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Zhao W.,Zhejiang Institute of Meteorological science | Zhao W.,Chinese Academy of Meteorological Sciences | Li Z.,State Grid Corporation of China | Tong H.,Zhejiang Electrical Power Test and Research Institute
Gaodianya Jishu/High Voltage Engineering | Year: 2017

In order to improve the effectiveness and scientificalness of risk assessment of lightning trip-out in power grid and realize the differentiated lightning protection, it is necessary to study the hazard-pregnant environment of lightning trip-out in power grid. Based on 1:50 000 digital elevation model (DEM) and the data of accidents of lightning trip-out on 110 kV and above transmission lines from 2005 to 2013 in Zhejiang Power Grid, the topographic factors of lightning trip-out spots, including elevation, slope, aspect, land use type and river network density are obtained by using the GIS technology. The topographic characteristics of lightning trip-out spots are quantitatively studied. The hazard-pregnant environment evaluating model in Zhejiang Power Gird is established on Analytic Hierarchy Process (AHP) method with elevation, slope, aspect, land use type and river network density as five assessment indices and a hazard-pregnant environment risk zoning map of Zhejiang power grid is drawn. Correlation analysis with the risk distribution of disaster-causing factor shows that the correlation coefficient is 0.451 and the hazard-pregnant environment sensitivity zoning map for Zhejiang Power Grid is reasonable and could be applied to risk assessment of lightning trip-out in Zhejiang Power Grid. From the analysis of the hazard-pregnant environment sensitivity distribution, the high hazard-pregnant environment sensitivity distribution of lightning trip-out in Zhejiang Power Grid is mainly located in the north of northern Zhejiang and the coast of eastern Zhejiang. The low hazard-pregnant environment sensitivity distribution of lightning trip-out in Zhejiang Power Grid is mainly located in the central Zhejiang and the western Zhejiang. © 2017, High Voltage Engineering Editorial Department of CEPRI. All right reserved.

Jia B.,CAS Institute of Atmospheric Physics | Xie Z.,CAS Institute of Atmospheric Physics | Dai A.,University at Albany | Dai A.,U.S. National Center for Atmospheric Research | And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

Surface solar radiation plays a crucial role in surface energy and water budgets, and it is also an important forcing for land hydrological models. In this study, the downward surface solar radiation (DSSR) from two satellite products, the Fengyun-2C satellite (FY-2C) and the Fast Longwave and Shortwave Radiative Fluxes project (FLASHFlux), and two reanalysis datasets, NCEP-DOE and ERA-Interim, was evaluated against ground-based observations (OBS) from 94 stations over mainland China during July 2006 to June 2009. It is found that the mean DSSR derived from FY-2C is comparable to OBS, with small positive biases of 3.0 Wm-2 for daily data and 3.5 Wm-2 for monthly data and moderate RMSEs of 49.3 Wm-2 (daily) and 31.9 Wm-2 (monthly). These results are comparable to those for FLASHFlux, which has the lowest RMSEs (43.2 Wm-2 and 30.5 Wm-2 for daily and monthly data, respectively) and the strongest correlations with OBS (r = 0.90 and 0.93 for daily and monthly data, respectively) among the four products. The DSSR from the reanalyses has much larger RMSEs and generally lower correlations with OBS than the satellite products, especially for the NCEP-DOE products. Results also show that daily DSSR values are sensitive to the averaging grid size, while monthly mean DSSR is largely insensitive to the averaging scale. The DSSR from the four datasets over East Asia shows similar spatial patterns with large seasonal variations but differs in magnitude. In summer, high DSSR is observed over western China, while low DSSR is seen primarily over South Asia and the Sichuan Basin associated with extensive cloud cover (CC) and large precipitable water (PW). In winter, the high DSSR center shifts to South Asia due to decreased CC and PW, and the DSSR decreases from the South to the North. Deficiencies in the parameterizations of clouds, aerosols, and water vapor, as well as errors in atmospheric and surface properties for the retrieval algorithms contribute to the lower correlation of the DSSR derived from FY-2C (r = 0.82 and 0.90 for daily and monthly data) with OBS than those from FLASHFlux product. Further improvements to the representation of clouds and aerosols in the FY-2C retrieval algorithm are needed. © 2013. American Geophysical Union. All Rights Reserved.

Zhao W.,Zhejiang Institute of Meteorological science | Tong H.,Hangzhou Electric Power | Zhang J.,Hangzhou Electric Power | Pu J.,Zhejiang Institute of Meteorological science
Dianwang Jishu/Power System Technology | Year: 2013

Based on the recorded data of thunderstorm days from 70 surface observation stations in Zhejiang province ever since their building up to 2011 and the cloud-to-ground lightning data recorded by lightning detection and location system of Zhejiang power bureau and the record of damages caused by thunders from 2005 to 2011, the temporal-spatial distribution characteristics of thunder and lightning in Zhejiang province and influencing factors are analyzed and researched. Research results show that the lightning phenomena mainly appear from March to September and mostly happen in the time period from 15: 00 to 16: 00. The distribution of thunderstorm days present such a feature that the amount of thunderstorm days appear in mountain area is more than that in plain area, and that in inland area is more than that in coastal areas. There is obvious regional difference in the density distribution of cloud-to-ground lightning: it appears as the distribution in two large areas and several points. The percentage of negative cloud-to-ground lightning in total cloud-to-ground lightning is 94.91%. The positive and negative lightning intensities mainly appear in the range from 0 kA to 50 kA. The distribution of areas with high density of cloud-to-ground lightning in Zhejiang province is bound up with whether, landform, topographic feature, surface large-scale water mass and urban heat island effect.

Zhang Y.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Gao J.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Liu L.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Wang Z.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | And 3 more authors.
Global and Planetary Change | Year: 2013

Considerable researches during the past several decades have focused on monitoring changes in vegetation growth due to its important role in regulating the terrestrial carbon cycle and the climate system. In this study, we combined datasets of the satellite-derived Normalized Difference Vegetation Index (NDVI) and climatic factors to analyze spatio-temporal patterns of vegetation growth in 1982-2006 in the Koshi River Basin (KRB) in the middle Himalayas. In addition, the dataset from the global land surface satellite sensor from SPOT-4's Vegetation instrument in 1998-2011 was used to further verify the results of this study. At the regional scale, although a statistically significant increase in average growing season NDVI was observed (0.0008yr-1, P=0.03) during the entire study period, there existed three distinct periods with opposing trends. Growing season NDVI significantly increased in 1982-1994 (0.0019yr-1, P=0.03), and then decreased in 1994-2000 (-0.0058yr-1, P<0.001), while increased again in 2000-2006 (0.0049yr-1, P<0.001) and in 2000-2011 (0.0034yr-1, P<0.001). A sudden drop in NDVI in 1994-2000 largely contributed to these fluctuations in growing season NDVI over the KRB. Spring, summer and autumn NDVI significantly decreased in 1994-2000 (-0.0077yr-1, P<0.001; -0.0067yr-1, P<0.001; and -0.0155yr-1, P<0.001; respectively). Our further spatial analyses supported the existence of the sudden decrease in spring, summer and autumn NDVI in 1994-2000. © 2013 Elsevier B.V.

Yang X.,Zhejiang Institute of Meteorological science | Yue W.,Zhejiang University | Yue W.,Key Laboratory of Carrying Capacity Assessment for Resource and Environment | Gao D.,Zhejiang Climate Center
International Journal of Remote Sensing | Year: 2013

A spatial mismatch of hazard data and exposure data (e.g. population) exists in risk analysis. This article provides an integrated approach for a rapid and accurate estimation of population distribution on a per-pixel basis, through the combined use of medium and coarse spatial resolution remote-sensing data, namely the Defense Meteorological Satellite Program Operational Linescan System (DMSP/OLS) night-time imagery, enhanced vegetation index (EVI), and digital elevation model (DEM) data. The DMSP/OLS night-time light data have been widely used for the estimation of population distribution because of their free availability, global coverage, and high temporal resolution. However, given its low-radiometric resolution as well as the overglow effects, population distribution cannot be estimated accurately. In the present study, the DMSP/OLS data were combined with EVI and DEM data to develop an elevation-adjusted human settlement index (EAHSI) image. The model for population density estimation, developed based on the significant linear correlation between population and EAHSI, was implemented in Zhejiang Province in southeast China, and a spatialized population density map was generated at a resolution of 250 m × 250 m. Compared with the results from raw human settlement index (59.69%) and single night-time lights (35.89%), the mean relative error of estimated population by EAHSI has been greatly reduced (17.74%), mainly due to the incorporation of elevation information. The accurate estimation of population density can be used as an input for exposure assessment in risk analysis on a regional scale and on a per-pixel basis. © 2013 Copyright Taylor and Francis Group, LLC.

Yu Y.,CAS Institute of Atmospheric Physics | Yu Y.,Zhejiang Institute of Meteorological science | Xie Z.,CAS Institute of Atmospheric Physics | Zeng X.,University of Arizona
Journal of Geophysical Research D: Atmospheres | Year: 2014

To remove the deficiency of the numerical solution of the mass conservation-based Richards equation for soil moisture in a regional climate model (RegCM4 with its land surface component Community Land Model 3.5 (CLM3.5)), a revised numerical algorithm that is used in CLM4.5 is implemented into CLM3.5. Compared with in situ measurements, the modified numerical method improves the ground water table depth simulations in RegCM4. It also improves the temporal and spatial variability of soil moisture to some extent. Its impact on simulated summer precipitation is mixed, with improvements over three subregions in China but with increased errors in three other subregions. The impact on the simulated summer temperature is relatively small (with the mean biases changed by less than 10% over most subregions). The evapotranspiration differences between modified and control land-atmosphere coupled simulations are enhanced over the northwest subregion and Tibetan Plateau compared to offline simulations due to land surface feedbacks to the atmosphere (in coupled simulations). Similarly the soil moisture differences in coupled simulations are geographically different from those in offline simulations over the eastern monsoon area. The summer precipitation differences between modified and control coupled simulations are found to be explained by the differences of both surface evapotranspiration and large-scale water vapor flux convergence which have opposite signs over the northwest subregion and Tibetan Plateau but have the same signs over other subregions. ©2014. American Geophysical Union. All Rights Reserved.

Chen F.,CAS Institute of Atmospheric Physics | Chen F.,Zhejiang Institute of Meteorological science | Xie Z.,CAS Institute of Atmospheric Physics
Climate Dynamics | Year: 2012

In this study, the CERES phenological growth and development functions were implemented into the regional climate model, RegCM3 to give a model denoted as RegCM3_CERES. This model was used to represent interactions between regional climate and crop growth processes. The effects of crop growth and development processes on regional climate were then studied based on two 20-year simulations over the East Asian monsoon area conducted using the original regional climate model RegCM3, and the coupled RegCM3_CERES model. The numerical experiments revealed that incorporating the crop growth and development processes into the regional climate model reduced the root mean squared error of the simulated precipitation by 2.2-10.7% over north China, and the simulated temperature by 5.5-30.9% over the monsoon region in eastern China. Comparison of the simulated results obtained using RegCM3_CERES and RegCM3 showed that the most significant changes associated with crop modeling were the changes in leaf area index which in turn modify the aspects of surface energy and water partitions and lead to moderate changes in surface temperature and, to some extent, rainfall. Further analysis revealed that a robust representation of seasonal changes in plant growth and developmental processes in the regional climate model changed the surface heat and moisture fluxes by modifying the vegetation characteristics, and that these differences in simulated surface fluxes resulted in different structures of the boundary layer and ultimately affected the convection. The variations in leaf area index and fractional vegetation cover changed the distribution of evapotranspiration and heat fluxes, which could potentially lead to anomalies in geopotential height, and consequently influenced the overlying atmospheric circulation. These changes would result in redistribution of the water and energy through advection. Nevertheless, there are significant uncertainties in modeling how monsoon dynamics responds to crop modeling and more research is needed. © 2011 The Author(s).

Chen F.,Zhejiang Institute of Meteorological science | Yang X.,Zhejiang Institute of Meteorological science | Yang X.,Zhejiang University | Zhu W.,Hangzhou Normal University | Zhu W.,Zhejiang Provincial Key Laboratory of Urban Wetlands and Regional Change
Atmospheric Research | Year: 2014

The urban heat island (UHI) effect over Hangzhou, east China during a long-lasting heat wave was simulated by a weather research and forecasting (WRF) model coupled with an urban canopy model (UCM) at a horizontal resolution of 1. km. Based on satellite-measured nighttime light data and the normalized difference vegetation index, a human settlement index was used to represent the current urban land cover and define three urban land subcategories in the UCM. Three numerical simulations representing different urbanization scenarios and an idealized simulation with all the urban surface replaced with cropland were performed. Using up-to-date urban land use data, the coupled WRF/UCM model reasonably reproduced the majority of the observed spatial and temporal characteristics of the 2-m temperature field over the simulation period in Hangzhou. Strong UHI effects that can cause intensification and expansion of the areas experiencing extreme heat stress were observed in both actual measurements and simulations. In the simulation, an average temperature increase of 0.74. °C in the city center was observed under high urbanization conditions. The UHI peak reached a maximum value of 1.6. °C at 1900 LST around sunset. Analysis of the surface energy balance showed that the UHI is mainly caused by a greater heat storage in the urban fabric during the day and the release of this heat in the evening. Comparisons among the results of four sensitivity runs showed that urban land use, classification of three urban land subcategories, and consideration of anthropogenic heat release respectively contributed 56.8% (0.42. °C), 13.5% (0.10. °C), and 29.7% (0.22. °C) to the simulated UHI effects. © 2013 Elsevier B.V.

Chen F.,CAS Institute of Atmospheric Physics | Chen F.,Zhejiang Institute of Meteorological science | Xie Z.,CAS Institute of Atmospheric Physics
Advances in Atmospheric Sciences | Year: 2011

In this study, the Crop Estimation through Resource and Environment Synthesis model (CERES3. 0) was coupled into the Biosphere-Atmosphere Transfer Scheme (BATS), which is called BATS CERES, to represent interactions between the land surface and crop growth processes. The effects of crop growth and development on land surface processes were then studied based on numerical simulations using the land surface models. Six sensitivity experiments by BATS show that the land surface fluxes underwent substantial changes when the leaf area index was changed from 0 to 6 m2 m -2. Numerical experiments for Yucheng and Taoyuan stations reveal that the coupled model could capture not only the responses of crop growth and development to environmental conditions, but also the feedbacks to land surface processes. For quantitative evaluation of the effects of crop growth and development on surface fluxes in China, two numerical experiments were conducted over continental China: one by BATS CERES and one by the original BATS. Comparison of the two runs shows decreases of leaf area index and fractional vegetation cover when incorporating dynamic crops in land surface simulation, which lead to less canopy interception, vegetation transpiration, total evapotranspiration, top soil moisture, and more soil evaporation, surface runoff, and root zone soil moisture. These changes are accompanied by decreasing latent heat flux and increasing sensible heat flux in the cropland region. In addition, the comparison between the simulations and observations proved that incorporating the crop growth and development process into the land surface model could reduce the systematic biases of the simulated leaf area index and top soil moisture, hence improve the simulation of land surface fluxes. © 2011 Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.

Pu J.-J.,Zhejiang Institute of Meteorological science | Xu H.-H.,Zhejiang Institute of Meteorological science | He J.,The University of Nottingham Ningbo, China | Fang S.-X.,Chinese Academy of Meteorological Sciences | Zhou L.-X.,Chinese Academy of Meteorological Sciences
Atmospheric Environment | Year: 2014

A new method of extracting regional background concentration of CO2 in Yangtze River Delta was established based on the observations of both black carbon concentration and meteorological parameters. The concentrations of CO2 and black carbon were observed at Lin'an regional background station from 2009 to 2011. The regional background concentration of CO2 in Yangtze River Delta was obtained by means of this new method, and the impact of human activities on CO2 concentration in this area was also assessed. The results showed that the regional background concentration of CO2 extracted by this approach was comparable to the values obtained by R statistical filter method, and moreover this new method was better at picking up episodes heavily polluted by anthropogenic emissions. The annual regional average background concentration of CO2 in Yangtze River Delta from 2009 to 2011 was approximately 404.7±8.2ppm, 405.6±5.3ppm and 407.0±5.3ppm, respectively, much higher than global average value, indicating the distinct characteristic of this region. The anthropogenic emissions from Yangtze River Delta had significant influence on the concentration of CO2, increasing the value roughly 9.1ppm higher than the regional background concentration of this area. © 2014 Elsevier Ltd.

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