A method of inferring tropospheric gravity wave source characteristics from middle atmosphere observations has been adapted from previous studies for use with MF radar observations of the equatorial mesosphere-lower thermosphere at Christmas Island in the central Pacific. The nature of the techniques applied also permitted an analysis of the momentum flux associated with the characterised sources and its effects on the equatorial mean flow and diurnal solar thermal tide. An anisotropic function of gravity wave horizontal phase speed was identified as being characteristic of convectively generated source spectra. This was applied stochastically to a ray-tracing model to isolate numerical estimates of the function parameters. The inferred spectral characteristics were found to be consistent with current theories relating convective gravity wave spectra to tropospheric conditions and parameters characterising tropical deep convection. The results obtained provide observational constraints on the model spectra used in gravity wave parameterisations in numerical weather prediction and general circulation models. The interaction of gravity waves with the diurnal solar thermal tide was found to cause an amplification of the tide in the vicinity of the mesopause. The gravity wave-tidal interactions were highly sensitive to spectral width and amplitude. Estimates were made of the high frequency gravity wave contribution to forcing the MSAO with variable results. The data used in the analysis are part of a large archive which now has the potential to provide tighter constraints on wave spectra through the use of the methods developed here. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1352362 / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2009

<p>In this thesis various descriptions of the near surface atmospheric flow over a high latitude glacier is used in an effort to increase our understanding of the basic flow dynamics there.</p><p>Through their contribution to sea-level change, mountain glaciers play a significant role in Earth’s climate system. Properties of the near surface atmospheric flow are important for understanding glacier response to climate change.</p><p>Here, the near surface atmospheric flow is studied from several perspectives including the effects of both rotation and slope. Rotation is an important aspect of most atmospheric flows and its significance for mesoscale flows have gained recognition over the last years. Similarly, the very stable boundary layer (VSBL) has lately gained interest. Within a VSBL over sloping terrain katabatic flow is known to be usual and persistent. For the present thesis a combination of numerical and simple analytical models as well as observations from the Vatnajökull glacier on Iceland have been used. The models have continuously been compared to available observations. Three different approaches have been used: linear wave modeling, analytic modeling of katabatic flow and of the Ekman layer, and numerical simulations of the katabatic flow using a state of the art mesoscale model. The analytic models for the katabatic flow and the Ekman layer used in this thesis both utilizes the WKB method to allow the eddy diffusivity to vary with height. This considerably improves the results of the models. Among other findings it is concluded that: a large part of the flow can be explained by linear theory, that good results can be obtained for surface energy flux using simple models, and that the very simple analytic models for the katabatic flow and the Ekman layer can perform adequately if the restraint of constant eddy diffusivity is relieved.</p>

The global analysis fields of the Met Office stratospheric assimilated data set have been investigated. Systematic biases for select years were identified through val- idation with independent satellite observations. Particular attention was given to analyses from January 2005 to October 2009 produced from a 50 level (L50) configuration of the UM with model lid at ∼0.1 hPa, and the impact on analyses fields from November 2009 to September 2010 when the middle atmospheric configuration of the UM was extended to ∼0.01 hPa using 70 levels (L70). Validation results from both the L50 and L70 analyses show that largest tem- perature biases occur at polar latitudes approaching the model lid in the meso- sphere, exhibiting a clear seasonal cycle. Here cold biases in the winter season of the L50 analyses and warm biases in the summer season of the L70 analyses would strongly suggest that the mean meridional circulation in the mesosphere is underestimated, and that small scale gravity wave forcing supplied by the op- erational Ultra Simple Spectral Parameterisation (USSP) scheme is insufficient. Based on the above validation results numerous experiments were conducted to investigate the temperature response in the mesosphere to increased gravity wave forcing. Such experiments concentrated on tuning the energy scale factor (β) in the USSP scheme and the application of a momentum conserving ”opaque” lid. Furthermore, the impact of developing the USSP scheme to include direct heating from gravity wave induced turbulent dissipation was also investigated. Maximum temperature responses in the summer polar upper mesosphere of ∼22 K were found when increasing the standard value of β=0.1 to β=0.14 combined with the application of an opaque lid. Magnitudes of direct heating rates due to gravity wave turbulent dissipation diagnosed via the USSP scheme were found to be consistent with previous estimates. However applying such heating would most likely have a negative impact on the L70 analyses, which already display warm biases in the upper mesosphere, strongly suggesting that additional phys- ical processes such as eddy diffusion must also be accounted for when applying direct heating from gravity wave breaking.

Gravity waves in the atmosphere are the waves with gravity and buoyancy force as the restoring forces. Gravity waves will significantly impact the Mesosphere Lower / Thermosphere (MLT), and the breaking of gravity waves is the key factor to cause the cool summer and warm winter in the Mesopause region. Therefore, it is important for us to investigate gravity waves. In this dissertation, we mainly use USU Na lidar data to explore gravity waves in the MLT. The exploration is made up of two projects. One is the investigation of gravity wave breaking and the associated dynamic instability by USU Na Lidar and Advanced Mesosphere Temperature Mapper (AMTM). Another is the calculation of gravity wave temperature perturbations and potential energy density by least-squares fitting based on the data from the full-diurnal cycle observation of Na lidar. The sporadic sodium layer is the sharp increase of Na density in a small vertical range (several kilometers) above the Na main layer in the MLT. The formation of the sporadic sodium layer above 100 km remains unknown until now. Here we will investigate the mechanism of the generation of sporadic sodium layer using numeric modeling, including the effect of tide and gravity wave on the variation of Na density.

In this thesis various descriptions of the near surface atmospheric flow over a high latitude glacier is used in an effort to increase our understanding of the basic flow dynamics there. Through their contribution to sea-level change, mountain glaciers play a significant role in Earth’s climate system. Properties of the near surface atmospheric flow are important for understanding glacier response to climate change. Here, the near surface atmospheric flow is studied from several perspectives including the effects of both rotation and slope. Rotation is an important aspect of most atmospheric flows and its significance for mesoscale flows have gained recognition over the last years. Similarly, the very stable boundary layer (VSBL) has lately gained interest. Within a VSBL over sloping terrain katabatic flow is known to be usual and persistent. For the present thesis a combination of numerical and simple analytical models as well as observations from the Vatnajökull glacier on Iceland have been used. The models have continuously been compared to available observations. Three different approaches have been used: linear wave modeling, analytic modeling of katabatic flow and of the Ekman layer, and numerical simulations of the katabatic flow using a state of the art mesoscale model. The analytic models for the katabatic flow and the Ekman layer used in this thesis both utilizes the WKB method to allow the eddy diffusivity to vary with height. This considerably improves the results of the models. Among other findings it is concluded that: a large part of the flow can be explained by linear theory, that good results can be obtained for surface energy flux using simple models, and that the very simple analytic models for the katabatic flow and the Ekman layer can perform adequately if the restraint of constant eddy diffusivity is relieved.

Approved for public release; distribution is unlimited / Capacitance and conductance measurements using two and four wire techniques were developed and statically and dynamically calibrated in this thesis. The voltage sensitivities range from 7.3 to 8.1 ± 0.1 mV/cm for the two wire capacitance system static calibrations. This is ± 5.2% of the limiting theoretical value. The voltage sensitivities range from 0.3 to 0.4 ± 0.1 V/cm for the four wire conductance system static calibrations. Dynamic calibrations were only completed for the conductance system. The dynamic calibration results were weakly frequency dependent with a qj-0.15 decay in a limited, 2-4 Hz range. Wind power spectrum measurements were taken in the existing Upper Ocean Simulations Facility at the Naval Postgraduate School. There was excellent agreement in the spectra with both techniques. Driven gravity wave frequency downshifting and wind energy dumping was observed in the combined gravity wave and wind-wave measurements. The power spectra peaked near two Hertz and decayed at 50 to 70 dB per decade, or as CO -5 to G)" 7 for both systems. Gravity wave phase speed and wavelength measurements were performed with the capacitance system. The results were approximately 40% higher than theory. / http://archive.org/details/developmentcalib00yarb

L’objectif de la thèse était d’analyser deux types de perturbations de l’ionosphère supérieure observées sur les mesures de plasma fournies par le satellite DEMETER.Les premières sont des Perturbations Ionosphériques Itinérantes de moyenne échelle engendrées par l’action sur le plasma des ondes de gravité atmosphériques qui se propagent jusqu’à haute altitude. Elles prennent la forme de variations quasi-périodiques de densité du plasma qui peuvent atteindre des amplitudes considérables et sont plus fréquentes dans l’hémisphère Sud avec un maximum au-dessus de l’Océan Pacifique. Elles peuvent modifier l’électrodynamique de l’ionosphère et amplifier le champ électrique d’origine dynamo.Les secondes sont observées dans l’ionosphère équatoriale comme des augmentations à grande échelle de la densité du plasma sous la forme de plateaux. En fonction des conditions d’activité magnétique, des dépressions de densité à moyenne échelle peuvent apparaitre sur les plateaux et conduire à la formation des bulles de plasma équatoriales. / This thesis aims at analyzing two kinds of ionospheric disturbances observed on plasma measurements on-board the DEMETER satellite.The first events are Mid-Scale Traveling Ionospheric Disturbances that develop through the interaction between atmospheric gravity waves and the ionospheric plasma. They are observed as quasi-periodic variations of the plasma density that may reach very large amplitudes and are more frequently observed in the Southern hemisphere with a maximum over the Pacific Ocean. These MSTID may strongly modify the electrodynamics of the mid latitude ionosphere and form structures where the dynamo electric field is significantly enhanced.The second events are detected in the equatorial ionosphere as large scale enhancements of the plasma density under the form of plateau. Depending on the level of magnetic activity these large scale structures may be modified by mid-scale density depletions that, eventually, get instable and led to the formation of depleted plasma bubbles.

A mechanistic global circulation model is used to simulate the mesospheric and lower thermospheric circulation during austral winter. The model includes a gravity wave (GW) parameterization that is initiated by prescribed GW parameters in the troposphere. In standard configuration, these waves are described by a simple distribution with large amplitudes in the winter hemisphere and small ones in summer. Here we replace this distribution by a more realistic one, which is based on observations of potential GW energy using GPS radio occultations, but which is normalized to the same global mean amplitude. The model experiment shows that this new gravity wave distribution leads to weaker zonal winds in the mesosphere, a downward shift of the meridional poleward mesospheric wind jet, enhanced downwelling in the mid-to-high-latitude winter mesosphere and warming of the polar stratopause. / Ein globales mechanistisches Zirkulationsmodell wird verwendet um die Dynamik der Mesosphäre und unteren Thermosphäre im Südwinter zu simulieren. Das Modell beinhaltet eine Schwerewellenparametrisierung die durch eine vorgeschriebene Schwerewellenverteilung in der oberen Troposphäre angetrieben wird. In der Standardkonfiguration besteht diese aus einer einfachen zonal gemittelten Verteilung mit größeren Amplituden im Winter als im Sommer. Wir ersetzen diese Verteilung durch eine realistischere, die auf der beobachteten globalen Verteilung der potentiellen Energie von Schwerewellen basiert und auf die gleiche global gemittelte Amplitude normiert wird. Das Modellexperiment zeigt, dass die neue Schwerewellenverteilung zu schwächeren zonalen Winden in der Mesosphäre, einer Verschiebung des meridionalen Jets nach unten, verstärkten Abwinden in der Mesosphäre mittlerer und höherer Breiten im Winter, und einer Erwärmung der polaren Winterstratopause führt.

Ein neues Schema für die Parametrisierung der Schwerewellen und ihres Einflusses auf die mittlere Atmosphäre ist für COMMA-LIM (COlogne Model of the Middle Atmosphere - Leipzig Institute for Meteorology) übernommen worden. Während das bisher in COMMA-LIM genutzte aktualisierte Lindzen-Schema (Lindzen, 1981) die Ausbreitung und das Brechen einzelner Wellen berechnet, geht das Warner und McIntyre-Schema von einem Spektrum der Schwerewellen aus. Beide Schemata gehen von Schwerewellen im mittleren Frequenzbereich zwischen Brunt-Väisäla Frequenz und Rotationsrate der Erde aus (N >> ω >> f). Erste Ergebnisse werden vorgestellt. / A new scheme for the parametrizing of the gravity waves and their impact on the mean circulation of the middle atmosphere has been adapted to COMMA-LIM (COlogne Model of the Middle Atmosphere - Leipzig Institute for Meteorology). The current version based on the Lindzen-scheme (Lindzen, 1981) calculates the propagation and breaking of 48 single waves while the new Warner and McIntyre - scheme uses a spectral approach of gravity waves. Both schemes are based on the medium frequency approach locating the gravity waves between the Brunt-Väisälä-frequency and the rotation rate of the earth ((N >> ω >> f). First results are presented.

In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crests. / Atmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist.