Global analyses of gravity wave activity in the stratosphere are presented for the first time using German Low Earth Orbit (LEO) satellite CHAMP. Temperature profiles obtained from CHAMP/GPS radio occultations are first compared with ground based instruments. In general, good agreement is found between these different techniques. Monthly mean Ep values of potential energy, Ep values, being a measure of gravity wave activity, which is estimated with radiosonde observations are compared with CHAMP/GPS data and found that radiosonde observed Ep values are higher than those estimated with radio occultations. There exists a strong diurnal variation of gravity wave activity. From the global morphology of gravity wave activity, large values Ep are noticed even at mid latitudes during winter months besides the tropical latitudes but not during equinoxes suggesting that wave activity, especially at stratospheric heights, is not only modulated due to orography (mountain/lee waves) but mainly depends on seasonal variations at respective latitudes. Latitudinal and vertical variation of gravity wave activity reveals the existence of large Ep values below 25 km and low values in between 25 and 30 km in all the seasons near equator. During southern hemisphere winter, large values are noticed. During equinoxes, these values are nearly same between northern and southern hemispheres (NH and SH) at mid-latitudes. During the months of solstices, Ep distribution involves a larger hemispheric asymmetry at middle and higher latitudes. Large values of Ep are noticed at SH polar latitudes during Sep-Oct months and the latitude range is wider (±300° latitude in both the hemispheres) with large Ep values in all the seasons except winter. / Zum ersten Mal werden globale Analysen der Schwerewellenaktivität, bestimmt unter Verwendung des CHAMP LEO-Satelliten, vorgestellt. Temperaturprofile der CHAMP/RO-Okkultationen werden zunächst mit bodengestützten Messungen verglichen. Generell ist die Übereinstimmung gut. Monatliche Mittelwerte der potentiellen Energie Ep, die als Maß für Schwerewellenaktivität gilt, wurden aus Radisonden- und CHAMP-Messungen bestimmt, wobei die CHAMP-Daten höhere Werte lieferten. Es existiert eine deutlicher Tagesgang von Ep. Die globale Morphologie der Schwerewellenaktivität zeigt hohe Werte nicht nur am Äquator, sondern auch in mittleren Breiten, dies aber nicht während der Äquinoktien. Dies weist darauf hin, dass Schwerewelleaktivität nicht nur orographisch angetrieben ist, sondern in verschiedenen Breiten vom Jahresgang abhängt. Die Breiten- und Höhenabhängigkeit der Schwerewellenaktivität zeigt zwischen 25 und 30 km niedrige, unterhalb von 25 km hohe Werte von Ep am Äquator. Während des Winters in der Südhemisphäre sind die Werte hoch, während zu den Äquinoktien hohe Werte in mittleren Breiten beider Hemisphären zu finden sind. Während der Solstitien zeigt die Ep-Verteilung stärkere hemisphärische Asymmetrie. Hohe Werte von Ep werden während des südpolaren Frühjahrs gemessen. Der äquatoriale Bereich hoher Varianz ist in allen Jahreszeiten außer im Winter breit (±300°).

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.

Knowing what goes on in the upper atmosphere (∼80-140 km) is very important to the space science community. There are several competing forces that influence the temperature and densities of neutral molecules in that region. OPAL (Optical Profiling of the Atmospheric Limb) is funded by the National Science Foundation (NSF) to measure the temperature there using light from oxygen molecules (∼760 nm). To accomplish this,OPAL is built into a CubeSat (a satellite the size of a loaf of bread) to be launched from the International Space Station (ISS) at an altitude of about 400 km. This vantage point is needed to see the light that is absorbed before it makes it to the ground, so a satellite is the optimal choice. Similar to looking at a tennis ball in your hand and trying to see the details of the yellow fuzz fibers on the outer edges of the ball, OPAL is trying to see the light emitted from oxygen at the outer edge of the atmosphere (also called the limb). In order to see how well OPAL can detect space weather signatures affecting the oxygen emissions a suite of models are made to simulate its output. This suite is made of: simulating the flight path of CubeSat, modeling where the OPAL instrument is looking, and how the oxygen light changes with where the instrument is looking. Because we are currently in a solar minimum, the occurrence of solar storms and geomagnetic storms are considered rare events. This allows for the concentrating on detecting gravity waves in this region and the minimum values of detecting them with this developed model.

Laboratory work were conducted to investigate the behaviors of an internal solitary wave (ISW) in a two-layer free surface fluid system in a wave flume (12m¡Ñ0.5m¡Ñ0.7m) at the National Sun Yat-sen University, Kaohsiung, Taiwan. A series of fundamental experiments on wave generation, propagation and interaction with uniform slopes and topographic features were carried out in the flume with stratified two-layer fresh/brine water. Factors governing the experiments included the thickness ratio of the upper and lower layers H1/H2, interface difference

In this study, a month-long simulation of gravity waves over North America and North Atlantic Ocean is performed using the mesoscale model MM5 for January 2003, verified with Advanced Microwave Sounding Unit-A (AMSU-A) radiance observations in the upper troposphere and lower stratosphere. According to the monthly mean statistics, four regions of strong gravity wave activities are found both in the simulation and the AMSU-A observations: northwestern Atlantic, Appalachian Mountains, Rocky Mountains and Greenland, respectively. Those over the northwestern Atlantic Ocean are strongly associated with the midlatitude baroclinic jet-front systems, while the other three regions are apparently collocated with high topography. Imbalance diagnosis and numerical sensitivity experiments of a strong gravity wave event during January 18-22 show that the gravity waves are strongly linked to the unbalanced flow in the baroclinic jet-front system. The gravity waves are usually radiated from the upper tropospheric jet exit region with maximum nonlinear balance equation residual ( Δ NBE; key indicator of flow imbalance), distinctly different from other surface sources. Flow imbalance related strongly to tropopause folding and frontogenesis of the large-scale background flow. Similar wave characteristics are simulated in experiments with different microphysics and grid resolutions. The Δ NBE is again shown to be a good predictor for jet-front related gravity waves, suggesting its potential application to gravity wave parameterizations for global and climate models.

No description available.

Internal gravity waves grow in amplitude as they propagate upwards in a non-Boussinesq fluid and weakly nonlinear effects develop due to interactions with an induced horizontal mean flow. In this work, a new derivation for this wave-induced mean flow is presented and nonlinear Schrodinger equations are derived describing the weakly nonlinear evolution of these waves in an anelastic gas and non-Boussinesq liquid. The results of these equations are compared with fully nonlinear numerical simulations. It is found that interactions with the wave-induced mean flow are the dominant mechanism for wave evolution. This causes modulational stability for hydrostatic waves, resulting in propagation above the overturning level predicted by linear theory for a non-Boussinesq liquid. Due to high-order dispersion terms in the Schrodinger equation for an anelastic gas, hydrostatic waves become unstable and break at lower levels. Non-hydrostatic waves are modulationally unstable, overturning at lower levels than predicted by linear theory.

Global analyses of gravity wave activity in the stratosphere are presented for the first time using German Low Earth Orbit (LEO) satellite CHAMP. Temperature profiles obtained from CHAMP/GPS radio occultations are first compared with ground based instruments. In general, good agreement is found between these different techniques. Monthly mean Ep values of potential energy, Ep values, being a measure of gravity wave activity, which is estimated with radiosonde observations are compared with CHAMP/GPS data and found that radiosonde observed Ep values are higher than those estimated with radio occultations. There exists a strong diurnal variation of gravity wave activity. From the global morphology of gravity wave activity, large values Ep are noticed even at mid latitudes during winter months besides the tropical latitudes but not during equinoxes suggesting that wave activity, especially at stratospheric heights, is not only modulated due to orography (mountain/lee waves) but mainly depends on seasonal variations at respective latitudes. Latitudinal and vertical variation of gravity wave activity reveals the existence of large Ep values below 25 km and low values in between 25 and 30 km in all the seasons near equator. During southern hemisphere winter, large values are noticed. During equinoxes, these values are nearly same between northern and southern hemispheres (NH and SH) at mid-latitudes. During the months of solstices, Ep distribution involves a larger hemispheric asymmetry at middle and higher latitudes. Large values of Ep are noticed at SH polar latitudes during Sep-Oct months and the latitude range is wider (±300° latitude in both the hemispheres) with large Ep values in all the seasons except winter. / Zum ersten Mal werden globale Analysen der Schwerewellenaktivität, bestimmt unter Verwendung des CHAMP LEO-Satelliten, vorgestellt. Temperaturprofile der CHAMP/RO-Okkultationen werden zunächst mit bodengestützten Messungen verglichen. Generell ist die Übereinstimmung gut. Monatliche Mittelwerte der potentiellen Energie Ep, die als Maß für Schwerewellenaktivität gilt, wurden aus Radisonden- und CHAMP-Messungen bestimmt, wobei die CHAMP-Daten höhere Werte lieferten. Es existiert eine deutlicher Tagesgang von Ep. Die globale Morphologie der Schwerewellenaktivität zeigt hohe Werte nicht nur am Äquator, sondern auch in mittleren Breiten, dies aber nicht während der Äquinoktien. Dies weist darauf hin, dass Schwerewelleaktivität nicht nur orographisch angetrieben ist, sondern in verschiedenen Breiten vom Jahresgang abhängt. Die Breiten- und Höhenabhängigkeit der Schwerewellenaktivität zeigt zwischen 25 und 30 km niedrige, unterhalb von 25 km hohe Werte von Ep am Äquator. Während des Winters in der Südhemisphäre sind die Werte hoch, während zu den Äquinoktien hohe Werte in mittleren Breiten beider Hemisphären zu finden sind. Während der Solstitien zeigt die Ep-Verteilung stärkere hemisphärische Asymmetrie. Hohe Werte von Ep werden während des südpolaren Frühjahrs gemessen. Der äquatoriale Bereich hoher Varianz ist in allen Jahreszeiten außer im Winter breit (±300°).

With the help of MERRA-2 (Modern-Era Retrospective Analysis for Research and Application, version 2) reanalysis data of the zonal wind, measurements of the mesopause region wind over Collm by low-frequency observations, and data of the Horizontal Wind Model, a height profile for the zonal wind in January and July was created by linear interpolation over altitude. Subsequently, three different 5-year periods (1980-1984, 1994-1998 und 1999-2003) were selected, and the obtained wind profiles and NRLMSISE (Naval Research Labatory Mass Spectrometer Incoherent Scatter, Extended) temperatures (January and July) were averaged over these time intervals. This allowed to run the whole atmosphere nonlinear spectral gravity wave (GW) routine of Yiğit et al. (2008) with these data as background profiles. We obtained a height profile of the GW momentum flux (MF) over these three 5-year periods. Based on this, the long-term tendencies of GW MF are estimated and in this way a statement about the trend of the GW activity in the mesosphere and lower thermosphere can be made. GW MF increases in magnitude in both summer and winter. The results are in qualitative agreement with trends of GW proxies obtained from the meteor radar measurements at Collm. / Mit Hilfe von MERRA-2 - Reanalysedaten des Zonalwindes, Messungen des Meteorradars in Collm und mit Daten des Horizontal Wind Models wurde durch lineare Interpolation ein Höhenprofil für den Zonalwind für die Monate Januar und Juli erstellt. Anschließend wurden aus den gewonnenen Windprofilen und NRLMSISE (Naval Research Labatory Mass Spectrometer Incoherent Scatter, Extended) Temperatur Reanalysen (Januar und Juli) drei verschiedene 5-Jahreszeiträume gewählt (1980-1984, 1994-1998 und 1999-2003) und über diese gemittelt. Diese Daten wurden als Hintergrund für die nichtlineare spektrale Schwerewellenroutine nach Yiğit et al. (2008) verwendet, wodurch der Schwerewellenfluss über die drei 5-Jahreszeiträume bestimmt werden konnte. Aus diesen Analysen ließ sich nun der Trend zwischen den jeweiligen Zeiträumen berechnen und so eine Aussage über den Trend der Schwerewellenaktivität in der Mesosphäre und unteren Thermosphäre ableiten. Die Ergebnisse zeigen gute Übereinstimmungen zu anderen Forschungsergebnissen bzgl. der Trends der GW Proxies von Meteorradarmessungen in Collm.