An approximate energy cycle for inter-member variability in ensemble simulations of a regional climate model

The presence of internal variability (IV) in ensembles of nested regional climate model (RCM) simulations is now widely acknowledged in the community working on dynamical downscaling. IV is defined as the inter-member spread between members in an ensemble of simulations performed by a given RCM driven by identical lateral boundary conditions (LBC), where different members are being initialised at different times. The physical mechanisms responsible for the time variations and structure of such IV have only recently begun to receive attention. Recent studies have shown empirical evidence of a close parallel between the energy conversions associated with the time fluctuations of IV in ensemble simulations of RCM and the energy conversions taking place in weather systems. Inspired by the classical work on global energetics of weather systems, we sought a formulation of an energy cycle for IV that would be applicable for limited-area domain. We develop here a novel formalism based on local energetics that can be applied to further our understanding IV. Prognostic equations for ensemble-mean kinetic energy and available enthalpy are decomposed into contributions due to ensemble-mean variables (EM) and those due to deviations from the ensemble mean (IV). Together these equations constitute an energy cycle for IV in ensemble simulations of RCM. Although the energy cycle for IV was developed in a context entirely different from that of energetics of weather systems, the exchange terms between the various reservoirs have a rather similar mathematical form, which facilitates some interpretations of their physical meaning

Energy cycle associated with inter-member variability in a large ensemble of simulations with the Canadian RCM (CRCM5)

In an ensemble of Regional Climate Model\ud (RCM) simulations where different members are initialised\ud at different times but driven by identical lateral\ud boundary conditions, the individual members provide\ud different, but equally acceptable, weather sequences.\ud In others words, RCM simulations exhibit the phenomenon\ud of Internal Variability (or inter-member variability—\ud IV), defined as the spread between members in an\ud ensemble of simulations. Our recent studies reveal that\ud RCM’s IV is associated with energy conversions similar\ud to those taking place in weather systems. By analogy\ud with the classical work on global energetics of weather\ud systems, a formulation of an energy cycle for IV has been\ud developed that is applicable over limited-area domains.\ud Prognostic equations for ensemble-mean kinetic energy\ud and available enthalpy are decomposed into contributions\ud due to ensemble-mean variables and those due to\ud deviations from the ensemble mean (IV). Together these\ud equations constitute an energy cycle for IV in ensemble\ud simulations of an RCM. A 50-member ensemble of\ud 1-year simulations that differ only in their initial conditions\ud was performed with the fifth-generation Canadian\ud RCM (CRCM5) over an eastern North America domain.\ud The various energy reservoirs of IV and exchange terms\ud between reservoirs were evaluated; the results show a\ud remarkably close parallel between the energy conversions\ud associated with IV in ensemble simulations of RCM and the energy conversions taking place in weather systems\ud in the real atmosphere

Constructed wetland technology for the treatment and reuse of urban household greywater under conditions of Africa's Sahel region

Three pilot systems of a constructed wetland were assessed to advance the urban reuse of greywater for household gardening in areas of the world representative of Africa's Sahel (one unplanted and two planted with local species, namely Andropogon gayanus and Chrysopogon zizanioides). Principal component analysis showed planted systems provided higher removal efficiencies than the unplanted system and A. gayanus performed better for treating most water quality parameters. As expected, removal efficiencies for suspended solids (SS) and chemical oxygen demand (COD) were greater than 90% in all filters. The removal of five-day biochemical oxygen demand (BOD5) was, however, significantly greater in the filter planted with A. gayanus than in the unplanted control. For plant-beneficial parameters such as nutrients (NO3−, NO2−, NH4+, and PO43−), the removal in the planted filters was significantly higher than in the unplanted filter (>90% versus 73%–78%). The reduction of fecal coliforms was significantly greater in the two planted systems and exceeded 2.5 log10 removal. Analysis of the microbial water quality characteristics showed the concentration of fecal microbial indicators would achieve WHO guidelines for restricted irrigation with retention of some embedded nutrients, thus reducing pressures on areas experiencing climate variability, water scarcity, and land degradation. HIGHLIGHTS Planted filters produced treated greywater compliant with the WHO reuse guidelines for restricted irrigation.; Reduction of fecal coliforms was highest in the two planted systems, exceeding 2.5 log10 removal.; Filter planted with A. gayanus exhibited higher removal efficiencies of organic matter than the filter planted with C. zizanioides.; A. gayanus performed better than C. zizanioides for most water quality effluent parameters.

Future Projections of Wind Energy Potentials in the Arctic for the 21st Century Under the RCP8.5 Scenario From Regional Climate Models (Arctic-CORDEX)

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