Changsha, China
Changsha, China

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Zhang J.,Hunan Climate Center | Zhang J.,Nanjing University of Information Science and Technology | Wang Y.,Nanjing University of Information Science and Technology | Zhong W.,PLA University of Science and Technology | Zhong W.,Nanjing University
Chinese Journal of Atmospheric Sciences | Year: 2016

The redistribution of physical factors and its impacts on the intensity of squall lines under the influence of low-level Vertical Wind Shear (VWS) and moisture content are examined through two-dimensional idealized simulations with the ARPS model (the University of Oklahoma's Advanced Research Prediction System). It shows that the redistribution of momentum, heat and moisture during the evolution of squall lines leads to the change of inner vertical circulation and the configuration of perturbation temperature and humidity, which affects the organization of deep convection and the intensity of the system. The results of sensitivity tests of low-level VWS and moisture content show that increasing (decreasing) the low-level VWS decelerates (accelerates) the propagation of the squall line, and makes the connection (separation) between the mid-level upward current and the new forced updrafts at the front edge of the cold pool, which corresponds to the intensification (weakening) of the squall line. On the other hand, increasing (decreasing) the low-level moisture content results in an increase (decrease) of moisture delivery from the low to middle level, which enhances (weakens) the mid-level latent heating and upward movement. Energy analysis indicates that the low-level moisture change influences the release of Convective Available Potential Energy (CAPE), and the intensity of the new convection. The combined effects of latent heating and CAPE released from low-level moisture change also affect the squall line intensity through exerting an influence on the organization of the upper-level upward currents and the new forced updrafts at the front edge of the cold pool. Copyright © Chinese Journal of Atmospheric Sciences.

Wu H.,Hunan Climate Center | Wu H.,National Climate Center | Hou W.,National Climate Center | Yan P.-C.,National Climate Center | And 4 more authors.
Chinese Physics B | Year: 2015

In recent years, the phenomenon of a critical slowing down has demonstrated its major potential in discovering whether a complex dynamic system tends to abruptly change at critical points. This research on the Pacific decadal oscillation (PDO) index has been made on the basis of the critical slowing down principle in order to analyze its early warning signal of abrupt change. The chaotic characteristics of the PDO index sequence at different times are determined by using the largest Lyapunov exponent (LLE). The relationship between the regional sea surface temperature (SST) background field and the early warning signal of the PDO abrupt change is further studied through calculating the variance of the SST in the PDO region and the spatial distribution of the autocorrelation coefficient, thereby providing the experimental foundation for the extensive application of the method of the critical slowing down phenomenon. Our results show that the phenomenon of critical slowing down, such as the increase of the variance and autocorrelation coefficient, will continue for six years before the abrupt change of the PDO index. This phenomenon of the critical slowing down can be regarded as one of the early warning signals of an abrupt change. Through calculating the LLE of the PDO index during different times, it is also found that the strongest chaotic characteristics of the system occurred between 1971 and 1975 in the early stages of an abrupt change (1976), and the system was at the stage of a critical slowing down, which proves the reliability of the early warning signal of abrupt change discovered in 1970 from the mechanism. In addition, the variance of the SST, along with the spatial distribution of the autocorrelation coefficient in the corresponding PDO region, also demonstrates the corresponding relationship between the change of the background field of the SST and the change of the PDO. © 2015 Chinese Physical Society and IOP Publishing Ltd.

Liao Y.-F.,Hunan Climate Center | Wu X.-Y.,Hunan Climate Center | Du D.-S.,Hunan Climate Center | Zhao F.-H.,Hunan Climate Center | And 2 more authors.
Journal of Natural Disasters | Year: 2011

Based on the meteorological staions ' observations, radionsonde records, NCEP reanalysis data and SSTA, the severe cold air,snow storm and frozen rain events in Hunan Province were studied,and the events occur in whole south China during the middle of Jan. to the beginning of Feb., 2008. The results show that, firstly, the longterm lasting atmospheric circulation abnormality is the main atmospheric circulation background ; Secondly, by analyzing the vertical stucture of temperature, we find the strong thermal inversion constantly existing between 925hPa and 700hPa offers a favorable condition for frozen rain ; Thirdly, SSTA abnormal plays a positive role to some extent in this low temperature. According to statistics, in the start year of Lania, the winter mean temperature is lower than that in other year in Hunan Province, that is to say, it is easily being a cold winter. The MM5, a meso-scale numeric model, was used to simulate the weather precess of the selected forzen rain days, and the results also verify the formation process of the frozen rain and snow. Finally, in view of the characteristics of cold air, snow storm and frozen rain, a standpoint is offered that the research on winter ' s severe weather disaster should be strengthened and the disaster prevention and mitigation measures should be improved thought climate is getting warmer, as the same time, the disaster situation report mechanism should be enhanced and perfected.

Ma C.,Zhejiang University | Pan S.,Zhejiang University | Wang G.,Nanjing Hydraulic Research Institute | Liao Y.,Hunan Climate Center | Xu Y.-P.,Zhejiang University
Theoretical and Applied Climatology | Year: 2015

Global warming brings a huge challenge to society and human being. Understanding historic and future potential climate change will be beneficial to regional crop, forest, and water management. This study aims to analyze the precipitation and temperature changes in the historic period and future period 2021–2050 in the Xiangjiang River Basin, China. The Mann–Kendall rank test for trend and change point analysis was used to analyze the changes in trend and magnitude based on historic precipitation and temperature time series. Four global climate models (GCMs) and a statistical downscaling approach, LARS-WG, were used to estimate future precipitation and temperature under RCP4.5. The results show that annual precipitation in the basin is increasing, although not significant, and will probably continue to increase in the future on the basis of ensemble projections of four GCMs. Temperature is increasing in a significant way and all GCMs projected continuous temperature increase in the future. There will be more extreme events in the future, including both extreme precipitation and temperature. © 2015 Springer-Verlag Wien

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