This is the second part of a three-part paper on NorthAmerican climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that evaluates the twentieth-century simulations of intraseasonal tomultidecadal variability and teleconnections with NorthAmerican climate. Overall, themultimodel ensemble does reasonably well at reproducing observed variability in several aspects, but it does less well at capturing observed teleconnections, with implications for future projections examined in part three of this paper. In terms of intraseasonal variability, almost half of themodels examined can reproduce observed variability in the eastern Pacific andmostmodels capture the midsummer drought over CentralAmerica.The multimodelmean replicates the density of traveling tropical synoptic-scale disturbances but with large spread among themodels.Ontheother hand, the coarse resolutionof the models means that tropical cyclone frequencies are underpredicted intheAtlantic and eastern North Pacific. The frequency and mean amplitude of ENSO are generally well reproduced, although teleconnections with North American climate are widely varying among models and only a few models can reproduce the east and central Pacific types of ENSO and connections with U.S. winter temperatures. The models capture the spatial pattern of Pacific decadal oscillation (PDO) variability and its influenceoncontinental temperature andWestCoast precipitation but less well for the wintertime precipitation.The spatial representation of the Atlantic multidecadal oscillation (AMO) is reasonable, but the magnitude of SST anomalies and teleconnections are poorly reproduced. Multidecadal trends such as the warming hole over the central–southeastern United States and precipitation increases are not replicated by the models, suggesting that observed changes are linked to natural variability.

This study investigates the changes of the North Atlantic subtropical high (NASH) and its impact on summer precipitation over the southeastern (SE) United States using the 850-hPa geopotential height field in the National Centers for Environmental Prediction (NCEP) reanalysis, the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), long-tertii rainfall data, and Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) model simulations during the past six decades (1948-2007). The results show that the NASH in the last 30 yr has become more intense, and its western ridge has displaced westward with an enhanced meridional movement compared to the previous 30 yr. When the NASH moved closer to the continental United States in the three most recent decades, the effect of the NASH on the interannual variation of SE U.S. precipitation is enhanced through the ridge's north south movement. The study's attribution analysis suggested that the changes of the NASH are mainly due to anthropogenic warming. In the twenty-first century with an increase of the atmospheric CO(2) concentration, the center of the NASH would be intensified and the western ridge of the NASH would shift farther westward. These changes would increase the likelihood of both strong anomalously wet and dry summers over the SE United States in the future, as suggested by the IPCC AR4 models.

This paper assesses the variability and trends in summer-season rainfall from 1948 to 2009 for the Atlanta, Georgia region. The rainfall variables are total rainfall, frequency of rainfall days, and frequency of heavy-rainfall days. The main methods involve classifying daily 500-hPa geopotential height fields into synoptic types, determining the rainfall characteristics of the synoptic types, testing for significant temporal trends in rainfall, middle-troposphere circulation, lower-troposphere circulation, and atmospheric humidity, and using multiple linear regression to determine the impact of circulation and humidity variables on inter-annual variations in the rainfall variables. There were a total of eight synoptic types: the wet types involved troughing across or to the immediate west of the Atlanta region, while the dry types involved either an anticyclone across or to the immediate west of the region. The rainfall variables and two lower-troposphere circulation indices, the Bermuda High Index (BHI) and the Western Bermuda High Index (WBHI), had significant positive trends in variance over time. Among the three rainfall variables, only the frequency of rainfall days had a significant trend: the periods 1976–2009 and 1977–2009 had significant positive trends in rainfall days. The BHI had a significant positive trend from the 1970s to 2009, and the western ridge of the Bermuda High moved significantly southeastward from approximately the mid-1970s to 2009. Atmospheric humidity (i.e. 850-hPa specific humidity, 500-hPa specific humidity, and precipitable water) over the region had significant positive trends during most periods, with all humidity variables having significant increases from the 1970s to 2009. Increased interannual variability in the WBHI appears to be the cause of the increased variance in rainfall variables. An increase in atmospheric humidity, which is actually a global phenomenon, appears to be the principal cause of the increase in rainfall days during the past three decades. Copyright © 2012 Royal Meteorological Society

The role of satellite remote sensing in climate change studies Jun Yang, Peng Gong, Rong Fu, Minghua Zhang, Jingming Chen, Shunlin Liang, Bing Xu, Jiancheng Shi and Robert Dickinson Nature Clim. Change 3, 875–883 (2013); published online 15 September 2013; corrected aſter print 27 September 2013; 2 December 2013. In the version of this Review Article originally published, the temperature anomaly trends for RSS and UAH in Fig. 2b,c should have been positive values. These errors have now been corrected in the online versions of the Review Article. In the previous corrigendum, the mass balance of glaciers in the Karakarom region should have read 0.11±0.22 m yr−1 . CORRIGENDUM

This study shows that the North American monsoon system's (NAMS) strength, onset, and retreat over northwesternMexico exhibitmultidecadal variations during the period 1948–2009.Two dry regimes, associated with late onsets, early retreats, and weaker rainfall rates, occurred in 1948–70 and 1991–2005, whereas a strong regime, associatedwith early onsets, late retreats, and stronger rainfall rates, occurred in 1971–90.Arecovery of the monsoon strength was observed after 2005. This multidecadal variation is linked to the sea surface tem- perature anomalies' (SSTAs) variability,which is a combinationof theAtlanticmultidecadal oscillation(AMO) and thewarming SSTtrends.TheseSSTmodes appear to cause ananomalous cyclonic circulation and enhanced rainfall over the southeastern United States and the Gulf ofMexico, which in turn increases the atmospheric stability over the monsoon region. However, these SST modes cannot fully explain the circulation and rainfall anomalies observed during the early-retreat monsoons. An expansion of the North Atlantic surface high (NASH) in recent decades also contributes to the anomalous circulation associatedwith the early retreats of the NAMS. A northwestward expansion of the NASH further enhances the anomalous cyclonic circulation and rainfall over the southeastern United States and the Gulf ofMexico. Its associated northwestward shift of the subtropical jets over the western United States enhances subsidence over the NAMS region. The combined effects of the AMO, the warming trends, and the NASH expansion on atmospheric circulation contribute to a stronger and more persistent earlier retreat during the recent dry regime (1991–2005), while the earlier dry regime (1948–70) appears to be only influenced by the positive phase of the AMO.

Past studies have identified a variety of pathways by which carbon$\backslash$nmonoxide (CO) may be transported from the surface to the tropical upper$\backslash$ntroposphere (UT); however, the relative roles that these transport$\backslash$npathways play in determining the distribution and seasonality of CO in$\backslash$nthe tropical UT remain unclear. We have developed a method to automate$\backslash$nthe identification of two pathways ('local convection' and `advection$\backslash$nwithin the lower troposphere (LT) followed by convective vertical$\backslash$ntransport') involved in CO transport from the surface to the UT. This$\backslash$nmethod is based on the joint application of instantaneous along-track,$\backslash$nco-located, A-Train satellite measurements. Using this method, we find$\backslash$nthat the locations and seasonality of the UT CO maxima in the tropics$\backslash$nwere strongly correlated with the frequency of local convective$\backslash$ntransport during 2007. We also find that the `local convection' pathway$\backslash$n(convective transport that occurred within a fire region) typically$\backslash$ntransported significantly more CO to the UT than the `LT advection -\textgreater$\backslash$nconvection' pathway (advection of CO within the LT from a fire region to$\backslash$na convective region prior to convective transport). To leading order,$\backslash$nthe seasonality of CO concentrations in the tropical UT reflected the$\backslash$nseasonality of the `local convection' transport pathway during 2007. The$\backslash$nUT CO maxima occurred over Central Africa during boreal spring and over$\backslash$nSouth America during austral spring. Occurrence of the `local$\backslash$nconvection' transport pathway in these two regions also peaked during$\backslash$nthese seasons. During boreal winter and summer, surface CO emission and$\backslash$nconvection were located in opposite hemispheres, which limited the$\backslash$neffectiveness of transport to the UT. During these seasons, CO transport$\backslash$nfrom the surface to the UT typically occurred via the `LT advection -\textgreater$\backslash$nconvection' pathway.

0416 Biogeosciences: Biogeophysics; 0438 Biogeosciences: Diel, seasonal, and annual cycles (4227); 0439 Biogeosciences: Ecosystems, structure and dynamics (4815); 0476 Biogeosciences: Plant ecology (1851); 0480 Biogeosciences: Remote sensing

This study shows a decrease of seasonal mean convection, cloudiness and an increase of surface shortwave down-welling radiation during 1984–2007 over the Amazon rainforests based on the analysis of satellite-retrieved clouds and surface radiative flux data. These changes are consistent with an increase in surface temperature, increased atmospheric stability, and reduction of moisture transport to the Amazon based on in situ surface and upper air meteorological data and reanalysis data. These changes appear to link to the expansion of the western Pacific warm pool during the December–February season, to the positive phase of the Atlantic Multidecadal Oscillation and increase of SST over the eastern Pacific SST during the March–May season, and to an increase of the tropical Atlantic meridional SST gradient and an expansion of the western Pacific warm pool during September–November season. The resultant increase of surface solar radiation during all but the dry season in the Amazon could contribute to the observed increases in rainforest growth during recent decades.

An investigation is made of the influence of fire-caused deforestation on precipitation-triggered, shallow landslide susceptibilities in southern California, using a scalable and extensible geo-fluid model (SEGMENT), that accounts for soil mechanics, root distribution, and relevant hydrologic processes. SEGMENT is applicable to variable regional topography, soil thickness profiles, and vegetation coverage. In this study, for southern California following the 2007 wildfires, three experiments were performed with rainfall recurrence periods chosen to be 2, 10, and 25Â years. These intervals correspond to 24-h storm rainfall totals of 17, 25.4, and 33Â mm. The model generated landslide stability maps that identified three areas of high instability. These unstable regions are located in the San Fernando Valley, the San Gabriel Mountains, and the Santa Monica Mountains. In each case, the vegetation cover had been severely burned during the preceding 2007 wildfires. The model results showed that burning from wildfires is a major destabilizing factor for southern California. Burn sites are more prone to landslides than vegetated slopes because the soil more readily exceeds its critical moisture content. Severe droughts in a future warming climate are expected to increase the likelihood of more frequent and intense wild fires. Higher temperatures combined with decreased total rainfalls facilitate more intense landslides, including devastating mudslides, following heavy precipitation. Finally, the model is designed to assist in developing timely mitigation measures for post-fire, storm-triggered landslides.

An overview of storm-triggered landslides is presented. Then a recently developed and extensively verified landslide modeling system is used to illustrate the importance of two important but presently overlooked mechanisms involved in landslides. The model's adaptive design makes the incorporation of new physical mechanisms convenient. For example, by implementing a land surface scheme that simulates macropore features of fractured sliding material in the draining of surface ponding, it explains why precipitation intensity is critical in triggering catastrophic landslides. Based on this model, the authors made projections of landslide occurrence in the upcoming 10 years over a region of Southern California, using atmospheric parameters provided by a highresolution climate model under a viable emission future scenario. Current global coupled ocean–atmosphere climate model (CGCM) simulations of precipitation, properly interpreted, provide valuable information to guide studies of storm-triggered landslides. For the area of interest, the authors examine changes in recurrence frequency and spatial distribution of storm-triggered landslides. For some locations, the occurrences of severe landslides (i.e., those with a sliding mass greater than 104 m3) are expected to increase by \~5%% by the end of the twenty-first century. The authors also provide a perspective on the ecosystem consequences of an increase in storm-triggered mudslides. For single plants, the morphological features required for defense against extreme events and those required to maximize growth and reproduction are at odds. Natural selection has resulted in existing plants allocating just enough resources to cope with natural hazards under a naturally varying climate. Consequently, many plant species are not prepared for the expected large changes in extremes caused by anthropogenic climate changes in the present and future centuries. A supplement to this article is available online: DOI: [ABSTRACT FROM AUTHOR] Copyright of Bulletin of the American Meteorological Society is the property of American Meteorological Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract This study applies a multi-phase, multiple-rheology, scalable and extensible geofluid model to the Greenland Ice Sheet (GrIS). The model is driven by monthly atmospheric forcing from global climate model simulations. Novel features of the model, referred to as SEGMENT-Ice, include using the full Navier-Stokes equations to account for non-local dynamic balance and its influence on ice flow; and a granular sliding layer between the bottom ice layer and the lithosphere layer to provide a mechanism for possible large scale surges in a warmer future climate (granular basal layer is for certain specific region, though). Monthly climate of SEGMENT-Ice allows an investigation of detailed features such as seasonal melt area extent (SME) over Greenland. The model reproduced reasonably well the annual maximum SME and total ice mass lost rate when compared observations from the Special Sensing Microwave Imager (SSM/I) and Gravity Recovery and Climate Experiment (GRACE) over the past few decades. The SEGMENT-...

The relative contributions of Southeast Asian convective source regions during boreal summer to water vapor in the tropical stratosphere are examined using Lagrangian trajectories. Convective sources are identified using global observations of infrared brightness temperature at high space and time resolution, and water vapor transport is simulated using advection-condensation. Trajectory simulations are driven by three different reanalysis data sets, GMAO MERRA, ERA-Interim, and NCEP/NCAR, to establish points of consistency and evaluate the sensitivity of the results to differences in the underlying meteorological fields. All ensembles indicate that Southeast Asia is a prominent boreal summer source of tropospheric air to the tropical stratosphere. Three convective source domains are identified within Southeast Asia: the Bay of Bengal and South Asian subcontinent (MON), the South China and Philippine Seas (SCS), and the Tibetan Plateau and South Slope of the Himalayas (TIB). Water vapor transport into the stratosphere from these three domains exhibits systematic differences that are related to differences in the bulk characteristics of transport. We find air emanating from SCS to be driest, from MON slightly moister, and from TIB moistest. Analysis of pathways shows that air detrained from convection over TIB is most likely to bypass the region of minimum absolute saturation mixing ratio over the equatorial western Pacific; however, the impact of this bypass mechanism on mean water vapor in the tropical stratosphere at 68 hPa is small (\textless0.1 ppmv). This result contrasts with previously published hypotheses, and it highlights the challenge of properly quantifying fluxes of atmospheric humidity. Copyright 2011 by the American Geophysical Union.

Accurate prediction of future sea level rises requires models which can reproduce recent observed change in ice sheet behavior. This study describes a new multiphase, multiple-rheology ice dynamics model (SEGMENT-ice), which is used to examine Greenland ice sheet (GrIS) responses both to past and to possible future warming climate conditions. When applied to the GrIS, SEGMENT-ice exhibits skill in reproducing the mass loss rate derived from the Gravity Recovery and Climate Experiment (GRACE), the interferometric synthetic aperture radar (InSAR) measured surface flow speed, and the microwave remotely sensed surface melt area over the past decade. When forced by the NCEP/NCAR reanalysis atmospheric parameters, the ice model simulates closely the GrIS mass loss rate obtained from GRACE. An increase of summer maximum melt area extent (SME) is indicative of an expansion of the ablation zone. The modeled SME from 1979 to 2006 also simulates well the observed interannual variability of SME, with a high correlation of 0.88 between the two time series. The geographical distributions of the modeled and observed SME also agree well. Comparison of modeled and observed velocity over three regions, covering the west, northeast, and north sides of the GrIS, respectively, indicates a satisfactory model performance in delineating flow direction and magnitudes for regions with flow speed less than 500 m/y, with no region-specific systematic errors. However, the model cannot simulate extremes in the observations, mainly because it is limited by spatial resolution. The SEGMENT-ice simulations are sufficiently close to the observations to employ the model to project the future behavior of the GrIS. By the end of this century, if the moderate A1B scenario is realized, the total mass loss rate will reach ∼220 km3/y. The ice divergence contribution will be about 60%, outweighing the contribution from surface processes.

The variability of summer precipitation in the Southeastern United States is examined in this study using 60-yr (1948–2007) rainfall data. The Southeast summer rainfalls exhibited higher interannual variability with more intense summer droughts and anomalous wetness in the recent 30 years (1978–2007) than in the early 30 years (1948–77). Such intensification of summer rainfall variability was consistent with a decrease of light (0.1 – 1 mm day−1) and medium (1 – 10 mm day−1) rainfall events during extremely dry summers, and an increase of heavy (\textgreater 10 mm day−1) rainfall events in extremely wet summers. Changes in rainfall variability were also accompanied by a southward shift of the region of maximum zonal wind variability at the jet stream level in the latter period. The covariability between the Southeast summer precipitation and sea surface temperatures (SSTs) is also analyzed using the singular value decomposition (SVD) method. It is shown that the increase of Southeast summer precipitation variability is primarily associated with a higher SST variability across the equatorial Atlantic and also SST warming in the Atlantic.

Predicting the location and timing of mudslides with adequate lead time is a scientifically challenging problem that is critical for mitigating landslide impacts. Here, a new dynamic modeling system is described for monitoring and predicting storm-triggered landslides and their ecosystem implications. The model ingests both conventional and remotely sensed topographic and geologic data, whereas outputs include diagnostics required for the assessment of the physical and societal impacts of landslides. The system first was evaluated successfully in a series of experiments under idealized conditions. In the main study, under real conditions, the system was assessed over a mountainous region of China, the Yangjiashan Creeping (YC) slope. For this data-rich section of the Changjiang River, the model estimated creeping rates that had RMS errors of similar to 0.5 mm yr(-1) when compared with a dataset generated from borehole measurements. A prediction of the creeping curve for 2010 was made that suggested significant slope movement will occur in the next 5 years, without any change in the current precipitation morphology. However, sliding will become imminent if a storm occurs in that 5-yr period that produces over 150 mm of precipitation. A sensitivity experiment shows that the identified location fails first, triggering domino-effect slides that progress upslope. This system for predicting storm-triggered landslides is intended to improve upon present warning lead times to minimize the impacts of shallow, fast moving, and therefore hazardous landslides.

Accurate prediction of future sea level rise requires models that accurately reproduce and explain the recent observed dramatic ice sheet behaviours. This study presents a new multi-phase, multiple-rheology, scalable and extensible geofluid model of the Greenland ice sheet that shows the credential of successfully reproducing the mass loss rate derived from the Gravity Recovery and Climate Experiment (GRACE), and the microwave remote sensed surface melt area over the past decade. Model simulated early 21st century surface ice flow compares satisfactorily with InSAR measurements. Accurate simulation of the three metrics simultaneously cannot be explained by fortunate model tuning and give us confidence in using this modelling system for projection of the future fate of Greenland Ice Sheet (GrIS). Based on this fully adaptable three dimensional, thermo-mechanically coupled prognostic ice model, we examined the flow sensitivity to granular basal sliding, and further identified that this leads to a positive feedback contributing to enhanced mass loss in a future warming climate. The rheological properties of ice depend sensitively on its temperature, thus we further verified modelâŹs temperature solver against in situ observations. Driven by the NCEP/NCAR reanalysis atmospheric parameters, the ice model simulated GrIS mass loss rate compares favourably with that derived from the GRACE measurements, or about −147 km3/yr over the 2002–2008 period. Increase of the summer maximum melt area extent (SME) is indicative of expansion of the ablation zone. The modeled SME from year 1979 to 2006 compares well with the cross-polarized gradient ratio method (XPGR) observed melt area in terms of annual variabilities. A high correlation of 0.88 is found between the two time series. In the 30-year model simulation series, the surface melt exhibited large inter-annual and decadal variability, years 2002, 2005 and 2007 being three significant recent melt episodes.

Six rainfall datasets are compared over the Amazon basin, Northeast Brazil, and the Congo basin. These datasets include three gauge-only precipitation products from the Climate Prediction Center (CPC), Global Precipitation Climatology Center (GPCC), and Brazilian Weather Forecast and Climate Studies Center (CLMNLS), and three combined gauge and satellite precipitation datasets from the CPC Merged Analysis of Precipitation (CMAP), Global Precipitation Climatology Project (GPCP), and Tropical Rainfall Measuring Mission (TRMM) product. The pattern of the annual precipitation is consistently represented by these data, despite the differences in methods and periods of averaging. Quantitatively, the differences in annual precipitation among these datasets are 5% more than the Amazon domain (0°–15°S, 50°–70°W), 22% more than Northeast Brazil (5°–10°S, 35°–45°W), and 11% more than the Congo domain (5°N–10°S, 15°–30°E). Over the Amazon domain the rainfall variation is well correlated between CPC, TRMM, GPCP, and GPCC (r2 \textgreater 0.9) except for the northwestern Amazon, whereas CMAP and CLMNLS were different from these four datasets. Over the Congo basin, the coefficient of determination between these rainfall datasets is generally below 0.7. The empirical orthogonal functions analysis suggests large discrepancies in interannual and decadal variations of rainfall among these datasets, especially for the Congo basin and for the South American region after 1998. In general, CMAP, GPCC, TRMM, and GPCP significantly agree over the tropical areas in South America.