Waves and Turbulence in Stably Stratified Flows

Waves and Turbulence in Stably Stratified Flows
Author: S. D. Mobbs
Publisher: Oxford University Press, USA
Total Pages: 488
Release: 1993
Genre: Mathematics
ISBN:

This volume, containing twenty papers, includes the majority of those presented at the third IMA conference on stably stratified flows, held in Leeds in December 1989. The theme of the conference was waves and turbulence in stably stratified flows, although papers covering other aspects ofstably stratified flows are also included. A wide variety of techniques are described, ranging from numerical simulation, through laboratory studies, to field observations of the atmosphere. Some papers address fundamental aspects of turbulence in stably stratfied flows such as turbulence collapseand local scaling. Six of the papers report investigations motivated by Antarctic field studies, reflecting the importance of that region for research on the stably stratified atmosphere. Eight papers deal with aspects of mixing in stably stratified flows, of which four are directly concerned withindustrial applications. Observations of atmospheric internal gravity waves are discussed in two papers whilst a further two report studies of rotating, stratified flows with application to large-scale atmospheric and oceanic dynamics.

An Introduction to Atmospheric Gravity Waves

An Introduction to Atmospheric Gravity Waves
Author: Carmen J. Nappo
Publisher: Elsevier
Total Pages: 300
Release: 2002-09-12
Genre: Science
ISBN: 0080491669

Gravity waves exist in all types of geophysical fluids, such as lakes, oceans, and atmospheres. They play an important role in redistributing energy at disturbances, such as mountains or seamounts and they are routinely studied in meteorology and oceanography, particularly simulation models, atmospheric weather models, turbulence, air pollution, and climate research. An Introduction to Atmospheric Gravity Waves provides readers with a working background of the fundamental physics and mathematics of gravity waves, and introduces a wide variety of applications and numerous recent advances. Nappo provides a concise volume on gravity waves with a lucid discussion of current observational techniques and instrumentation. Foreword is written by Prof. George Chimonas, a renowned expert on the interactions of gravity waves with turbulence. CD containing real data, computer codes for data analysis and linear gravity wave models included with the text

Internal Wave Generation by Convection

Internal Wave Generation by Convection
Author: Daniel Lecoanet
Publisher:
Total Pages: 143
Release: 2016
Genre:
ISBN:

In nature, it is not unusual to find stably stratified fluid adjacent to convectively unstable fluid. This can occur in the Earth's atmosphere, where the troposphere is convective and the stratosphere is stably stratified; in lakes, where surface solar heating can drive convection above stably stratified fresh water; in the oceans, where geothermal heating can drive convection near the ocean floor, but the water above is stably stratified due to salinity gradients; possible in the Earth's liquid core, where gradients in thermal conductivity and composition diffusivities maybe lead to different layers of stable or unstable liquid metal; and, in stars, as most stars contain at least one convective and at least one radiative (stably stratified) zone. Internal waves propagate in stably stratified fluids. The characterization of the internal waves generated by convection is an open problem in geophysical and astrophysical fluid dynamics. Internal waves can play a dynamically important role via nonlocal transport. Momentum transport by convectively excited internal waves is thought to generate the quasi-biennial oscillation of zonal wind in the equatorial stratosphere, an important physical phenomenon used to calibrate global climate models. Angular momentum transport by convectively excited internal waves may play a crucial role in setting the initial rotation rates of neutron stars. In the last year of life of a massive star, convectively excited internal waves may transport even energy to the surface layers to unbind them, launching a wind. In each of these cases, internal waves are able to transport some quantity--momentum, angular momentum, energy--across large, stable buoyancy gradients. Thus, internal waves represent an important, if unusual, transport mechanism. This thesis advances our understanding of internal wave generation by convection. Chapter 2 provides an underlying theoretical framework to study this problem. It describes a detailed calculation of the internal gravity wave spectrum, using the Lighthill theory of wave excitation by turbulence. We use a Green's function approach, in which we convolve a convective source term with the Green's function of different internal gravity waves. The remainder of the thesis is a circuitous attempt to verify these analytical predictions. I test the predictions of Chapter 2 via numerical simulation. The first step is to identify a code suitable for this study. I helped develop the Dedalus code framework to study internal wave generation by convection. Dedalus can solve many different partial differential equations using the pseudo-spectral numerical method. In Chapter 3, I demonstrate Dedalus' ability to solve different equations used to model convection in astrophysics. I consider both the propagation and damping of internal waves, and the properties of low Rayleigh number convective steady states, in six different equation sets used in the astrophysics literature. This shows that Dedalus can be used to solve the equations of interest. Next, in Chapter 4, I verify the high accuracy of Dedalus by comparing it to the popular astrophysics code Athena in a standard Kelvin-Helmholtz instability test problem. Dedalus performs admirably in comparison to Athena, and provides a high standard for other codes solving the fully compressible Navier-Stokes equations. Chapter 5 demonstrates that Dedalus can simulate convective adjacent to a stably stratified region, by studying convective mixing near carbon flames. The convective overshoot and mixing is well-resolved, and is able to generate internal waves. Confident in Dedalus' ability to study the problem at hand, Chapter 6 describes simulations inspired by water experiments of internal wave generation by convection. The experiments exploit water's unusual property that its density maximum is at 4C, rather than at 0C. We use a similar equation of state in Dedalus, and study internal gravity waves generation by convection in a water-like fluid. We test two models of wave generation: bulk excitation (equivalent to the Lighthill theory described in Chapter 2), and surface excitation. We find the bulk excitation model accurately reproduces the waves generated in the simulations, validating the calculations of Chapter 2.

Internal Gravity Waves Observed in Mesospheric Temperature Measurements

Internal Gravity Waves Observed in Mesospheric Temperature Measurements
Author: S. P. Zimmerman
Publisher:
Total Pages: 26
Release: 1970
Genre: Atmosphere, Upper
ISBN:

Temperature height profiles determined from falling sphere and Arcasonde measurements, made at White Sands, New Mexico from 23 to 25 January 1967, exhibit unusually large variability in the vicinity of the mesopause. Spatial and temporal analysis of the data exhibit a wave-like structure with vertical half wavelengths of the order of 3 and 30 km and a characteristic period of approximately 12 hours for the longer wavelength. Comparison with meteorological data below 60 km and application of appropriate theory leads to the tentative suggestion that the observed temperature variations were due to internal gravity waves. The analysis also infers that the source of these waves was a large scale, low altitude (approximately 200 mb) synoptic disturbance. This work has been performed in support of re-entry studies for Air Force space vehicles and investigations for improving DOD missile impact prediction capability. (Author).

Stably Stratified Flows

Stably Stratified Flows
Author: I. P. Castro
Publisher: Oxford University Press, USA
Total Pages: 384
Release: 1994
Genre: Mathematics
ISBN:

The first papers of this conference addressed the long-standing issues of the nature of the upstream effects that occur in stratified flow over obstacles (P G Baines, CSIRO, Australia, A P Taylor, York University, Ontario, Canada; K W Ayotte, Boulder, Colorado, USA). Then followed a sessionon internal wave motions followed by a session on modelling the atmospheric boundary layer (J C King, British Antarctic Survey, Cambridge; A Kay, Loughborogh University of Technology). There was a session on numerical modelling (O Matais, Instite de Mecanique de Grenoble, France; A S Smedman,Uppsala University). The various aspects of dispersion were discussed and the final papers in the conference described laboratory experiments on flow and dispersion around buildings in light wind conditions.

Infrasound Monitoring for Atmospheric Studies

Infrasound Monitoring for Atmospheric Studies
Author: Alexis Le Pichon
Publisher: Springer Science & Business Media
Total Pages: 739
Release: 2010-01-19
Genre: Science
ISBN: 1402095082

The use of infrasound to monitor the atmosphere has, like infrasound itself, gone largely unheard of through the years. But it has many applications, and it is about time that a book is being devoted to this fascinating subject. Our own involvement with infrasound occurred as graduate students of Prof. William Donn, who had established an infrasound array at the Lamont-Doherty Geological Observatory (now the Lamont-Doherty Earth Observatory) of Columbia University. It was a natural outgrowth of another major activity at Lamont, using seismic waves to explore the Earth’s interior. Both the atmosphere and the solid Earth feature velocity (seismic or acoustic) gradients in the vertical which act to refract the respective waves. The refraction in turn allows one to calculate the respective background structure in these mediums, indirectly exploring locations that are hard to observe otherwise. Monitoring these signals also allows one to discover various phenomena, both natural and man-made (some of which have military applications).