| Polar mesospheric clouds (PMC) are characterized by thin layers of ice particles that form in the summer months at polar latitudes and centered around 83 km. Although much research has been performed to advance the understanding of this phenomenon, there are still many questions related to their occurrence and variability. This dissertation presents the seasonal characteristics of four northern and three southern PMC seasons and the first direct dynamical analysis on global PMC measurements. The measurements were made from the ultraviolet spectrometer instrument on the Student Nitric Oxide Explorer satellite. The SNOE spacecraft is in a near polar, sun-synchronous orbit that provides almost complete latitudinal coverage from 82.5° South to 82.5° North and covers 360° of longitude in a 24 hour period (15 orbits a day). It therefore obtains a global, constant local time snapshot of the mesosphere. By combining 15 orbits, daily global images of PMC location and brightness are produced, providing a means for a Fourier analysis. A strong 5-day periodicity is apparent from the analysis corresponding to the gravest atmospheric Rossby normal mode of wavenumber 1, the so-called 5-day wave. The 5-day planetary wave is observed in both hemispheres and its temporal and latitudinal structure is variable from year-to-year. In addition, statistical results show that PMC altitudes and occurrence frequency illustrate inter-hemispherical differences. |
