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1.
在中尺度WRF-EnSRF系统中最新引入的采样误差订正局地化方法不仅考虑了回归系数偏差,而且计算量较小。该方法基于状态变量和对应观测值的相关系数的分布关系,根据离线蒙特卡洛技术制作的关于集合数和样本相关系数的查找表格确定局地化系数因子,进而订正由集合数选取有限造成的背景误差协方差被低估引起的采样误差。本文利用风暴过程的雷达观测资料做了一系列风暴尺度的资料同化理想试验,探讨了采样误差订正局地化方法在风暴尺度集合卡尔曼滤波同化中的技术特点和同化效果。结果表明:相比于经验局地化方法,采样误差订正局地化方法能够有效地改善集合同化的效果,对距离的敏感度更低,尤其在天气系统发展变化较快的阶段,新方法优势更大。并且,对不同观测变量以及在风暴发展的不同阶段使用不同的局地化方法,所得的结果都存在一定的差异,因此需要根据同化对象合理地选择局地化方法。 相似文献
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3.
David Pierotti 《Journal of Atmospheric Chemistry》1990,10(4):373-382
A technique has been developed which can measure low-molecular-weight (C2–C5) oxygenated hydrocarbons down to concentrations of less than 10 parts per trillion (10-12) in the atmosphere. The method uses cryogenic trapping of trace gases from the air, and two-dimensional gas chromatography (2DGC) with flame ionization and photo-ionization detectors to analyze the samples. The method has been used to make extensive measurements in the field, and it is capable of measuring all of the C2–C5 carbonyl compounds in clean tropospheric air. The 2DGC analytical system also makes it possible to prepare accurate, reproducible standards of the low-molecular-weight oxygenated hydrocarbons at trace levels. 相似文献
4.
Barry J. Huebert Scott Vanbramer Kristie L. Tschudy 《Journal of Atmospheric Chemistry》1988,6(3):251-263
Slotted rods were used to collect liquid water from summer stratocumulus clouds during the Dycoms program near San Diego. The rods were mounted on a pylon atop the fuselage of NCAR's Electra. Their collection efficiency (relative to King probe liquid water content measurements) averaged 84±15% after an initial conditioning period. During collection runs in which the average LWC exceeded 0.1 g/m3, the efficiency averaged 91±12%. We have identified several factors necessary to achieve this level of performance. 相似文献
5.
Time-Expanded Sampling Approach for Ensemble Kalman Filter:Experiment Assimilation of Simulated Soundings 
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下载免费PDF全文 In the Ensemble Kalman Filter (EnKF) data assimilation-prediction system, most of the computation
time is spent on the prediction runs of ensemble members. A limited or small ensemble size does reduce the
computational cost, but an excessively small ensemble size usually leads to filter divergence, especially when
there are model errors. In order to improve the efficiency of the EnKF data assimilation-prediction system
and prevent it against filter divergence, a time-expanded sampling approach for EnKF based on the WRF
(Weather Research and Forecasting) model is used to assimilate simulated sounding data. The approach
samples a series of perturbed state vectors from Nb member prediction runs not only at the analysis time
(as the conventional approach does) but also at equally separated time levels (time interval is △t) before
and after the analysis time with M times. All the above sampled state vectors are used to construct the
ensemble and compute the background covariance for the analysis, so the ensemble size is increased from
Nb to Nb+2M￡Nb=(1+2M)×Nb) without increasing the number of prediction runs (it is still Nb). This
reduces the computational cost. A series of experiments are conducted to investigate the impact of △t (the
time interval of time-expanded sampling) and M (the maximum sampling times) on the analysis. The results
show that if △t and M are properly selected, the time-expanded sampling approach achieves the similar
effect to that from the conventional approach with an ensemble size of (1+2M)×Nb, but the number of
prediction runs is greatly reduced. 相似文献
6.
The diffraction angular distributions are calculated for different ice crystals (e.g,solid and hollow hexagonal columns,solid plates and single hexagonal bullet) randomly oriented in space,based on the theory of Cai and Liou.Results of solid column and plate are compared with those from formulas of Wendling et al and Liou.The resull comparison shows that all three procedures discussed in this paper have good agreement.After considering the coin putation time and comparison results,it is suggested that the formula of Wendling et al.can be used to calculate the solid column diffraction,and the formula of Liou can be used to calculate the plate diffraction.The comparison also shows that the diffraction results of solid columu,hollow column and single bullet ice particles randomly oriented in space are very close. 相似文献
7.
回顾了国内外土壤采样装置的发展
历史,针对国内土壤采集的实际需求,确
定了液压振动式土壤采集装置的总体方
案。为了提高装置的可靠性与稳定性,进
行了液压系统管路的优化设计,设计了
具有双凸结构的采样管,进行了一般土
质与杂硬土质的采样试验。试验结果表
明,该装置既可以进行松软土质的采样,
也可以进行杂硬土质的采样。 相似文献
8.
The vertical distribution of the CH3Cl mixing ratio in the stratosphere has been measured from samples collected during two balloon flights on the 21 October 1982 and 10 September 1983. Measurements were made with two analytical techniques that were also employed for previous analyses of stratospheric samples: gas chromatography (GC) and a gas chromatograph/mass spectrometer (GC/MS) combination. The results from all balloon flights performed to date are combined to derive an average experimental profile of CH3Cl at midlatitudes. The profile shows that the CH3Cl mixing ratio decreases by about one order of magnitude between 20 and 30 km altitude. A comparison of the new observations with model profiles reveals discrepancies in the lower stratosphere that amount to a factor of about 3. Possible causes for these discrepancies are discussed. 相似文献
9.
Optimization of mooring observations in Northern Bering Sea 总被引：1，自引：0，他引：1
The problem of the optimal sampling strategy for moored current velocity observations in the Northern Bering Sea is addressed. We analyze dynamically induced correlations in the North Bering Sea currents and conduct their sensitivity analysis to optimize positions of a limited number of moorings. Optimization of the sampling strategy is performed with respect to robustness of the reconstruction of the North Bering Sea circulation with a particular emphasis on the accurate monitoring of the mean Bering Strait transport. Computations reveal four major regions in the North Bering Sea basin that are highly correlated with the Bering Strait transport. Apart from the regions within the Bering Strait itself, they include the Anadyr Strait and a region 100 km south of the Cape of Prince of Wales. Results of the sensitivity analysis are tested in the framework of twin data experiments with the quasi-stationary and oscillatory background circulations. 相似文献
10.
I. J. Simpson J. J. Colman A. L. Swanson A. R. Bandy D. C. Thornton D. R. Blake F. S. Rowland 《Journal of Atmospheric Chemistry》2001,39(2):191-213
We present a technique for the measurement of dimethyl sulfide (DMS) from airborne and ground-based platforms, using whole air sampling followed by gas chromatography with mass spectrometer and flame ionization detection. DMS measurements that were obtained during the 1999 NASA Pacific Exploratory Mission-Tropics B showed excellent agreement with independent in-flight DMS measurements, over a wide range of concentrations. The intercomparison supports two key results from this study, first that DMS can be accurately quantified based on ethane and propane per-carbon-response-factors (PCRFs), and second that DMS is stable in water-doped electropolished stainless steel canisters for at least several weeks. In addition, our sampling frequency and duration are flexible and allow detail in the vertical structure of DMS to be well captured. Sampling times as fast as 8 s were achieved and these data are suitable for DMS flux calculations using the mixed-layer gradient technique. Correlations between DMS and other marine tracers can also be readily investigated by this whole air sampling technique, because DMS is analyzed together with more than 50 simultaneously sampled hydrocarbons, halocarbons, and alkyl nitrates. The detection limit of the DMS measurements is 1 part per trillion by volume (pptv), and we conservatively estimate the accuracy to be ±20% or 3 pptv, whichever is larger. The measurement precision (1 ) is 2–4% at high mixing ratios (> 25 pptv), and 1 pptv or 15%, whichever is larger, at low mixing ratios (<10 pptv). 相似文献
11.
2010年初采暖季,应用FA-3型气溶胶粒度分布采样器在乌鲁木齐市天山区对粒径在10μm以下的气溶胶分九级进行采样,并应用ICS3000离子色谱仪对其进行离子成分测定,结合同期AE-31型黑碳仪和Aurora-1000型积分浊度计测量所得的吸收系数和散射系数数据进行分析。研究结果表明,乌鲁木齐冬季气溶胶质量浓度0级(9.0-10μm)至2级(4.7-5.8μm)逐渐减小,2级至5级(1.1-2.1μm)逐渐增至最大值,5级到8级(亚微米级)又逐渐减小。离子总浓度的分布与气溶胶质量浓度类似,6级(0.65-1.1μm) 吸附可溶性离子能力最强,出现总离子浓度的峰值。各离子除Ca2 和Mg2 分布于粗模态外,SO42-,Na ,NH4 ,NO3-,Cl-和K 均在5-6级达到峰值。细粒子质量浓度远大于粗粒子,且吸附可溶性离子的能力也远大于粗粒子。消光系数与PM10,PM2.5,PM1.0和PM2.5-10的回归分析表明,用PM2.5质量浓度来模拟消光更有意义。采用多元线性逐步回归的方法分析不同粒径段上化学成分与气溶胶散射系数的关系,只有1.1-2.1μm和0.65-1.1μm这两个分级的硫酸盐和铵盐进入回归公式,可见这两分级的硫酸盐和铵盐对消光系数的贡献最大。 相似文献
12.
大气电场,电流多路同步测量的数据实时采集和滚动显示记录系统 总被引：6，自引：5，他引：6
阐述了利用微机对大气电场及麦克斯韦电流密度进行实时多路长时间记录、显示的原理，操作方式及编程。在野外观测的基础获得了电场、电流密度的同步数字化资料，实现了电场、电流密度观测记录的自动化、该系统测量信号以模式所形式实时连续滚动显示在ＶＧＡ显示器上、数字化信号实时存储在计算机硬盘上，记录后的数据可再处理，也可再显示。 相似文献
13.
根据"有效照射体"的基本概念,采用微分理论来回避椭球面近似为平面的假设,推导了双基地雷达系统有效照射体积表达式,证明双基地雷达系统有效照射体积与单基地雷达有效照射体积之比值Vb/Vm,在数值上等于双基地系统主站极轴长度Rt相对于半长轴长度a的导数.有效照射体积数值计算结果与以往相同,放宽了推导过程中的假设条件,显得更加严谨、易懂.还给出了双基地雷达系统各几何量(如Vb/Vm、Rt、主站共面方位Φ、辅站极轴长度Rr、辅站共面方位Φr、双基地角β)之间的一些关系式,分析了在双基地雷达系统探测过程中有效照射体积随有关量变化的特征,为双基地偏振雷达系统天线控制、资料处理、旁瓣影响分析、探测精度提高等提供理论依据. 相似文献
14.
作物花粉自动采集传感器通过ARM（advanced RIS Cmachines）控制简易机械臂操作采样平台上的载玻片捕获空气中自由扩散的花粉粒子,并将载玻片置于生物显微镜下,通过CMOS（complementary metal-oxide-semiconductor）视频传感器将生物显微镜生成的光学图像转换成数字图像,经嵌入式ARM单片机计算处理并存储。利用外场实测资料和标准医用血球计数板,对仪器进行几何尺度标定及载玻片拍摄抽样定标。仪器光学放大倍数F定为328,视场真实面积S为1.516mm2,当拍摄抽样数N为50次时,花粉密度相关系数大于95%。当抽样精度一定,花粉浓度大时,可适当减少抽样数目。体积较小的水稻花粉需要拍摄抽样40次,而体积较大的玉米花粉则需要拍摄抽样80次。因系统几何失真引起的光学放大倍数F随显微视场半径变化,使得实测取样面积误差最大可达13.75%。 相似文献
15.
Data from a convective internal boundary layer (IBL) are analyzed by focusing on the instantaneousstructure of the top of the IBL instead of the time-average structure.A conditional averaging technique is developed todiscriminate between air from above the IBL and air from below the IBL , which alternately invade some instrument levels due tosubstantial variation of the top of the convective IBL.Sensitivity to the conditional sampling criteria is examined.Inside the IBL , buoyant and mechanicalproduction and dissipation dominate the turbulent kinetic energy budget.The horizontal advection and turbulent transport terms are smaller, but not negligible. The inferred pressure correlation term is negligible.Above the IBL , buoyant production and dissipation, although weak,dominate the turbulent kinetic energy budget. Shear generation andturbulent transport are smaller but significant. 相似文献
16.
时间扩展取样集合卡尔曼滤波同化模拟探空试验研究 总被引：2，自引：0，他引：2
目前,集合卡尔曼滤波同化预报循环系统主要的计算量和时间都花费在样本成员的预报上,小样本数虽能减少计算量,但样本数过少,特别是当有模式误差时,又会导致滤波发散。为了提高集合卡尔曼滤波同化预报循环系统的效率并减轻滤波发散等问题,开展了基于WRF的时间扩展取样集合卡尔曼滤波同化模拟探空的试验研究,以考察其在中尺度模式中的同化效果。预报时对一组样本数为Nb的样本,不仅在分析时刻取样,同时也在分析时刻前和后每间隔Δt时间进行M次取样,即在没增加预报样本数的情况下,增加了分析样本成员数(Nb+2M×Nb),从而在保证不降低分析精度的前提下,也达到减小集合卡尔曼滤波的计算量的要求。通过一系列试验来检验时间扩展取样的时间间隔Δt及在分析时刻前和后最大取样次数M对同化结果的影响。试验结果表明,当选择合适的Δt和M时,时间扩展集合卡尔曼滤波的同化效果非常接近于样本数为(1+2M)×Nb的传统集合卡尔曼滤波效果,具有一定的可行性。 相似文献
17.
1999年在常熟农业生态站试验稻田于水稻主要生长季, 利用进口的条件采样装置对水稻低层大气N2O的垂直通量进行了观测, 并在2000年做了补充观测。结果如下:各生长季测定的N2O垂直通量值最多出现在0～2.0 mg·m-2·h-1之间;N2O垂直通量平均日变化最大值出现在下午;插秧期和收割后N2O垂直通量是各个生长季中最小的;观测到N2O负通量现象的出现;在稻田用条件采样技术观测到的低层大气N2O垂直通量大于国内用箱式法观测报道的土壤N2O排放通量。 相似文献
18.
Two situations observed during the second Aerosol Characterization Experiment (ACE-2) are analysed from aircraft measurements in the broken stratocumulus (Sc)-topped marine boundary layer. The first one (26 June 1997), characterized by a non-polluted, oceanic air mass, presents a decoupling between the Sc layer (1400–1520 m) and the turbulent mixed layer, this latter extending from the surface up to 580 m. In contrast, the second case (9 July 1997), during which continental air had been advected over the experimental area, presents a well-coupled layer extending from the surface up to the top of the Sc layer(910 m). This coupling, uncommon in this area in the middle of the day, isrelated to the relative shallowness of the boundary layer. For both situations,it is shown that the turbulent fluxes can be computed with reasonably goodaccuracy (better than 10 %), taking into account both the random and thesystematic errors involved in the eddy-correlation technique. Estimationof random error is based on the computation of the integral scale of thecovariance, and systematic error is estimated from the parameterizationof Mann and Lenschow. The fluxes show that the buoyancy, as a sourceof turbulence, is due to latent heat flux rather than sensible heat flux,with values comparable to previous experiments in the Azores-Canariesbasin. In addition, we propose a method to analyse, for coupled situations,the relationship between the fractional cloudiness and the organization ofthe turbulent field below the clouds. This method is based on a conditionalsampling technique. It is shown that this organization cannot be deducedfrom the analysis of the velocity signal, which is dominated by turbulence.However, when the signals are conditionally sampled according to thepresence or absence of clouds, a weak cloud-related organization can beshown, and the cloud-related transports quantified; the values found areof the order of 10 % of the total transfers, i.e. the same order of magnitude asthe errors on the total flux computation. The method developed is thereforepromising, provided that the uncertainties can be reduced by analyzing a highamount of data. 相似文献
19.
By sampling perturbed state vectors from each ensemble prediction run at properly selected time levels in the vicinity of the analysis time, the recently proposed time-expanded sampling approach can enlarge the ensemble size without increasing the number of prediction runs and, hence, can reduce the computational cost of an ensemble-based filter. In this study, this approach is tested for the first time with real radar data from a tornadic thunderstorm. In particular, four assimilation experiments were performed to test the time-expanded sampling method against the conventional ensemble sampling method used by ensemble- based filters. In these experiments, the ensemble square-root filter (EnSRF) was used with 45 ensemble members generated by the time-expanded sampling and conventional sampling from 15 and 45 prediction runs, respectively, and quality-controlled radar data were compressed into super-observations with properly reduced spatial resolutions to improve the EnSRF performances. The results show that the time-expanded sampling approach not only can reduce the computational cost but also can improve the accuracy of the analysis, especially when the ensemble size is severely limited due to computational constraints for real-radar data assimilation. These potential merits are consistent with those previously demonstrated by assimilation experiments with simulated data. 相似文献
20.
Radiation and particle measurements have been performed with an aircraft in deep cirrus cloud fields near the island of Svalbard. The data of 12 March 1993, when measurements at 10 different levels could be obtained, are used in a comparative study with radiative transfer calculations. In a first analysis, the cirrus cloud field was assumed to be horizontally homogeneous and invariable during the time of measurements (frozen properties). Calculations of the up and downward radiative flux densities showed root mean square differences of 9 Wm−2 from the measurements. To estimate the possible effect of changes of the optical properties of cirrus with time, the flux densities in the upper part (6000–8500 m) and the lower part (3000–5500 m) of the cirrus cloud were analyzed separately. In these simulations, the optical thickness in the lower (upper) part was increased (decreased) by 50%. By this treatment, most of all calculated flux densities were within one standard deviation of the natural variability in each leg. Finally, the effect of inhomogeneities in the cloud field on the solar flux density has been simulated using a Monte Carlo method, since the upper part of the cirrus field has indeed been very inhomogeneous. This paper is a result of a collaborative effort between the MRI in Tsukuba, Japan, and the GKSS in Geesthacht, Germany. 相似文献