Features of generation and propagation of the extremely low frequency waves excited in the ionosphere under the powerful HF radioemission influence

The experimental results of the extremely low frequency emission characteristics excited in the outer ionosphere under the ionospheric plasma heating by high-latitude EISCAT facility are presented. The experiments have been conducted in the period of 20062010 yr. using two main schemes of extremely low frequency generation including the impact of the heating facility amplitude modulated emission and two unmodulated pump waves with the frequency detuning. In-situ measurements of the plasma wave disturbances were performed at the outer ionosphere heights using on-board equipment of DEMETER microsatellite. In work the spatial, amplitude and spectral characteristics of the generated extremely low frequency emissions are determined. It is shown that the characteristic size of the extremely low frequency emission is about 400600 km along the trajectory of the DEMETER microsatellite. The registration area spatial position is determined by both the applied generation scheme and the background plasma density distribution. The extremely low frequency emission electric field strength at the Earths outer ionosphere heights is 50330 V/m.

African monsoons, Part 2: Synoptic-scale wave disturbances in the intertropical convergence zone over north Africa

In this part, the paper discusses several aspects of the origin, structure, development and movement of wave disturbances over the North African tropical zone during the northern summer. Analyzing the cases often actual wave disturbances which later in their life cycles developed into hurricanes over the Atlantic, it finds that though the horizontal and vertical shear of the mean zonal wind associated with the mid-tropospheric easterly jet over Africa satisfies the condition of dynamical instability under certain restrictive boundary conditions, it is the influence of a large-amplitude baroclinic wave in mid-latitude westerlies upon a stationary wave in the mountainous region of the east-central north Africa that appears to trigger the birth of a wave disturbance in the intertropical convergence zone over the Nile valley of Sudan between the Marra and the Ethiopian mountains. Physical processes likely to be important in the formation, development and movement of the disturbances are pointed out.

Structure and Branching of Unstable Modes in a Swirling Flow

Swirling has a significant effect on the main characteristics of flow and can lead to its fundamental restructuring. On the flow axis, a stagnation point with zero velocity is possible, behind which a return flow zone is formed. The apparent instability leads to the formation of secondary vortex motions and can also be the cause of vortex breakdown. In the paper, a swirling flow with a velocity profile of the Batchelor vortex type has been studied on the basis of the linear hydrodynamic stability theory. An effective numerical method for solving the spectral problem has been developed. This method includes the asymptotic solutions at artificial and irregular singular points. The stability of flows was considered for the values of the Reynolds number in the range 10≤Re≤5×106. The calculations were carried out for the value of the azimuthal wavenumber parameter n=−1. As a result of the analysis of the solutions, the existence of up to eight simultaneously occurring unstable modes has been shown. The paper presents a classification of the detected modes. The critical parameters are calculated for each mode. For fixed values of the Reynolds numbers 60≤Re≤5000, the curves of neutral stability are plotted. Branching points of unstable modes are found. The maximum growth rates for each mode are determined. A new viscous instability mode is found. The performed calculations reveal the instability of the Batchelor vortex at large values of the swirl parameter for long-wave disturbances.

Numerical Simulation of Mechanical Characteristics of Roadway Surrounding Rock under Dynamic and Static Loading

Mechanical characteristics of roadway surrounding rock under different stress wave disturbances are the key to design roadway supporting scheme. In this study, the 2802 transportation roadway in Zhangcun Coal Mine is selected as the engineering background. The distribution of stress, displacement, and plastic zone in surrounding rock under the impact of different stress waves is studied. Results show that the stress and displacement of the roof, floor, and coal walls present fluctuating change with time during the stress wave loading process. With the increase of disturbing intensity of stress wave, the resistance ability for stress wave disturbance of the roof is lower than that of the floor, while the resistance ability of two sides is the same. The volume of plastic zone in roadway surrounding rock was calculated by the self-compiled FISH code. The relationship between the plastic zone volume and the stress wave disturbing intensity in different states is explored. The cubic polynomial relationship between the volume and the disturbing intensity in the state of shear_past and tension_past is obtained. Under the simulated condition, the disturbing intensity of stress wave has the greatest influence on the increase of shear_past volume when it equals 11 MPa. While the disturbing intensity of stress wave has the greatest influence on the increase of tension_past volume, it equals 7 MPa. Meanwhile, the relation between stress wave disturbing intensity and surrounding rock stress and displacement is obtained respectively. The achievements provide a theoretical base for roadway surrounding rock support under dynamic and static loading.

On the onset of summer monsoon over India in relation to interactions of the monsoon stationary wave with transient baroclinic waves leading to monsoon cyclogenesis

The important problem of the early or late onset of summer monsoon over India is addressed in the present study and found to be related to the structure and behaviour of a monsoon stationary wave that forms over the region due to land-sea thermal contrast and interacts with travelling wave disturbances in the westerlies and the easterlies associated with the subtropical belt over Asia. Depending upon the type of coupling and decoupling that occurs between the interacting waves, monsoon advances towards India either slowly or speedily. Since northward-propagating monsoon depressions are found to accelerate the onset processes. the study carries out a detailed analysis of the interaction processes which give rise to such disturbances and determine their development and movement.

Capillary-gravitational waves and storage of liquid CO2 in the oceans

A theory of capillary-gravitational waves in the transition region between seawater and liquid carbon dioxide in deep oceans is proposed. It is shown that the thickness of the transition layer affects the properties of capillary-gravity waves. The question of the structure and stability of wave disturbances at the interface between seawater and liquefied carbon dioxide is essential for the safe storage of liquefied carbon dioxide in the ocean. This is an important issue on the current agenda in light of global warming.

Intense Precipitation and Area of Risk: A Case Study of Mass Movement in the City of Natal, Brazil

This study aims to analyze the atmospheric conditions associated with an event of intense precipitation caused by Easterly Wave Disturbances (EWDs), as well as the environmental conditions related to the mass gravitational movement that occurred between 14th June and 15th June of 2014, in the district of Mãe Luiza, Natal/RN/Brazil. The synoptic conditions, the vertical integrated moisture flux and the energetic behavior in the EWD’s performance phases were analyzed. In addition to these factors, local environmental aspects were assessed, classifying the vulnerability to disaster events in the affected area. Over the days of the operation of the atmospheric system, the daily accumulation of precipitation was greater than 100 mm, with precipitation accumulated in 3 h in the order of 60 mm for the stages of maturation of the disturbance. The main synoptic conditions associated with EWDs were exhibited by the intense anomalies of wind speed and high humidity flux on the east coast of the Northeast, which intensified the influx of moisture into the continent over the period of the operation of the system. Conditions of high to very high vulnerability were identified in the area where the event took place and also in other expressive parts of the district.

Effect of surfactants on the long-wave stability of two-layer oscillatory film flow

The stability of the two-layer film flow driven by an oscillatory plate under long-wave disturbances is studied. The influence of key factors, such as thickness ratio ( $n$ ), viscosity ratio ( $m$ ), density ratio ( $r$ ), oscillatory frequency ( $\beta$ ) and insoluble surfactants on the stability behaviours is studied systematically. Four special Floquet patterns are identified, and the corresponding growth rates are obtained by solving the eigenvalue problem of the fourth-order matrix. A small viscosity ratio ( $m\le 1$ ) may stabilize the flow but it depends on the thickness ratio. If the viscosity ratio is not very small ( $m>0.1$ ), in the $(\beta ,n)$ -plane, stable and unstable curved stripes appear alternately. In other words, under the circumstances, if the two-layer film flow is unstable, slightly adjusting the thickness of the upper film may make it stable. In particular, if the upper film is thin enough, even under high-frequency oscillation, the flow is always stable. The influence of density ratio is similar, i.e. there are curved stable and unstable stripes in the $(\beta ,r)$ -planes. Surface surfactants generally stabilize the flow of the two-layer oscillatory membrane, while interfacial surfactants may stabilize or destabilize the flow but the effect is mild. It is also found that gravity can generally stabilize the flow because it narrows the bandwidth of unstable frequencies.

Vortex Layer on the β-Plane in the Miles – Ribner Formulation. Pole on the Real Axis

Purpose. The problem of a non-zonal vortex layer on the β-plane in the Miles – Ribner formulation is considered. It is known that in the absence of the β-effect, the vortex layer has no neutral eigenmodes, and the available two ones (varicose and sinusoidal) are unstable. Initially, generalization of the problem to the β-plane concerned only the zonal case. The problem for a non-zonal vortex layer is examined for the first time in the paper. It is known that in the WKB approximation for the linear wave disturbances (regardless of whether a zonal or non-zonal background flow is considered), there is an adiabatic invariant in the form of the law of the enstrophy (vorticity) conservation. For the zonal vortex layer, the enstrophy conservation law also holds, and no vorticity exchange occurs between the waves and the flow in the zonal case. The non-zonal vortex layer has qualitatively different features; particularly, it does not retain enstrophy. Thus, as a result, there appears a new class of solutions which can be interpreted as pure radiation of the Rossby waves by a non-zonal flow. Generalizing the vortex layer problem on the β-plane to the non-zonal case constitutes the basic aim of the present study. Methods and Results. A new class of linear stationary wave solutions, namely the Rossby waves, is found. It is shown a non-zonal flow can be directed in one way, whereas the stationary wave disturbances can move in the opposite (contrary) direction. The coexistence of such solutions for the shear non-zonal flow and stationary wave disturbances takes place due to the influence of the external force and mathematically comes from a non-self-adjoining character of the linear operator for a non-zonal background flow. Conclusions. There exists a new class of solutions that can be interpreted as pure radiation of the Rossby waves by a non-zonal flow. There is no such solution for a zonal flow. It is just non-zoning that gives the effect of pure radiation and corresponds to the classical definition of radiation. This approach makes it possible to eliminate inconsistency in terminology, when instabilities are mistakenly called radiation, and radiation – pure radiation.