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Zhang D.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Zhang D.,University of Chinese Academy of Sciences | Xu W.,National Meteorological Information Center | Li J.,Bozhou Meteorological Bureau | And 2 more authors.
Theoretical and Applied Climatology | Year: 2014

Frost-free season was an important index for extreme temperature, which was widely discussed in agriculture and applied meteorology research. The frost-free season changed, which was associated with global warming in the past few decades. In this study, the changes in three indices (the last frost day in spring, the first frost day in autumn, and the frost-free season length) of the frost-free season were investigated at 73 meteorological stations in the Tibetan Plateau from 1960 to 2010. Results showed that the last frost day in spring occurred earlier, significantly in 39 % of the 73 stations. For the regional average, the last frost day in spring occurred earlier, significantly at the rate of 1.9 days/decade during the last 50 years. The first frost day in autumn occurred later, significantly in 31 % of the stations, and the regional average rate was 1.5 days/decade from 1960 to 2010. The changing rate of the first frost day in autumn below 3,000 m was 1.8 times larger than the changing rate above 3,000 m. In addition, the first frost day in autumn above 3,000 m fluctuated dramatically before the early 1990s and then it was later sharply after the early 1990s. The frost-free season length increased significantly at almost all stations in the Tibetan Plateau from 1960 to 2010. For the regional average, the frost-free season lengthened at the rate of 3.1 days/decade. The changing rate of the frost-free season length below 3,000 m was more significant than the changing rate above 3,000 m. Eight indices of large-scale atmospheric circulation were employed to investigate the potential cause of the frost-free season length change in the Tibetan Plateau during the past 50 years. There was a significant relationship between the frost-free season length and the Northern Hemisphere Polar Vortex indices. The weakening cold atmospheric circulation might be an essential factor to the Tibetan Plateau warming since 1960. © 2013 Springer-Verlag Wien.


Tian X.-R.,Jiangsu Meteorological Observatory | Han Y.-X.,Nanjing University of Technology | Chen G.-C.,Proof Engineering | Wu Y.,Xuzhou Meteorological Bureau | Wang W.-L.,Jiangsu Meteorological Observatory
Zhongguo Huanjing Kexue/China Environmental Science | Year: 2014

Heavy fog days, duration hours, temporal and spatial distribution and the causes of Jiangsu heavy fog in recent 50 years were analyzed to explore aerosol effect mechanism on heavy fog formation. The result show that heavy fog might occur at any time, but the most frequent time was early morning and autumn. The changing rule could be explained by seasonal circulation background characteristics of the area and the fog formation mechanism. The days of heave fog changes annually showed parabolic distribution (up then down) in recent 50 years, and the duration hours of heavy fog shows a volatility rising tendency. Meteorological factors could not explain all the variation characteristics. Aerosol might have important effects on the formation and duration of heavy fog. The combined effects of meteorology factors and aerosol could explain the changing characteristics of heavy fog days and duration hours. ©, 2014, Editorial Board of China Environmental Science. All right reserved.


Zhang Z.-X.,Xuzhou Institute of Technology | Sun G.-D.,Xuzhou Meteorological Bureau | Sun J.-Y.,Xuzhou Meteorological Bureau | Peng C.-G.,Xuzhou Municipal Engineering Design Institute
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2013

Conventional method for determining the parameters of the storm intensity multi-period formula usually consists of two fitting processes, fitting the theory frequency curve and fitting the parameters of storm intensity multi-period formula. By such way to fit samples of the observed storm intensity, sum of squared error cannot reach the minimum. In this paper, a direct fitting method for storm intensity multi-period formula has been studied by nonlinear regression to directly fit the samples. With the storm intensity multi-period formula obtained by the direct fitting method, the minimum sum of squared error can be acquired in the process of fitting samples of observed storm intensity, and the best parameters are directly estimated. Combined two examples, the direct fitting method were compared with the conventional methods by using different theory frequency curve. The results indicate that the direct fitting method is feasible, which can increase the fitting accuracy, decrease the processes of choosing and fitting for different theory frequency curve, and avoid arbitrariness of deriving parameters for the storm intensity multi-period formula.


Zhang Z.,Xuzhou Institute of Technology | Sun G.,Xuzhou Meteorological Bureau | Sun J.,Xuzhou Meteorological Bureau | Peng C.,Xuzhou Municipal Engineering Design Institute
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2015

Conventional method for determining the parameters of the storm intensity multi-period formula usually consists of two fitting processes, fitting theory frequency curve and fitting the parameters of storm intensity multi-period formula. However, the direct fitting method directly fit the samples of observed storm intensity by nonlinear regression method. In this paper, the error of fitting samples of observed storm intensity was analyzed and compared in theory by these two different paths to determine the storm intensity multi-period formula. The result shows that error sum of squares of fitting samples of observed storm intensity by direct fitting method obtained multi-period formula is smaller than the result from the conventional method. This conclusion has universality. So the direct fitting method not only avoid tangle of choosing theory frequency curve, and arbitrariness of deriving parameters for the storm intensity multi-period formula, but also can increase the fitting accuracy. ©, 2015, China Water Power Press. All right reserved.

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