The report captures the achievements made by WCRP and its Core Projects since 2009.

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In their online first JGR article from 25 March 2013, SPARC DynVar scientist Andrew Charlton-Perez and co-authors describe the main differences in simulations of stratospheric climate and variability by models within the fifth Coupled Model Intercomparison Project (CMIP5) that have a model top above the stratopause and relatively fine stratospheric vertical resolution (high-top), and those that have a model top below the stratopause (low-top).

Although the simulation of mean stratospheric climate by the two model ensembles is similar, the low-top model ensemble has very weak stratospheric variability on daily and interannual time scales. The frequency of major sudden stratospheric warming events is strongly underestimated by the low-top models with less than half the frequency of events observed in the reanalysis data and high-top models. The lack of stratospheric variability in the low-top models affects their stratosphere-troposphere coupling, resulting in short-lived anomalies in the Northern Annular Mode, which do not produce long-lasting tropospheric impacts, as seen in observations. The lack of stratospheric variability, however, does not appear to have any impact on the ability of the low-top models to reproduce past stratospheric temperature trends. The authors find little improvement in the simulation of decadal variability for the high-top models compared to the low-top, which is likely related to the fact that neither ensemble produces a realistic dynamical response to volcanic eruptions.

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The review period for expert and government review of the 2nd order draft of the Working Group II contribution to the Fifth IPCC Assessment Report will run from 25 March until 24 May 2013.

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Find an article on the joint IGAC-SPARC Chemistry Climate Model Initiative (CCMI) on page 12 of the IGAC newsletter.

In their Journal of Climate article, SPARC Data Centre scientist Marv Geller and co-authors conduct for the first time, a formal comparison between gravity wave momentum fluxes in models and those derived from observations.

Abstract. Although gravity waves occur over a wide range of spatial and temporal scales, the authors concentrate in this paper on scales that are being parameterized in present climate models, sub-1,000 km scales. Only observational methods that permit derivation of gravity wave momentum fluxes over large geographical areas are discussed, and these are from satellite temperature measurements, constant-density long-duration balloons, and high vertical-resolution radiosonde data. The models discussed include two high-resolution models in which gravity waves are explicitly modeled, Kanto and CAM5, and three climate models containing gravity wave parameterizations, MAECHAM5, HadGEM3, and GISS. Measurements generally show similar flux magnitudes as in models, except that the fluxes derived from satellite measurements fall off more rapidly with height. This is likely due to limitations on the observable range of wavelengths, although other factors may contribute. When one accounts for this more rapid fall-off, the geographical distribution of the fluxes from observations and models compare reasonably well, except for certain features that depend on the specification of the non-orographic gravity wave source functions in the climate models. For instance, both the observed fluxes and those in the high-resolution models are very small at summer high latitudes, but this is not the case for some of the climate models. This comparison between gravity wave fluxes from climate models, high-resolution models, and fluxes derived from observations indicates that such efforts offer a promising path toward improving specifications of gravity wave sources in climate models.

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