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Richard Cullather
Division
of Ocean & Climate Physics
Lamont-Doherty Earth Observatory of Columbia University 61 Route 9W Palisades, NY 10964-1707 USA Phone: +1 845 365-8769 Fax: +1 845 365-8736 E-mail: cullat '"at'" ldeo.columbia.edu
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My research interests are associated with describing the atmospheric general circulation of the polar regions and its interaction with the surface climate. The climate of the Arctic and the Antarctic are topics of current interest, both to the science community and to the general public, as a result of recent climate variability and the potential for future rapid change. In southern high latitudes, interest is focused on the warming of the near-surface atmosphere over the Antarctic Peninsula that is recognized as one of the largest temperature trends on Earth over the last 50 years. In part, this has resulted in the recent collapse of ice shelves along the Peninsula coast. If it continues, this warming trend has important implications for the Peninsula region, but also for the Antarctic continent as a whole and its close relation to global sea level. In the Arctic, attention has focused on large air temperature trends in Alaska and in western Siberia, but also importantly on the decreasing perennial Arctic sea ice cover. The Arctic ice pack is a signature characteristic of the northern high latitudes. The loss of perennial sea ice would have important consequences for a range of disciplines including marine biology, oceanography, commerce, foreign relations, and resource exploration.
I provide analysis of trends and spatial patterns of variability from observations and from climate models. The observations that I examine are taken from meteorological station records, field studies, satellite remote sensing, and output from atmospheric models that have been adjusted to fit available sparse observations made at some time in the past, which are known as “numerical analyses”. I also examine output from global coupled atmosphere, ocean, sea ice, and land surface model simulations of the 20th Century and from simulations of future climate. My approach includes the identification of dominant patterns or modes of variability and the examination of the evolving spatial distribution and transport of energy and moisture within the climate system.
The motivation for this work is based on recent studies documenting trends in the late summer sea ice area extent over the multichannel satellite era, and in particular the dramatic minima in the perennial ice cover from 2002 to the present. Climate models are important tools used in studying Arctic sea ice cover and its sensitivity to surface air temperature anomalies, atmospheric circulation, and oceanic process. Numerical models represent an integration of current knowledge of the climate system and are essential for quantitative prognostic assessments. The goals of this study are to document differences in U.S. climate model simulations of the contemporary Arctic as compared to observation, and to identify mechanisms that produce sea ice anomalies in the coupled model regime.
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| Average March sea ice fraction from
observation (left), NCAR CCSM3 (center), and GFDL CM2.1 (right). |
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The wintertime sea ice pack in the Southern Hemisphere is known to be highly divergent, owing to the absence of significant land surfaces and the lack of multiyear ice. Atmospheric teleconnection patterns may then be readily documented in the sea ice extent and distribution. The sea ice pack may then be seen as a transmitter of climate variables from the large-scale circulation to Antarctica. Recent studies have provided an understanding of interannual Antarctic sea ice variability and its association with climate variables of the Southern Hemisphere with particular emphasis on the Antarctic Peninsula region. The purpose of this work is to examine these identified phenomena in a quantitative format and to relate them to the Antarctic surface climate.
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| First
principal component of observed wintertime sea ice fraction. |
The Little Ice Age (LIA) is a term used to describe a period of glacier advance over the approximate time period 1450 until 1890. In many regions the maximum advance coincided with a decrease in solar activity known as the Maunder Minimum. From the analysis of multiproxy records, it has become clear that the LIA was manifest as a complex spatial and temporal pattern in the Northern Hemisphere. Analysis of the Southern Hemisphere is limited by the small amount of terrestrial surface from which proxy records may be retrieved. Given the strongly zonal circulation and the predominantly zonal character of variability found in the recent instrumental record, one may speculate that the patterns may be more uniform and widespread in the Southern Hemisphere. In this study simulations of the Maunder Minimum from a climate model that includes a detailed representation of stratospheric chemistry processes are investigated for the purpose of advancing the understanding of LIA patterns in the Southern Hemisphere.
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| Regression of the Antarctic
Oscillation Index onto sea level pressure. |
AnSlope is an integrated observational and modeling program that is based on the identification of the Antarctic upper continental slope as the critical gateway for the exchange of shelf and deep ocean waters. The primary goal is to identify the principal physical processes that govern the transfer of Antarctic shelf-modified dense water into intermediate and deep layers of the adjacent deep ocean. The observational component of AnSlope has concentrated on the acquisition of a set of measurements focused over the outer continental shelf and upper slope of the northwestern Ross Sea. Three cruises were conducted beginning in the Austral summer of 2003. The purpose of this study is to review the meteorological and surface conditions that are associated with this region and to assess the conditions that were present during the AnSlope observational period.
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| Ship
tracks of three AnSlope cruises. |
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