Abstract
Available Enthalpy (AE) and Kinetic Energy (KE) associated with the natural Transient-Eddy (or Time-Variability, TV) and models’ Internal Variability (or Inter-member Variability, IV) are studied using two ensembles of simulations, one from a nested Regional Climate Model (RCM) driven by reanalyses over a regional domain covering eastern North America, and one from a Global Climate Model (GCM), and the Era-interim reanalyses as reference. The fields of TV and IV energies are first examined, both globally and over the regional domain. Results from GCM simulations reveal that GCM TV is similar to that of reanalyses, confirming the realism of the GCM simulations, and TV and IV are approximately equal, in agreement with the ergodicity property. For RCM simulations, TV energies are similar to those of reanalyses driving them. On the other hand, the IV energies of reanalyses-driven RCM simulations are much smaller than those of the GCM, because of the control exerted by the lateral boundary conditions imposed in nested models. While GCM IV energies present similar seasonal variations as the TV energies, the RCM IV greatly fluctuates in time, with short episodes of large variations. The second part of this study is devoted to the analysis of TV and IV energetic budgets. Results indicate similar physical interpretations of conversions, generations and destructions for both TV and IV energetics, although TV is associated with natural phenomena of weather disturbances and IV is a model feature contributing to the uncertainties of simulations.
Highlights
Climate models are powerful tools that allow better understanding of past, present and future climatic phenomena
On the other hand maximum values of KTV occur over the oceans, in the circumpolar belt around Antarctica and off the East coasts of the North American and Eurasian continents, in association with the strongest storms tracks in the respective winter, with values reaching about 20 × 105 J/m2
We compare transient-eddy variability (TV) and inter-member variability (IV) energy contributions computed over the regional domain shown as the blue rectangle in Fig. 1c, using data from reanalysis, Global Climate Model (GCM) and Regional Climate Model (RCM)
Summary
Climate models are powerful tools that allow better understanding of past, present and future climatic phenomena. Nikiéma and Laprise (2011a, b) have developed a diagnostic approach that furthers our physical understanding of RCM’s IV as a source of uncertainty They established IV diagnostic equations for different atmospheric variables taking into account the model equations and Reynolds’ decomposition applied to the atmospheric field equations, as well as some statistic tools since an ensemble of simulations is considered. Following an alternative approach, Marquet (1991, 2003a, b) proposed a formalism based on Available Enthalpy (AE) instead of APE Inspired by these previous works, Nikiéma and Laprise (2013, 2015) established an approximate energy cycle of IV applicable for a limited-area domain, and afterward adapted to study TV in a particular intense storm observed over the North America (Clément et al 2016).
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