A diagnostic of Northern Hemisphere winter extratropical stratosphere-troposphere interactions is presented to facilitate the study of stratosphere-troposphere coupling and to examine what might influence these interactions. The diagnostic is a multivariate EOF combining lower-stratospheric planetary wave activity flux in December with sea level pressure in January. This EOF analysis captures a strong linkage between the vertical component of lower-stratospheric wave activity over Eurasia and the subsequent development of hemisphere-wide surface circulation anomalies, which are strongly related to the Arctic Oscillation. Wintertime stratosphere-troposphere events picked out by this diagnostic often have a precursor in autumn: years with large October snow extent over Eurasia feature strong wintertime upwardpropagating planetary wave pulses, a weaker wintertime polar vortex, and high geopotential heights in the wintertime polar troposphere. This provides further evidence for predictability of wintertime circulation based on autumnal snow extent over Eurasia. These results also raise the question of how the atmosphere will respond to a modified snow cover in a changing climate.

[1] Winter 2009-2010 made headlines for extreme cold and snow in most of the major population centers of the industrialized countries of the Northern Hemisphere (NH). The major teleconnection patterns of the Northern Hemisphere, El Niño/Southern Oscillation (ENSO) and the Arctic Oscillation (AO) were of moderate to strong amplitude, making both potentially key players during the winter of 2009-2010. The dominant NH winter circulation pattern can be shown to have originated with a two-way stratosphere-troposphere interaction forced by Eurasian land surface and lower tropospheric atmospheric conditions during autumn. This cycle occurred twice in relatively quick succession contributing to the record low values of the AO observed. Using a skillful winter temperature forecast, it is shown that the AO explained a greater variance of the observed temperature pattern across the extratropical landmasses of the NH than did ENSO.

A significant portion of the large amount of carbon (C) currently stored in soils of the permafrost region in the Northern Hemisphere has the potential to be emitted as the greenhouse gases CO 2 and CH 4 under a warmer climate. In this study we evaluated the variability in the sensitivity of permafrost and C in recent decades among land surface model simulations over the permafrost region between 1960 and 2009. The 15 model simulations all predict a loss of near-surface permafrost (within 3 m) area over the region, but there are large differences in the magnitude of the simulated rates of loss among the models (0.2 to 58.8 × 10 3 km 2 yr À1 ). Sensitivity simulations indicated that changes in air temperature largely explained changes in permafrost area, although interactions among changes in other environmental variables also played a role. All of the models indicate that both vegetation and soil C storage together have increased by 156 to 954 Tg C yr À1 between 1960 and 2009 over the permafrost region even though model analyses indicate that warming alone would decrease soil C storage. Increases in gross primary production (GPP) largely explain the simulated increases in vegetation and soil C. The sensitivity of GPP to increases in atmospheric CO 2 was the dominant cause of increases in GPP across the models, but comparison of simulated GPP trends across the 1982-2009 period with that of a global GPP data set indicates that all of the models overestimate the trend in GPP. Disturbance also appears to be an important factor affecting C storage, as models that consider disturbance had lower increases in C storage than models that did not consider disturbance. To improve the modeling of C in the permafrost region, there is the need for the MCGUIRE ET AL.MODELING PERMAFROST CARBON DYNAMICS 1015 PUBLICATIONS

anomaly, is a surface temperature anomaly induced by the anomalous circulation. We will show that this anomaly pattern originates in the early fall, on a much more regional scale, in Siberia. As the season progresses this anomaly pattern propagates and amplifies to dominate much of the extratropical NH, making the Siberian high a dominant force in NH climate variability in winter. Also since the SLP and surface temperature anomalies originate in a region of maximum fall snow cover variability, we argue that snow cover partially forces the phase of winter variability and can potentially be used for the skillful prediction of winter climate.

[1] Decadal trends have been noted in the leading mode of boreal winter variability. Given that this mode is thought to be an internal mode of the atmosphere it remains unclear as to what is responsible for interannual to interdecadal oscillations of this mode. We demonstrate that continentalscale snow cover varies at the same multi-year time periods as the atmosphere but leads the atmosphere by several months through their mutual oscillations. Therefore we propose snow cover as a potential contributor to the interannual variability of the leading boreal winter mode of the atmosphere.

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Preindustrial changes in the Asian summer monsoon climate from the 1700s to the 1850s were estimated with an atmospheric general circulation model (AGCM) using historical global land cover/use change data reconstructed for the last 300 years. Extended cultivation resulted in a decrease in monsoon rainfall over the Indian subcontinent and southeastern China and an associated weakening of the Asian summer monsoon circulation. The precipitation decrease in India was marked and was consistent with the observational changes derived from examining the Himalayan ice cores for the concurrent period. Between the 1700s and the 1850s, the anthropogenic increases in greenhouse gases and aerosols were still minor; also, no long-term trends in natural climate variations, such as those caused by the ocean, solar activity, or volcanoes, were reported. Thus, we propose that the land cover/ use change was the major source of disturbances to the climate during that period. This report will set forward quantitative examination of the actual impacts of land cover/use changes on Asian monsoons, relative to the impact of greenhouse gases and aerosols, viewed in the context of global warming on the interannual, decadal, and centennial time scales.atmospheric water balance ͉ climate change ͉ historical land-cover change ͉ monsoon rainfall I n general, a monsoon is generated from a thermal contrast between land and ocean. Thus, the land's surface condition is an important factor in determining its climate. Monsoon Asia, where Ͼ50% of the world population is concentrated, has experienced large land cover/use changes due to agricultural development, particularly during the 18th and 19th centuries. In India and China between 1700 and 1850, extension of cultivation and habitation activities decreased the percentage of forested area from 40-50% to 5-10% of the entire territories between 1700 and 1850 (1).Changing the land cover/use from forest to croplands can affect the global and regional climate through changes in the energy and water balance at the earth's surface (2, 3). Among the various effects of vegetation change, 2 factors have been shown to have a major influence on the energy and water balance: (i) an increase in surface albedo leading to a reduction in solar energy absorption at the surface and (ii) a decrease in surface roughness, resulting in low-level wind speed intensification. As a consequence, the partitioning of turbulent heat fluxes into its sensible and latent heat fluxes would subsequently affect the planetary boundary layer and deep cumulus convection and, hence, the large-scale atmospheric phenomena (3). Previous modeling studies that investigated the impact of those effects used either a model of intermediate complexity with historical land cover changes (4, 5) or a general circulation model with a simplified setup in which the indigenous forests were totally and uniformly replaced by cultivated land. These latter studies have shown how different vegetation distributions affect the global surface energy-water balance...

GIS analysis of the French database of Pleistocene periglacial features allows an improved evaluation of the maximum extent of past permafrost. The distribution of typical ice-wedge pseudomorphs does not extend south of 47°N and therefore suggests that widespread discontinuous permafrost did not affect the regions south of the Paris Basin. The exclusive presence of sand wedges with primary infill between 45 and 47°N, mainly in the periphery of coversand areas, suggests that thermal contraction cracking of the ground occurred together with sand drifting in a context of deep seasonal frost or sporadic discontinuous permafrost, unfavourable for the growth of significant ground-ice bodies. The latitudinal variation of the wedge dimensions clearly shows that the sand wedges were located in the southern margin of the area affected by thermal contraction. The proposed map of Pleistocene permafrost in France partially reconciles field data with palaeoclimatic simulations. The remaining discrepancies may arise primarily from the time lag between the Last Permafrost Maximum (c. 31-24 ka) and the Last Glacial Maximum (21 ka).