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C. A. M. Brenninkmeijep and P. A. Roberts

special attention to the problem ofcollecting air in the lower stratosphere for the isotopic analysis of carbon monoxide.1. Introduction Isotopic analysis is being increasingly used for betterunderstanding the cycles of atmospheric trace gases,and in several cases rather unique information is beingobtained. For instance the ~4C activity of atmosphericCH4, when combined with its ~3C/~2C ratio is a goodestimator of the biogenic fraction of this greenhousegas (Lowe et al. 1988; Wahlen et al. 1989). In

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Kate E. Sinclair, Nancy A. N. Bertler, W. J. Trompetter, and W. T. Baisden

heavy stable isotopes in air masses that traverse WAIS. This analysis gives us insight into the airmass pathways associated with snow delivery and the seasonality of synoptic-scale flow to the Ross Sea region. It demonstrates that large snowfall events are associated with cyclonic flow around the margin of the Ross Sea and suggests that airmass incursions across West Antarctica may affect stable isotope ratios in the western Ross Sea, leading to “cooler” isotopic signals. It gives us a qualitative

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Luis Gimeno, Raquel Nieto, Ricardo M. Trigo, Sergio M. Vicente-Serrano, and Juan Ignacio López-Moreno

of the moisture source regions is considerably more difficult than estimating the ratio between advected and recycled moisture. Isotope analysis has traditionally been used to identify the origin of the moisture that feeds precipitation. This method is based on knowledge of the relationship between the relative proportions of certain isotopes of oxygen and hydrogen, which depend on the conditions (altitude, temperature, distance from the coast) under which the water evaporated to the atmosphere

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Stefan Metzger, Edward Ayres, David Durden, Christopher Florian, Robert Lee, Claire Lunch, Hongyan Luo, Natchaya Pingintha-Durden, Joshua A. Roberti, Michael SanClements, Cove Sturtevant, Ke Xu, and Rommel C. Zulueta

4 . In short, gaseous-phase stable carbon and water isotopes are measured along the tower vertical profile. Wet deposition sampling occurs at the tower top across 37 TIS sites, which were selected to represent a range of concentrations of nitrate, ammonium, and sulfate. Analysis occurs at the Illinois State Water Survey laboratory at the University of Illinois, which handles the analysis of other atmospheric deposition sampling programs. Stable isotopes in wet deposition are also sampled and

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G. W. K. Moore and Gerald Holdsworth

of an extratropical cyclone, form the filamentary structure that extends northward toward the ice core site. It is this pathway from tropical reservoir to ice core site that has to be modeled if we are to improve our understanding of the climate signal contained in the stable isotope record in the Mount Logan and other ice cores. Finally, this analysis does not address the important cloud microphysical processes that are of course important in the production of precipitation from the water vapor

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G. Vettoretti and W. R. Peltier

1. Introduction The glacial–interglacial cycles that have dominated climate system variability of the late Pleistocene are characterized by transitions into a glacial climate state from interstadial conditions, transitions that may occur fairly rapidly and that are accompanied by large drops in sea level. Oxygen isotope ( δ 18 O) records from deep sea sedimentary cores (e.g., Hays et al. 1976 ; SPECMAP: Imbrie et al. 1984 ) and polar ice cores ( Greenland Ice Core Project Members 1993

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Guido Vettoretti and W. Richard Peltier

critical role in marine isotopic stage 3 (MIS3) D-O-related climate variability. While there currently remains little doubt that the AMOC plays a major role in the dynamics of the D-O cycle, there have previously been numerous attempts to explain the underlying dynamics with different models of modest complexity. Some of the semiquantitative ideas that have been suggested to provide an explanation of the D-O process have invoked internally generated AMOC “loop” or “deep decoupling” oscillations (e

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Anthony J. Broccoli

atmospheric temperatures warmer than those estimated from a variety of snow line depression and pollen data. The recent development of new methods of paleotemperature estimation have not satisfactorily resolved this issue. Broecker (1995) provides an excellent summary of these methods and the results they have produced. Temperature reconstructions based on noble gases in aquifers and isotopic analysis of corals indicate low-latitude glacial temperatures approximately 5 K cooler than today, generally

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A. Henderson-Sellers, H. Zhang, G. Berz, K. Emanuel, W. Gray, C. Landsea, G. Holland, J. Lighthill, S-L. Shieh, P. Webster, and K. McGuffie

The very limited instrumental record makes extensive analyses of the natural variability of global tropical cyclone activities difficult in most of the tropical cyclone basins. However, in the two regions where reasonably reliable records exist (the North Atlantic and the western North Pacific), substantial multidecadal variability (particularly for intense Atlantic hurricanes) is found, but there is no clear evidence of long-term trends. Efforts have been initiated to use geological and geomorphological records and analysis of oxygen isotope ratios in rainfall recorded in cave stalactites to establish a paleoclimate of tropical cyclones, but these have not yet produced definitive results. Recent thermodynamical estimation of the maximum potential intensities (MPI) of tropical cyclones shows good agreement with observations.

Although there are some uncertainties in these MPI approaches, such as their sensitivity to variations in parameters and failure to include some potentially important interactions such as ocean spray feedbacks, the response of upper-oceanic thermal structure, and eye and eyewall dynamics, they do appear to be an objective tool with which to predict present and future maxima of tropical cyclone intensity. Recent studies indicate the MPI of cyclones will remain the same or undergo a modest increase of up to 10%–20%. These predicted changes are small compared with the observed natural variations and fall within the uncertainty range in current studies. Furthermore, the known omissions (ocean spray, momentum restriction, and possibly also surface to 300-hPa lapse rate changes) could all operate to mitigate the predicted intensification.

A strong caveat must be placed on analysis of results from current GCM simulations of the “tropical-cyclone-like” vortices. Their realism, and hence prediction skill (and also that of “embedded” mesoscale models), is greatly limited by the coarse resolution of current GCMs and the failure to capture environmental factors that govern cyclone intensity. Little, therefore, can be said about the potential changes of the distribution of intensities as opposed to maximum achievable intensity. Current knowledge and available techniques are too rudimentary for quantitative indications of potential changes in tropical cyclone frequency.

The broad geographic regions of cyclogenesis and therefore also the regions affected by tropical cyclones are not expected to change significantly. It is emphasized that the popular belief that the region of cyclogenesis will expand with the 26°C SST isotherm is a fallacy. The very modest available evidence points to an expectation of little or no change in global frequency. Regional and local frequencies could change substantially in either direction, because of the dependence of cyclone genesis and track on other phenomena (e.g., ENSO) that are not yet predictable. Greatly improved skills from coupled global ocean–atmosphere models are required before improved predictions are possible.

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A. Henderson-Sellers, K. McGuffie, D. Noone, and P. Irannejad

; Henderson-Sellers et al. 2002 ). b. Applying stable water isotope knowledge The hypothesis we test here is that aspects of large-basin water budgets and fluxes can be examined using measurements and simulations of stable water isotopes. If correct, isotopic analysis will be able to explain and improve aspects of large-basin hydrological simulations. In this paper, we focus on simulations of stable water isotopic characteristics in three of the Global Energy and Water Cycle Experiment (GEWEX) Continental

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