Regionally aggregated, stitched and de‐drifted CMIP‐climate data, processed with netCDF‐SCM v2.0.0

The world's most complex climate models are currently running a range of experiments as part of the Sixth Coupled Model Intercomparison Project (CMIP6). Added to the output from the Fifth Coupled Model Intercomparison Project (CMIP5), the total data volume will be in the order of 20PB. Here, we present a dataset of annual, monthly, global, hemispheric and land/ocean means derived from a selection of experiments of key interest to climate data analysts and reduced complexity climate modellers. The derived dataset is a key part of validating, calibrating and developing reduced complexity climate models against the behaviour of more physically complete models. In addition to its use for reduced complexity climate modellers, we aim to make our data accessible to other research communities. We facilitate this in a number of ways. Firstly, given the focus on annual, monthly, global, hemispheric and land/ocean mean quantities, our dataset is orders of magnitude smaller than the source data and hence does not require specialized ‘big data’ expertise. Secondly, again because of its smaller size, we are able to offer our dataset in a text-based format, greatly reducing the computational expertise required to work with CMIP output. Thirdly, we enable data provenance and integrity control by tracking all source metadata and providing tools which check whether a dataset has been retracted, that is identified as erroneous. The resulting dataset is updated as new CMIP6 results become available and we provide a stable access point to allow automated downloads. Along with our accompanying website (cmip6.science.unimelb.edu.au), we believe this dataset provides a unique community resource, as well as allowing non-specialists to access CMIP data in a new, user-friendly way

Effects of the quasi-biennial oscillation on low-latitude transport in the stratosphere as derived from model driven trajectory calculations

The quasi-biennial oscillation (QBO) of stratospheric zonal winds induces a secondary meridional circulation (SMC) consisting of QBO variations in meridional and vertical winds. In this work, we investigate how these instantaneous meridional circulation anomalies add over time to variations of stratospheric transport. To that end, we compute backward parcel trajectories on the basis of the output of a chemistry-climate model (CCM). At the equator, the trajectories show the strongest vertical parcel displacement over a seasonal timescale when the QBO progresses toward easterly phase in the middle stratosphere. During the solstitial seasons a large number of parcels come from the summer hemisphere, causing in addition a QBO variation in the spread of the total ascent among equatorial parcels. A QBO effect on meridional transport is diagnosed from PV gradients during summer in the easterly phase of the QBO, which suggests a variation of the tropical-subtropical barrier strength. Analyses of the parcel trajectories and CCM trace gas distributions confirm this finding. We suggest that this variation is due to the combined effects of QBO and annual variation in meridional advection and in wave-induced eddy transport

Der Einfluss der quasi-zweijaehrigen Oszillation auf die allgemeine Zirkulation: Modellsimulationen mit ECHAM4

In dieser Arbeit wurden fuenf verschiedene potentielle Einflussgebiete der QBO untersucht. Dies sind die Dynamik im QBO-Bereich, physikalische Mechanismen, durch die die QBO die Zirkulation in der Troposphaere modulieren kann, der QBO-Beitrag zur Variabilitaet des indischen Suedwestmonsuns, die Beeinflussung der stratosphaerischen Winterzirkulation und die Modulation des Wasserdampftransports durch die tropische Tropopause. (orig./KW)This paper looks at five different potential areas which may be influence by QBOs. These are: dynamics in the QBO range, physical mechanisms by way of which QBO may modulate circulation in the troposphere, the contribution of QBO on the variability of the Southwestern Monsun in India, the influence on stratospheric winter circulation and modulation of water vapour transport by the tropic tropopause. (orig./KW)SIGLEAvailable from TIB Hannover: RR 9(40) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Kelvin and Rossby-gravity wave packets in the lower stratosphere of some high-top CMIP5 models

International audienceWe analyze the stratospheric Kelvin and Rossby-gravity wave packets with periods of a few days in nine high-top (i.e., with stratosphere) models of the fifth Coupled Model Intercomparison Project (CMIP5). These models simulate realistic aspects of these waves and represent them better than the tropospheric convectively coupled waves analyzed in previous studies. There is nevertheless a large spread among the models, and those with a quasi-biennial oscillation (QBO) produce larger amplitude waves than the models without a QBO. For the Rossby-gravity waves this is explained by the fact that models without a QBO never have positive zonal mean zonal winds in the lower stratosphere, a situation that is favorable to the propagation of Rossby-gravity waves. For the Kelvin waves, larger amplitudes in the presence of a QBO is counter intuitive because Kelvin waves are expected to have larger amplitude when the zonal mean zonal wind is negative, and this is always satisfied in models without a QBO. We attribute the larger amplitude to the fact that models tuned to have a QBO require finer vertical resolution in the stratosphere. We also find that models with large precipitation variability tend to produce larger amplitude waves. However, the effect is not as pronounced as was found in previous studies. In fact, even models with weak precipitation variability still have quite realistic stratospheric waves, indicating either that (i) other sources can be significant or that (ii) the dynamical filtering mitigates the differences in the sources between models. © 2014. American Geophysical Union. All Rights Reserved

The simulation of the Antarctic ozone hole by chemistry-climate models

International audienceWhile chemistry-climate models are able to reproduce many characteristics of the global total column ozone field and its long-term evolution, they have fared less well in simulating the commonly used diagnostic of the area of the Antarctic ozone hole i.e. the area within the 220 Dobson Unit (DU) contour. Two possible reasons for this are: (1) the underlying Global Climate Model (GCM) does not correctly simulate the size of the polar vortex, and (2) the stratospheric chemistry scheme incorporated into the GCM, and/or the model dynamics, results in systematic biases in the total column ozone fields such that the 220 DU contour is no longer appropriate for delineating the edge of the ozone hole. Both causes are examined here with a view to developing ozone hole area diagnostics that better suit measurement-model inter-comparisons. The interplay between the shape of the meridional mixing barrier at the edge of the vortex and the meridional gradients in total column ozone across the vortex edge is investigated in measurements and in 5 chemistry-climate models (CCMs). Analysis of the simulation of the polar vortex in the CCMs shows that the first of the two possible causes does play a role in some models. This in turn affects the ability of the models to simulate the large observed meridional gradients in total column ozone. The second of the two causes also strongly affects the ability of the CCMs to track the observed size of the ozone hole. It is shown that by applying a common algorithm to the CCMs for selecting a delineating threshold unique to each model, a more appropriate diagnostic of ozone hole area can be generated that shows better agreement with that derived from observations

The effects of aggressive mitigation on steric sea level rise and sea ice changes

International audienceWith an increasing political focus on limiting global warming to less than 2 °C above pre-industrial levels it is vital to understand the consequences of these targets on key parts of the climate system. Here, we focus on changes in sea level and sea ice, comparing twenty-first century projections with increased greenhouse gas concentrations (using the mid-range IPCC A1B emissions scenario) with those under a mitigation scenario with large reductions in emissions (the E1 scenario). At the end of the twenty-first century, the global mean steric sea level rise is reduced by about a third in the mitigation scenario compared with the A1B scenario. Changes in surface air temperature are found to be poorly correlated with steric sea level changes. While the projected decreases in sea ice extent during the first half of the twenty-first century are independent of the season or scenario, especially in the Arctic, the seasonal cycle of sea ice extent is amplified. By the end of the century the Arctic becomes sea ice free in September in the A1B scenario in most models. In the mitigation scenario the ice does not disappear in the majority of models, but is reduced by 42 % of the present September extent. Results for Antarctic sea ice changes reveal large initial biases in the models and a significant correlation between projected changes and the initial extent. This latter result highlights the necessity for further refinements in Antarctic sea ice modelling for more reliable projections of future sea ice. © 2012 The Author(s)

Erratum to: Climate change under aggressive mitigation: The ENSEMBLES multi-model experiment (Clim Dyn, (2011), 10.1007/s00382-011-1005-5)

International audienceUnfortunately, in the aforementioned contribution, Table 2 of this paper erroneously reported two separate rows of data for the BCM-C model for both the A1B and E1 scenarios, only one of which was correct in each case. The lower of the two rows of data for each scenario (i.e. those corresponding to T changes of 2.44 K for A1B and 1.18 K for E1) contained correct data. The upper rows of data reported (i.e. those corresponding to T changes of 2.65 K for A1B and 1.38 for E1) contained some errors and should not have appeared. A corrected version of Table 2 appears below