Latitudinal- and height-dependent long-term climatology of propagating quasi-16-day waves in the troposphere and stratosphere

The global amplitude of the westward propagating quasi-16-day waves (16DW) with wavenumber 1 (Q16W1), the strongest component of 16DW, are derived from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis temperature and zonal wind data sets from February 1979 to January 2018. In terms of temperature and zonal wind, strong climatologically average amplitudes of Q16W1 appear in the upper stratosphere at mid–high latitudes in both hemispheres, and the wave amplitude is stronger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Multivariate linear regression is separately applied to calculate the responses of the Q16W1 temperature and zonal wind amplitudes to the QBO (quasi-biennial oscillation), ENSO (El Niño-Southern Oscillation), solar activity and linear trends of the Q16W1 amplitude. The QBO signatures of the Q16W1 temperature and zonal wind amplitudes are mainly located in the stratosphere. The Q16W1 has significant QBO responses at low latitudes. In addition, only the temperature amplitude presents a larger QBO signature in its strongest climatological amplitude region. No significant responses to ENSO and solar activity are observed in temperature and zonal wind amplitudes. The linear trends of the monthly mean Q16W1 temperature and zonal wind amplitude are generally positive, especially in the mid-upper stratosphere. The trend is asymmetric about the equator and significantly stronger in the NH than in the SH. The seasonal variation in the trend of the temperature amplitude is studied and illustrated to be stronger in winter and weaker in spring and autumn. Further investigation suggests that the background and local instability trends contribute most of the increasing trend of the Q16W1 amplitude. In winter in both hemispheres, a weakening trend of eastward zonal wind provides more favourable background wind for Q16W1 upward propagation, in autumn and winter in the NH and in spring, autumn and winter in the SH, and the increasing trend of local instability may enhance wave excitation. Graphical Abstract

Numerical Prediction of Local Instability in Double Corrugated Profiles

The technological process of forming the double-corrugated structures of the K-span system causes deep transverse embossing on the surface of the profiles. Such profile geometry makes it difficult to apply classical theories related to plastic failure mechanisms to identify the formation of local instabilities. This article presents an original method for the prediction of local instabilities of double-corrugated structures. The method was developed on the basis of a hierarchical validated FEM model. The geometrically and materially nonlinear analysis method was adopted to perform numerical calculations. The results of calculations enabled the determination of reference equilibrium paths for the eccentrically compressed shell element. Based on the analysis of nonlinear equilibrium paths, a method for predicting the beginning and the end of the appearance of local instabilities in the elastoplastic pre-buckling range was developed.

Study on Nonuniform Evolution Characteristics of Rock Friction and Sliding

By means of experimental research and theoretical analysis, the nonuniform evolution characteristics of rock friction and sliding were studied. Using digital speckle correlation (DIC) as observation method, the whole process of friction and sliding of a granite specimen in double-sided shear experiment is studied. A spring slider model considering the microscopic characteristics of interface asperities was established to simulate the microscopic process of rock friction and sliding. By comparing the theoretical analysis results with the experimental results, the effect of interface nonuniformity on rock friction sliding instability is studied. The results demonstrated that, with the increase of nonuniformity of sliding interface, the degree of local instability before stick-slip decreases, the stick-slip period shortens, and the value of shear drop during stick-slip period decreases. The nonuniformity of sliding interface will increase after local instability.

Latitudinal- and Height- Dependent Long-Term Climatology of Propagating Quasi-16-day in the Troposphere and Stratosphere

The global amplitude of the westward propagating quasi-16-day wave (16DW) with wavenumber 1 (Q16W1), the strongest component of 16DW, is derived from European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis temperature data set from February 1979 to January 2018. The strong climatological mean amplitudes of the Q16W1 appear in winter in the upper stratosphere at high latitudes in both hemispheres, and the wave amplitude is stronger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Multivariate linear regression is applied to calculate responses of the Q16W1 amplitude to QBO (quasi-biennial oscillation), ENSO (El Niño-Southern Oscillation), solar activity and the linear trend of the Q16W1 amplitude. The QBO signatures of the Q16W1 amplitude are mainly located in the stratosphere. In addition to the significant QBO response in the low latitude and low stratosphere, the largest QBO response occurs in the region with the strongest Q16W1 climatology amplitude. There no significant responses to ENSO and solar activity are observed. The linear trend of the monthly mean Q16W1 amplitude is generally positive, especially in the mid-high latitudes of the stratosphere. The trend is asymmetric about the equator and significantly stronger in the NH than in the SH. The trend shows obvious seasonal changes, that is, stronger in winter, weaker in spring and autumn. Further investigation suggests that the background and local instability trends contribute most of the increasing trend of the Q16W1 amplitude. In winter in both hemispheres, the weakening trend of eastward zonal wind provide more favourable background wind for Q16W1 upward propagation, in autumn and winter in the NH and in spring, autumn and winter in the SH, the increasing trend of local instability may enhance the wave excitation.

Local Stability of Trench for Diaphragm Walls Passing through Deep Weak Interlayer

When trench construction of the diaphragm wall passes through an ultradeep and weak interlayer, local instability of the trench wall occurs easily. To study the mechanism of the local instability in the trench and by considering the effect of soil arching based on the length of the trench and the angle of internal friction in the weak interlayer, the disturbed area of the trench is defined to be a semiellipse and the local failure stability model of the semiellipse is established. The local stability safety factor of the trench wall is obtained by the limit equilibrium analysis of the model. By conducting parameter sensitivity studies, the results show that the thickness of the overlying strata, the unit weight of the slurry, the angle of internal friction, and the cohesion of the weak interlayer have a great influence on the stability of the trench wall. The semiellipsoid model is used to analyze the stability of the trench wall of the diaphragm wall of a subway station. The calculated results are basically consistent with the field monitoring results. All the work of the paper shows that the model is practical to some extent.