DescriptionThis dissertation is the first comprehensive study to define climatological seasons for temperature, snow, vegetation, and carbon dioxide on a hemispheric scale. The spatial propagation of climatological seasonal onsets and offsets as defined in this study differentiates the dynamical characteristics of empirical floating seasons from conventional static seasons such as the three month interval meteorological seasons. Spatial patterns of dynamical seasonal progression and its association with static and dynamic geographical factors are examined. Long-term trends and spatial patterns of identified changes in the dynamical floating onsets/offsets and durations are also discussed based on the past 40 years of observational data. The coherences and/or differences amongst various floating seasons and their potential linkages with large scale atmospheric circulation patterns are examined to develop seasonal prediction models. Finally, directions of future changes in seasonal onset/offset and duration are predicted by comparing current (1981-2000) and future (2081-2100) seasons derived from climate models.
Various temporal and spatial patterns of floating climatological seasons - thermal, snow, vegetation, and carbon dioxide - show significant associations with dynamic factors such as oceanic and atmospheric circulation, as well as static factors such as latitude, elevation, topography, surface condition, and proximity to water bodies. Various floating seasonal onsets/offsets and durations show coherences at mid-latitudes but differences in the circumpolar regions or in lower mid-latitude regions. A consistent temporal trend exhibited in time series analyses of various floating seasons is the reduction of winter duration, primarily due to an earlier spring onset. In particular, the earlier spring onset observed in Europe, East Asia, and the southwestern United States shows significant associations with the hemispheric circulation pattern driven by a positive winter AO phase. Observed and modeled seasonal data suggest that the reduction of thermal winter duration is predicted to continue in the future over continents mainly due to an earlier winter offset. It is also predicted that, primarily due to an earlier summer onset, thermal summer duration will continue to increase along 30° N over oceans, suggesting potential changes in low latitude atmospheric circulation.