Analysis of the Antarctic Ozone Hole in November

The factors responsible for the size of Antarctic ozone hole in November are analyzed. Comparing two samples of anomalously large and small November ozone hole with respect to 1980–2017 climatology in November, the results show that the anomalously large ozone hole in austral late winter is not a precondition for the anomalously large ozone hole in November. The size of Antarctic ozone hole in November is mainly influenced by dynamical processes from the end of October to mid-November. During large November ozone hole events, weaker dynamical ozone transport appears from the end of October to mid-November, which is closely related to planetary wave divergence in the stratosphere between 60°S and 90°S. Further analyses indicate that the wave divergence is partially attributed to less upward propagation of planetary waves from the troposphere, which is associated with weak baroclinic disturbances at the end of October. Subsequently, zonal wind speed in the upper stratosphere intensifies, and the distance between critical layer (U=0) and wave reflecting surfaces becomes larger. As a result, more planetary waves are reflected and then wave divergence enhances. The processes responsible for the anomalously small Antarctic ozone holes in November are almost opposite to those for the anomalously large Antarctic ozone holes.

A numerical investigation on ultrasonic bulk wave propagation features in functionally graded plates

The goal of this research is to numerically look for a proper feature for functionally graded materials mechanical property distribution function evaluation based on through transmitted ultrasonic bulk wave amplitude variation. A numerical approximation called homogenous layers approximation is introduced and employed for wave propagation formulation in functionally graded plate, followed by finite element utilization for verification. As the amplitude of the propagated ultrasonic wave is affected by acoustic impedance and wave divergence angle variation in the functionally graded material plate thickness, while neglecting the attenuation phenomenon, numerical investigation has been performed in order to quantify the contribution of each mechanism on the wave amplitude behavior. One-dimensional investigations, using homogenous layers approximation and finite element method, show that the final value of the wave amplitude is the same for all functionally graded material property distribution function power index, while two-dimensional results, obtained from finite element method, provide a suitable amplitude variation manner based on the wave divergence angle variation in functionally graded material thickness direction. The final results shows that it is possible to calibrate the received wave amplitude distribution on the receiving side of the plate, in a through transmission test, for the material property distribution function power index evaluation. Moreover, the concept of functionally graded material ultrasonic shoe is introduced, suitable for beam focusing applications instead of expensive phased array systems.

Characterization of Nonplanar Second Harmonic Lamb Waves With a Refined Nonlinear Parameter

Structural health monitoring (SHM) methods based on the cumulative second harmonic Lamb waves show attractive advantages. An ideal nonlinear parameter should allow precise characterization of the cumulative effects of the distributed nonlinear sources such as the material nonlinearity of a plate (MNP), in the presence of other unavoidable localized nonlinear components. While highlighting the deficiencies of the traditional nonlinear parameter (TNP) in the nonplanar cases, a refined nonlinear parameter (RNP) is proposed. Through compensations for the wave attenuation associated with the wave divergence, the new parameter entails a better characterization and differentiation of the cumulative MNP and other noncumulative localized nonlinear sources. Theoretical findings are ascertained by both finite element (FE) simulations and experiments, through tactically adjusting the dominance level of different nonlinear sources in the system. Results confirm the appealing features of the proposed RNP for SHM applications.

THE POINT SPREAD FUNCTION OF A FOUR-WAVE CONVERTER IN A RESONANT MEDIUM WITH ALLOWANCE FOR PUMP WAVE DIVERGENCE

An expression for point spread function has been obtained for a four-waveconverter in resonant medium modelled by four-level energy scheme. The dependences of point spread function width from pumping wave intensity and resonantmedium parameters have been found.