Time elements in rectangular coordinates

In a paper by the second author (Nacozy, 1981), various time elements are presented for use with the Sundman time transformation. In that paper, the time elements are given in terms of Keplerianorbital elements. We give here the corresponding time elements in terms ofrectangular coordinates. Extensive references are given in the previous paper and will be omitted here.We present additional numerical experiments comparing the use of time elementsand time transformationstogether with the use of time transformationsalone. The results indicate a reduction in computational error when time elements are used.     

在EBEX-2000实验资料中湍流耗散率、长度尺度和结构参数特征

采用2000年8月在美国加州棉花地两个高度上应用超声三分量仪、快速响应温度和湿度仪进行的EBEX-2000 (International Energy Balance Experiment, 2000, 简称EBEX-2000) 风速三分量、温度和湿度湍流实验观测数据, 计算分析了在不同稳定度下的湍流能量和热量耗散率和湍流结构参数特征.并与Kansas和长白山原始森林湍流实验得到的结果进行了比较, 得到了一些湍流特征量在不同下垫面情况下的一些有意义的特征.     

Isolation of wells contaminated by tannery industries using principal component analysis

The groundwater in the upper Kodaganar basin is contaminated due to the discharge of effluents from tannery industries. The water in the wells, whose physico-chemical characteristics are altered due to the influence of the effluents, is statistically analyzed. The physico-chemical variables such as EC, Na⁺, K⁺, Ca²⁺, Mg²⁺, F^?, Cl^?, HCO₃ ^?,CO₃ ^2?, NO₃ ^?, SO₄ ^2?, pH, and Cr_total were used for this study. An attempt was made to identify the contaminated wells based on suitability for drinking, suitability for industrial requirements, and through principal component analysis (PCA). Classification based on suitability helped in identifying the contaminated wells. However, this resulted in failure when identifying the wells that are contaminated by tanneries. PCA has proved to be effective in the segregation of contaminated wells influenced by tannery industries. The physico-chemical variables that are 13 in number are transformed into two orthogonal components and Eigen values based on the variance. The Eigen values are used to select the first two principal components PC1 (7.26) and PC2 (2.24) that accounted for 73.04% variance in the data. The components of the variables and the wells are plotted in a biplot to isolate the contaminated samples. The contaminated samples are analyzed in the spatial domain in geographic information system and found to be clustered around the tannery belt. The study reveals that 35% of the samples are contaminated due to discharge from tannery industries.     

Preface to the Special Issue: Climate Change and Variability of Tropical Cyclone Activity

Tropical cyclones(TCs) are one of the most destructive natural phenomena on Earth in terms of human-life and economic losses. It is currently a matter of prodigious public and scientific interest how TC activity has changed and will change in a warming climate. This special issue focuses on a challenging subject raised in the Intergovernmental Panel on Climate Change(IPCC) report and numerous research papers.     

The role of MJO and mid-latitude fronts in the South China Sea summer monsoon onset

Previous studies have suggested that the South China Sea (SCS) summer monsoon onset is concurrent with the arrival of a 30–60-day northward-propagating trough. On the other hand, from a synoptic viewpoint, some studies pointed out that the arrival of a mid-latitude front may be the triggering mechanism of the SCSSM onset. This study attempts to link these two viewpoints and to investigate their relative role in inducing the SCSSM onset. Composites of low-level zonal winds, geopotential heights and temperatures during the 1991–1999 SCSSM onsets based on the European Centre for Medium Range Weather Forecast ERA-40 data indicate that both the Madden and Julian Oscillation (MJO)/Kelvin waves and mid-latitude trough are apparently involved in the onset. The MJO/Kelvin waves play a major role in inducing the large-scale easterly-westerly shift over the central SCS, while the effect of the acceleration of westerlies ahead of the mid-latitude trough is limited to the northern SCS only. Numerical experiments using a regional climate model further demonstrate that the MJO/Kelvin waves control the timing of the onset by changing the background meridional geopotential height gradient over the SCS. When the MJO is at its peak phase over the Maritime continent, it imposes a positive meridional geopotential height gradient over the SCS such that easterly winds are induced, which significantly reduces the strength of a mid-latitude trough. After the equatorial convection has dissipated, a Rossby-wave response is induced, leading to the formation of a northward-moving trough. When this trough moves northward, the meridional geopotential height gradient is reversed and westerly winds are induced. At the same time, if a mid-latitude trough arrives in south China, the westerlies associated with the mid-latitude trough will strengthen because of the background meridional geopotential height gradient, which gives the impression that both the northward-moving trough and mid-latitude trough are in phase and work together to induce the onset.     

Thermal periodicities in the Venus atmosphere

A search was made for periodic fluctuations in the thermal brightness temperatures recorded by the Pioneer Venus orbiter's infrared radiometer. Data were averaged in 10 × 10° latitude-longitude bins for each of the 72 days the instrument was in operation. This time series of thermal brightness temperatures was then analyzed to determine the amplitude of fluctuations at periods from 2 to 64 days at four levels in the atmosphere (at the cloud tops and at approximately 70, 80, and 90 km). The amplitude of such fluctuations is small at equatorial latitudes and increases to a maximum at 60–70° latitude at most altitudes. The period of the highest amplitude fluctuation is 5.3±0.4 days (at all altitudes) except at 70–80°, where a 2.9-day period which appears to correspond to the polar dipole dominates the cloud-top channel. The amplitude of the periodic fluctuations is a maximum at the cloud tops, decreasing to a minimum at the 80-km channel, and increasing again at the 90-km channel.     

Growing Threat of Rapidly-Intensifying Tropical Cyclones in East Asia

This study examines the long-term change in the threat of landfalling tropical cyclones(TCs) in East Asia over the period 1975–2020 with a focus on rapidly intensifying(RI) TCs. The increase in the annual number of RI-TCs over the western North Pacific and the northwestward shift of their genesis location lead to an increasing trend in the annual number of landfalling RI-TCs along the coast of East Asia. The annual power dissipation index(PDI), a measure of the destructive potential of RI-TCs at landfall, also shows a significant increasing trend due to increases in the annual frequency and mean landfall intensity of landfalling RI-TCs. The increase in mean landfall intensity is related to a higher lifetime maximum intensity(LMI) and the LMI location of the landfalling RI-TCs being closer to the coast. The increase in the annual PDI of East Asia is mainly associated with landfalling TCs in the southern(the Philippines, South China, and Vietnam) and northern parts(Japan and the Korean Peninsula) of East Asia due to long-term changes in vertical wind shear and TC heat potential. The former leads to a northwestward shift of favorable environments for TC genesis and intensification, resulting in the northwestward shift in the genesis, RI, and LMI locations of RI-TCs. The latter provides more heat energy from the ocean for TC intensification, increasing its chances to undergo RI.     

Sensitivity of the simulation of tropical cyclone size to microphysics schemes

The sensitivity of the simulation of tropical cyclone(TC) size to microphysics schemes is studied using the Advanced Hurricane Weather Research and Forecasting Model(WRF). Six TCs during the 2013 western North Pacific typhoon season and three mainstream microphysics schemes–Ferrier(FER), WRF Single-Moment 5-class(WSM5) and WRF Single-Moment6-class(WSM6)–are investigated. The results consistently show that the simulated TC track is not sensitive to the choice of microphysics scheme in the early simulation, especially in the open ocean. However, the sensitivity is much greater for TC intensity and inner-core size. The TC intensity and size simulated using the WSM5 and WSM6 schemes are respectively higher and larger than those using the FER scheme in general, which likely results from more diabatic heating being generated outside the eyewall in rainbands. More diabatic heating in rainbands gives higher inflow in the lower troposphere and higher outflow in the upper troposphere, with higher upward motion outside the eyewall. The lower-tropospheric inflow would transport absolute angular momentum inward to spin up tangential wind predominantly near the eyewall, leading to the increment in TC intensity and size(the inner-core size, especially). In addition, the inclusion of graupel microphysics processes(as in WSM6) may not have a significant impact on the simulation of TC track, intensity and size.     

The response of a gravel‐bed river planform configuration to flow variations and bed reworking: a modelling study

A 2D depth‐averaged model has been developed for simulating water flow, sediment transport and morphological changes in gravel‐bed rivers. The model was validated with a series of laboratory experiments and then applied to the Nove reach of the Brenta River (Northern Italy) to assess its bed material transport, interpret channel response to a series of intensive flood events (R.I. ≈ 10 years) and provide a possible evolutionary scenario for the medium term. The study reach is 1400 m long with a mean slope of 0.0039 m m^?1. High‐resolution digital terrain models were produced combining LiDAR data with colour bathymetry techniques. Extensive field sedimentological surveys were also conducted for surface and subsurface material. Data were uploaded in the model and the passage of two consecutive high intensity floods was simulated. The model was run under several hypotheses of sediment supply: one considering substantial equilibrium between sediment input and transport capacity, and the others reducing the sediment supply. The sediment supply was then calibrated comparing channel morphological changes as observed in the field and calculated by the model. Annual bed material transport was assessed and compared with other techniques. Low‐frequency floods (R.I. ≈ 1.5 years) are expected to produce negligible changes in the channel while high floods may erode banks rather than further incising the channel bed. Location and distribution of erosion and deposition areas within the Nove reach were predicted with acceptable biases stemming from imperfections of the model and the specified initial, boundary and forcing conditions. A medium‐term evolutionary scenario simulation underlined the different response to and impact of a consecutive sequence of floods. Copyright © 2015 John Wiley & Sons, Ltd.