ALBERT

Description:    A wide range of statistical tools is used to investigate the decadal variability of the Atlantic Meridional Overturning Circulation (AMOC) and associated key variables in a climate model (CHIME, Coupled Hadley-Isopycnic Model Experiment), which features a novel ocean component. CHIME is as similar as possible to the 3rd Hadley Centre Coupled Model (HadCM3) with the important exception that its ocean component is based on a hybrid vertical coordinate. Power spectral analysis reveals enhanced AMOC variability for periods in the range 15–30 years. Strong AMOC conditions are associated with: (1) a Sea Surface Temperature (SST) anomaly pattern reminiscent of the Atlantic Multi-decadal Oscillation (AMO) response, but associated with variations in a northern tropical-subtropical gradient; (2) a Surface Air Temperature anomaly pattern closely linked to SST; (3) a positive North Atlantic Oscillation (NAO)-like pattern; (4) a northward shift of the Intertropical Convergence Zone. The primary mode of AMOC variability is associated with decadal changes in the Labrador Sea and the Greenland Iceland Norwegian (GIN) Seas, in both cases linked to the tropical activity about 15 years earlier. These decadal changes are controlled by the low-frequency NAO that may be associated with a rapid atmospheric teleconnection from the tropics to the extratropics. Poleward advection of salinity anomalies in the mixed layer also leads to AMOC changes that are linked to processes in the Labrador Sea. A secondary mode of AMOC variability is associated with interannual changes in the Labrador and GIN Seas, through the impact of the NAO on local surface density. Content Type Journal Article Pages 1-22 DOI 10.1007/s00382-012-1432-y Authors A. Persechino, Ocean and Earth Science, University of Southampton, European Way, Southampton, Hampshire, SO14 3ZH UK R. Marsh, Ocean and Earth Science, University of Southampton, European Way, Southampton, Hampshire, SO14 3ZH UK B. Sinha, National Oceanography Centre, European Way, Southampton, Hampshire, SO14 3ZH UK A. P. Megann, National Oceanography Centre, European Way, Southampton, Hampshire, SO14 3ZH UK A. T. Blaker, National Oceanography Centre, European Way, Southampton, Hampshire, SO14 3ZH UK A. L. New, National Oceanography Centre, European Way, Southampton, Hampshire, SO14 3ZH UK Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description:    The objective of this study is to examine, based on recently available high resolution satellite and observational data, the evolution and role of sea surface temperature (SST) in influencing the intraseasonal variability of the South China Sea (SCS) summer monsoon (SM). The study focuses on the 30–60 day timescale when the northward propagating anomalies are dominant over the SCS. Composite analysis of the SST maximum events during SCS SM shows that increased SST anomalies over the SCS are significantly influenced by the downward shortwave radiation flux anomalies, with the suppressed surface latent heat flux anomalies supplementing to it. A thermal damping of the positive SST anomalies induces positive upward heat fluxes, which then destabilize the lower atmosphere between 1,000 and 700 hPa. The positive SST anomalies lead the positive precipitation anomalies over the SCS by 10 days, with a significant correlation ( r  = 0.44) between the SST-precipitation anomalies. The new findings here indicate an ocean-to-atmosphere effect over the SCS, where underlying SST anomalies tend to form a favorable condition for convective activity and sustain enhanced precipitation during the SCS SM. It is also argued, based on our observations, that the negative sea level pressure anomalies induced by the positive SST anomalies play a role in enhancing the northward propagation of the intraseasonal anomalies over the SCS. Content Type Journal Article Pages 1-10 DOI 10.1007/s00382-011-1118-x Authors Mathew Roxy, Centre for Climate Change Research, Indian Institute of Tropical Meteorology, Pune, 411008 India Youichi Tanimoto, Faculty of Environmental Earth Science and Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido, Japan Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description:    In this paper, we evaluate several timely, daily air-sea heat flux products (NCEP, NCEP2, ERA-Interim and OAFlux/ISCCP) against observations and present the newly developed TropFlux product. This new product uses bias-corrected ERA-interim and ISCCP data as input parameters to compute air-sea fluxes from the COARE v3.0 algorithm. Wind speed is corrected for mesoscale gustiness. Surface net shortwave radiation is based on corrected ISCCP data. We extend the shortwave radiation time series by using “near real-time” SWR estimated from outgoing longwave radiation. All products reproduce consistent intraseasonal surface net heat flux variations associated with the Madden-Julian Oscillation in the Indian Ocean, but display more disparate interannual heat flux variations associated with El Niño in the eastern Pacific. They also exhibit marked differences in mean values and seasonal cycle. Comparison with global tropical moored buoy array data, I-COADS and fully independent mooring data sets shows that the two NCEP products display lowest correlation to mooring turbulent fluxes and significant biases. ERA-interim data captures well temporal variability, but with significant biases. OAFlux and TropFlux perform best. All products have issues in reproducing observed longwave radiation. Shortwave flux is much better captured by ISCCP data than by any of the re-analyses. Our “near real-time” shortwave radiation performs better than most re-analyses, but tends to underestimate variability over the cold tongues of the Atlantic and Pacific. Compared to independent mooring data, NCEP and NCEP2 net heat fluxes display ~0.78 correlation and 〉65 W m −2 rms-difference, ERA-I performs better (~0.86 correlation and ~48 W m −2 ) while OAFlux and TropFlux perform best (~0.9 correlation and ~43 W m −2 ). TropFlux hence provides a useful option for studying flux variability associated with ocean–atmosphere interactions, oceanic heat budgets and climate fluctuations in the tropics. Content Type Journal Article Pages 1-23 DOI 10.1007/s00382-011-1115-0 Authors B. Praveen Kumar, Physical Oceanography Division, National Institute of Oceanography, Council of Scientific and Industrial Research (CSIR), Dona Paula, Goa 403004, India J. Vialard, Physical Oceanography Division, National Institute of Oceanography, Council of Scientific and Industrial Research (CSIR), Dona Paula, Goa 403004, India M. Lengaigne, Physical Oceanography Division, National Institute of Oceanography, Council of Scientific and Industrial Research (CSIR), Dona Paula, Goa 403004, India V. S. N. Murty, National Institute of Oceanography Regional Centre, Council of Scientific and Industrial Research (CSIR), Visakhapatnam, India M. J. McPhaden, NOAA/Pacific Marine Research Laboratory, Seattle, WA, USA Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description:    The impact of land use change on regional climate can be substantial but also is variable in space and time. Past observational and modeling work suggests that in a ‘Mediterranean’ climate such as in California’s Central Valley, the impact of irrigated agriculture can be large in the dry season but negligible in the wet season due to seasonal variation in surface energy partitioning. Here we report further analysis of regional climate model simulations showing that diurnal variation in the impact of irrigated agriculture on climate similarly reflects variation in surface energy partitioning, as well as smaller changes in net radiation. With conversion of natural vegetation to irrigated agriculture, statistically significant decreases of 4–8 K at 2 m occurred at midday June–September, and small decreases of ~1 K occurred in winter months only in relatively dry years. This corresponded to reduced sensible heat flux of 100–350 W m −2 and increased latent heat fluxes of 200–450 W m −2 at the same times and in the same months. We also observed decreases of up to 1,500 m in boundary layer height at midday in summer months, and marginally significant reductions in surface zonal wind speed in July and August at 19:00 PST. The large decrease in daytime temperature due to shifts in energy partitioning overwhelmed any temperature increase related to the reduced zonal sea breeze. Such changes in climate and atmospheric dynamics from conversion to (or away from) irrigated agriculture could have important implications for regional air quality in California’s Central Valley. Content Type Journal Article Pages 1-13 DOI 10.1007/s00382-011-1123-0 Authors Lara M. Kueppers, School of Natural Sciences and Sierra Nevada Research Institute, University of California, Merced, 5200 N. Lake Rd., Merced, CA 95343, USA Mark A. Snyder, Climate Change and Impacts Laboratory, Department of Earth and Planetary Sciences, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description:    The present study focuses on the leading interannual mode of continental-scale atmospheric variability over South America, which is characterized by an equivalent barotropic vortex (referred to as VOSA in the text) centered over the eastern subtropical coast of the continent. The principal aim is to determine whether and in what season VOSA is the downstream extension of the leading Pacific South American mode (PSA1). Another objective is to examine the extent to which VOSA and PSA1 are forced by El Niño Southern Oscillation (ENSO). The research is based on examination of reanalysis data and output of experiments with an atmospheric general circulation model. The emphasis is on the southern spring, summer and fall seasons, during which VOSA modulates the interannual precipitation variability over the continent. A similar relationship is not found during the southern winter. It is found that VOSA is an integral part of PSA1 during spring and fall. In these seasons, PSA1/VOSA is originated primarily by large-scale atmospheric internal variability with the forcing by ENSO accounting for 14 and 8% of the total variance, respectively. During the southern summer season, when ENSO peaks, PSA1 is not a dominant mode of atmospheric variability, and VOSA primarily results from continental-scale internal variability. Content Type Journal Article Pages 1-15 DOI 10.1007/s00382-011-1116-z Authors Laura Zamboni, Mathematics and Computer Science Division, Argonne National Laboratory, 9700 S.Cass Ave TCS Bldg #240, Argonne, IL 60439, USA Fred Kucharski, Earth System Physics Section, Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34014 Trieste, Italy C. Roberto Mechoso, Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, CA, USA Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description:    The leading mode of southern hemisphere (SH) climatic variability, the southern annular mode (SAM), has recently seen a shift towards its positive phase due to stratospheric ozone depletion and increasing greenhouse gas (GHG) concentrations. Here we examine how sensitive the SAM (defined as the leading empirical orthogonal function of SH sea level pressure anomalies) is to future GHG concentrations. We determine its likely evolution for three intergovernmental panel on climate change (IPCC) special report on emission scenarios (SRES) for austral summer and winter, using a multi-model ensemble of IPCC fourth assessment report models which resolve stratospheric ozone recovery. During the period of summer ozone recovery (2000–2050), the SAM index exhibits weakly negative, statistically insignificant trends due to stratospheric ozone recovery which offsets the positive forcing imposed by increasing GHG concentrations. Thereafter, positive SAM index trends occur with magnitudes that show sensitivity to the SRES scenario utilised, and thus future GHG emissions. Trends are determined to be strongest for SRES A2, followed by A1B and B1, respectively. The winter SAM maintains a similar dependency upon GHG as summer, but over the entire twenty-first century and to a greater extent. We also examine the influence of ozone recovery by comparing results to models that exclude stratospheric ozone recovery. Projections are shown to be statistically different from the aforementioned results, highlighting the importance of ozone recovery in governing SAM-evolution. We therefore demonstrate that the future SAM will depend both upon GHG emissions and stratospheric ozone recovery. Content Type Journal Article Pages 1-10 DOI 10.1007/s00382-011-1121-2 Authors Graham R. Simpkins, Climatic Research Unit, School of Environmental Science, University of East Anglia, Norwich, UK Alexey Yu. Karpechko, Climatic Research Unit, School of Environmental Science, University of East Anglia, Norwich, UK Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description:    The El Niño Southern Oscillation (ENSO) is known as the strongest natural inter-annual climate signal, having widespread consequences on the global weather, climate, ecology and even on societies. Understanding ENSO variations in a changing climate is therefore of primordial interest to both the climate community and policy makers. In this study, we focus on the change in ENSO nonlinearity due to climate change. We first analysed high statistical moments of observed Sea Surface Temperatures (SST) timeseries of the tropical Pacific based on the measurement of the tails of their Probability Density Function (PDF). This allows defining relevant metrics for the change in nonlinearity observed over the last century. Based on these metrics, a zonal “see-saw” (oscillation) in nonlinearity patterns is highlighted that is associated with the change in El Niño characteristics observed in recent years. Taking advantage of the IPCC database and the different projection scenarios, it is showed that changes in El Niño statistics (or “flavour”) from a present-day climate to a warmer climate are associated with a significant change in nonlinearity patterns. In particular, in the twentieth century climate, the “conventional” eastern Pacific El Niño relates more to changes in nonlinearity than to changes in mean state whereas the central Pacific El Niño (or Modoki El Niño) is more sensitive to changes in mean state than to changes in nonlinearity. An opposite behaviour is found in a warmer climate, namely the decreasing nonlinearity in the eastern Pacific tends to make El Niño less frequent but more sensitive to mean state, whereas the increasing nonlinearity in the west tends to trigger Central Pacific El Niño more frequently. This suggests that the change in ENSO statistics due to climate change might result from changes in the zonal contrast of nonlinearity characteristics across the tropical Pacific. Content Type Journal Article Pages 1-21 DOI 10.1007/s00382-011-1119-9 Authors J. Boucharel, Université de Toulouse; UPS (OMP-PCA), LEGOS, 14 Av. Edouard Belin, 31400 Toulouse, France B. Dewitte, Université de Toulouse; UPS (OMP-PCA), LEGOS, 14 Av. Edouard Belin, 31400 Toulouse, France Y. du Penhoat, Université de Toulouse; UPS (OMP-PCA), LEGOS, 14 Av. Edouard Belin, 31400 Toulouse, France B. Garel, Institut de Mathématiques de Toulouse (UPS), Université de Toulouse, INP-ENSEEIHT, Toulouse, France S.-W. Yeh, Department of Environmental Marine Science, Hanyang University, Ansan, South Korea J.-S. Kug, Korea Ocean Research and Development Institute, Ansan, South Korea Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description: Erratum to: Climate change under aggressive mitigation: the ENSEMBLES multi-model experiment Content Type Journal Article Pages 1-2 DOI 10.1007/s00382-011-1102-5 Authors T. C. Johns, Hadley Centre, Met Office, FitzRoy Road, Exeter, EX1 3PB UK J.-F. Royer, Centre National de Recherches Météorologiques-Groupe d’Etude de l’Atmosphère Météorologique (CNRM-GAME Meteo-France CNRS), 42 Avenue G. Coriolis, 31057 Toulouse, France I. Höschel, Institute for Meteorology, Freie Universität Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165 Berlin, Germany H. Huebener, Hessian Agency for the Environment and Geology, Rheingaustraße 186, 65203 Wiesbaden, Germany E. Roeckner, Max Planck Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany E. Manzini, Max Planck Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany W. May, Danish Climate Centre, Danish Meteorological Institute, Lyngbyvej 100, 2100 Copenhagen, Denmark J.-L. Dufresne, UMR 8539 CNRS, ENS, UPMC, Ecole Polytechnique, Laboratoire de Météorologie Dynamique (LMD/IPSL), 75252 Paris Cedex 05, France O. H. Otterå, Nansen Environmental and Remote Sensing Center, Thormøhlensgt. 47, 5006 Bergen, Norway D. P. van Vuuren, Utrech University, Utrech, The Netherlands D. Salas y Melia, Centre National de Recherches Météorologiques-Groupe d’Etude de l’Atmosphère Météorologique (CNRM-GAME Meteo-France CNRS), 42 Avenue G. Coriolis, 31057 Toulouse, France M. A. Giorgetta, Max Planck Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany S. Denvil, FR 636 CNRS, UVSQ, UPMC, Institut Pierre Simon Laplace (IPSL), 75252 Paris Cedex 05, France S. Yang, Danish Climate Centre, Danish Meteorological Institute, Lyngbyvej 100, 2100 Copenhagen, Denmark P. G. Fogli, Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC), Bologna, Italy J. Körper, Institute for Meteorology, Freie Universität Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165 Berlin, Germany J. F. Tjiputra, Department of Geophysics, University of Bergen, Allegt. 70, 5007 Bergen, Norway E. Stehfest, Planbureau voor de Leefomgeving (PBL), Bilthoven, The Netherlands C. D. Hewitt, Hadley Centre, Met Office, FitzRoy Road, Exeter, EX1 3PB UK Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description:    The evolution of El Niño-Southern Oscillation (ENSO) variability can be characterized by various ocean–atmosphere feedbacks, for example, the influence of ENSO related sea surface temperature (SST) variability on the low-level wind and surface heat fluxes in the equatorial tropical Pacific, which in turn affects the evolution of the SST. An analysis of these feedbacks requires physically consistent observational data sets. Availability of various reanalysis data sets produced during the last 15 years provides such an opportunity. A consolidated estimate of ocean surface fluxes based on multiple reanalyses also helps understand biases in ENSO predictions and simulations from climate models. In this paper, the intensity and the spatial structure of ocean–atmosphere feedback terms (precipitation, surface wind stress, and ocean surface heat flux) associated with ENSO are evaluated for six different reanalysis products. The analysis provides an estimate for the feedback terms that could be used for model validation studies. The analysis includes the robustness of the estimate across different reanalyses. Results show that one of the “coupled” reanalysis among the six investigated is closer to the ensemble mean of the results, suggesting that the coupled data assimilation may have the potential to better capture the overall atmosphere–ocean feedback processes associated with ENSO than the uncoupled ones. Content Type Journal Article Pages 1-14 DOI 10.1007/s00382-011-1104-3 Authors Arun Kumar, Climate Prediction Center, NCEP/NWS/NOAA, 5200 Auth Road (Suite 605), Camp Springs, MD 20746, USA Zeng-Zhen Hu, Climate Prediction Center, NCEP/NWS/NOAA, 5200 Auth Road (Suite 605), Camp Springs, MD 20746, USA Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575

Description:    The GLACIOCLIM-SAMBA (GS) Antarctic accumulation monitoring network, which extends from the coast of Adelie Land to the Antarctic plateau, has been surveyed annually since 2004. The network includes a 156-km stake-line from the coast inland, along which accumulation shows high spatial and interannual variability with a mean value of 362 mm water equivalent a −1 . In this paper, this accumulation is compared with older accumulation reports from between 1971 and 1991. The mean and annual standard deviation and the km-scale spatial pattern of accumulation were seen to be very similar in the older and more recent data. The data did not reveal any significant accumulation trend over the last 40 years. The ECMWF analysis-based forecasts (ERA-40 and ERA-Interim), a stretched-grid global general circulation model (LMDZ4) and three regional circulation models (PMM5, MAR and RACMO2), all with high resolution over Antarctica (27–125 km), were tested against the GS reports. They qualitatively reproduced the meso-scale spatial pattern of the annual-mean accumulation except MAR. MAR significantly underestimated mean accumulation, while LMDZ4 and RACMO2 overestimated it. ERA-40 and the regional models that use ERA-40 as lateral boundary condition qualitatively reproduced the chronology of interannual variability but underestimated the magnitude of interannual variations. Two widely used climatologies for Antarctic accumulation agreed well with the mean GS data. The model-based climatology was also able to reproduce the observed spatial pattern. These data thus provide new stringent constraints on models and other large-scale evaluations of the Antarctic accumulation. Content Type Journal Article Pages 1-12 DOI 10.1007/s00382-011-1103-4 Authors Cécile Agosta, UJF-Grenoble 1 / CNRS, Laboratoire de Glaciologie et de Géophysique de l’Environnement UMR 5183, 54 rue Molière, BP 96, 38402 Saint Martin d’Hères Cedex, France Vincent Favier, UJF-Grenoble 1 / CNRS, Laboratoire de Glaciologie et de Géophysique de l’Environnement UMR 5183, 54 rue Molière, BP 96, 38402 Saint Martin d’Hères Cedex, France Christophe Genthon, CNRS / UJF-Grenoble 1, Laboratoire de Glaciologie et de Géophysique de l’Environnement UMR 5183, 54 rue Molière, BP 96, 38402 Saint Martin d’Hères Cedex, France Hubert Gallée, CNRS / UJF-Grenoble 1, Laboratoire de Glaciologie et de Géophysique de l’Environnement UMR 5183, 54 rue Molière, BP 96, 38402 Saint Martin d’Hères Cedex, France Gerhard Krinner, CNRS / UJF-Grenoble 1, Laboratoire de Glaciologie et de Géophysique de l’Environnement UMR 5183, 54 rue Molière, BP 96, 38402 Saint Martin d’Hères Cedex, France Jan T. M. Lenaerts, Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands Michiel R. van den Broeke, Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands Journal Climate Dynamics Online ISSN 1432-0894 Print ISSN 0930-7575