-persistent event. Meanwhile, in the Yangtze River Basin and South China, both types ofextreme precipitation increased particularly the persistent extreme precipitation; persistent extreme precipitation occurred more compared withnon-persistent events.
基金the Open Fund of Jiangsu Provincial Meteorological Bureau under Grant No.200702.
文摘In early 2008, a persistent cold and snowy weather process occurred in South China. Severe freezing rain （FR） and blizzards hit the region, which was not seen in the past 50 years. This work studied the disaster at its most severe stage （25 January 2 February 2008） and addressed the reason for the occurrence of three rainfall types and particularly the FR that resulted from the temperature inversion and low sur- face temperature. Evidence suggests that the south-to-north distribution of rainfall, FR, and snowfall was determined by the surface temperature conditions and the stratification features of the northward-tilting front in the mid-lower troposphere over different parts of South China. Under the above frontal conditions, the temperature inversion in the mid-lower troposphere and the cold ground temperature took place and the FR formed. The temperature layer （〉 0℃） inside the inversion in this region depended on necessary intensity, depth, and height of the inversion, i.e., the depth of the inversion can be neither too thick or low nor too thin or high. For those too thick and low （too thin and high） inversions, the precipitation fell as rain （snow and ice pellets）. In the early 2008 case, the 0 6℃ layer occupied 650-850 hPa, below which was the sub-freezing level with temperature 〈 0℃. With the presence of the low sub-freezing level, FR or ice damage could occur even at the 0-1℃ surface temperature condition. Besides, even in the absence of a suitable inversion, a low ground temperature might have made ice-covered water and supercooled drops or water from melted ice freeze rapidly into ice at the surface, and the ground ice maintained and accumulated, which resulted in the severe disaster.
基金supported by the Foundation of Fujian Education Bureau (JA08253)the Technology Innovation Platform Project of Fujian Province (2009J1007)
文摘A predator-prey system with independent harvesting in either species and BeddingtonDeAngelis functional response is investigated. By analyzing characteristic equations and using an iterative technique,we obtain a set of easily verifiable sufficient conditions,which ensure the local and global stability of the nonnegative equilibria of the system. It is also shown that the time delay can cause a stable equilibrium to become unstable and even a switching of stabilities. Numerical simulations are carried out to illustrate the validity of our results.
文摘A delayed biological system of predator-prey interaction with stage structure and density dependent juvenile birth rate is investigated. It is assumed that the prey population has two stages: immature and mature. The growth of the immature prey is density dependent and is a function of the density of adult prey. Such phenomenon has been reported for beetles, tribolium, copepods, scorpions, several fish species and even crows. The growth of the predator is affected by the time delay due to gestation. By some Lemmas and methods of delay differential equation, the conditions for the uniform persistence and extinction of the system are obtained. Numerical simulations illustrate the feasibility of the main results and demonstrate that the density dependent coefficient has influence on the system populations’ densities though it has no effect on uniform persistence and extinction of the system.
基金This work is supported by Master's Science Research Foundation of Anhui Institute of Architecture and Industry (Y2004-43).
文摘In this paper, a two-species nonautonomous competitive model with stage structure and harvesting is considered. Sufficient conditions for the existence, uniqueness, global attractivity of positive periodic solution and the existence, uniform asymptotic stability of almost periodic solution are obtained.
