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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Seasonal and spatial structure of the gravity waves and vertical winds over the central USA derived from the NOAA Profiler Network data

Karabanov, Oleksandr G. 28 June 2006 (has links)
Data from the National Oceanic and Atmospheric Administration wind profiling radar network for the period 2002 2005 were used to investigate the effects of precipitation, topography and gravity waves on the measurements of winds by wind profilers, and to study the climatology and sources of atmospheric gravity waves. The comparison of the profiler winds to the NCAR/NCEP reanalysis and MM5 model winds revealed that monthly averaged wind profiler vertical velocities are strongly affected by precipitation in the lowest 3 km of the troposphere, both directly by hydrometeor velocity and indirectly via gravity wave activity produced by convection. We have determined that presence of downward wind velocities with magnitudes larger than 0.25 m/s is the sign of precipitation-affected data. This velocity threshold was used for identifying and correcting the contaminated data. The characteristics of the gravity waves in three period bands (6 min - 1 hour, 1 - 3 hours and 3 - 12 hours) and three orthogonal spatial components were obtained using spectral analysis of the profiler winds. The most kinetic energy was found to be associated with the low-frequency horizontal component of gravity waves. A consistent seasonal pattern and geographical distribution of kinetic gravity wave energy were observed in the troposphere, with maxima reaching ~25 J/kg in winter at 8 - 10 km altitude. A technique for quantifying the topography variance near the measurement sites was developed and applied to evaluate the effects of topography on gravity wave generation. We have determined that topography is an important source of the medium- and high-frequency waves in the middle troposphere. Correlation and regression analyses were used to study sources of the gravity waves. Convection was found to explain a significant part of the vertical component of the kinetic gravity wave energy throughout the troposphere and total kinetic energy in the lower troposphere, while vertical shear of the zonal wind was the predominant source in the upper troposphere. The results of this study are important for interpreting the wind measurements by wind profiling radars and for improving gravity wave parameterizations in global circulation models.
2

The Atmospheric Gravity Wave Transfer Function above Scott Base

Geldenhuis, Andre January 2008 (has links)
Gravity waves have a significant dynamic effect in the mesosphere. In particular, they drive the mesospheric circulation and are the reason that the summer polar mesosphere is cooler than the winter polar mesosphere. This thesis examines whether the effects of gravity waves are largely determined by filtering effects which allow only gravity waves with certain properties to propagate into the atmosphere. The filtering of gravity waves above Scott Base, Antarctica is examined using a radiosonde derived gravity wave source function, an MF-radar derived mesospheric gravity wave climatology, and a model derived filtering function. Least squares fitting of the source function and filtering function to the observed mesospheric gravity wave climatology allows us to determine which gravity wave phase velocities and propagation direction are likely to be present in the mesosphere and the relative importance of filtering and sources in this region. It is concluded the blocking of eastward gravity waves is important in winter and westward waves in summer.
3

The Atmospheric Gravity Wave Transfer Function above Scott Base

Geldenhuis, Andre January 2008 (has links)
Gravity waves have a significant dynamic effect in the mesosphere. In particular, they drive the mesospheric circulation and are the reason that the summer polar mesosphere is cooler than the winter polar mesosphere. This thesis examines whether the effects of gravity waves are largely determined by filtering effects which allow only gravity waves with certain properties to propagate into the atmosphere. The filtering of gravity waves above Scott Base, Antarctica is examined using a radiosonde derived gravity wave source function, an MF-radar derived mesospheric gravity wave climatology, and a model derived filtering function. Least squares fitting of the source function and filtering function to the observed mesospheric gravity wave climatology allows us to determine which gravity wave phase velocities and propagation direction are likely to be present in the mesosphere and the relative importance of filtering and sources in this region. It is concluded the blocking of eastward gravity waves is important in winter and westward waves in summer.

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