DARWIN Digitale Dissertationen German Version Strich

FU Berlin
Digitale Dissertation

Kathrin Schöllhammer :
Climatology of Gravity Wave Activity in the mid latitudes
Klimatologie von Schwerewellenaktivität in den mittleren Breiten

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Abstract

This thesis examines the characteristics of gravity waves. Gravity waves occur over the small scale portion of the atmospheric wave spectrum. Gravity waves are associated with oscillations of meteorological parameters such as temperature, wind velocity, pressure, and density and they arise when air becomes stratified due to gravity. Gravity waves can propagate to high altitudes in the atmosphere and exhibit a broad spectrum of possible periods (minutes until hours) as well as horizontal wavelengths (few hundred kilometres up to approximately thousand kilometres). Gravity waves may therefore transport momentum and energy from their origin (e.g. orography in the troposphere) into other altitudes, e.g. the stratosphere und mesosphere hence influence the general circulation of the atmosphere. The characteristics of non-orographic gravity waves, which arise in mid latitudes, are to a large extent unknown. It prevails so far to ambiguity over it where such non-stationary gravity waves develop and are as large their portion. Observed rising of gravity wave activity near frontal zones and "Jetstreams" over the ocean [Fritts and Nastrom 1992] is a reference on the fact that also different non-orographic sources possess a not insignificant portion of the gravity wave activity. Through systematic evaluation of a four years data record of radiosonde data of a station in the mid latitudes (Lindenberg) a further contribution could be made here for the production of a global climatology for gravity wave activity within the SPARC gravity wave initiative: It was shown that the gravity wave activity in the mid latitudes is clearly smaller (factor 1/2) than in tropical areas and possesses a typical annual variation (maximum gravity wave activity in the winter and minimum activity in the summer) which dependent on the background wind, and from which the synoptic situation. The observed gravity waves propagate on the average against the usually dominant west winds. The portion of the upward propagation of the gravity wave energy (Troposphere 50%, Stratosphere 80%) points on a source of the gravity waves in the upper troposphere. As sources for gravity waves in the mid latitudes fronts and the "jetstream" during the adjustment of ageostrophic winds to the geostrophic equilibrium ("geostrophic adjustment") come due to the results in question. The observed waves have frequencies near the local inertial frequency, the horizontal wavelengths lie within the range of some hundred kilometres. Several case studies in this thesis showed that the occurrence of increased power densities over Lindenberg with increased wind velocities in the tropopause region collapses and a similar synoptic situation was present, as in the simulation of inertial gravity waves during the development of a baroclinic instability by O'Sullivan and Dunkerton [1995]. Thus the suggestion of gravity waves over Lindenberg appears by the adjustment of a geostrophic imbalance as dominating developing mechanism to prevail.

Table of Contents

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Titel
Inhaltsverzeichnis
Einleitung 1
1. Schwerewellen in der Atmosphäre 6
1.1 Der Aufbau der Atmosphäre 6
1.2 Schwerewellen 12
2. Theorie 21
2.1 Dispersionsgleichung für Schwerewellen 22
2.2 Spektraltheorie der Schwerewellen 29
2.3 Parametrisierungsmodell 32
2.3.1 Impulsfluss durch Schwerewellen 34
2.4 Analyseprozeduren 36
2.4.1 Radiosondendaten 36
2.4.2 Spektralanalyse der Temperaturfluktuation 42
2.4.3 Vertikale Ausbreitungsrichtung der Wellen 44
2.3.4 Stokes-Parameter-Analyse 46
2.5 Zusammenfassung 49
3. Ergebnisse 51
3.1 Zustand der Atmosphäre im Beobachtungszeitraum 51
3.2 Variabilität der Schwerewellen 54
3.2.1 Powerspektrum vertikaler Wellenzahlen aus Temperaturfluktuationen 55
3.2.2 Schwerewellenaktivität 61
3.2.3 Anteile kinetischer und potentieller Energie 66
3.2.4 Ausbreitungsrichtung der Wellen 67
3.2.5 Wellenfrequenz 73
3.2.6 Vertikale und horizontale Wellenlänge 74
3.2.7 Phasen- und Gruppengeschwindigkeiten 77
3.3 Vertikaler Impulsfluss durch Schwerewellen 79
3.4 Zusammenfassung der Parameter 80
3.5 Quellen der Schwerewellenaktivität über Lindenberg 81
3.5.1 Fronten und Schwerewellenaktivität 84
3.5.2 Windgeschwindigkeit und Schwerewellenaktivität 96
3.6 Fallstudien zur Quellen-Identifizierung 99
4. Zusammenfassung und Ausblick 116
4.1 Zusammenfassung 116
4.2 Ausblick 118
Anhang 120
Symbolverzeichnis 133
Literaturverzeichnis 134
Danksagung 142
Lebenslauf 143

More Information:

Online available: http://www.diss.fu-berlin.de/2002/284/indexe.html
Language of PhDThesis: german
Keywords: gravity wave activity, non-orographic, geostrophic adjustment
DNB-Sachgruppe: 31 Geowissenschaften
Date of disputation: 23-Apr-2002
PhDThesis from: Fachbereich Geowissenschaften, Freie Universität Berlin
First Referee: Prof. Dr. Karin Labitzke
Second Referee: Dr. habil. Peter Nevir
Contact (Author): schoellh@zedat.fu-berlin.de
Contact (Advisor): labitzke@strat01.met.fu-berlin.de
Date created:10-Dec-2002
Date available:12-Dec-2002

 

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