Long-range Propagation, Interaction, and Dissipation of Small-Scale Gravity Waves in the Mesosphere and Lower Thermosphere

• Main Author: Heale, Christopher J.
• Format: Text
• Language: unknown
• Published: Scholarly Commons 2014
• Subjects: Cosmology; Relativity; and Gravity; Engineering Physics; Pasko; Antarc*; Antarctica
• Online Access: https://commons.erau.edu/edt/156; https://commons.erau.edu/context/edt/article/1155/viewcontent/Heale_Christopher_2014_HL10190.pdf

A 2-D nonlinear, compressible numerical model [Snively and Pasko, 2008] 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. The research in this thesis is made up of three distinct studies which build upon each other. The first investigates the thermospheric dissipation of three gravity wave packets representing: (1) A quasi-monochromatic packet, (2) A monochromatic, steady state wave, and (3) A spectrally broad packet, as well as an initial condition specified packet. It is found that dissipation due to molecular viscosity and thermal conduction acts to decrease the vertical wavelength of the packet in time (except in the steady-state case, when it remains constant). This is due to the higher frequencies (longer wavelengths) reaching the thermsophere first and dissipating before the lower frequencies (shorter wavelengths), thus the spectral content of the packet shifts from higher frequencies (longer wavelengths) to lower frequencies (shorter wavelengths) in time. At any instant of time, the vertical wavelength increases with altitude in the thermosphere when the wave has reached a steady state. The second study investigated the potential for long-range propagation of three small-scale wave packets under averaged high latitude conditions. The three packets were chosen to represent wave parameters typically observed over Halley, Antarctica [Nielsen et al., 2009, 2012] and ones that may be considered favorable for long-range propagation [ Snively, 2013]. It was found that the stratosphere provides an efficient region of the atmosphere to trap waves and allow them to propagate large horizontal distances. Ducting in the mesosphere was less likely when considering averaged meridional winds, and it is suggested that waves observed in the mesopause, far from the source region, may be the result of leakage from the stratosphere. It was also shown that leakage from the ...