Using observational data and the data of disastrous investigation of tornado in Zhujiang River Delta and Guangzhou's sounding from March to May of 1976-1983, the environmental conditions of genesis of tornado are ...Using observational data and the data of disastrous investigation of tornado in Zhujiang River Delta and Guangzhou's sounding from March to May of 1976-1983, the environmental conditions of genesis of tornado are analysed and compared with those of nontornadic local storm. It is found that the favorable conditions of genesis of tornado are lower pressure, unstable stratification and stronger wind in the deep layer of troposphere and higher temperature and humidity in low level, among which, lower pressure, more unstable stratification and layer wind are primary conditions for a severe local storm to possibly develop into a storm with accompanying tornado. The tornado mechanism is not related to vertical wind shear.展开更多
The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the veg...The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the vegetation growing season(SOS)based on remote sensing data is easily affected by outliers because this data series is short. In this study, we determine that the spring minimum temperature is the most influential factor for SOS. The significant negative linear relationship between the two variables in the region is evaluated using Moderate Resolution Imaging Spectroradiometer–Normalized Difference Vegetation Index data for 2000–13. We then reconstruct the SOS time series based on the temperature data for 1960–2013.The regional mean SOS shows an advancing trend of 1.42 d(10 yr)during 1960–2013, with the SOS occurring on the 160th and 151st days in 1960 and 2013, respectively. The advancing trend enhances to 6.04 d(10 yr)during the past 14 years. The spatiotemporal variations of the reconstructed SOS data are similar to those deduced from remote sensing data during the past 14 years. The latter exhibit an even larger regional mean trend of SOS [7.98 d(10 yr)] during 2000–13. The Arctic Oscillation is found to have significantly influenced the changing SOS, especially for the eastern part of the region,during 2000–13.展开更多
The distribution of winter-spring snow cover over the Tibetan Plateau （TP） and its relationship with summer precipitation in the middle and lower reaches of Yangtze River Valley （MLYRV） during 2003-2013 have been ...The distribution of winter-spring snow cover over the Tibetan Plateau （TP） and its relationship with summer precipitation in the middle and lower reaches of Yangtze River Valley （MLYRV） during 2003-2013 have been investigated with the moderate-resolution imaging spectrometer （MODIS） Terra data （MOD10A2） and precipitation observations. Results show that snow cover percentage （SCP） remains approximately 20% in winter and spring then tails off to below 5% with warmer temperature and snow melt in summer. The lower and highest percentages present a declining tendency while the middle SCP exhibits an opposite variation. The maximum value appears from the middle of October to March and the minimum emerges from July to August. The annual and winter-spring SCPs present a decreasing tendency. Snow cover is mainly situated in the periphery of the plateau and mountainous regions, and less snow in the interior of the plateau, basin and valley areas in view of snow cover frequency （SCF） over the TP. Whatever annual or winter-spring snow cover, they all have remarkable declining tendency during 2003-2013, and annual snow cover presents a decreasing trend in the interior of the TP and increasing trend in the periphery of the TP. Hie multi-year averaged eight-day SCP is negatively related to mean precipitation in the MLYRV. Spring SCP is negatively related to summer precipitation while winter SCP is positively related to summer precipitation in most parts of the MLYRV. Hence, the influence of winter snow cover on precipitation is much more significant than that in spring on the basis of correlation analysis. The oscillation of SCF from southeast to northwest over the TP corresponds well to the beginning,development and cessation of the rain belt in eastern China.展开更多
喀斯特流域是岩石风化碳汇的关键区域,同时也是CO_(2)逸散研究的热点区域。为探究喀斯特地下河涌出后CO_(2)分压(pCO_(2))及其逸散通量的时空变化格局,选择喀斯特流域巴马盘阳河为对象,分析水体的pH、碱度、总溶解性固体(TDS)、溶解无机...喀斯特流域是岩石风化碳汇的关键区域,同时也是CO_(2)逸散研究的热点区域。为探究喀斯特地下河涌出后CO_(2)分压(pCO_(2))及其逸散通量的时空变化格局,选择喀斯特流域巴马盘阳河为对象,分析水体的pH、碱度、总溶解性固体(TDS)、溶解无机碳(DIC)、溶解有机碳(DOC)、pCO_(2)的时空变化特征,探讨pCO_(2)的调控因素并估算了CO_(2)逸散通量。结果表明,流域内地下水碱度、TDS、DIC和pCO_(2)显著高于地表水,表明喀斯特碳酸盐风化释放大量DIC进入地下水,地下水涌出后产生CO_(2)逸散降低了地表水DIC含量和pCO_(2)。在时间尺度上,旱季常规地表、地下水的碱度、TDS、DIC、pCO_(2)、CO_(2)逸散通量均显著高于雨季,主要归结于雨季雨水的稀释效应。然而次降雨事件下地表、地下水的pH、碱度、TDS、DIC、DOC、pCO_(2)无显著性差异,可能由于降雨量不足或降雨持续时间短。研究期间,巴马盘阳河流域地表水、地下水CO_(2)逸散通量范围分别为-0.10~9.20 kg C m^(-2)year^(-1),-0.12~17.28kg C m^(-2)year^(-1),平均CO_(2)逸散通量分别为1.06±1.46 kg C m^(-2)year^(-1)和2.40±3.14 kg C m^(-2)year^(-1),远高于全球主要大型流域的平均CO_(2)逸散通量(0.64 kg Cm^(-2)year^(-1))。阐明喀斯特流域的CO_(2)逸散通量及其时空变化特征对准确评估河流碳收支状况与评估岩石风化碳汇具有重要意义。展开更多
文摘Using observational data and the data of disastrous investigation of tornado in Zhujiang River Delta and Guangzhou's sounding from March to May of 1976-1983, the environmental conditions of genesis of tornado are analysed and compared with those of nontornadic local storm. It is found that the favorable conditions of genesis of tornado are lower pressure, unstable stratification and stronger wind in the deep layer of troposphere and higher temperature and humidity in low level, among which, lower pressure, more unstable stratification and layer wind are primary conditions for a severe local storm to possibly develop into a storm with accompanying tornado. The tornado mechanism is not related to vertical wind shear.
基金supported by the National Key Research and Development Program of China(Grant Nos.2016YFA0600400 and 2016YFA0602500)supported by the Open Research Fund of the Key Laboratory of Tibetan Environmental Changes and Land Surface Processes,Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant No.41405082)
文摘The variation of the vegetation growing season in the Three-Rivers Headwater Region of the Tibetan Plateau has recently become a controversial topic. One issue is that the estimated local trend in the start of the vegetation growing season(SOS)based on remote sensing data is easily affected by outliers because this data series is short. In this study, we determine that the spring minimum temperature is the most influential factor for SOS. The significant negative linear relationship between the two variables in the region is evaluated using Moderate Resolution Imaging Spectroradiometer–Normalized Difference Vegetation Index data for 2000–13. We then reconstruct the SOS time series based on the temperature data for 1960–2013.The regional mean SOS shows an advancing trend of 1.42 d(10 yr)during 1960–2013, with the SOS occurring on the 160th and 151st days in 1960 and 2013, respectively. The advancing trend enhances to 6.04 d(10 yr)during the past 14 years. The spatiotemporal variations of the reconstructed SOS data are similar to those deduced from remote sensing data during the past 14 years. The latter exhibit an even larger regional mean trend of SOS [7.98 d(10 yr)] during 2000–13. The Arctic Oscillation is found to have significantly influenced the changing SOS, especially for the eastern part of the region,during 2000–13.
基金supported by the National Natural Science Foundation of China(Grant No.41130960)the Project of the China Meteorological Administration(Grant Nos.CCSF201515 and CMAGJ2013M51)
文摘The distribution of winter-spring snow cover over the Tibetan Plateau （TP） and its relationship with summer precipitation in the middle and lower reaches of Yangtze River Valley （MLYRV） during 2003-2013 have been investigated with the moderate-resolution imaging spectrometer （MODIS） Terra data （MOD10A2） and precipitation observations. Results show that snow cover percentage （SCP） remains approximately 20% in winter and spring then tails off to below 5% with warmer temperature and snow melt in summer. The lower and highest percentages present a declining tendency while the middle SCP exhibits an opposite variation. The maximum value appears from the middle of October to March and the minimum emerges from July to August. The annual and winter-spring SCPs present a decreasing tendency. Snow cover is mainly situated in the periphery of the plateau and mountainous regions, and less snow in the interior of the plateau, basin and valley areas in view of snow cover frequency （SCF） over the TP. Whatever annual or winter-spring snow cover, they all have remarkable declining tendency during 2003-2013, and annual snow cover presents a decreasing trend in the interior of the TP and increasing trend in the periphery of the TP. Hie multi-year averaged eight-day SCP is negatively related to mean precipitation in the MLYRV. Spring SCP is negatively related to summer precipitation while winter SCP is positively related to summer precipitation in most parts of the MLYRV. Hence, the influence of winter snow cover on precipitation is much more significant than that in spring on the basis of correlation analysis. The oscillation of SCF from southeast to northwest over the TP corresponds well to the beginning,development and cessation of the rain belt in eastern China.
文摘喀斯特流域是岩石风化碳汇的关键区域,同时也是CO_(2)逸散研究的热点区域。为探究喀斯特地下河涌出后CO_(2)分压(pCO_(2))及其逸散通量的时空变化格局,选择喀斯特流域巴马盘阳河为对象,分析水体的pH、碱度、总溶解性固体(TDS)、溶解无机碳(DIC)、溶解有机碳(DOC)、pCO_(2)的时空变化特征,探讨pCO_(2)的调控因素并估算了CO_(2)逸散通量。结果表明,流域内地下水碱度、TDS、DIC和pCO_(2)显著高于地表水,表明喀斯特碳酸盐风化释放大量DIC进入地下水,地下水涌出后产生CO_(2)逸散降低了地表水DIC含量和pCO_(2)。在时间尺度上,旱季常规地表、地下水的碱度、TDS、DIC、pCO_(2)、CO_(2)逸散通量均显著高于雨季,主要归结于雨季雨水的稀释效应。然而次降雨事件下地表、地下水的pH、碱度、TDS、DIC、DOC、pCO_(2)无显著性差异,可能由于降雨量不足或降雨持续时间短。研究期间,巴马盘阳河流域地表水、地下水CO_(2)逸散通量范围分别为-0.10~9.20 kg C m^(-2)year^(-1),-0.12~17.28kg C m^(-2)year^(-1),平均CO_(2)逸散通量分别为1.06±1.46 kg C m^(-2)year^(-1)和2.40±3.14 kg C m^(-2)year^(-1),远高于全球主要大型流域的平均CO_(2)逸散通量(0.64 kg Cm^(-2)year^(-1))。阐明喀斯特流域的CO_(2)逸散通量及其时空变化特征对准确评估河流碳收支状况与评估岩石风化碳汇具有重要意义。
