Results 1 - 10 of 2076
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[en] Although the term 'east coast low' is normally associated with intense cyclones near the east coast of mainland Australia, cutoff lows of similar type also affect Tasmania. This paper demonstrates that the cutoff low is a major source of rainfall for the agricultural districts and water catchments of eastern Tasmania. In particular, an analysis of synoptic systems and daily rainfall reveals that cutoff lows are responsible for almost 50% of April to October rainfall in parts of the northeast and a slightly lower proportion in the southeast. The other large contribution to rainfall is from frontal systems but the relative effects of the various synoptic types vary widely across the state as a result of the complex topography. Cutoff lows commonly form the cyclonic portion of a blocking dipole which can have opposing influences on Tasmanian rainfall. The high latitude anticyclone suppresses rainfall in western and southwestern Tasmania, while the cutting off of a relatively small cyclonic component equatorwards of the high frequently results in enhanced rainfall over eastern Tasmania. Results from two climate models indicate that the accurate simulation of blocking and cutoff lows remains difficult to achieve and this has implications for projections of Tasmanian rainfall on seasonal and longer time scales.
[en] The representation of land surface processes and fluxes in climate models critically affects the simulation of near-surface climate over land. Here we present an evaluation of COSMO-CLM2, a model which couples the COSMO-CLM Regional Climate Model to the Community Land Model (CLM4.0). CLM4.0 provides a more detailed representation of land processes compared to the native land surface scheme in COSMO-CLM. We perform historical reanalysis-driven simulations over Europe with COSMO-CLM2 following the EURO-CORDEX intercomparison protocol. We then evaluate simulations performed with COSMO-CLM2, the standard COSMO-CLM and other EURO-CORDEX RCMs against various observational datasets of temperature, precipitation and surface fluxes. Overall, the results indicate that COSMO-CLM2 outperforms both the standard COSMO-CLM and the other EURO-CORDEX models in simulating sensible, latent and surface radiative fluxes as well as 2-meter temperature across different seasons and regions. The performance improvement is particularly strong for turbulent fluxes and for daily maximum temperatures and more modest for daily minimum temperature, suggesting that land surface processes affect daytime even more than nighttime conditions. COSMO-CLM2 also alleviates a long-standing issue of overestimation of interannual summer temperature variability present in most EURO-CORDEX RCMs. Finally, we show that several factors contribute to these improvements, including the representation of evapotranspiration, radiative fluxes and ground heat flux. Overall, these results demonstrate that land processes represent a key area of development to tackle current deficiencies in RCMs. (letter)
[en] This special report is the third in a series of reports aimed at explaining and assessing our current understanding of the more complex and controversial aspect of climate change science. It describes recent results from climate change experiments undertaken with the first version of the Canadian coupled climate model, including a discussion of the credibility and limitations of the results. The results are also compared to those reported by other climate modelling groups. The report concludes with a brief review of current and future developments in Canadian climate modelling research. The results of modelling studies strongly suggest that the probability of extensive climate change is both real and imminent. They suggest that the rate and magnitude of warming over the next century is likely to be in the upper range of previous expectations, if not higher. While modelling studies provide approximations and not precise forecasts of future conditions, if these approximations are close to the mark, as there is every reason to believe that they are, both natural ecosystems and human societies will have difficulty adapting to a rate of climatic change that is virtually without precedent. Clearly, the related risks are significant, and the need for urgent action to reduce greenhouse gas emissions through the Kyoto Protocol and other relevant mechanisms, is long overdue. 12 refs., 20 figs
[en] Extra-tropical cyclones that develop near the east coast of Australia often have severe consequences such as flash flooding and damaging winds and seas, as well as beneficial consequences such as being responsible for heavy rainfall events that contribute significantly to total rainfall and runoff. There is subjective evidence that the development of most major events, commonly known as East Coast Lows, is associated with the movement of a high amplitude upper-tropospheric trough system over eastern Australia. This paper examines a number of upper-tropospheric diagnostic quantities that might provide a basis for preparing a climatology of the large-scale drivers of east-coast cyclogenesis. A preliminary climatology of these diagnostic quantities, based on ECMWF interim reanalyses, is compared with a database of observed East Coast Low events. The potential application of these diagnostics to global climate model simulations of past and future climates is also discussed.