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51.
This paper presents normal time–frequency transform (NTFT) application in harmonic/quasi-harmonic signal prediction. Particularly, we use the normal wavelet transform (a special NTFT) to make long-term polar motion prediction. Instantaneous frequency, phase and amplitude of Chandler wobble, prograde and retrograde annual wobbles of Earth’s polar motion are analyzed via the NTFT. Results show that the three main wobbles can be treated as quasi-harmonic processes. Current instantaneous harmonic information of the three wobbles can be acquired by the NTFT that has a kernel function constructed with a normal half-window function. Based on this information, we make the polar motion predictions with lead times of 1 year and 5 years. Results show that our prediction skills are very good with long lead time. An abnormality in the predictions occurs during the second half of 2005 and first half of 2006. Finally, we provide the future (starting from 2013) polar motion predictions with 1- and 5-year leads. These predictions will be used to verify the effectiveness of the method proposed in this paper. 相似文献
52.
Random variable simulation has been applied to many applications in hydrological modelling, flood risk analysis, environmental impact assessment, etc. However, computer codes for simulation of distributions commonly used in hydrological frequency analysis are not available in most software libraries. This paper presents a frequency‐factor‐based method for random number generation of five distributions (normal, log–normal, extreme‐value type I, Pearson type III and log‐Pearson type III) commonly used in hydrological frequency analysis. The proposed method is shown to produce random numbers of desired distributions through three means of validation: (1) graphical comparison of cumulative distribution functions (CDFs) and empirical CDFs derived from generated data; (2) properties of estimated parameters; (3) type I error of goodness‐of‐fit test. An advantage of the method is that it does not require CDF inversion, and frequency factors of the five commonly used distributions involves only the standard normal deviate. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
53.
Regularities exist in fluid flows and can be represented by a set of constants. These constants are functions of the parameter of a probability distribution that exhibits resilience and stability under various flow conditions. Together, these regularities form a network and interact with each other, such that if one is known then the others can be determined from it. The regularities and their network explain the various fluid‐flow phenomena and can be used in analysis of rivers and streams. For example, they can be used as the basis to develop simple and efficient methods of discharge measurements as presented herein, which only require velocity sampling at a single point on a water surface or a few points on a single vertical. Because of their simplicity and the short time requirement, these methods can be easily automated for collecting discharge data in unsteady, high flows that are badly needed for real‐time flow forecasting and design of flood control structures, and for advancing the fundamental, scientific knowledge in hydrology. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
54.
In this paper, we perform an inverse method to simultaneously estimate aquifer parameters, initial condition, and boundary conditions in groundwater modelling. The parameter estimation is extended to a complete inverse problem that makes the calibrated groundwater flow model more realistic. The adjoint state method, the gradient search method, and the least square error algorithm are combined to build the optimization procedure. Horizontal two‐dimensional groundwater flow in a confined aquifer is exemplified to demonstrate the correlation between unknowns, the contribution of observation, as well as the suitability of applying the inverse method. The correlation analysis shows the connection between storage coefficient and initial condition. Besides, transmissivity and boundary conditions are also highly correlated. More observations at different location and time are necessary to provide sufficient information. A time series of unsteady head is requested for estimation of storage coefficient and initial condition. Observation near boundary is very effective for boundary condition estimation. The observation at pumping well mostly contributes to the estimation of transmissivity. According to all observations, it is possible to identify parameters, initial condition, and boundary condition simultaneously. Furthermore, the results not only illustrate the traditional assumption of known boundary condition but also initial condition, which may cause an incorrect estimation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
55.
Examination of the consequences of the stoichiometric association constant for MgSO4 in seawater as advocated by Johnson and Pytkowicz (1979) leads to a thermodynamic association constant Ka = 212.6, a value 32% greater than KA = 160 derived from conductance data. Use of Ka = 160 leads to a in essential agreement with the value of 10.2 reported by Kester and Pytkowicz (1969). 相似文献
56.
Waves reflecting obliquely from structures establish short-crested waves which are conducive to scour of the bed adjacent to them. The pore pressures and effective stresses induced by this wave system are derived analytically for an unsaturated, anisotropic soil matrix of infinite depth in a three-dimensional domain. Verification is available by the solutions being readily reduced to the two-dimensional cases of the progressive and standing wave, for which some closed-form solutions are available. It is shown that wave obliquity is coupled with soil permeability. The effects of wave obliquity, relative water depth, soil stiffness and soil permeability on wave-induced pore pressure are discussed in detail. 相似文献
57.
Man-Ting Cheng Wei-Chun Chou Chia-Pin Chio Shih-Chieh Hsu Yi-Ru Su Pei-Hsuan Kuo Ben-Jei Tsuang Shuen-Hsin Lin Charles C.-K. Chou 《Journal of Atmospheric Chemistry》2008,61(2):155-173
A study has been carried out on water soluble ions, trace elements, as well as PM2.5 and PM2.5–10 elemental and organic carbon samples collected daily from Central Taiwan over a one year period in 2005. A source apportionment
study was performed, employing a Gaussian trajectory transfer coefficient model (GTx) to the results from 141 sets of PM2.5 and PM2.5–10 samples. Two different types of PM10 episodes, local pollution (LOP) and Asian dust storm (ADS) were observed in this study. The results revealed that relative
high concentrations of secondary aerosols (NO3−, SO42− and NH4+) and the elements Cu, Zn, Cd, Pb and As were observed in PM2.5 during LOP periods. However, sea salt species (Na+ and Cl−) and crustal elements (e.g., Al, Fe, Mg, K, Ca and Ti) of PM2.5–10 showed a sharp increase during ADS periods. Anthropogenic source metals, Cu, Zn, Cd, Pb and As, as well as coarse nitrate
also increased with ADS episodes. Moreover, reconstruction of aerosol compositions revealed that soil of PM2.5–10 elevated approximately 12–14% in ADS periods than LOP and Clear periods. A significantly high ratio of non-sea salt sulfate
to elemental carbon (NSS-SO42−/EC) of PM2.5–10 during ADS periods was associated with higher concentrations of non-sea-salt sulfates from the industrial regions of China.
Source apportionment analysis showed that 39% of PM10, 25% of PM2.5, 50% of PM2.5–10, 42% of sulfate and 30% of nitrate were attributable to the long range transport during ADS periods, respectively. 相似文献
58.
Ocean Dynamics - Loop Current Eddies (LCEs) are warm-core, anticyclonic rings that shed from the Loop Current and migrate westward providing kinetic and potential energy to the Gulf of... 相似文献
59.
The impact of the boreal summer intraseasonal oscillation (BSISO) on extreme hot and cool events was investigated, by analyzing the observed and reanalysis data for the period from 1983 to 2012. It is found that the frequency of the extreme events in middle and high latitudes is significantly modulated by the BSISO convection in the tropics, with a 3–9-day lag. During phases 1 and 2 when the BSISO positive rainfall anomaly is primarily located over a northwest–southeast oriented belt extending from India to Maritime Continent and a negative rainfall anomaly appears in western North Pacific, the frequency of extreme hot events is 40% more than the frequency of non-extreme hot events. Most noticeable increase appears in midlatitude North Pacific (north of 40°N) and higher-latitude polar region.Two physical mechanisms are primarily responsible for the change of the extreme frequency. First, an upper-tropospheric Rossby wave train (due to the wave energy propagation) is generated in response to a negative heating anomaly over tropical western North Pacific in phases 1 and 2. This wave train consists of a strong high pressure anomaly center northeast of Japan, a weak low pressure anomaly center over Alaska, and a strong high pressure anomaly center over the western coast of United States. Easterly anomalies to the south of the two strong midlatitude high pressure centers weaken the climatological subtropical jet along 40°N, which is accompanied by anomalous subsidence and warming in North Pacific north of 40°N. Second, an enhanced monsoonal heating over South Asia and East Asia sets up a transverse monsoonal overturning circulation, with large-scale ascending (descending) anomalies over tropical Indian (Pacific) Ocean. Both the processes favor more frequent extreme hot events in higher-latitude Northern Hemisphere. An anomalous atmospheric general circulation model is used to confirm the tropical heating effect. 相似文献
60.
利用1994-2013年ERA-Interim及NCEP/NCAR再分析数据,对国家气候中心(BCC)次季节到季节尺度模式(S2S)1994-2013年的回报试验数据进行亚洲季风区准双周振荡(QBWO)预报能力评估,并诊断模式预报误差来源。结果表明:BCC S2S模式对QBWO的预报能力随着预报提前时间的增长而降低,9 d后预报技巧明显减弱,其周期、传播特征和强度出现误差;在提前9 d预报中,印度洋地区QBWO对流-环流系统结构松散,信号偏弱,对流向东传播,这与印度洋平均态的预报误差有关,夏季对流平均态低层水汽场在西太平洋和阿拉伯海较强,而东印度洋、孟加拉湾一带偏弱;西北太平洋地区QBWO具有向西北传播的特征,但强度偏弱,可能原因是预报低估了QBWO对流西北侧低层涡度的超前信号,经涡度方程诊断发现,地转涡度平流正贡献微弱,相对涡度平流在对流西北侧引发负涡度,从而减弱了对流西北侧由低层正涡度引发的有利条件。 相似文献