1880年以来华北降水及水资源的变化

分析了１８８０年以来华北地区降水的季节、年际和年代际变化,研究表明,华北降水存在着显著的年际和年代际变化,１８８３￣１８９８年和１９４９￣１９６４年是华北降水较丰沛时段,１８９９￣１９２０年和１９６５￣１９９７年华北降水处于偏少阶段,其中１９８０￣１９９３年降水持续偏少,干旱现象严重研究指出：华北夏季降水的年际和年代际变 夏季东亚－西太平洋地区上空５００ｈＰａ位势高度场以及西太平洋副热带高压脊线位     

基于三参数Weibull分布的安徽省年最大风速均一性检验

以安徽省56个国家级气象站1980—2018年年最大风速序列为研究对象,采用基于三参数Weibull分布的变点检验方法对年最大风速序列均一性进行检验,以郎溪站数据为例,给出了检验和分析的具体过程,最后将该方法检验结果与PM-FT法、SNHT法检验结果进行了对比分析.结果表明:56个站点的年最大风速序列均通过Weibul...     

银川市主要污染物变化特征及其关系研究

利用2013-2019年银川市主要污染物浓度数据,分析了近年来银川市主要污染物浓度变化特征,并运用主成分分析法对主要污染物之间的关系进行研究。结果表明：近年来银川市主要污染物浓度除O₃逐年呈上升趋势外,其他均呈下降趋势;市区站O₃浓度较郊区背景站低,其他污染物市区较郊区背景站高;市区站PM₁₀和PM_2.5浓度超国家二级标准;除O₃浓度夏季高,冬季低外,其他污染物冬季高,夏季低;CO、NO₂、PM₁₀、PM_2.5浓度呈"双峰型"日变化特征,O₃和SO₂呈"单峰型"日变化特征。银川市主要污染物NO₂浓度与CO和O₃相关性显著,PM₁₀和PM_2.5之间相关性显著;污染物第一主成分是NO₂、CO和O₃,方差贡献率达到50%以上,加之银川市O₃浓度逐年呈升高趋势,表明近年来银川市大气光化学污染增加。     

Time-series of surface water CO2 and oxygen measurements on a platform in the central Arkona Sea (Baltic Sea): Seasonality of uptake and release

High resolution measurements of carbon dioxide and oxygen were made in surface waters of the central Arkona Sea (Baltic Sea) from May 2003 to September 2004. Sensors for CO₂ partial pressure (pCO₂^w) and oxygen (O₂) concentration were mounted in 7 m depth on a moored platform which is used for hydrographic and meteorological monitoring. The pCO₂^w data were obtained in half hour intervals and O₂ was measured each hour as an average of a 10 min measurement. To check the performance of the sensors, pCO₂^w and O₂ were determined by shipboard measurements on a research vessel which visited the site in 1–2 month intervals. In addition, pCO₂^w was measured on a “volunteer observing ship” (VOS) passing the platform each second day at a distance of about 25 km. Minima of 220 to 250 μatm of pCO₂^w were observed at the time of the spring bloom and a cyanobacteria bloom in mid-summer. During winter the pCO₂^w was mostly close to equilibrium with the atmosphere but maxima of 430 to 530 μatm were also observed. The seasonality of oxygen and pCO₂^w showed an opposing pattern. From a multiple regression analysis, we concluded that two processes primarily controlled pCO₂^w during our study: biological turnover and mixing. A parameterization, based on apparent oxygen utilisation (AOU) and salinity (S) only (pCO₂^w = 1.23 AOU + 43 S), reproduced the seasonality of pCO₂^w in surface water reasonably well. Based on our pCO₂, salinity, and temperature data set, we attempted to separate processes changing total inorganic carbon concentrations (C_T) by using an alkalinity–salinity relation for the area. The contribution of CO₂ gas exchange and mixing were calculated and from this the biological turnover was deduced to reveal the calculated C_T changes.The net annual uptake of CO₂ in the central Arkona Sea was estimated to be about 1.5 Tg (1.5·10¹² g) which was approximately balanced by a net oxygen release considering the uncertainties of the flux calculations. Near-coast CO₂ emission due to episodic upwelling partly compensated the uptake of the central part of the Arkona Sea reducing the overall magnitude of the CO₂ uptake.     

Annual and decadal variability in the western subtropical North Atlantic: signal characteristics and sampling methodologies

Upper ocean (above 750 m) temperature structure of the northwestern subtropical Atlantic, including the Gulf Stream and a recirculation gyre south of the Stream, is characterized using primarily bathythermograph (BT) data collected between 1950 and 2003. Geostrophic calculations, using mean temperature-salinity relationships to compute dynamic height, are used to estimate velocities and transports. The mean annual Gulf Stream transport at 72° W relative to 750 m, 36.1 Sv, is approximately equal to the sum of the transport of the Florida Current, 32.0 Sv, and a shallow recirculation gyre described by Wang and Koblinsky [Journal of Physical Oceanography 26 (1996) 2462-2479], 5.5 Sv. The annual cycle of geostrophic transport relative to 750 m at 72° W is in phase with both an earlier published annual cycle of transport relative to 2000 m derived from hydrographic observations and the annual cycle of Florida Current transport measured indirectly by a submarine cable (i.e., maximum transports are observed in the summer and minimum in the fall, early winter). However, simple Sverdrup dynamics are inadequate to explain these cycles as maximum Sverdrup transports extend from winter to summer, while observed transports are minimum (maximum) in fall/winter (summer). The annual cycles derived from the BT data of the size of the shallow southern recirculation gyre, Gulf Stream position and upper layer transport (relative to 300 m) are in phase (maximum size, northern position and transport in fall) and consistent with the WK results derived from altimetry. However, the shallower annual cycles are out of phase with the deeper signals (i.e., maximum for the former (latter) are observed in fall (summer)). Decadal signals after 1965 in Gulf Stream position, geostrophic transport relative to 450 m, and the size of a recirculation gyre south of the Stream are approximately in phase as observed for the annual signal. This gyre and the shallow WK gyre exhibit the same horizontal structure, however, the decadal signal propagates deeper into the water column (at least to 700 m). The eastern expansion and contraction of the gyre on decadal time-scales is correlated with propagating SST signals. The sampling implications of these findings are addressed.     

西南地区臭氧空间分布及变化趋势

本文利用2003年1月—2012年12月的MSR2臭氧总量月平均资料对四川盆地(28～31°N,104～106°E)、青藏高原(27～37°N,80～95°E)、云贵高原(23～27°N,98～106°E)3个区域的臭氧总量空间分布及变化趋势进行了对比分析。得到了以下结论,四川盆地常年存在臭氧总量最大值,青藏高原次之,云贵高原最低。在2003—2012年这10 a间西南地区臭氧总量总体呈上升趋势,这同全球臭氧总量近几十年的变化趋势相一致,其中上升趋势云贵高原四川盆地青藏高原。西南地区在这十年间分别出现了臭氧总量最小值年(2008年)和臭氧总量最大值年(2010年),其中青藏高原还出现了一个臭氧总量最小值年(2004年)。就臭氧总量季节变化而言,在2003—2012年10 a间西南地区臭氧总量在春季存在最大值,但是青藏高原的臭氧总量在秋季存在最小值,而四川盆地和云贵高原的臭氧总量在冬季存在最小值。     

The influence of plant removal on succession in Wyoming big sagebrush

Restoration treatments are based on the largely untested notion that desired recovery of plant communities following disturbance wouldn’t occur in the absence of active intervention. We identified rate of short-term (10 year) floristic changes following removal of plant functional groups in Wyoming big sagebrush plant communities in 1999-2005 and 2008. Treatments imposed on 6 × 6 m plots were: 1) removal of all plant functional groups, 2) perennial grass removal, 3) shrub removal and 4) control. Our data suggest recovery of the shrub component on shrub removal plots could take decades. Similarly, perennial grass cover and density on perennial grass removal plots was less than half that of unaltered plots 10 years after treatment. When all functional groups were removed, cover of annual forbs, annual grasses, and shrubs returned to unaltered levels within ten years or less. Perennial forbs were unaffected (p > 0.05) by treatment. The fact that natural recovery of some components occurred within a relatively short post-disturbance time interval (i.e. <10 years) suggests that intervention may not be necessary for some functional groups. Restoring shrubs in areas dominated by perennial grasses may require targeted reductions of competing perennial grasses. Conversely, shrub dominance may limit perennial grass re-establishment.     

Drought Forecasting in a Semi-arid Watershed Using Climate Signals:a Neuro-fuzzy Modeling Approach

Large-scale annual climate indices were used to forecast annual drought conditions in the Maharlu-Bakhtegan watershed,located in Iran,using a neuro-fuzzy model.The Standardized Precipitation Index（SPI） was used as a proxy for drought conditions.Among the 45 climate indices considered,eight identified as most relevant were the Atlantic Multidecadal Oscillation（AMO）,Atlantic Meridional Mode（AMM）,the Bivariate ENSO Time series（BEST）,the East Central Tropical Pacific Surface Temperature（NINO 3.4）,the Central Tropical Pacific Surface Temperature（NINO 4）,the North Tropical Atlantic Index（NTA）,the Southern Oscillation Index（SOI）,and the Tropical Northern Atlantic Index（TNA）.These indices accounted for 81% of the variance in the Principal Components Analysis（PCA） method.The Atlantic surface temperature（SST：Atlantic） had an inverse relationship with SPI,and the AMM index had the highest correlation.Drought forecasts of neuro-fuzzy model demonstrate better prediction at a two-year lag compared to a stepwise regression model.     

利用GRACE卫星重力资料解算气候驱动的地表周年垂直形变

卫星重力和GPS测量技术可以监测地表流体(大气、海洋和陆地水)质量季节性迁移引起的地表周年形变;与陆地水等地表流体模型综合模拟的地表形变相比,卫星重力的形变监测结果避免了模型的精度不确定性带来的误差.本文利用前60阶GRACE卫星时变重力资料和“去相关”、组合滤波两类滤波方法分别解算了中国及邻区的地表季节性垂直形变,并与区内42个GPS台站上观测到的季节性信号进行了比较,发现采用“去相关”滤波方法处理后的结果优于采用组合滤波处理后的结果.文中采用“去相关”滤波方法,GRACE解算的周年垂直形变的振幅、相位和GPS结果总体上一致;少数站上GRACE和GPS得到的振幅或相位相差较大,主要因素可能与GPS解算策略、GPS观测资料的连续性或局部大气、水文过程等地球物理因素有关.在中国及邻区的陆地上GRACE解算的周年垂直形变的振幅最小值出现在TASH台站东南,约1×10^-3 m;最大值出现在恒河-澜沧江流域,可达10×10^-3 m.文中的结果证实了在中国及邻区可以用GRACE卫星重力这种新手段监测大尺度的地表周年垂直形变.     

中强地震活动区地震年平均发生率确定方法的比较

Two kinds of methods for determining seismic parameters are presented,that is,the potential seismic source zoning method and grid-spatially smoothing method. The Gaussian smoothing method and the modified Gaussian smoothing method are described in detail, and a comprehensive analysis of the advantages and disadvantages of these methods is made. Then,we take central China as the study region,and use the Gaussian smoothing method and potential seismic source zoning method to build seismic models to calculate the mean annual seismic rate. Seismic hazard is calculated using the probabilistic seismic hazard analysis method to construct the ground motion acceleration zoning maps. The differences between the maps and these models are discussed and the causes are investigated. The results show that the spatial smoothing method is suitable for estimating the seismic hazard over the moderate and low seismicity regions or the hazard caused by background seismicity; while the potential seismic source zoning method is suitable for estimating the seismic hazard in well-defined seismotectonics. Combining the spatial smoothing method and the potential seismic source zoning method with an integrated account of the seismicity and known seismotectonics is a feasible approach to estimate the seismic hazard in moderate and low seismicity regions.