Dynamical Processes of Gravity Waves Propagation and Dissipation, and Statistical Characteristics of Their Momentum Flux in the Mesosphere and Lower Thermosphere PDF Download
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Author: Bing Cao
Publisher:
ISBN:
Category : Atmospheric physics
Languages : en
Pages : 308
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Book Description
Abstract The mesosphere and lower thermosphere (MLT) (~80-110 km) is dominated by abundant atmospheric waves, of which gravity waves are one of the least understood due to large varieties in wave characteristics as well as potential sources. Gravity waves play an important role in the atmosphere by influencing the thermal balance and helping to drive the global circulation. But due to their sub-grid scale, the effects of gravity waves in General Circulation Models (GCMs) are mostly parameterized. The investigations of gravity waves in this dissertation are from two perspectives: the dynamical processes of gravity wave propagation and dissipation in the MLT region, and the climatology and statistical characteristics of gravity waves as physical basics of gravity wave parameterization. The studies are based on the data acquired from an airglow imager and a sodium lidar, with the assistance of some simulation data from a meso-scale numerical model and GCMs. To understand the dynamical processes in gravity wave propagation and dissipation, a gravity wave should be resolved as fully as possible. The first topic of this dissertation is motivated by the fact that most observational instruments can only capture part of the gravity waves spectrum, either horizontal or vertical structures. Observations from multiple complementary instruments are used to study gravity waves in 3-D space. There are two cases included in this topic. In case 1, a co-located sodium lidar and an airglow imager were used to depict a comprehensive picture of a wave event at altitude between 95-105 km. Thus, the horizontal and vertical gravity waves structures and their ambient atmosphere states were fully characterized, which suggests that a gravity wave undergoes reflection at two different altitudes and near-critical layer filtering in-between. All the retrieved parameters were then applied to a 2-D numerical model whose outputs help to interpret the observations. In case 2, the lidar system is configured in a 5-direction mode, whose laser beams were pointed to zenith and 30° off-zenith at four cardinal directions. Thus, there is a ~50 km separation at 90 km altitude between zenith and any off-zenith directions. Besides the vertical information from traditional lidar measurement pro horizontal wavelength and propagation direction are derived from the phase among measurements in different directions. With a full set of wave and parameters, multiple dispersion validate the goodness of different assumptions involved in linear gravity wave files, differences background and polarization relations are examined and the results theory Better knowledge of gravity waves from observational and numerical, as well as theoretical studies directly contribute to the development of physically-based parameterizations. The second topic of this dissertation is about long-term climatology and statistical characteristics of gravity waves observed by an airglow imager. The results provide some insights on how the source spectrum can be specified and tuning factors are constrained in the parameterization. Results from two sites are compared, one is in the middle of the Pacific Ocean, and the other above the Andes Mountains. The difference and similarity provide some clues to the effects of wave sources and background flow on the gravity wave climatology and intermittency in the mesopause region. Firstly, the long-term climatology of intrinsic wave parameters and propagation direction preferences for high-frequency quasi-monochromatic gravity waves observed by an airglow imager is presented. Wave occurrence and propagation direction are related to convective activities nearby and local background winds. The preferential wave propagation during austral summer is poleward and equatorward during winter. The estimated momentum fluxes show a clear anti-correlation with background winds. Secondly, intermittency of gravity waves near mesopause region is studied. The concept of intermittency is originally from the factors used in wave parameterization schemes to describe the fractional coverage of waves within a large spatial grid and/or temporal period in order to accurately quantify the forcing on the atmosphere by dissipating gravity waves. Intermittency of gravity waves was described by the probability density functions of absolute momentum flux and some diagnostic parameters. An explicit probability function that is a piecewise function of lognormal and power law functions is obtained from airglow data. The relative importance of abundant waves with smaller amplitudes and rare waves with dramatically large amplitudes were compared. Lastly, the duration of gravity waves in the airglow layer is studied. The observed gravity waves duration in the airglow layer is exponentially distributed. Several mechanisms that could lead to such a distribution are put forward from the perspective of wave breaking due to instabilities and blocking due to evanescent regions. Ducted propagation is also a possible factor. Through individual cases and statistical studies, this dissertation investigates the dynamical processes and statistical characteristics of gravity in the MLT region. The results are expected to provide more insight in both observational and modeling research on gravity waves.
Author: Bing Cao
Publisher:
ISBN:
Category : Atmospheric physics
Languages : en
Pages : 308
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Book Description
Abstract The mesosphere and lower thermosphere (MLT) (~80-110 km) is dominated by abundant atmospheric waves, of which gravity waves are one of the least understood due to large varieties in wave characteristics as well as potential sources. Gravity waves play an important role in the atmosphere by influencing the thermal balance and helping to drive the global circulation. But due to their sub-grid scale, the effects of gravity waves in General Circulation Models (GCMs) are mostly parameterized. The investigations of gravity waves in this dissertation are from two perspectives: the dynamical processes of gravity wave propagation and dissipation in the MLT region, and the climatology and statistical characteristics of gravity waves as physical basics of gravity wave parameterization. The studies are based on the data acquired from an airglow imager and a sodium lidar, with the assistance of some simulation data from a meso-scale numerical model and GCMs. To understand the dynamical processes in gravity wave propagation and dissipation, a gravity wave should be resolved as fully as possible. The first topic of this dissertation is motivated by the fact that most observational instruments can only capture part of the gravity waves spectrum, either horizontal or vertical structures. Observations from multiple complementary instruments are used to study gravity waves in 3-D space. There are two cases included in this topic. In case 1, a co-located sodium lidar and an airglow imager were used to depict a comprehensive picture of a wave event at altitude between 95-105 km. Thus, the horizontal and vertical gravity waves structures and their ambient atmosphere states were fully characterized, which suggests that a gravity wave undergoes reflection at two different altitudes and near-critical layer filtering in-between. All the retrieved parameters were then applied to a 2-D numerical model whose outputs help to interpret the observations. In case 2, the lidar system is configured in a 5-direction mode, whose laser beams were pointed to zenith and 30° off-zenith at four cardinal directions. Thus, there is a ~50 km separation at 90 km altitude between zenith and any off-zenith directions. Besides the vertical information from traditional lidar measurement pro horizontal wavelength and propagation direction are derived from the phase among measurements in different directions. With a full set of wave and parameters, multiple dispersion validate the goodness of different assumptions involved in linear gravity wave files, differences background and polarization relations are examined and the results theory Better knowledge of gravity waves from observational and numerical, as well as theoretical studies directly contribute to the development of physically-based parameterizations. The second topic of this dissertation is about long-term climatology and statistical characteristics of gravity waves observed by an airglow imager. The results provide some insights on how the source spectrum can be specified and tuning factors are constrained in the parameterization. Results from two sites are compared, one is in the middle of the Pacific Ocean, and the other above the Andes Mountains. The difference and similarity provide some clues to the effects of wave sources and background flow on the gravity wave climatology and intermittency in the mesopause region. Firstly, the long-term climatology of intrinsic wave parameters and propagation direction preferences for high-frequency quasi-monochromatic gravity waves observed by an airglow imager is presented. Wave occurrence and propagation direction are related to convective activities nearby and local background winds. The preferential wave propagation during austral summer is poleward and equatorward during winter. The estimated momentum fluxes show a clear anti-correlation with background winds. Secondly, intermittency of gravity waves near mesopause region is studied. The concept of intermittency is originally from the factors used in wave parameterization schemes to describe the fractional coverage of waves within a large spatial grid and/or temporal period in order to accurately quantify the forcing on the atmosphere by dissipating gravity waves. Intermittency of gravity waves was described by the probability density functions of absolute momentum flux and some diagnostic parameters. An explicit probability function that is a piecewise function of lognormal and power law functions is obtained from airglow data. The relative importance of abundant waves with smaller amplitudes and rare waves with dramatically large amplitudes were compared. Lastly, the duration of gravity waves in the airglow layer is studied. The observed gravity waves duration in the airglow layer is exponentially distributed. Several mechanisms that could lead to such a distribution are put forward from the perspective of wave breaking due to instabilities and blocking due to evanescent regions. Ducted propagation is also a possible factor. Through individual cases and statistical studies, this dissertation investigates the dynamical processes and statistical characteristics of gravity in the MLT region. The results are expected to provide more insight in both observational and modeling research on gravity waves.
Author: PLUMB
Publisher: Birkhäuser
ISBN: 3034858256
Category : Science
Languages : en
Pages : 465
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Book Description
PAGEOPH, stratosphere, these differences provide us with new evidence, interpretation of which can materially help to advance our understanding of stratospheric dynamics in general. It is now weil established that smaller-scale motions-in particular gravity waves and turbulence-are of fundamental importance in the general circulation of the mesosphere; they seem to be similarly, if less spectacularly, significant in the troposphere, and probably also in the stratosphere. Our understanding of these motions, their effects on the mean circulation and their mutual interactions is progressing rapidly, as is weil illustrated by the papers in this issue; there are reports of observational studies, especially with new instruments such as the Japanese MV radar, reviews of the state of theory, a laboratory study and an analysis of gravity waves and their effects in the high resolution "SKYHI" general circulation model. There are good reasons to suspect that gravity waves may be of crucial significance in making the stratospheric circulation the way it is (modeling experience being one suggestive piece of evidence for this). Direct observational proof has thus far been prevented by the difficulty of making observations of such scales of motion in this region; in one study reported here, falling sphere observations are used to obtain information on the structure and intensity of waves in the upper stratosphere.
Author: Zhenhua Li
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
In this thesis, investigations on gravity waves are conducted in two regions of the middle atmosphere: the lower stratosphere using high-resolution radiosonde at South Pole and the mesopause region using OH airglow imager at Maui, Hawaii and Cerro Pachon, Chile. Wave characteristics at these regions are deduced and the seasonal variation of wave activity, wave sources, and propagation effect are studied. The study of gravity waves in the lower stratosphere at South Pole reveals that sources other than topography are important even for the lower part of middle atmosphere. Horizontal propagation must be included in parameterization schemes to reflect the fact that waves derived from radiosondes have slant propagation paths. They travel long distance horizontally before they reach higher altitudes. Long term gravity wave characteristics over Maui from 2002 to 2007 are deduced from OH airglow imager. Wave parameters from the long term imager observation provide robust statistics of high-frequency gravity wave in the midlatitudes. Poleward wave propagation preference during summer and equatorward wave propagation preference during winter are observed over Maui. They are also opposite to the seasonal mean meridional wind direction which are always pointing toward winter pole. Momentum fluxes deduced from OH imager are also highly anti-correlated with background winds. At least for the part of spectrum observed by airglow imager, gravity waves act as damping mechanism for diurnal tide. Gravity wave occurrence frequency does not follow the variation of local convective sources and convective sources in a large domain when ducted waves are considered. In fact, with a constant wave source and monthly mean background atmospheric condition, the simulated wave transmission resembles the wave occurrence frequency observed by OH airglow imager at Maui. Thus, at Maui the propagation effect dominates the seasonal variation in wave activity. Gravity wave momentum fluxes deduced from airglow imager provide important observation constraint for gravity wave parameterization for the mesopause region. To explain the cause of seasonal change on meridional propagation preference, three mechanisms are investigated: critical-layer filtering, wave ducting, and Doppler-shifting by local mean wind. Critical-layer filtering failed to explain the propagation preference. Observed gravity wave propagation directions are largely related to the background wind in the airglow layer. This is caused by Doppler-shifting of gravity waves by background wind. Background wind Doppler shifts gravity waves propagating against (along) background wind to higher (lower) frequency and larger (smaller) vertical wavelength. Thus, the observed gravity waves tend to propagate against background wind. The apparent against background wind propagation is largely caused by the contrast in cancellation factor for waves propagate in different direction. To a lesser degree, the difference in dissipation for waves propagate in different direction also contributes to the observed against background wind propagation. The results from this work show gravity wave's propagation in middle atmosphere is strongly affected by atmospheric field. For low frequency waves, their propagation paths are slant and can travel hundreds of kilometers before they reach the middle atmosphere. For high frequency gravity waves, though their propagation paths are mostly vertical, they are subject to ducting and reflection. Due to the large contribution of momentum flux in the Mesosphere and Lower Thermosphere (MLT) by high-frequency, short-horizontal-scale waves, these propagation effects must be included in gravity wave parameterizations.
Author: Kevin Hamilton
Publisher: Springer Science & Business Media
ISBN: 3642606547
Category : Science
Languages : en
Pages : 568
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Book Description
The subject of this volume is the observation and modelling of the gravity wave field in the atmosphere. The focus is on the question of how to include the effects of small-scale gravity waves in sophisticated global climate models. The book comprises 26 chapters, including contributions from distinguished experts in observation and theory, along with results from studies of gravity wave parameterization within comprehensive climate models.
Author: Christopher J. Heale
Publisher:
ISBN:
Category : Gravity waves
Languages : en
Pages : 328
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Book Description
"A 2-D nonlinear compressible model is used in conjunction with ray-theory to investigate the long-range propagation, dissipation and interaction of small-scale gravity waves in the Mesosphere and Lower Thermosphere (MLT) region"--Abstract.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 108
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Book Description
Author: Mangalathayil Ali Abdu
Publisher: Springer Science & Business Media
ISBN: 9400703260
Category : Science
Languages : en
Pages : 479
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Book Description
This book is a multi-author treatise on the most outstanding research problems in the field of the aeronomy of the Earth’s atmosphere and ionosphere, encompassing the science covered by Division II of the International Association of Geomagnetism and Aeronomy (IAGA). It contains several review articles and detailed papers by leading scientists in the field. The book is organized in five parts: 1) Mesosphere-Lower Thermosphere Dynamics and Chemistry; 2) Vertical Coupling by Upward Propagating Waves; 3) Ionospheric Electrodynamics and Structuring; 4) Thermosphere- Ionosphere Coupling, Dynamics and Trends and 5) Ionosphere-Thermosphere Disturbances and Modeling. The book consolidates the progress achieved in the field in recent years and it serves as a useful reference for graduate students as well as experienced researchers.
Author: Carmen J. Nappo
Publisher: Elsevier
ISBN: 0080491669
Category : Science
Languages : en
Pages : 300
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Book Description
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
Author: Bruce R. Sutherland
Publisher: Cambridge University Press
ISBN: 1316184323
Category : Science
Languages : en
Pages : 395
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Book Description
The study of internal gravity waves provides many challenges: they move along interfaces as well as in fully three-dimensional space, at relatively fast temporal and small spatial scales, making them difficult to observe and resolve in weather and climate models. Solving the equations describing their evolution poses various mathematical challenges associated with singular boundary value problems and large amplitude dynamics. This book provides the first comprehensive treatment of the theory for small and large amplitude internal gravity waves. Over 120 schematics, numerical simulations and laboratory images illustrate the theory and mathematical techniques, and 130 exercises enable the reader to apply their understanding of the theory. This is an invaluable single resource for academic researchers and graduate students studying the motion of waves within the atmosphere and ocean, and also mathematicians, physicists and engineers interested in the properties of propagating, growing and breaking waves.
Author: Xian Lu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Gravity waves (GWs) and tides are two strongest and most persistent waves in the middle atmosphere of the Earth. They are usually generated in the lower atmosphere and propagate upward to the middle and upper atmosphere, where they play important roles in the atmospheric composition, chemistry, dynamics and energetics. This dissertation focuses on a case-study of the propagation and dissipation characteristics of an inertial GW, the seasonal variation of the diurnal tide based on both the observations and models, and also the interactions between GWs and tides. One-night (October 28, 2003) temperature and horizontal wind measurements by a resonance sodium (Na) wind/temperature lidar in Maui (20.7 N, 156.3 W) and temperature measurement by a Rayleigh lidar at Mauna Loa Observatory (MLO, 19.5 N, 155.6 W), HI, are used as a case study of the GW propagation from the lower stratosphere to the lower thermosphere (35-103 km). A dominant wave mode is identi ed from the simultaneous temperature observations by both lidars. The wave is partially dissipated and propagates upward with an e-fold height of temperature amplitude at 14 km. A damping layer is present around the stratopause where the wave amplitude is relatively smaller, corresponding to a low static stability layer. The vertical wavelengths are larger in the mesosphere (12-13 km) than in the stratosphere (6-7 km), consistent with the decreasing static stability with altitude. The wave is propagating northward and the horizontal wavelength is 2140 km and intrinsic period is 15 hrs in the region of 84-103 km. The apparent period is 6 hrs and consistent with Doppler shift of the background wind. It is suggested that the convective zone over the equator to the south of Hawaii provides a constant GW source that is responsible for the observed GW throughout the night. The seasonal variability of the diurnal tide in the mesosphere and lower thermosphere (MLT) over Maui, HI is investigated using the meteor radar horizontal wind measurement from years 2002 to 2007. The semiannual oscillation (SAO) of tidal amplitudes is dominant above 88 km, with amplitudes at the equinoxes 2-3 times larger than at the solstices. Below 88 km, the annual oscillation (AO) dominates and its magnitude is smaller than the SAO. The AO dominates in the phase variation of the diurnal tide, which advances in winter and lags in summer as compared with the equinoxes. The vertical wavelength also has a noticeable seasonal variation with shorter vertical wavelengths found at the equinoxes. The reconstruction of the diurnal tide by superposing the migrating and nonmigrating tides derived from Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Doppler Interferometer (TIMED/TIDI) and TIMED/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature is compared with the meteor radar observation, and a consistency is found in the seasonal variation of the tidal amplitude. Based on the TIDI and SABER measurements, the migrating diurnal tide (DW1) is the dominant tidal component while three other nonmigrating tides, DW2, DS0 and DE3, are non-negligible. The seasonal variation of the diurnal tide is well captured by the Global Scale Wave Model (GSWM) and the Whole Atmosphere Community Climate Model (WACCM) while discrepancies are also presented and discussed. Since the WACCM is capable of reproducing the tidal seasonality, it is used to examine the physical mechanisms. First, the e ects of GW forcing and advection on the momentum balance of DW1 are investigated, because they are the two most dominant terms in the momentum equation that account for the discrepancies between classical tidal theory and the calculations based on the full primitive equations. In the WACCM, GW forcing in the wave breaking region always damps DW1 and advances its phase, thus shortening the vertical wavelength of the tide locally. The linear advection largely determined by the latitudinal shear of the zonal mean wind mostly contributes to the phase change in the zonal wind. For the meridional wind, however, nonlinear advection is more important than GW drag and linear advection for the amplitude and phase changes. The DW1 amplitudes are smaller than TIMED observations, suggesting that the GW forcing is overestimated in the WACCM and result in an unrealistic large damping on DW1. Second, the seasonal variations of GW forcing, tidal heating and mean wind e ects are examined using the WACCM. Similar to the tidal amplitude, stronger GW forcing is also found at the equinox, which can not account for the tidal seasonality because GW forcing always damps DW1. Instead, the radiative tidal heating due to the water vapor absorption of infrared solar radiation largely determines the SAO of DW1. The e ffect of mean winds leads to a 1-month time shift of the maximum amplitude. The AO in the tidal phase is due to the seasonal change of mean winds. At the solstice, a stronger antisymmetric (1,2) Hough mode is generated which signi cantly distorts the tidal structure. Because the phase of the (1,2) mode changes by 12-hrs every half a year, it causes a phase advance in winter and a lag in summer, thus leading to an AO of the phase. As GWs and tides reach the MLT region, they can maintain large amplitudes thus strong interactions between them are expected. High-frequency GW variances are calculated as the residual horizontal wind variances based on the meteor radar measurements in Maui, HI and Urbana, IL (40 N, 88 W). Monte-Carlo simulations are performed in order to evaluate the sensitivity of the GW variance calculation on the meteor rate. It is indicated that the residual horizontal wind variance can be used as a good proxy of GW activities. The diurnal and semidiurnal variations of the GW variances are most dominant, while periods of 2-day, 5-day and 10-day are also observed. The vertical phase structures of the GW variances and tidal winds are consistent with each other, implying the GW variances are modulated by tides. In most cases, the GW variances increase with altitude and the growth rates are slower than freely propagating waves. A further study on the physical mechanisms resulting in the tidal modulations is needed in the future.
