Estimating longitudinal dispersion in rivers using Acoustic Doppler Current Profilers

The longitudinal dispersion coefficient (D) is an important parameter needed to describe the transport of solutes in rivers and streams. The dispersion coefficient is generally estimated from tracer studies but the method can be expensive and time consuming, especially for large rivers. A number of empirical relations are available to estimate the dispersion coefficient; however, these relations are known to produce estimates within an order of magnitude of the tracer value. The focus of this paper is on using the shear-flow dispersion theory to directly estimate the dispersion coefficient from velocity measurements obtained using an Acoustic Doppler Current Profiler (ADCP). Using tracer and hydrodynamic data collected within the same river reaches, we examined conditions under which the ADCP and tracer methods produced similar results. Since dead zones / transient storage (TS) are known to influence the dispersion coefficient, we assessed the relative importance of dead zones in different stream reaches using two tracer-based approaches: (1) TS modeling which explicitly accounts for dead zones and (2) the advection–dispersion equation (ADE) which does not have separate terms for dead zones. Dispersion coefficients based on the ADE tend to be relatively high as they describe some of the effects of dead zones as well. Results based on the ADCP method were found to be in good agreement with the ADE estimates indicating that storage zones play an important role in the estimated dispersion coefficients, especially at high flows. For the river sites examined in this paper, the tracer estimates of dispersion were close to the median values of the ADCP estimates obtained from multiple datasets within a reach. The ADCP method appears to be an excellent alternative to the traditional tracer-based method if care is taken to avoid spurious data and multiple datasets are used to compute a distance-weighted average or other appropriate measure that represents reach-averaged conditions.     

Comparison of manual and automatic methods for measurement of methane emission from rice paddy fields

The methane emission flux from rice paddies was simultaneously measured with automatic and manual methods in the suburban of Suzhou. Both methods were based on the static chamber/ GC-FID techniques. Detail analysis of the experimental results indicates: a) The data of methane emission measured with the automatic method is reliable. b) About 11 or 19 o’clock of local time is recommended as the optimum sampling time for the manual spot measurement of methane emission from rice paddies. The methane emission fluxes measured by manual sampling at local time other than the optimum time have to be corrected. The correction coefficient may be determined by automatic and continuous measurement. c) In order to get a more accurate result, an empirical correction factor, such as 18%, is recommended to correct the seasonally total amount of measured methane emission by enlarging the au-tomatically measured data or reducing the manually measured ones.     

我国部份地区雷暴活动、大气电场等与太阳活动的关系

本文用时序迭加法统计分析了1976—1985年太阳黑子一个完整周期内太阳活动与雷暴活动及地面大气电场之间的可能相关性。结果表明:高纬度地区有较好的相关性,耀斑爆发以后雷暴指数有明显增大趋势,最大关联日在+5日以后。中、低纬度地区几乎不存在相关性。随着耀斑强度增强,相关性也增大,且影响区域从高纬度向中、低纬度移动。在耀斑爆发后2天左右,地面电场强度增大,其关联日比雷暴指数提前。太阳黑子数和雷暴活动之间的相关性很微弱。本文又从全球电路概念出发,简单地解释了形成上述相关性的可能原因。     

青海黄南地区近54年蒸发量变化特征及其影响因子

利用青海省黄南地区近54a(1960—2013年)蒸发量、气温、降水量、日照时数、水汽压等资料,应用地理信息系统、数理统计、线性回归和Mann-Kendall检验等方法分析了黄南地区蒸发量的空间及时间变化趋势,并对黄南地区蒸发量变化特征及其影响因子进行了诊断研究。结果表明:黄南地区年平均蒸发量呈明显的下降趋势,20世纪60—70年代为蒸发量偏多阶段,80年代及后为偏少阶段;黄南地区蒸发量最大的季节是春季和夏季,各季蒸发量均呈减少趋势;黄南地区年蒸发量在1973年发生了由多到少的突变,春、夏、秋、冬季分别发在1973、1975、1976和1974年;分析影响蒸发量的相关因子,蒸发量与日照时数呈显著的正相关关系,与水汽压和降水量呈显著的负相关关系,日照时数的减小是蒸发量减少的主要影响因子。     

具有凝结加热反馈的对称不稳定的解析研究

本文采用非地转非静力条件下存在对流凝结加热反馈的Boussinesq方程组,借用Emanuel(1982)的Wave-CISK方案来考虑凝结反馈作用,并应用Green函数方法和Fourier方法,求得了任意加热廓线时对称不稳定的流函数的解析表达式及其频散关系。本文还对取某些特定的加热廓线时的情况进行了讨论。      

IAP GCM模式大气波谱结构及其在厄尔尼诺年的异常

本文分析了中国科学院大气物理研究所大气环流模式(IAP GCM)模式大气波谱结构(沿纬圈的谐波波谱和时域上的频率谱)及其在厄尔尼诺年的异常。结果表明,超长波是低纬波动的主要空间形式,准40天振荡在一定地理区域内显著存在,并与观测结果有一定联系,它们在厄尔尼诺年均发生明显异常。本工作对鉴定GCM性能及开发GCM的研究领域可能是一种有益的尝试。     

A simplified hydrodynamic mesoscale model suitable for use over high plateau regions

Summary A simplified hydrodynamic primitive equation model in -coordinates is described. This model includes the main physical processes that influence development and motion of mesoscale vortices over plateau regions: elevated terrain effects, effects of large-scale and synoptic-scale systems on the mesoscale systems, sensible heating from the earth's surface, moisture cycle and condensation heating released by both large-scale stable precipitation and cumulus convective precipitation, evaporation and the feedback effect of precipitation on evaporation, friction in the planetary boundary layer, horizontal diffusion by subgrid scale eddies and vertical eddy flux of meteorological elements (momentum, temperature, moisture, etc.) due to turbulence, cumulus convection and other smaller-scale physical processes. The model incorporates observed data as much as possible and equations are simplified so that it may be run using either a high-speed computer or a desktop computer.Two developing vortices that originated over the Qinghai-Xizang (Tibet) Platau and moved eastward producing heavy precipitation over the lower elevations are used to test the model. It is shown that the model is capable of simulating the major features of the vortices including the precipitation distribution and may be used for studies of mesoscale and synoptic scale weather systems over plateau regions.

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Ein vereinfachtes für hochländer geeignetes hydrodynamisches mesoscale-modell

Zusammenfassung Es wird ein vereinfachtes hydrodynamisches Grundgleichungsmodell in -Koordinaten be schrieben. Dieses Modell beinhaltet die wichtigsten physikalischen Prozesse, die die Entwicklung und Bewegung von mesoskaligen Wirbeln über Hochplateaus beeinflussen: Effekte der Hochfläche, Effekte von großräumigen und synoptischen Systemen, die fühlbare Wärme von der Erdoberfläche, den Feuchtigkeitskreislauf und die Kondensationswärme, sowohl von großräumigen als auch von Konvektionsniederschlägen, die Evaporation und die Beeinflussung der Evaporation durch den Niederschlag, die Reibung in der planetaren Grenzschicht, die horizontale Diffusion durch Turbulenzen, die kleiner als die Gitterkonstante sind und den vertikalen Fluß meteorologischer Elemente (Impuls, Temperatur, Feuchte etc.) durch Turbulenzen, Konvektion und andere kleinräumige Prozesse. In das Modell sind die Beobachtungswerte weitestgehend integriert und die Gleichungen soweit vereinfacht, daß es sowohl auf einem Hochleistungs- als auch auf einem Mikrocomputer laufen kann.Zum Testen des Modells wurden zwei sich entwickelnde Wirbel verwendet, die vom Qinghai-Xizang-Plateu (Hochland von Tibet) ausgingen, sich ostwärts bewegten und dabei zu schweren Niederschlägen in den Tiefländern führten. Es wird gezeigt, daß das Modell die wichtigsten Eigenschaften der Wirbel und die Niederschlagsverteilung simulieren und für Untersuchungen von mesoskaligen und synoptischen Wettersystemen über Hochländern herangezogen werden kann.

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With 18 figures     

对称扰动与纬向基流的相互作用 I. 倾斜E-P通量理论

该文对对称扰动与纬向基流的相互作用理论进行了深入的研究。这里是该文的第一部分,将E-P通量理论引入到中尺度对称扰动的动力学模型中,重新定义E-P通量为“倾斜E-P通量”。采用“倾斜E-P通量”的新概念,详细讨论了影响平均基流的几个因子作用。特别在中尺度系统对动量、热量的垂直输送项改变影响环境风场、温度场方面进行了讨论。