[1] The intensity and structure of the Northern Hemisphere DJF Hadley cell as depicted in various commonly used data sets are examined. We find that the NCEP/NCAR and ECMWF reanalyses show a statistically significant intensification of their Hadley circulation throughout their periods. In marked contrast the NCEP-DOE reanalysis does not show any discernible trend over its period. Furthermore, the Hadley cell structure differs substantially from the other two reanalyses. We also examine a data set of global rawinsonde observations in which the Hadley cell shows no intensification. Finally, we investigate the Hadley cell simulated by an atmospheric GCM. The ensemble mean shows a statistically significant intensification, though it is smaller in magnitude than the reanalyses. We conclude that the two major reanalyses appear to be in agreement on the strengthening of the Hadley cell in recent decades. However, discrepancies among data sets do raise questions about the robustness of this strengthening.Citation: Mitas, C. M., and A. Clement (2005), Has the Hadley cell been strengthening in recent decades?, Geophys.
[1] The behavior of the Hadley cell and the thermodynamic structure of the tropical atmosphere is analyzed over the period 1979 -2000 in climate models and reanalyses. Significant trends in the strength of the Hadley cell are present in reanalyses that are not reproduced by models. Analysis of the thermodynamic structure also shows significant discrepancies between models and reanalyses, the former show warming aloft and increased static stability while the latter show a cooling trend and decreased static stability in the tropical mid-troposphere. Additional energy balance analysis reveals that models and reanalyses have a fundamentally different balance between diabatic heating, circulation and thermodynamic structure over the period 1979 -2000. Uncertainties in the observations of tropospheric temperatures as well as potential biases and errors in the climate models raise questions about the true long-term behavior of the thermodynamic structure of the tropical troposphere and the Hadley cell. Citation: Mitas, C. M., and A. Clement
An index of Pacific decadal variability based on a multivariate empirical orthogonal function analysis of National Centers for Environmental Prediction reanalysis is used to extract associated signals in satellite‐based measurements of atmospheric parameters. This index captures the 1976–1977 “El Niño–Southern Oscillation (ENSO)‐like” warming shift of sea surface temperatures (SST) as well as a more recent transition of opposite sign in the 1990s. Utilizing measurements of water vapor, wind speed, precipitation, long‐wave radiation, as well as surface observations, our analysis shows evidence of the atmospheric changes in the mid‐1990s that accompanied the “ENSO‐like” interdecadal SST changes.
Abstract. In this paper, we present a conceptual framework for modelling clustered natural hazards that makes use of historical event data as a starting point. We review a methodology for modelling clustered natural hazard processes called Poisson mixtures. This methodology is suited to the application we have in mind as it naturally models processes that yield cross-event correlation (unlike homogeneous Poisson models), has a high degree of tunability to the problem at hand and is analytically tractable. Using European windstorm data as an example, we provide evidence that the historical data show strong evidence of clustering. We then develop Poisson and Clustered simulation models for the data, demonstrating clearly the superiority of the Clustered model which we have implemented using the Poisson mixture approach. We then discuss the implications of including clustering in models of prices of catXL contracts, one of the most commonly used mechanisms for transferring risk between primary insurers and reinsurers. This paper provides a number of unique insights into the impact clustering has on modelled catXL contract prices. The simple modelling example in this paper provides a clear and insightful starting point for practitioners tackling more complex natural hazard risk problems.
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