中国大陆夏季水汽稳定同位素空间特征

大气降水的水汽来源主要是海洋,而借助降水稳定同位素空间分布格局可以反演水汽输送路径,进而示踪水汽来源。利用全球降水同位素监测网数据,基于GIS平台完成了中国大陆夏季大气降水δD、δ¹⁸O和过量氘空间格局表征。中国大陆夏季氢氧稳定同位素空间分布存在着地域分异,其成因与不同水汽源及诸多环境效应密切相关。非季风区内的西北内陆高值中心与欧亚大陆自蒸发及经由西风带输送的大西洋水汽相关,青藏高原高值则是由高程效应所造成。季风区内大气降水稳定同位素总体呈现出自东南向西北递减趋势,多由纬度效应、大陆效应共同作用而形成;我国西南地区氢氧稳定同位素明显低于同纬度东南地区的,西南地区地形复杂和气流暖湿造成的雨量效应应该是主因。过量氘空间格局则与中国大陆三大气候带分界线基本吻合,区分了西北内陆低值区、青藏高原高值区及东部的自西南向东北递减趋势显著区。依据季风区内大气降水过量氘空间分布特征,大体推断出中国大陆西南夏季风与东南夏季风的区域影响分界可能在"长沙—西安"一线附近。     

Numerical Simulation of the Rapid Intensification of Hurricane Katrina(2005):Sensitivity to Boundary Layer Parameterization Schemes

Accurate forecasting of the intensity changes of hurricanes is an important yet challenging problem in numerical weather prediction. The rapid intensification of Hurricane Katrina(2005) before its landfall in the southern US is studied with the Advanced Research version of the WRF(Weather Research and Forecasting) model. The sensitivity of numerical simulations to two popular planetary boundary layer(PBL) schemes, the Mellor–Yamada–Janjic(MYJ) and the Yonsei University(YSU) schemes, is investigated. It is found that, compared with the YSU simulation, the simulation with the MYJ scheme produces better track and intensity evolution, better vortex structure, and more accurate landfall time and location. Large discrepancies(e.g.,over 10 hPa in simulated minimum sea level pressure) are found between the two simulations during the rapid intensification period. Further diagnosis indicates that stronger surface fluxes and vertical mixing in the PBL from the simulation with the MYJ scheme lead to enhanced air–sea interaction, which helps generate more realistic simulations of the rapid intensification process. Overall, the results from this study suggest that improved representation of surface fluxes and vertical mixing in the PBL is essential for accurate prediction of hurricane intensity changes.     

Stable Carbon Isotope Ratios and the Photochemical Age of Atmospheric Volatile Organic Compounds

Abstract

The dependence of ozone formation on the mixing ratios of volatile organic compounds (VOCs) and nitrogen oxides (NO_x) has been widely studied. In addition to the atmospheric levels of VOCs and NO_x, the extent of photochemical processing of VOCs has a strong impact on ozone levels. Although methods for measuring atmospheric mixing ratios of VOCs and NO_x are well established and results of those measurements are widely available, determination of the extent of photochemical processing of VOCs, known as photochemical age (PCA), is difficult. In this article a recently developed methodology for the determination of PCA for individual compounds based on the change in their stable carbon isotope composition is used to investigate the dependence between ozone and VOC or NO_x mixing ratios at a rural site in Ontario, Canada, during fall and winter. The results show that under these conditions the variability in VOC mixing ratios is predominantly a result of the varying impact of local emissions and not a result of changes in the extent of atmospheric processing. This explains why the mixing ratio of ozone shows no systematic dependence on the mixing ratios of VOCs or NO_x in this environment and at this time of the year.     

用于气候分析的树木年轮稳定同位素资料获取方法与质量控制?

随着稳定同位素分析技术的进步和植物生理学研究的发展,稳定同位素在树轮气候研究中扮演着日益重要的角色。本文总结了用于气候分析的树木年轮稳定同位素资料获取与质量控制方法。包括对分析树轮样品的要求、树轮纤维素提取实验流程、树轮同位素的质谱分析方法和稳定碳同位素数据的处理方法等。为树轮稳定同位素实验分析提供参考,便于获得可靠的树轮同位素数据,且能够进行不同实验室之间数据结果的对比,为建立树木年轮同位素网络奠定基础。     

Stable isotopic variations in precipitation in Southwest China

This study analyzes the relationships of stable isotopes in precipitation with temperature, air pressure and humidity at different altitudes, and the potential influencing mechanisms of control factors on the stable isotopes in precipitation in Southwest China. There appear marked negative correlations of the δ18O in precipitation with precipitation amount, vapor pressure and atmospheric precipitable water (PW)at the Mengzi, Simao and Tengchong stations on the synoptic timescale; the marked negative correlations between the δ18O in precipitation and the diurnal mean temperature at 400 hPa, 500 hPa, 700 hPa and 850hPa are different from the temperature effect in middle-high-latitude inland areas. In addition, the notable positive correlation between the δ18O in precipitation and the dew-point deficit △Td at different altitudes is found at the three stations. Precipitation is not the only factor generating an amount effect. Probably,the amount effect is related to the variations of atmospheric circulation and vapor origins. On the annual timescale, the annual precipitation amount weighted-mean δ18O displays negative correlations not only with annual precipitation but also with annual mean temperature at 500 hPa. It can be deduced that, in the years with an abnormally strong summer monsoon, more warm and wet air from low-latitude oceans is transported northward along the vapor channel located in Southwest China and generates abnormally strong rainfall on the way. Meanwhile, the abnormally strong condensation process will release more condensed latent heat in the atmosphere, and this will lead to a rise of atmospheric temperature during rainfall but a decline of δ18O in the precipitation. On the other hand, in the years with an abnormally weak summer monsoon, the precipitation and the atmospheric temperature during rainfalls decrease abnormally but the δ18O in precipitation increases.     

The Stable Carbon Isotope Ratio of Biogenic Emissions of Isoprene and the Potential Use of Stable Isotope Ratio Measurements to Study Photochemical Processing of Isoprene in the Atmosphere

A technique was developed that allows the determination of the stable carbon isotope ratio of isoprene in air. The method was used for a limited number of ambient measurements as well as laboratory studies of isoprene emitted from Velvet Bean (Mucana pruriens L. var. utilis), including the light and temperature dependence. The mean stable carbon isotope ratio ( ¹³C) of isoprene emitted from Velvet Bean (Mucana pruriens L. var. utilis) for all our measurements is –27.7 ± 2.0 (standard deviation for 23 data points). Our results indicate a small dependence of the stable carbon isotope ratios on leaf temperature and photosynthetic photon flux density (PPFD). The light dependence is 0.0026 ± 0.0012/( mol of photons m^–2 s^–1) for the studied range from 400 to 1700 mol of photons m^–2 s^–1. The temperature dependence is 0.16 ± 0.09/K. On average, the emitted isoprene is 2.6 ± 0.9 lighter than the leaf carbon. An uncertainty analysis of the possibility to use stable carbon isotope ratio measurements of isoprene for estimates of its mean photochemical age suggests that meaningful results can be obtained. This is supported by the results of a small number of measurements of the stable carbon isotope composition of ambient isoprene at different locations. The results range from approximately –29 to –16. They are consistent with vegetation emissions of isoprene that is slightly depleted in ¹³C relative to the plant material and enrichment of ¹³C in the atmosphere due to isotope fractionation associated with the reaction with OH-radicals. The stable carbon isotope ratio of ambient isoprene at locations directly influenced by isoprene emissions is very close to the values we found in our emission studies, whereas at sites located remote from isoprene emitting vegetation we find substantial enrichment of ¹³C. This suggests that stable carbon isotope ratio measurements will be a valuable, quantitative method to determine the extent of photochemical processing of isoprene in ambient air.     

中国降水稳定同位素的分布特点及其影响因素

利用IAEA＼WMO＼GNIP的降水稳定同位素资料,分析了中国降水稳定同位素的时空分布特征及其影响因素。结果表明,整体来看我国降水稳定同位素有明显的大陆效应和高度效应。各地大气降水线存在地域差异,内陆地区同一站点冬、夏半年也有明显差异,显示出水汽团特性的不同。不同地区降水稳定同位素（6和过量氘）的季节变化特征明显不同,表明主要水汽来源存在季节性差异。通过对比长序列降水稳定同位素的年际变化与季风和ENSO指数的关系,发现ENS0与降水稳定同位素有显著的正相关,但不一定通过影响降水量来引起降水稳定同位素（stable isotope in precipitation,SIP）的变化。重点分析了我国降水量效应、温度效应的特点,指出沿海和西南等季风区主要受降水量的影响,北方非季风区温度效应起主要作用,交叉地带则两种效应都有影响。     

中纬度地区混合云中稳定同位素分馏的数学模拟—以乌鲁木齐降水为例(英)

介绍的数学模型考虑了混合云中液、固态共存时以及冰面过饱和环境下稳定同位素的动力分馏效应。利用该数学模型,模拟了不同冷却条件下稳定同位素的温度效应。在相同的湿度条件下,湿绝热冷却过程中δ18O随温度的变化率小于等压冷却过程。冰面过饱和比Si的增大意味着动力分馏效应的增大。与平衡态相比,它的作用使得稳定同位素的综合分馏系数减小,从而使得降水中δ18O随温度的变化趋缓。模拟显示,湿绝热冷却过程中大气水线(MWL:=bδ18o+d)的斜率b和常数d均大于等压冷却过程。全球大气水线位于湿绝热冷却过程和等压冷却过程条件下分别模拟的两条大气水线之间。b和d的大小与Si呈正比。Si愈大,动力分馏效应愈强,b和d也愈大。反之亦然。然而,b和d的大小对云中含水量的变化具有低的敏感性。利用动力分馏模式模拟了乌鲁木齐降水中稳定同位素的变化。模拟的稳定同位素比率-温度以及δD-δ18O曲线分别与乌鲁木齐实测的稳定同位素比率-温度同归线以及大气水线有非常好的一致性。     

中纬度地区混合云中稳定同位素分馏的数学模拟-以乌鲁木齐降水为例

介绍的数学模型考虑了混合云中液、固态共存时以及冰面过饱和环境下稳定同位素的动力分馏效应.利用该数学模型,模拟了不同冷却条件下稳定同位素的温度效应.在相同的湿度条件下,湿绝热冷却过程中δ18O随温度的变化率小于等压冷却过程.冰面过饱和比Si的增大意味着动力分馏效应的增大.与平衡态相比,它的作用使得稳定同位素的综合分馏系数减小,从而使得降水中δ18O随温度的变化趋缓.模拟显示,湿绝热冷却过程中大气水线(MWL:=bδ18O+d)的斜率b和常数d均大于等压冷却过程.全球大气水线位于湿绝热冷却过程和等压冷却过程条件下分别模拟的两条大气水线之间.b和d的大小与Si呈正比.Si愈大,动力分馏效应愈强,b和d也愈大.反之亦然.然而,b和d的大小对云中含水量的变化具有低的敏感性.利用动力分馏模式模拟了乌鲁木齐降水中稳定同位素的变化.模拟的稳定同位素比率-温度以及δD-δ18O曲线分别与乌鲁木齐实测的稳定同位素比率-温度回归线以及大气水线有非常好的一致性.     

城市化与城市水环境

选取北京市观象台1941—2013年共73 a的逐分钟降雨量资料,以60 min和120 min两个历时一年一遇的降雨量作为临界阈值,提取降水场次样本,采用Pilgrim & Cordery法推求北京市短历时设计暴雨雨型。各历时的雨型样本选样分别采用自然降雨过程(方法一)和最大历时过程(方法二)。结果表明:两种方法的60 min和120 min雨型分布形状一致,均为单峰型,雨峰位置靠前;但在降雨量分配比例上,两种方法存在差异,自然降雨过程的60 min和120 min雨型雨峰所在时刻降雨量占总雨量的比例比最大历时过程的分别高3.79%和5.83%。

     

2008-2018年江南暖区暴雨特征

利用2008-2018年常规地面资料、探空站资料、逐小时自动站降水资料,NCEP/NCAR再分析资料及FY2E卫星TBB资料对江南暖区暴雨进行了统计分析和可能影响因子研究.2008-2018年共发生65次江南暖区暴雨,分为切变型、副高型、副高和切变相互作用型和西南急流型4类,可进一步细分为暖切变型、冷切变型、暖切变与副...     

我国东北地区夏季暴雨的气候学特征

利用东北三省和内蒙古东部200个测站1961～2005年的逐日降水资料,分析了东北地区夏季暴雨的空间分布特征和时间演变规律,以及各类暴雨与各种影响天气系统之间的气候统计关系。结果表明,在空间分布上,暴雨由东北地区的东南部向西北部递减的地域特征十分明显,绝大多数大范围和区域性暴雨一般都集中出现在东北地区的南部和中部,而局地暴雨的分布范围相对较广,地域差别也较小。在时间分布上,几十年来东北地区暴雨的阶段性变化特征十分明显,多暴雨和少暴雨的出现具有11～12年左右的低频变化周期。20世纪80年代初以来,暴雨日出现的年际变率有明显增加的趋势,特别是20世纪90年代中期以后,东北地区暴雨发生的次数虽然明显减少,但平均每个暴雨日的暴雨量却有所增加。在东北地区出现的局地暴雨中,以北方天气系统的影响贡献最大,而在区域性暴雨和大范围暴雨中,南方天气系统影响的比例明显增加。     

Q矢量理论在青藏高原东侧大暴雨过程中的诊断应用

利用常规探空和地面观测资料．对2002年6月8～9日发生在青藏高原东侧川陕地区的一次罕见大暴雨过程的环流特征及成因作了诊断分析。再利用MM4模式所提供的高时空分辨率资料．应用湿Q矢晕理论对暴雨过程进一步进行了中尺度诊断研究。结果表明，湿Q矢量散度场的分布反映了次级环流的方向和强弱，暴雨出现在中尺度环流明显增强时。湿Q矢量分解揭示了该次暴雨过程的中尺度特性。     

长江下游地区汛期暴雨气候特征分析

IPCC(1995)第二次科学评估报告指出了极端气象事件变化研究的重要意义[1].长江下游地区地势低平,往往是我国暴雨洪涝的多发区域,造成严重灾害,因此,研究长江下游地区暴雨的规律具有极其重要的意义.选取了长江下游地区52站1960～2003年逐日降水资料,运用EOF分析将其分为3个分区,采用小波分析,Mann-kendall非参数检验法及趋势系数法等分析方法研究各分区汛期暴雨降水的气候统计特征.结果表明:虽然汛期同为暴雨降水的集中时期,但各分区暴雨降水在汛期降水中所占比重略有差异,暴雨降水量、频次所占比例的空间分布为西区较大、东区和北区略小,暴雨平均强度则西区和北区东部强、其他区域小.同一区域中降水量与频次具有显著的正相关,不同区域间仅暴雨降水量的相关性较好.暴雨降水量44 a中呈现了增加的趋势.各区汛期暴雨具有多重时间尺度的周期变化,暴雨降水量和频次的周期在西区与全区的较为一致,主要是6～9 a的周期振荡.东区和北区有着不同尺度的振荡周期.各区的暴雨降水强度都不同程度地存在着3 a的周期振荡.长江下游地区汛期暴雨降水量除北区外,全区及其他分区的突变时刻均发生在1980年代末～1990年代初这一时期,暴雨降水量在1980年代中期～20世纪末出现了一个增长的过程,北区趋势并不显著.全区暴雨平均强度在突变时刻之后有一个减弱的过程,而西区和北区的暴雨平均强度变化并不显著.     

初夏青藏高原东侧一次特大暴雨的综合分析

分析了2002年初夏发生在高原东侧的一次特大暴雨,认为这次暴雨的成因是新疆低槽与高原槽合并东移并引导较强冷空气在高原东侧与四川至陕西的西南暖湿气流交汇而形成的。高空西风急流增强、我国东部高压的阻挡及低层偏南暖湿气流的加强、北伸为发生暴雨提供了有利条件。冷锋前暖区内中β尺度对流系统(MβCSs)的活跃直接导致了特大暴雨的发生。低层中尺度辐合系统与中β尺度对流云团的活动、大暴雨出现的时间和落区等密切相关。中尺度对流系统(MCSs)散度垂直分布的特殊结构,即从对流层低层列高层存在的辐合辐散“双重结构”对大暴雨时强烈上升运动和深对流形成有着重要作用。     

南京降水氢氧同位素监测特征

基于2018年7月—2019年6月南京降水同位素观测数据和中国气象局气象观测数据,研究南京降水稳定同位素组成的变化特征,对比热带气旋降水、梅雨降水和其他降水的降水同位素组成特征,研究降水同位素组成与热带气旋移动路径关系。结果表明：南京降水氧同位素组成(δ18O)和氢同位素组成(δ2H)的变化范围分别为-16.3‰~4.0‰和-103.0‰~32.9‰,雨季降水氢氧同位素组成相对贫化,非雨季相对富集;降水氘盈余的降水加权平均值为15.5‰,表明南京降水受陆面过程影响大。从降水量权重看,热带气旋降水和梅雨降水强度大,降水氢氧同位素组成严重贫化;其他降水的强度相对较弱,降水氢氧同位素组成比较富集;受水汽源地和陆面循环等过程的综合影响,热带气旋降水氘盈余小于全球平均值(10‰),梅雨降水氘盈余略高于全球平均值,其他降水氘盈余远高于全球平均值。登陆前仅在海洋上移动的热带气旋,降水氘盈余维持在7.5‰~8.6‰,但二次登陆的热带气旋降水氘盈余远大于10‰,可能是受到陆地蒸散过程的影响。     

清远地区前汛期雷雨大风和冰雹天气的物理量指标

选取清远地区7个国家气象观测站2006—2015年前汛期的地面观测记录资料和清远、梧州探空站的t-logp探空资料,统计分析沙氏指数SI等8个物理量对雷雨大风及冰雹天气预报的指示作用。结果表明:(1)清远探空站数据中,整层比湿积分IQ、沙氏指数SI、瑞士雷暴1(SWISS00)对雷雨大风天气预报的指示性较好;整层比湿积分IQ、瑞士雷暴1(SWISS00)和0℃层高度对冰雹天气预报的指示性较好。(2)梧州探空站数据中,整层比湿积分IQ、抬升指数LI和沙氏指数SI对雷雨大风天气预报的指示性较好;整层比湿积分IQ、0和-20℃层高度、潜在下冲气流指数(MDPI)和强天气威胁指数SWEAT对冰雹天气预报的指示性较好。合理利用物理量指标对清远地区前汛期雷雨大风和冰雹天气的潜势预报具有一定的可行性。     

Large-Eddy Simulations of the Stable Boundary Layer Using the Standard Kolmogorov Theory: Range of Applicability

Large-eddy simulations (LES) of the Stable Atmospheric Boundary Layer (SBL) are difficult because the turbulence is not isotropic for strong stratification and the Kolmogorov theory might be no longer valid. This fact compells us to work on modifications to the subgrid turbulence schemes, although there is not any widely accepted theory on anisotropic turbulence. In this work, a LES model is used to see what range of stable stratification can still be simulated with a subgrid turbulence scheme using the Kolmogorov theory for the dissipation. Twenty simulations of increasing stability have been performed using a horizontal resolution of 5 m. The model is able to simulate weakly and moderately stable conditions and experiences runaway cooling for strong stability. The goodness of the successful simulations is inspected through comparison to observations from the experimental campaigns SABLES-98 and CASES-99. Other supplementary tests have been performed on the resolution and the surface boundary condition.     

Development of giant drops and high-reflectivity cores in Hawaiian clouds: numerical simulations using a kinematic model with detailed microphysics

Cores of high radar reflectivity (>50 dBZ) and raindrops larger than 4 mm in diameter were occasionally reported in warm clouds, offshore from Hawaii. A kinematic numerical model with detailed microphysics was used to study the formation of these cores and the development of the giant drops. The role of collisional and spontaneous breakup of drops was evaluated. Our results show that spontaneous breakup of raindrops restricts the formation of giant drops (D>4 mm). This could be a result of the poor parameterization of the fragment size distribution, and the probabilities of the spontaneous breakup. The inclusion of only binary breakup mechanism explained the observed radar echoes and the drop spectra. These results corroborate the hypothesis that the updrafts in the Hawaiian clouds sort out different size drops in such a way that millimeter size drops are allowed to fall in an environment deficient of smaller raindrops. In this way, the large raindrops continue to grow by collection of small cloud droplets, but have a smaller chance for collisional breakup (the efficiency for this type of breakup is small for collisions with cloud droplets). The collisional breakup of big raindrops was also found to play a significant role in the formation of giant drops. Such drops are formed following collision–breakup of large raindrops in which one of the fragments is larger than the original drops.     

A MODELING STUDY OF PARAMETERIZATION SCHEMES FOR DEPOSITIONAL GROWTH OF ICE CRYSTAL: FOUR RAINFALL CASES OVER TROPICS AND MIDLATITUDES

Depositional growth of ice crystal is one of the major processes for development of precipitation systems and can be represented by depositional growth of cloud ice from cloud water (PIDW) and depositional growth of snow from cloud ice (PSFI) in cloud-resolving model. Four parameterization schemes are analyzed in the cloud-resolving model simulations of four rainfall cases over the tropics and midlatitudes. The comparison of time and model domain mean data shows that Shen’s scheme produces the closest rainfall simulation to the observation. Compared to Zeng’s scheme, Shen’s scheme improves the mean rain-rate simulation significantly through the dramatic decrease in depositional growth of cloud ice from cloud water. Compared to other schemes, Shen’s scheme produces the better rainfall simulation via the reduction in the mean rain rate associated with the enhanced gain of cloud water and ice.