The hazard produced by natural phenomena on infrastructure and urban populations has been widely studied in the last 50 years. Researchers have recognised that the real danger posed by these phenomena depends on their extreme values. Most researchers focus on the extremes of natural phenomena considered in isolation, one variable at a time. However, what is relevant in hazard studies is coincident extremes of several climatic variables, i.e., the presence of compound extremes. The peak value of these extremes seldom coincides, but off-peak values located in the tail of the distributions are often concurrent and can lead to catastrophic events. What is essential in hazard studies is to calculate the probabilistic distribution of the extremes of coincident climatic variables. The presence of correlations between these variables complicates the problem. This paper presents a computationally efficient and robust mathematical methodology to solve the problem. The procedure is based on the convolution of the distributions of the climatic variables. Once the probabilistic distribution of the compound variables is found, it is possible to calculate the curves of the return period, which is the indicator of importance in hazard and risk studies. This compound Return Period is computed using the Statistics of Extreme Values. To illustrate the problem, the case of a cyclone landing close to a low-gradient coastal city is discussed, and its probability of flooding and recurrence period is calculated. We show that the failure to correctly model the correlation between variables can result in overestimating the Return Period curve, consequently increasing mitigation costs.
In the Mei-yu region,there has been noticeable increase in the occurrence of compound hot drought(CHD)events in recent years.However,the underlying causes of these occurrences remain poorly understood.To address this knowledge gap,we conducted a comprehensive study utilizing observational datasets,reanalysis datasets,and four numerical experiments to investigate the associated physical mechanisms.Our findings indicated that the prevalence of CHD events in the Mei-yu region is influenced strongly by two key factors:the decline in Barents Sea ice during February and the presence of a La Ni?alike pattern of sea surface temperature(SST)in April.The decline in Barents Sea ice generates an anomalous Rossby wave in the Arctic that propagates southeastward.The La Ni?a-like SST pattern regulates a Rossby wave over western America,propagating along the subtropical jet stream.These two Rossby waves induce northward movement and strengthened intensity of the subtropical westerly jet in East Asia.The local circulation patterns in the Mei-yu region are influenced by the position and intensity of the subtropical jet,leading to downward motion in accordance with the secondary circulation theory for high-altitude jet streams.Consequently,these local circulation patterns might contribute to occurrence of CHD events.Moreover,our analysis revealed that the impact of Barents Sea ice and the La Ni?a-like SST pattern can explain approximately two-thirds of the mild CHD events in the Mei-yu region,and that the influence of each is relatively independent.This research underscores influences of polar–tropical systems on climate extremes in eastern Asia.
In this paper,the effect of vibration intensity on the spatial distribution of sulfur content in bed particles was studied.The effects of vibration and airflow on the mechanical characteristics of particles were studied,the collision behavior mode of particles was determined,the spatial saltation law of particles was investigated,the spatial functional axis of beds was determined,and the saltation separation period of particles was determined.The test results show that:When separation bed provides inlet airflow velocity(U_(in)) is 2.55 m/s,the airflow distribution interval of I,II and III areas were U_(I)=2.55-2.57 m/s,U_(II)=1.33-1.35 m/s,U_(III)=0.35-0.38 m/s,respectively;when separation bed vibration amplitude (A)A=2.4-2.5 mm,separation bed vibration frequency (f) f=23-24 Hz,the desulfurization effect is the best.When vibration intensity (Γ)Γ=1.22,U_(in)=1.05 m/s,the particles have disordered contact and collision behavior.WhenΓ=14.89,U_(in)=3.18 m/s,the particles have a transition cataclastic collision.WhenΓ=5.80,U_(in)=2.55 m/s,the particles have directional collision behavior.It is determined that the OX axis is the transverse stable diffusion axis of the material,the OY axis is the longitudinal gradient transport axis of the material,and the OZ axis is the vertical density cascade distribution axis of the material.When separation time (T) T=0-10 s was the period of disorderly diffusion and mixing of particles,T=10-20 s was the period of directional migration and stratification of particles,and T=20-30 s was the period of cascade distribution and separation of particles.Finally,separation experiments conducted under optimal operating parameters demonstrated that the clean coal yield was 72.02%with a sulfur content of 0.98%.
