大气点源扩散模型的GIS可视化研究

本文针对目前城市环境中大气污染扩散的可视化研究中存在的主要问题,利用大气点源扩散模型和GIS技术相集成的方法对点源污染扩散的可视化问题进行了探索。在研究中,首先在总体上介绍了点源扩散模型和GIS技术的集成框架,然后描述了大气点源扩散模型可视化实现的方法和过程,并给出了典型条件下的可视化结果图,它能够更加直观地表达大气点源扩散的动态可视化效果。     

Estimating surface ice velocity on Chhota Shigri glacier from satellite data using Particle Image Velocimetry (PIV) technique

Information about the surface ice velocity is one of the important parameters for Mass balance and Glacier dynamics. This study estimates the surface ice velocity of Chhota Shigri glacier using Landsat (TM/ETM+) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) temporal data-sets from a period of 2009 to 2016 and 2006 to 2007, respectively. A correlation based Particle Image Velocimetry (PIV) technique has been used for the estimation of surface ice velocity. This technique uses multiple window sizes in the same data-set. Four window sizes (low, medium, high, very high) are used for each image pair. Estimated results have been compared with the published data. The outcomes attained from the medium window size closely matches with the published results. The estimated mean surface ice velocities of medium window size are 24 and 28.5 myr^?1 for 2009/2010 and 2006/2007 images pair. Highest velocity is observed in middle part of the glacier while lowest in the accumulation zone of the glacier.     

Vertical distribution features of atmospheric water vapour in the Po valley area

Two sets of radiosounding measurements, taken at different hours from some stations in the Po Valley area, were examined in order to obtain the values of precipitable waterw and determine the shapes of the vertical distribution curves of absolute humidity. From these curves, we calculated the bestfit values of scale heightsH ₁ andH ₂ in the 0÷5 km and 5÷10 km altitude intervals, respectively. The analysis of the radiosounding data clearly shows that parametersw andH ₁ are closely related to the evolutionary features of the meteorological conditions on synoptic scale and are influenced, to a lesser extent, by the diurnal variations in the atmospheric ground layer. Seasonal average curves of temperature and absolute humidity, as functions of altitude, were also defined from the radiosounding measurements taken at various hours of the day. Moreover, interpolation methods in time (applied to a 12-hour range) and in space (range of about 300 km) were proposed for determining parametersw andH ₁ from the radiosounding measurements taken at different hours from the same station or from different stations at the same hour. Reliability tests, made by comparing the same station or from different stations at the same hour. Reliability tests, made by comparing the values given by the interpolation methods with those directly obtained from the radiosounding measurements, show that these evaluations ofw andH ₁ are affected by standard errors of estimate, which are comparable to the errors usually made in analyzing the radiosounding data.     

2010年西北太平洋与南海热带气旋活动异常的成因分析

利用中国气象局热带气旋（TC）资料、NCEP/NCAR 再分析资料和美国 NOAA 向外长波辐射（OLR）等资料,分析了2010年西北太平洋（WNP）及南海（SCS）热带气旋活动异常的可能成因,讨论了同期大气环流配置和海温外强迫对TC生成和登陆的动力和热力条件的影响。结果表明,2010年生成TC频数明显偏少,生成源地显著偏西,而登陆TC频数与常年持平。导致7～10月TC频数明显偏少的大尺度环境场特征为：副热带高压较常年异常偏强、西伸脊点偏西,季风槽位置异常偏西,弱垂直风切变带位置也较常年偏西且范围偏小,南亚高压异常偏强,贝加尔湖附近对流层低高层均为反气旋距平环流,这些关键环流因子的特征和配置都不利于 TC 在WNP的东部生成。影响TC活动的外强迫场特征为：2010年热带太平洋经历了El Ni?o事件于春末夏初消亡、La Ni?a事件于7月形成的转换;7～10月,WNP海表温度维持正距平,140°E以东为负距平且对流活动受到抑制;暖池次表层海温异常偏暖,对应上空850 hPa为东风距平,有利于季风槽偏西和TC在WNP的西北侧海域生成。WNP海表温度和暖池次表层海温的特征是2010年TC生成频数偏少、生成源地异常偏西的重要外强迫信号。有利于7～10月热带气旋西行和登陆的500 hPa风场特征为：北太平洋为反气旋环流距平,其南侧为东风异常,该东风异常南缘可到25°N,并向西扩展至中国大陆地区;南海和西北太平洋地区15°N以南的低纬也为东风异常;在这样的风场分布型下,TC容易受偏东气流引导西行并登陆我国沿海地区。这是2010年生成TC偏少但登陆TC并不少的重要环流条件。     

横断山脉地区大气环流演变特征分析

应用Lamb-Jenkinson大气环流分型方法对横断山脉地区的8个经度×10个纬度范围内1948-2012年逐日平均的海平面气压场进行环流分型,由日平均海平面气压场算出6个环流指数（u、v、V、ξu、ξv、ξ）,并由此划分出27种不同的环流型。分型结果表明：横断山脉地区主要环流分型为E型、NE型、SE型、N型和C型,其频率分别为：21.4%、14.6%、13.7%、9.8%和9.5%;E和NE型环流频率逐渐增加,C型环流型频率逐渐减少。春季横断山脉地区主导环流比较繁琐;NE、N型为夏季的主要环流型,但E型环流在夏季的频率也相当大;秋季和冬季横断山脉地区的主导环流型都为E型和SE型。夏季主导环流型持续时间较长,冬季也是主导环流持续的时间较长,个别年份主导环流型持续时间超过了一个月,这主要与横断山脉地区复杂的地形有联系。     

Nonstationary pearl pulsations as a signature of magnetospheric disturbances

We analyse long-lasting (several hours) Pc1 pearl pulsations with decreasing, increasing or constant central frequencies. We show that nonstationary pearl events (those with either decreasing or increasing central frequency) are observed simultaneously with increasing auroral magnetic activity at the nightside magnetosphere while the stationary events (constant central frequency) correspond to quiet magnetic conditions. Events with decreasing central frequency are observed mostly in the late morning and daytime whereas events with increasing central frequency appear either early in the morning or in the afternoon. We explain the diurnal distribution of the nonstationary pearl pulsations in terms of proton drifts depending on magnetic activity, and evaluate the magnetospheric electric field based on the variation of the central frequency of pearl pulsations.     

Paleo‐fires and Atmospheric Oxygen Levels in the Latest Permian: Evidence from Maceral Compositions of Coals in Eastern Yunnan,Southern China

Inertinite maceral compositions of the Late Permian coals from three sections in the terrestrial and paralic settings of eastern Yunnan are analyzed in order to reveal the paleo-fire events and the atmospheric oxygen levels in the latest Permian. Although the macerals in the studied sections are generally dominated by vitrinite, the inertinite group makes up a considerable proportion. Its content increases upward from the beginning of the Late Permian to the coal seam near the Permian-Triassic boundary. Based on the microscopic features and the prevailing theory that inertinite is largely a by-product of paleo-fires, we suggest that the increasing upward trend of the inertinite abundance in the latest Permian could imply that the Late Permian peatland had suffered from frequent wildfires. Since ignition and burning depend on sufficient oxygen, a model-based calculation suggests that the O2 levels near the Wuchiapingian/Changhsingian boundary and the Permian-Triassic boundary are 27% and 28% respectively. This output adds supports to other discoveries made in the temporal marine and terrestrial sediments, and challenges the theories advocating hypoxia as a mechanism for the Permian-Triassic boundary crisis.     

A DIAGNOSTIC ANALYSIS OF AIR TEMPERATURE ANOMALY MODE OVER CHINA IN 2009/2010 WINTER BASED ON GENERALIZED EQUILIBRIUM FEEDBACK ASSESSMENT (GEFA) METHOD

By using the observed monthly mean data over 160 stations of China and NCAR/NCEP reanalysis data, the generalized equilibrium feedback assessment(GEFA) method, combined with the methods of EOF analysis, correlation and composite analysis, is used to explore the influence of different SST modes on a wintertime air temperature pattern in which it is cold in the northeast and warm in the southwest in China. The results show that the 2009/2010 winter air temperature oscillation mode between the northern and southern part of China is closely related to the corresponding sea surface temperature anomalies(SSTA) and its associated atmospheric circulation anomalies. Exhibiting warming in Northeast China and cooling in Southwest China, the mode is significantly forced by the El Nio mode and the North Atlantic SSTA mode, which have three poles. Under the influence of SSTA modes, the surface northerly flow transported cold air to North and Northeast China, resulting in low temperatures in the regions. Meanwhile, the mid-latitude westerlies intensify and the polar cold air stays in high latitudes and cannot affect the Southwest China, resulting in the warming there.     

The Linkage between Midwinter Suppression of the North Pacific Storm Track and Atmospheric Circulation Features in the Northern Hemisphere

The midwinter suppression(MWS) of the North Pacific storm track(NPST) has been an active research topic for decades. Based on the daily-mean NCEP/NCAR reanalysis from 1948 to 2018, this study investigates the MWS-related atmospheric circulation characteristics in the Northern Hemisphere by regression analysis with respect to a new MWS index, which may shed more light on this difficult issue. The occurrence frequency of the MWS of the upper-tropospheric NPST is more than 0.8 after the mid-1980 s. The MWS is accompanied by significantly positive sea-level pressure anomalies in Eurasia and negative anomalies over the North Pacific, which correspond to a strengthened East Asian winter monsoon. The intensified East Asian trough and atmospheric blocking in the North Pacific as well as the significantly negative low-level air temperature anomalies, lying upstream of the MNPST, are expected to be distinctly associated with the MWS. However, the relationship between the MWS and low-level atmospheric baroclinicity is somewhat puzzling.From the diagnostics of the eddy energy budget, it is identified that the inefficiency of the barotropic energy conversion related to the barotropic governor mechanism does not favor the occurrence of the MWS. In contrast, weakened baroclinic energy conversion, buoyancy conversion, and generation of eddy available potential energy by diabatic heating are conducive to the occurrence of the MWS. In addition, Ural blocking in the upstream region of the MNPST may be another candidate mechanism associated with the MWS.     

应用纤维素示踪北京市PM2.5天然植被排放来源的研究

大气细粒子(PM_2.5)污染是全球尤其是我国许多城市的重要环境问题。利用示踪物质识别和估算大气颗粒物来源是公认的可靠技术,纤维素可以作为示踪物质表征一次颗粒物的天然植被排放来源。本文针对大气细粒子中纤维素含量低、全程序空白相对较高等难点,优化建立了纤维素酶水解、GOD-苯酚-四氨基安替比林测糖法,在我国首次应用于测定大气PM_2.5中纤维素的含量,估算天然植被排放源的贡献。方法检出限为0.26 μg/m³(纤维素),可以满足大气PM_2.5纤维素测定要求;而且有效地降低了空白,全程序空白值(36.5 μg葡萄糖)低于文献方法空白值(53.8 μg葡萄糖),使之更适合于PM_2.5的测定。使用本方法对2012年5月至6月采集的北京市大气PM_2.5样品进行分析,纤维素检出率为96%,纤维素的平均含量为(0.573±0.17) μg/m³,折合为天然植被排放量占PM_2.5质量浓度的1.37%±0.65%;天然植被排放源对有机碳的平均贡献率为4.4%,最大达到9.2%,反映出天然植被排放是北京市PM_2.5的重要来源之 一。本研究方法为我国城市大气颗粒物(包括总悬浮颗粒物、PM₁₀、PM_2.5等)来源识别提供了新的手段。