NORTH ATLANTIC OSCILLATION IMPACTS ON NORTHEAST US WINTER AIR MASS FREQUENCY

This investigation stems from my Master's Thesis research, and assesses daily frequencies of 7 air masses from December to March, 1950-2005 during various phases of the NAO. Positive and negative regimes are stratified by stronger and weaker than average phase types and the significance of all air mass frequency departures are evaluated across the states roughly situated between Pennsylvania and Maine. Results indicate that, depending on the air mass and location, weaker than average events can have as much (if not more) of an influence on NAO impacts to frequency departures as the stronger than average counterpart. For virtually all air mass types, the NAO has a significant influence on frequency, with negative regimes holding a stronger and more spatially unified, influence than positive regimes. In some instances, air mass frequency changes (more or less frequent) are over 10% during an NAO event. These results indicate that weather forecasting procedures that follow/ report on air mass dynamics across the winter season may be improved during times of teleconnection events (at least, for the NAO) considering the easy-to-trace relationships between these "umbrellas" of air and the patterns.

AN EVALUATION OF JANUARY TEMPERATURE ANOMALIES UTILIZING A SYNOPTIC CLIMATOLOGICAL APPROACH

Co-authors: Katrina L. Frank, Steven M. Quiring, Laurence S. Kalkstein

The January Thaw is a singularity that is widely regarded as a recurring several-day period of anomalously warm temperatures experienced around the coldest time of winter.  Defining the exact spatial and temporal parameters of the phenomenon in the United States has proven difficult, and is a source of considerable disagreement among the scientific community, as a causal mechanism for the Thaw has not been identified. This investigation is aimed at identifying a singularity signal across the country and assessing the relationship of these events to synoptic climatological variability, specifically changes in air mass frequency, over the past 50 years.  Singularities are defined as temperature departures that are greater than two standard deviations from a determined expected temperature.  Two singularities are distinguishable with this methodology, the January Thaw and a ‘January Freeze'.  At the timing of all singularities, anomalous temperature departures are correlated to air mass frequency changes for the equivalent time frame and r-values are tested for significance. Results indicate that a regionally coherent Thaw signal exists across the northern United States. The Freeze also exhibits a consistent regional trend in the western United States. The cold singularity generally occurs the first week of January and is often followed by a Thaw. The Thaw has an apparent systematic movement eastward, with an exception in the Great Plains, and occurs at far eastern stations 23-26 January. These episodes appear to correspond to variable warm air mass types more (less) frequent during a Thaw (Freeze) in combination with variable cold air masses less (more) frequent.

A HYDROCLIMATOLOGICAL HISTORY OF THE SUSQUEHANNA RIVER BASIN

Co-authors: Daniel J. Leathers, Tianna A. Bogart, Daria B. Kluver, Gina Henderson

This research project seeks to document the hydroclimatic history of the SRB and to understand the relationships between global-scale forcing mechanisms and the climatic variability of the Basin.  Results indicate that the hydroclimatic history of the SRB is very complex.  Prior to the advent of European settlement, the basin seems to have responded in concert with other land masses within the North Atlantic Sector evidencing a regional manifestation of both the medieval warm period and the Little Ice Age.  Since the beginning of European settlement, the hydroclimate of the basin has varied greatly on both interannual and decadal time scales.  Hydroclimatic variability since 1700 CE is documented through the reconstruction of temperature, precipitation and moisture indices using proxy and observational data.  The climatic variability of the basin is found to be only weakly associated with large-scale forcing mechanisms that are commonly assumed to influence the eastern United States.  A notable exception is a strong temperature response associated with volcanic activity.  Thus regional forcings and land cover variations may play an important role in the hydroclimatic variability of this important river system.