Adam W. Burnett

Increasing Great Lake–Effect Snowfall during the Twentieth Century: A Regional Response to Global Warming?

Abstract The influence of the Laurentian Great Lakes on the climate of surrounding regions is significant, especially in leeward settings where lake-effect snowfall occurs. Heavy lake-effect snow represents a potential natural hazard and plays important roles in winter recreational activities, agriculture, and regional hydrology. Changes in lake-effect snowfall may represent a regional-scale manifestation of hemispheric-scale climate change, such as that associated with global warming. This study examines records of snowfall from several lake-effect and non-lake-effect sites throughout most of the twentieth century in order to 1) determine whether differences in snowfall trends exist between these settings and 2) offer possible linkages between lake-effect snow trends and records of air temperature, water temperature, and ice cover. A new, historic record of oxygen isotope [δ18O(CaCO3)] data from the sediments of three eastern Finger Lakes in central New York is presented as a means of independently asses...

Antarctic Peninsula climate variability: historical and paleoenvironmental perspectives

The Antarctic Peninsula region represents our best natural laboratory to investigate how earths major climate systems interact and how such systems respond to rapid regional warming. The scale of environmental changes now taking place across the region is large and their pace rapid but the subsystems involved are still small enough to observe and accurately document cause and affect mechanisms. For example, clarification of ice shelf stability via the Larsen Ice Shelf is vital to understanding the entire Antarctic Ice Sheet, its climate evolution, and its response to and control of sea level. By encompassing the broadest range of interdisciplinary studies, this volume provides the global change research and educational communities a framework in which to advance our knowledge of the causes behind regional warming, the dramatic glacial and ecological responses, and the potential uniqueness of the event within the regions paleoclimate record. The volume also serves as a vital resource for public policy and governmental funding agencies as well as a means to educate the large number of ecotourists that visit the region each austral summer.

Late glacial–Holocene atmospheric circulation and precipitation in the northeast United States inferred from modern calibrated stable oxygen and carbon isotopes

As global climate changes because of anthropogenic influences, it has become critical to better understand past climate and its various forcing mechanisms as a baseline for future comparison. To this end, we present a continental isotopic record from an 11.2-m-long wetland piston core sampled at 10‐50 yr resolution; the core was taken in the heavily populated, economically vibrant northeastern United States (adjacent to Fayetteville Green Lake) and spans 14,600‐3200 cal. yr B.P. We use a historically based correlation between d 18 Ocalcite obtained from individual varves in a box core from Fayetteville Green Lake and winter atmospheric circulation over the northeast United States to examine the way in which changes in winter circulation have influenced d 18 O in precipitation from 14,600 to 3200 cal. yr B.P. Our correlation analysis suggests that in periods during which the circumpolar westerlies are expanded, storms track more frequently from the Gulf of Mexico region, delivering precipitation with relatively high d 18 O values to the study site. By contrast, contracted westerlies result in more frequent low-d 18 Oprecipitation cross-continental storms. By using this relationship we model winter-vortex latitudes over the northeast United States for the prehistoric oxygen isotope record, focusing on millennial-scale

Size Variations and Long-Wave Circulation within the January Northern Hemisphere Circumpolar Vortex: 1946–89

Abstract The close association between size variations in the Northern Hemisphere circumpolar vortex and surface and middle-troposheric thermal characteristics makes vortex measurement a valuable tool in monitoring and understanding climate change. Unfortunately, as with most hemispheric circulation indices, measures of total vortex size offer little insight into regional changes in the vortex. Traditional approaches to vortex size calculation, which are based upon planimeter measurements on a polar stereographic projection, limit the ability to examine regional contributions to the total vortex and cannot be used to assess specific linkages between vortex expansion and contraction and the broader class of long wave circulation phenomena. Furthermore, because the scale of the polar stereographic projection varies from one latitude to another, interannual variations in planimeter vortex size measurements are influenced somewhat by the position of the vortex relative to the North Pole. Many of these problem...

A 2500 year sediment record from Fayetteville Green Lake, New York: evidence for anthropogenic impacts and historic isotope shift

A series (N = 12) of short (< 1 m) sediment cores were collected from meromictic Green Lake in Fayetteville, New York to investigate potential anthropogenic impacts on the watershed during historic time and environmental change over the past ~ 2,500 years. Stratigraphic data document an abrupt basinwide change during the early 1800s A.D. from brown laminated sediments to grey varved sediments separated by a transition zone rich in aquatic moss. Deforestation of the region by European settlers during the early 1800s A.D. resulted in a flux of nutrients and increased biological productivity followed by a 7‐fold increase in sediment accumulation rates. Elemental geochemical data document the anthropogenic loading of lead to the to the lake basin via atmospheric fallout. Stable oxygen isotope (δ18O calcite) data also provide evidence for an abrupt shift in the isotopic composition of lake water ~ 150–200 years ago. This isotopic shift could have been a local phenomenon related to an increased supply of summer enriched precipitation following removal of forest vegetation, or it might have reflected broader scale climatic changes. We hypothesize that the δ18O calcite shift was the result of the polar front jet stream migrating from a more southerly prehistoric position to a contracted, northerly configuration ~ 150–200 years ago. Such a shift could have been natural, associated with the end of the Little Ice Age or it may have been anthropogenically forced.

Lacustrine isotopic evidence for multidecadal natural climate variability related to the circumpolar vortex over the northeast United States during the past millennium

A pervasive 20-30 yr periodicity is observed in stable oxygen isotope values over the past 1000 yr from varved lacustrine calcite obtained from Fayetteville Green Lake, New York. Correlation analysis between historical oxygen isotope values and winter vortex latitude shows an inverse relationship wherein an expanded vortex is associated with high d 18 Ocalcite values, and vice versa. An expansion of the vortex favors advection of cyclones from the Gulf of Mexico and the Atlantic regions characterized by high d 18 Oprecipitation values, whereas a contracted vortex favors the development of cross-continental storms originating in the Pacific, which preferentially rain out 18 O as they propagate eastward. We hypothesize that changes in the size of the winter vortex every 20-30 yr over the past 1000 yr modify the primary source regions for meteoric precipitation. We propose two possible climate forcings to explain our hypothesis: an external forcing related to solar variability and an internal forcing related to ocean-atmosphere links.

Interannual Variations in the Southern Hemisphere Winter Circumpolar Vortex: Relationships with the Semiannual Oscillation

Abstract Several studies of Southern Hemisphere circulation report changes in the late 1970s and 1980s through the mid- and high latitudes that are associated with a weakening in the semiannual oscillation (SAO) of sea level pressure and geopotential height. This weakening is thought to reflect changes in the amplitude of zonal wavenumber 3, a deepening of the subantarctic trough, intensification of subtropical ridging, and an increase in the strength of the westerlies. These conclusions suggest an equatorial expansion of the circumpolar vortex in high latitudes and a poleward contraction of the vortex in the midlatitudes. The goal of this study is to examine the size and spatial variation of the Southern Hemisphere circumpolar vortex in winter for evidence of such change. The size of the 500-hPa vortex was calculated for the mid- and high latitudes in 5° longitude sectors from both the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis dataset (1...

REGIONAL-SCALE TROUGHING OVER THE SOUTHWESTERN UNITED STATES: TEMPORAL CLIMATOLOGY, TELECONNECTIONS, AND CLIMATIC IMPACT

Regional-scale middle- and upper-tropospheric troughing over the southwestern United States represents a departure from the modal circulation pattern for western North America. Once developed, southwestern troughs often are associated with positive vorticity advection aloft, surface cyclone formation, and moisture advection over areas of the western Great Plains and Intermountain West. These trough systems may play an important role in the precipitation climatology of the western and central United States. However, very little work has focused on the temporal climatology, developmental characteristics, or climatic impacts of southwestern troughs. This study provides a detailed climatology of southwestern troughing that focuses on: (1) the temporal frequency of these events; (2) the teleconnective circulation changes that are associated with their development; and (3) the importance of these systems in the precipitation climatology of the western and central United States. The temporal climatology of south...

AGROCLIMATIC RESOURCE ASSESSMENT: AN EXAMPLE FOR PEACH CULTIVATION IN THE LOWER PENINSULA OF MICHIGAN

Detailed resource assessments can assist agricultural planners and growers select appropriate crops and cultivars for a region. This study employs a geographic information system (ARC/INFO) to develop a rating scheme suitable for evaluating the climatic resources of the Lower Peninsula of Michigan for commercial peach production. The rating scheme presented here improves on many previously developed indices by placing greater emphasis on identifying critical growth stages and the weather conditions that impact the critical stages. The use of a vector-based geographic information system in the analysis provided an efficient and flexible means for constructing the agroclimatic index. Suitability categories easily can be modified to meet requirements of different users, and additional climate variables readily can be added to the analysis. In addition, a computerized geographic information system allows the climatic suitability ratings to be combined easily with edaphic and topographic information. The clima...

REGIONAL SYNCHRONIES AND AMPLITUDE CHANGES IN THE JANUARY 500-MB MIDDLE LATITUDE GEOPOTENTIAL HEIGHT RECORD

The relationship between middle tropospheric long wave circulation and surface weather is recognized as an important component in the middle latitude climate system. Regional variations in long wave position and temporal variations in long wave amplitude exert a considerable influence on surface temperature and precipitation. This study seeks to organize the spatial and temporal structure of the long wave system within a climate regionalization that is based upon associated trends in the middle tropospheric geopotential height record for the purpose of assessing wave amplitude variations within these regions. This regionalization is performed using January 500-mb geopotential height data over the northern hemispheric middle latitudes for the period 1946–1987 and is constructed using a cluster analysis, in which the resultant clusters represent regions of synchronous height behavior during the data record. The resultant clusters are related spatially to long wave ridge and trough positions, and are charact...