| This dissertation is comprised of a series of studies conducted to improve understanding of the role of snow cover in the climate system. The investigation includes: (1) identifying and characterizing the passive response of snow cover over the Eurasian and North American continents to low-frequency atmospheric variability; and (2) an assessment of the significance of east Asian snow cover as an active driver of climate variability.; Results of this study show that snow cover over the Northern Hemisphere responds more strongly to the less-dominant modes of atmospheric variability. Over Eurasia, snow cover is more strongly influenced by variations in the phase and amplitude of the mid-tropospheric wave train over the continent than the North Atlantic Oscillation (NAO). Over the United States, the largest and most extensive positive snowfall signals occur under the comparitively rare situation when the wave train is shifted well west of its preferred position. Thus, in order to understand the role of snow cover as an interactive component of the climate system it is necessary to understand how variations in the more slowly varying components of the climate system (e.g., ocean temperatures, sea ice, land surface processes) influence not only the dominant circulation modes (i.e., the NAO) and Pacific North American teleconnection patterns) but also the less dominant modes, as they appear to be more important for snow cover change.; Turning to the effect of variations in east Asian snow cover on climate variability over the North Pacific Ocean, results show that snow cover over east Asia does not persist for long enough to be useful for probabilistic climate prediction on seasonal time scales. However, the observed circulation response over the North Pacific is nevertheless substantial, in agreement with earlier modeling studies. This underlies the need for an accurate portrayal of snow cover in short-to-medium range forecast models. The snow cover impact on circulation over the North Pacific is stronger in mid-winter when the east Asian jet is extended further east into the central Pacific than in transitional seasons. It was also shown that while variations in east Asian snow cover have only a relatively small local impact on lower-tropospheric air temperatures, positive storm track feedbacks act to reinforce this initial perturbation resulting in a strong circulation response over the North Pacific Ocean. This encourages a search for other small perturbations that could possibly be reinforced and magnified by internal dynamics of the climate system. |
