Re-study on Recurrence Period of Stokes Wave Train with High Order Spectral Method

Owing to the Benjamin-Feir instability, the Stokes wave train experiences a modulation-demodulation process, and presents a recurrence characteristics. Stiassnie and Shemer researched the unstable evolution process and provided a theoretical formulation for the recurrence period in 1985 on the basis of the nonlinear cubic Schrodinger equation （NLS）. However, NLS has limitations on the narrow band and the weak nonlinearity. The recurrence period is re-investigated in this paper by using a highly efficient High Order Spectral （HOS） method, which can be applied for the direct phase- resolved simulation of the nonlinear wave train evolution. It is found that the Stiassnie and Shemer＇s formula should be modified in the cases with most unstable initial conditions, which is important for such topics as the generation mechanisms of freak waves. A new recurrence period formula is presented and some new evolution characteristics of the Stokes wave train are also discussed in details.

Kinematic features of the seismogenic fault of the Tangshan earthquake and the recurrence period of large earthquakes

By the inversion method of uneven slippage of faults in the depths(Liu et al ., 1995) and using the crustal deformation data of six phases, the movement states of seismic fault of the Tangshan earthquake in five time periods before, during and after that earthquake are computed. The result of computation has revealed the movement process of seismic fault, during which the fault moved at an increasing rate before the quake, slipped suddenly during the quake, and became relaxed, adjusted and stabilized gradually after the quake. Moreover, the recurrence period of earthquakes in Tangshan is computed using the relation that the slippage of seismic fault bears with strain energy.

Spatial Distribution of High-temperature Risk with a Return Period of Different Years in the Yangtze River Delta Urban Agglomeration

Against the background of global warming,research on the spatial distribution of high-temperature risk is of great significance to effectively prevent the adverse effects of high temperatures.By using air temperature data from 1951 to 2018 measured by meteorological stations located in the Yangtze River Delta urban agglomeration,the daily maximum air temperature distribution is interpolated at a resolution of 1 km based on the local thin disk smooth spline function;the high-temperature threshold for return periods of 5,10,20 and 30 yr are then calculated by using the generalized extreme value method.The yearly average high-temperature intensity and high-temperature days are finally calculated as high-temperature danger factors.Socioeconomic statistical data and remotely sensed image data in 2018 are used as the background data to calculate the spatial distribution of high-temperature vulnerability factors and prevention capacity factors,which are then used to compute the high-temperature risk index during different recurrence periods in the Yangtze River Delta urban agglomerations.The results show that the spatial distribution features of high-temperature risk in different return periods are similar.The high-temperature risk index gradually increases from northeast to southwest and from east coast to inland,which has obvious latitude variation characteristics and a relationship with the comprehensive influence of the underlying surface and urban scale.In terms of time variation,the high-temperature risk index and its spatial distribution difference gradually decreases with increasing return period.In different cities,the high-temperature risk in the central area of the city is generally higher than that in the surrounding suburban areas.Jinhua,Hangzhou of Zhejiang Province and Xuancheng of Anhui Province are the top three cities with high-temperature risk in the study area.

Seismic risk analysis of coastal area of Pakistan

Estimation of seismic hazard for the fast developing coastal area of Pakistan is carried out using deterministic and probabilistic approaches. On the basis of seismotectonics and geology, eleven faults are recognized in five seismic provinces as potential hazard sources. Maximum magnitude potential for each of these sources is calculated. Peak ground acceleration (PGA) values at the seven coastal cities due to the maximum credible earthquake on the relevant source are also obtained. Cities of Gwadar and Ormara with acceleration values of 0.21g and 0.25g respectively fall in the high seismic risk area. Cities of Turbat and Karachi lie in low seismic risk area with acceleration values of less than 0.1g. The Probabilistic PGA maps with contour interval of 0.05g for 50 and 100 years return period with 90% probability of non-exceedance are also compiled.

A Study of the Impacts of the Spatial Differences in Climate Engineering Programs on the Intensities of Extreme High-Temperature Events in China Under A 1.5℃ Temperature Control Target

Based on the daily maximum temperature data and average temperature data prediction for the period ranging from 2020 to 2099 under the scenario of BNU-ESM climate engineering(G4 test)and non-climate engineering(RCP4.5),the regional differences in the extreme high-temperature intensities in China during the implementation of climate engineering programs(2020 to 2069)and after the implementation of those programs(2070 to 2099)were analyzed using the Weibull Distribution Theory.The results are as follows.(1)The comparison of the two scenarios shows that climate engineering has not fundamentally changed the spatial variation of the intensity of extreme hightemperature events in different recurring periods in China.It was found that in both scenarios,the extreme hightemperature intensities were characterized by the spatial differentiations of low-temperature intensities on the QinghaiTibet Plateau,and high-temperature intensities in the eastern and northwestern region.(2)The comparison of the two scenarios shows that climate engineering in the two study periods could help mitigate the extreme high-temperature intensities with different recurrence periods in China,and the mitigation effects during the implementation period would be significantly higher than those after the implementation.(3)The comparison between the periods ranging from 2020 to 2069 and 2070 to 2099 under the proposed climate engineering scenarios suggests that there would be no strong rebounding of extreme high-temperatures following the implementation of climate engineering programs.Moreover,the mitigation effect of extreme high-temperature intensity during the implementation of climate engineering is significantly higher than that after the completion of climate engineering.(4)According to the comparison between the average temperature changes in China before and after the implementation of the climate project,the average temperature in China has been reduced by at least 1.25℃,which effectively alleviates global warming and is conducive to the realization of the 1.5℃temperature control target of the Paris Agreement.