Periodic oscillation and fine structure of wedge-induced oblique detonation waves

An oblique detonation wave for a Mach 7 inlet flow over a long enough wedge of 30 turning angle is simulated numerically using Euler equation and one-step rection model.The fifth-order WENO scheme is adopted to capture the shock wave.The numerical results show that with the compression of the wedge wall the detonation wave front structure is divided into three sections：the ZND model-like strcuture,single-sided triple point structure and dual-headed triple point strucuture.The first structure is the smooth straight,and the second has the characteristic of the triple points propagating dowanstream only with the same velocity,while the dual-headed triple point structure is very complicated.The detonation waves facing upstream and downstream propagate with different velocities,in which the periodic collisions of the triple points cause the oscillation of the detonation wave front.This oscillation process has temporal and spatial periodicity.In addition,the triple point trace are recorded to obtain different cell structures in three sections.

The Leading Mode of Wintertime Cold Wave Frequency in Northern China during the Last 42 Years and Its Association with Arctic Oscillation

This study examined wintertime (November-April) cold wave frequency (CWF) in northern China during the last 42 years and its association with Arctic Oscillation (AO) through analysis of daily mean surface temperature from 280 stations across northern China and European Centre for Medium-Range Weather Forecasts (ECMWF) 40-Year Re-analysis ERA-40 data. The leading empirical orthogonal function EOF mode of wintertime CWF (CWF-EOF1) indicates an identical signal over most northern China, with the characteristic trend of linear decline for the leading principal component (CWF-PC1). After the linear trend is removed, remarkable inter-annual variability is found to be the dominant feature of the CWF-PC1. The regression map for sea level pressure based on CWF-PC1 corresponds to the negative phase of AO. Correlation analysis further proves that CWF-PC1 has a significant negative correlation with AO at the inter-annual time scale. The relationship between AO and global surface air temperature is also investigated in order to understand its association with cold air activity over East Asia, and it is suggested that the anomalies of atmospheric circulation in Siberia may serve as a bridge for interaction between AO and CWF in northern China during wintertime.

CISK Kelvin Wave with Evaporation-Wind Feedbackand Air-Sea Interaction-A Further Study ofTropical Intraseasonal Oscillation Mechanism

The wave-CISK (cumulus convection heating feedback), the air-sea interaction and the evaporation-wind feedback are together introduced into a simple theoretical model, in order to understand their effect on driving tropical atmospheric intraseasonal oscillation (ISO). The results showed that among the introduced dynamical processes the wave-CISK plays a major role in reducing phase speed of the wave to be closer to the observed tropical ISO. While the evaporation-wind feedback plays a major role in unstabilizing the wave. The air-sea interaction has certain effect on slowing down the phase speed of the wave. Therefore, the wave-CISK and evaporation-wind feedback can be regarded as fundamental dynamical mechanism of the tropical ISO. This study also shows that since the effects of the evaporation-wind feedback and the air-sea interaction were introduced, the excited wave is zonally dispersive, which can dynamically explain the activity feature of the observed ISO in the tropical atmosphere very well.

Influence of the Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation on Antarctic surface air temperature during 1900 to 2015

The importance of the Atlantic Multidecadal Oscillation(AMO)and Interdecadal Pacific Oscillation(IPO)in influencing zonally asymmetric changes in Antarctic surface air temperature(SAT)has been established.However,previous studies have primarily concentrated on examining the combined impact of the contrasting phases of the AMO and IPO,which have been dominant since the advent of satellite observations in 1979.This study utilizes long-term reanalysis data to investigate the impact of four combinations of+AMO+IPO,–AMO–IPO,+AMO–IPO,and–AMO+IPO on Antarctic SAT over the past 115 years.The+AMO phase is characterized by a spatial mean temperature amplitude of up to 0.5℃over the North Atlantic Ocean,accompanied by positive sea surface temperature(SST)anomalies in the tropical eastern Pacific and negative SST anomalies in the extratropical-mid-latitude western Pacific,which are indicative of the+IPO phase.The Antarctic SAT exhibits contrasting spatial patterns during the+AMO+IPO and+AMO–IPO periods.However,during the–AMO+IPO period,apart from the Antarctic Peninsula and the vicinity of the Weddell Sea,the entire Antarctic region experiences a warming trend.The most pronounced signal in the SAT anomalies is observed during the austral autumn,whereas the combination of–AMO and–IPO exhibits the smallest magnitude across all the combinations.The wavetrain excited by the SST anomalies associated with the AMO and IPO induces upper-level and surface atmospheric circulation anomalies,which alter the SAT anomalies.Furthermore,downward longwave radiation anomalies related to anomalous cloud cover play a crucial role.In the future,if the phases of AMO and IPO were to reverse(AMO transitioning to a negative phase and IPO transitioning to a positive phase),Antarctica could potentially face more pronounced warming and accelerated melting compared to the current observations.

Nonlinear Oscillations of Semigeostrophic Eady Waves in the Presence of Diffusivity

Analyses are performed to examine the physical processes involved innonlinear oscillations of Eady baroclinic waves obtained from viscous semigeostrophic models withtwo types of boundary conditions (free-slip and non-slip). By comparing with previous studies forthe case of the free-slip boundary condition, it is shown that the nonlinear oscillations areproduced mainly by the interaction between the baroclinic wave and zonal-mean state (totalzonal-mean flow velocity and buoyancy stratification) but the timescale of the nonlinearoscillations is largely controlled by the diffusivity. When the boundary condition is non-slip, thenonlinear oscillations are further damped and slowed by the diffusive process. Since the free-slip(non-slip) boundary condition is the zero drag (infinite drag) limit of the more realistic dragboundary condition, the nonlinear oscillations obtained with the two types of boundary conditionsare two extremes for more realistic nonlinear oscillations.

CISK-rossby wave and the 30-60 Day Oscillation in the Tropics

The 30-60 day oscillation is an important aspect of the atmospheric variance in the tropical area. A number of works have been done on this phenomenon, this article is a further one. A quasi-geostrophic linear model that consists of a two-layer free atmosphere and a well-mixed boundary layer is used to investigate the instability of intraseasonal oscillation, its propagation and vertical structures. Results show that the dynamical coupling and interaction between the barotropic and baroclinic components via boundary layer convergence / divergence are responsible for the appearance of a new kind of low-frequency wave. Such wave is very different from the traditional tropical Rossby wave. It can propagate westward and eastward. Some behaviours of it appear to resemble the observed 30-60 day oscillation mode in many aspects, such,as vertical structures, zonal and meridional propagations. Now many researchers emphasize the direct relationship between CISK-Kelvin mode and the tropical atmospheric 30-60 oscillation. It is considered that CISK-Rossby mode should not be neglected.

ON THE CHARACTERISTICS OF PROPAGATION OF INTRASEASONAL OSCILLATIONS AND THEIR OBSERVED ASSOCIATION WITH TROPICAL SYNOPTIC WAVES IN THE ASIAN-WESTERN PACIFIC REGION IN BOREAL SUMMER

Using the daily average outgoing longwave radiation and NCEP/NCAR reanalysis data in boreal summer(Mays to Octobers)from 1979 to 2007,the propagating characteristics of convection intraseasonal oscillations(ISOs)in the Asian-western Pacific(AWP)region and the relationship between tropical synoptic waves and ISOs are examined by means of finite-domain wavenumber-frequency energy spectrum analysis and lagged linear regression technique.The results are shown as follows.(1)The AWP ISOs propagate both eastward and westward,showing seasonality and regionality.The ISOs propagate eastward with a period of 30 to 60 days over equatorial regions in the whole AWP region,while the westward propagation occurs over 10 to 20°N western Pacific or in the late summers(August,September and October) with periods of 20 to 40 days.The ISOs eastward propagation mainly occurs in primary summers while the westward propagation enhances in late summers.(2)Deep ISO convections associate with westerly and cyclonic circulation anomalies that first form in the Indian Ocean,propagate eastward to the dateline in the Pacific and then turn northwestward.The ISOs convections show northwestward propagating characteristics in the western North Pacific.(3)The ISOs link with the tropical synoptic waves closely.Both convection signals,though with different spatio-temporal scale,enhance simutaneously in the northwestern Pacific,and the ISOs facilitate the forming of a cluster of tropical cyclones(TCs),while a cluster of TCs convection becomes one portion of the northwestward ISOs.

Bifurcation of Nonlinear Kelvin Wave-CISK with ConditionalHeating in a Truncated Spectral Model: A PossibleMechanism of 30-60-Day Oscillation at the Equator

In this paper, the nonlinear Kelvin wave equations with 'positive-only' nonlinear (conditional) heating at the equator are reduced to a sixth-order nonlinear ordinary differential equation by using the Galerkin spectral truncated method. The stability analysis indicates that when the heating parameter increases, the supercritical pitchfork and Hopf bifurcations can occur for the prescribed three heating profiles. Numerical calculations are made with the help of the fourth-order Rung-Kutta method. It is found that the convection heating-related Hopf bifurcation can lead to limit cycle and chaotic solutions. In a wide range of heating parameter, the solutions possess 30-60-day periods, and are dominated by wavenumbers one and two, especially by wavenumber-one. In addition, the zonal winds of the low-frequency solutions have a phase reversal between the upper and lower tropospheres. Thus, it appears that the convection heating-related Hopf bifurcation might be a possible mechanism of 30-60-day oscillation in the tropical atmosphere.

Ocean internal waves interpreted as oscillation travelling waves in consideration of ocean dissipation

Most studies of the synthetic aperture radar remote sensing of ocean internal waves are based on the solitary wave solutions of the Korteweg-de Vries （KdV） equation, and the dissipative term in the KdV equation is not taken into account. However, the dissipative term is very important, both in the synthetic aperture radar images and in ocean models. In this paper, the traveling-wave structure to characterize the ocean internal wave phenomenon is modeled, the results of numerical experiments are advanced, and a theoretical hypothesis of the traveling wave to retrieve the ocean internal wave parameters in the synthetic aperture radar images is introduced.

On-Line Measurement of Ion Density in Atmospheric Nitrogen Discharge Filaments via Radiation Signals from Plasma Oscillation

Diagnosis of the particle number density of plasma plays an important role in the understanding of plasma sources and processing.Regular radiation signals from plasma oscillation in filaments of atmospheric nitrogen discharge,which were excited by the injection of secondary electron beams during the propagation of the streamer,are employed to determine the ion density of plasma and its evolution in the filaments.Results show that the density of N4＋ in a filament of atmospheric nitrogen discharge is of the order of 1013 cm-3.It is also found that the recombination processes play a dominant role in plasma decay,and that the ion density decreases non-monotonically with time during streamer propagation.

STUDY ON DYNAMICS OF TROPICAL CISK-ROSSBY WAVES AND MECHANISM OF 30-50 DAY OSCILLATIONS

To add to the growing mature research on the tropical 30-50 day oscillations from a new prospective, the current work bases on dynamic analysis of baroclinic quasi-geostrophic models to discuss dynamic mechanisms for the generation and propagation of CISK-Rossby waves, and to understand restraints and effects of different wave structures and thermodynamic forcing on the 30-50 day oscillations in the tropical atmosphere. Some important properties of the oscillation propagation have been explained and, in detail, with respect to its meridional propagation and vertical "baroclinic" structure. The work has come up with some new opinions and viewpoints. New opinions about the propagation and energy dispersion are to be proved by more observations and study.

Wave Motion in an Ice Covered Ocean Due to Small Oscillations of a Submerged Thin Vertical Plate

In this paper we study the problem of generation of surface waves produced due to a） rolling of the plate and b） presence of a line source in front of a fixed vertical plate. The amplitudes of radiated waves at large distance from the plate, in both cases, are obtained by a suitable application of Green＇s integral theorem. These are then studied graphically for various values of the ice cover parameter.

Oscillation properties of matter–wave bright solitons in harmonic potentials

We investigate the oscillation periods of bright soliton pair or vector bright soliton pair in harmonic potentials. We demonstrate that periods of low-speed solitons are greatly affected by the position shift during their collisions. The modified oscillation periods are described by defining a characterized speed, with the aid of asymptotic analysis on related exact analytic soliton solutions in integrable cases. The oscillation period can be used to distinguish the inter-and intra-species interactions between solitons. However, a bright soliton cannot oscillate in a harmonic trap, when it is coupled with a dark soliton(without any trapping potentials). Interestingly, it can oscillate in an anti-harmonic potential, and the oscillation behavior is explained by a quasi-particle theory. The modified period of two dark-bright solitons can be also described well by the characterized speed. These results address well the effects of position shift during soliton collision, which provides an important supplement for previous studies without considering phase shift effects.

Introduction to the Rotating Wave Approximation (RWA): Two Coherent Oscillations

In this note, I introduce a mysterious approximation called the rotating wave approximation (RWA) to undergraduates or non-experts who are interested in both Mathematics and Quantum Optics. In Quantum Optics, it plays a very important role in order to obtain an analytic approximate solution of some SchrÖdinger equation, while it is curious from the mathematical point of view. I explain it carefully with two coherent oscillations for them and expect that they will overcome the problem in the near future.

Kinematics Modeling and Experiments of Pectoral Oscillation Propulsion Robotic Fish

A robotic fish driven by oscillating fins, 'Cownose Ray-I', is developed, which is in dorsoventrally flattened shape without a tail. The robotic fish is composed of a body and two lateral fins. A three-factor kinematic model is established and used in the design of a mechanism. By controlling the three kinematic parameters, the robotic fish can accelerate and maneuver. Forward velocity is dependent on the largest amplitude and the number of waves in the fins, while the relative contribution of fin beat frequency to the forward velocity of the robotic fish is different from the usual result. On the other hand, experimental results on maneuvering show that phase difference has a stronger effect on swerving than the largest amplitude to some extent. In addition, as propulsion waves pass from the trailing edge to the leading edge, the robotic fish attains a backward velocity of 0. 15 m·s^(-1).

Enhancement of the Summer North Atlantic Oscillation Influence on Northern Hemisphere Air Temperature

This study investigates the relationship between the summer North Atlantic Oscillation （SNAO） and the simultaneous Northern Hemisphere （NH） land surface air temperature （SAT） by using the Climate Research Unit （CRU） data. The results show that the SNAO is related to NH land SAT, but this linkage has varied on decadal timescales over the last 52 years, with a strong connection appearing after the late 1970s, but a weak connection before. The mechanism governing the relationship between the SNAO and NH land SAT is discussed based on the NCEP/NCAR reanalysis data. The results indicate that such a variable relationship may result from changes of the SNAO mode around the late 1970s. The SNAO pattern was centered mainly over the North Atlantic before the late 1970s, and thus had a weak influence on the NH land SAT. But after the late 1970s, the SNAO pattern shifted eastward and its southern center was enhanced in magnitude and extent, which transported the SNAO signal to the North Atlantic surrounding continents and even to central East Asia via an upper level wave train along the Asian jet.

Investigation on the Oscillating Buoy Wave Power Device

An oscillating buoy wave power device (OD) is a device extracting wave power by an oscillating buoy. Being excited by waves, the buoy heaves up and down to convert wave energy into electricity by means of a mechanical or hydraulic device. Compared with an Oscillating Water Column (OWC) wave power device, the OD has the same capture width ratio as the OWC does, but much higher secondary conversion efficiency. Moreover, the chamber of the OWC, which is the most expensive and difficult part to be built, is not necessary for the OD, so it is easier to construct an OD. In this paper, a numerical calculation is conducted for an optimal design of the OD firstly, then a model of the device is built and, a model test is carried out in a wave tank. The results show that the total efficiency of the OD is much higher than that of the OWC and that the OD is a promising wave power device.

Numerical Study of Air Chamber for Oscillating Water Column Wave Energy Convertor

Oscillating Water Column （OWC） wave energy converting system is one of the most widely used facilities all over the world. The air chamber is utilized to convert the wave energy into the pneumatic energy. The numerical wave tank based on the two-phase VOF model is established in the present study toinvestigate the operating performance of OWC air chamber. The RANS equations, standard k-ε turbulence model and dynamic mesh technology are employed in the numerical model. The effects of incident wave conditions and shape parameters on the wave energy converting efficiency are studied and the capability of the present numerical wave tank on the corresponding engineering application is validated.

STABILITY OF VISCOUS SHOCK WAVES FOR THE ONE-DIMENSIONAL COMPRESSIBLE NAVIER-STOKES EQUATIONS WITH DENSITY-DEPENDENT VISCOSITY

We study the large-time behavior toward viscous shock waves to the Cauchy problem of the one-dimensional compressible isentropic Navier-Stokes equations with density- dependent viscosity. The nonlinear stability of the viscous shock waves is shown for certain class of large initial perturbation with integral zero which can allow the initial density to have large oscillation. Our analysis relies upon the technique developed by Kanel~ and the continuation argument.

The Impact of Global Warming on the Pacific Decadal Oscillation and the Possible Mechanism

The response of the Pacific Decadal Oscillation （PDO） to global warming according to the Fast Ocean Atmosphere Model （FOAM） and global warming comparison experiments of 11 IPCC AR4 models is investigated. The results show that North Pacific ocean decadal variability, its dominant mode （i.e., PDO）, and atmospheric decadal variability, have become weaker under global warming, but with PDO shifting to a higher frequency. The SST decadal variability reduction maximum is shown to be in the subpolar North Pacific Ocean and western North Pacific （PDO center）. The atmospheric decadal variability reduction maximum is over the PDO center. It was also found that oceanic baroclinic Rossby waves play a key role in PDO dynamics, especially those in the subpolar ocean. As the frequency of ocean buoyancy increases under a warmer climate, oceanic baroclinic Rossby waves become faster, and the increase in their speed ratio in the high latitudes is much larger than in the low latitudes. The faster baroclinic Rossby waves can cause the PDO to shift to a higher frequency, and North Pacific decadal variability and PDO to become weaker.