Planetary waves and dynamical processes associated with seasonal perturbations and transitions

• Main Author: Chshyolkova, Tatyana
• Other Authors: Manson, Alan, Xiao, Chijin, Sofko, George J., Shepherd, Gordon, Mitchell, Caroline E. J. (Katie), Guo, Xulin, Degenstein, Douglas A.
• Format: Thesis
• Language: English
• Published: University of Saskatchewan 2007
• Subjects: planetary waves; middle atmosphere dynamics; stratospheric warming; Arctic
• Online Access: http://hdl.handle.net/10388/etd-04112007-154231

This thesis provides highlights of the atmospheric research conducted during the program of studies 2003-07. The theme is variability of the winds at mesospheric heights (60-100 km) due to Planetary Waves (PW, 2-30 days) over middle and high latitudes. Considerable energy and momentum are transported by atmospheric waves, and their global characteristics are required to understand many phenomena and explain coupling processes within the atmosphere. The vertical propagation of PW from the upper troposphere to the mesosphere is investigated by applying the Morlet wavelet and wave number analysis to the MetO (United Kingdom Meteorological Office) stratospheric assimilated fields, TOMS total (column) ozone, and Medium Frequency (MFR) and Meteor Wind (MWR) radar measurements. The results show that large-scale eastward propagating PW dominate at tropopause and low stratospheric heights, while westward PW become comparable or even stronger in the upper stratosphere and above during months other than summer. There are also strong seasonal dependences of the PW activity in each of the stratospheric and mesospheric regions, which are attributed, at least partially, to the influence of the background wind on PW propagation. Longitudinal variations in PW activity are explained by longitudinal variations in these winds.During summer (westward zonal winds) PW activity is reduced in the stratosphere and only relatively fast westward propagating PW, such as quasi 2-day wave (Q2DW), are able to reach mesospheric heights from below. The results obtained using 14 years of MFR data at Saskatoon provide a unique climatology (70-100 km) of this wave: in addition to summer activity the Q2DW is also present at low mesospheric heights in winter, especially when the eastward winds are weak; there are significant interannual variations in Q2DW activity in both seasons. Strong latitudinal and longitudinal differences in Q2DW occurrence and amplitude are shown from the comparisons of wind data at several stations.During winter, when zonal winds are eastward, the PW coupling between stratosphere and mesosphere is stronger than during other seasons. Detailed data analysis has been performed for the Arctic winter of 2004/05, for which the stratospheric state is described using conventional zonal mean parameters as well as the newer Q-diagnostic. Spectral analyses for this winter show relatively weak PW activity at stratospheric and mesospheric heights and strong latitudinal and longitudinal differences of mean winds and PW characteristics consistent with the form and location of the polar vortex. In addition to the vertical coupling it has also been shown that weaker horizontal “inter-hemispheric” coupling occurs during equinoctial months, when eastward winds dominate globally. It is demonstrated that with favorable conditions, planetary waves with 10, 16 and 25 day periods penetrate to the opposite hemisphere.