Formation Of Gravity Waves Research Articles

Analysis of Gravity Wave Characteristics during a Hailstone Event in the Cold Vortex of Northeast China

Based on high-resolution pressure data collected by a microbarograph and Fourier transform (FFT) data processing, a detailed analysis of the frequency spectra characteristics of gravity waves during a hailstone event in the cold vortex of Northeast China (NECV) on 9 September 2021 is presented. The results show that the deep NECV served as the large-scale circulation background for the hailstone event. The development of hailstones was closely related to gravity waves. In different hail stages, the frequency spectra characteristics of gravity waves were obviously different. One and a half hours before hailfall, there were gravity wave precursors with periods of 50–180 min and corresponding amplitudes ranging from 30 to 60 Pa. During hailfall, the center amplitudes of the gravity waves were approximately 50 Pa and 60 Pa, with the corresponding period ranges expanding to 60–70 min and 160–240 min. Simultaneously, hailstones initiated shorter periods (26–34 min) of gravity waves, with the amplitudes increasing to approximately 12–18 Pa. The relationship between hailstones and gravity waves was positive. After hailfall, gravity waves weakened and dissipated rapidly. As shown by the reconstructed gravity waves, key periods of gravity wave precursors ranged from 50–180 min, which preceded hailstones by several hours. When convection developed, there was thunderstorm high pressure and an outflow boundary. The airflow converged and diverged downstream, resulting in the formation of gravity waves and finally triggering hailfall. Gravity wave predecessors are significant for hail warnings and artificial hail suppression.

Simulation of an orographic gravity wave above the Amazon rainforest and its influence on gases transport near the surface

The influence of the topography at the ATTO site (Amazon Tall Tower Observatory) in the formation of Gravity Waves (GW) was investigated in this work. The role of these waves in gas transport on different heights in the nocturnal boundary layer, was also investigated. For this, were analyzed: experimental data of wind speed, temperature, humidity and CO2 to identify the GW. Furthermore satellite images, ECMWF ERA5 (European Center for Medium-Range Weather Forecasts) reanalysis, and numerical simulations from the mesoscale JULES-CCATT-BRAMS model (Brazilian Regional Atmospheric Modeling System) version 5.3 were used to perform GW simulations. The simulations involved two configurations (Control-With Topography and No Topography). The sattelite images made it clear that the GW was not associated with convective activities. The simulations showed clear ondulatory signs in air temperature, vertical component of the wind, and gases like CO and O3. Moreover, they also reveal that the wave originated by the presence of the local topography and this orograph gravity wave had and important role in the transport of gases above the ATTO site.

Deflection of broken ice caused by an external load moving along a channel

The unsteady problem of a load moving along a channel covered with broken ice is considered. Deflection of the broken ice is described by the equation of flotating liquid. The channel has a rectangular cross-section. The fluid in the channel is inviscid and incompressible. The flow caused by deflections of broken ice is potential. The external load is modeled by a smooth localized pressure distribution which moves along the centre line of the channel at a constant speed. With the help of the Fourier transform along the channel the original problem was reduced to the problem of the wave profile across the channel, which was solved by the method of separating variables. The deflections of the broken ice are studied for large times. The solution is presented in the form of sum of local deflection near the load and infinite system of waves propagating from the load with the speed of the load. Dispersion relations, phase and group speeds of these waves are found. The formation of gravity waves in a channel covered with broken ice depending on the speed of the load is studied.

Analysis on the Global Morphology of Middle Atmospheric Gravity Waves

AbstractUsing temperature profiles obtained by the SABER/TIMED experiment from January 2002 to December 2009, we have extracted mesoscale temperature perturbations with vertical wavelengths ranging from 2 to 10 km. Global distribution of middle atmospheric gravity wave activity is revealed by observing the temperature perturbations. Comparison shows that gravity wave fluctuations in summer and winter are stronger than those in spring and autumn, below 70 km the disturbance intensity in summer is weaker with respect to winter, and contrary above 70 km. The larger gravity waves appear in winter hemisphere and in the tropics between 25°N and 25°S. Meanwhile, the perturbation peak points in the tropics move northward with increasing altitude. Furthermore, relatively larger values of gravity wave activity are present at the edge of the Antarctic polar vortex. They also appear to vary with longitudes at equatorial latitudes, which may be resulted from wind filtering, topography, planetary wave modulations and other factors. Moreover, gravity wave disturbance intensity changes with height. It indicates a decrease at 25~30 km and an increase above 42 km. Comparing the average distribution of gravity waves of eight years at different heights, we can see that the strength of gravity waves is related to topography obviously at lower altitudes, but the relationship is not significant at higher altitudes. It indicates that the formation of gravity waves is closely correlated with topography, but in the process of propagation the distribution significantly changes with altitudes.

Modeling nonequilibrium and history effects of homogeneous turbulence in a stably stratified medium

Abstract Homogeneous turbulence decay in a stably stratified flow has two distinct characteristics. One is countergradient fluxes that are developed to keep the energy budget in equilibrium. Another is the formation of gravity waves that contribute to the velocity variance with little vertical mixing. The prediction of these characteristics are investigated using a hierarchy of turbulence models. They include second-order models as well as models that solve the transport equations for the turbulent kinetic energy, its dissipation rate, the temperature variance and its dissipation rate. In the latter class of models, the vertical heat flux is calculated either from an algebraic equation or from a transport equation. The algebraic equation is derived by invoking equilibrium and nonequilibrium turbulence assumption. Thus, modeling level and the relative importance of nonequilibrium and history effects in the predictions of countergradient fluxes and gravity waves could be assessed. The investigation reveals that countergradient heat flux can be predicted even when the equilibrium assumption is invoked. However, the formation of gravity waves can be predicted only when the history effects of the vertical heat flux are accounted for properly. The decay rate of the total energy is very much affected by two model constants in the temperature variance dissipation rate equation. On the other hand, the calculated frequency and amplitude of the gravity waves are influenced by the model constants in the heat flux equation.