Cyclone tropical | EPFL Graph Search

Un cyclone tropical est un type de cyclone (dépression) qui prend forme dans les océans de la zone intertropicale à partir d'une perturbation atmosphérique qui s'organise en dépression tropicale puis en tempête. Son stade final est connu sous divers noms à travers le monde : ouragan dans l'Atlantique nord et le Pacifique Nord-Est, typhon en Asie de l'Est et cyclone dans les autres bassins océaniques. Structurellement, un cyclone tropical est une large zone de nuages d'orage en rotation accompagnée de vents forts. On peut les classer dans la catégorie des systèmes convectifs de méso-échelle puisqu'ils ont un diamètre inférieur à une dépression classique, dite « synoptique », et que leur source d'énergie principale est le dégagement de chaleur latente causé par la condensation de la vapeur d'eau en altitude dans leurs orages. Le cyclone tropical est semblable à une machine thermique, au sens de la thermodynamique. Le dégagement de chaleur latente dans les niveaux supérieurs de la tem

Towards a Minergie Standard for tropical climates

Fouad Aabid, Claude-Alain Roulet, Jean-Louis Scartezzini, Franco Vigliotti

The Swiss Minergie®-standard is, by the number of labelled buildings (> 20'000) one of the most successful building energy labels in the world. It is obviously a strong incentive for designing comfortable, low energy buildings. This standard is now valid for temperate - cold climates only. There is therefore a need for a similar standard for buildings dominated by cooling loads, as it is common in the tropical and sub-tropical climates of the world. Since the new EPFL campus planned in Ras al Kaimah (United Arab Emirates) should be exemplary, a project was launched by the Dean of EPFL Middle East, together with Minergie®-Association and the Solar Energy and Building Physics Laboratory of EPFL, aiming to set-up such a standard. In order to initiate this project, two buildings (a single family dwelling and an office building) were chosen. The single-family dwelling was simulated at an hourly time step using a detailed dynamic thermal model based on the computer simulation programme Energy plus issued from LBNL. The monthly energy consumption of the dwelling shows a good correlation with the monitored data. In addition to that, both energy consumptions, calculated with the dynamic and the simplified models are close to each other, giving confidence to the predictions of the latter. Therefore, both buildings were assessed using a simplified monthly energy balance method. Starting from the current buildings configurations, several variants implementing various improvements towards energy efficiency were considered. These simulations show that considerable energy saving (up to a factor 5) can be achieved by implementing together several improvements to these buildings. In addition, the building reaches a higher level of users comfort.

EPFL2011

Modeling study of the interannual variability in global tropospheric hydroxyl radical and methane concentrations over the last two decades

Jérôme Drevet

Methane (CH4) is a major greenhouse gas whose global warming potential is 23 times more important than carbon dioxide (CO2). CH4 concentrations have steadily increased since the beginning of the industrial era, reaching an unprecedent level (almost 1800 ppb at present times). CH4 is currently considered as a one of the major driver of the climate change and its warming potential has leaded the Kyoto protocol to plan a significative reduction of its emissions. The objective of this thesis is to examine the factors that contribute to the CH4 global budget as well as its year-to-year variations. To that purpose, we have implemented a methane simulation in a global model of chemistry and transport. Conducting a CH4 simulation requires a comprehensive set of interannual varying CH4 emission inventories as well as a year-to-year varying 3-D fields of concentrations of hydroxyl radicals (OH) that is the main sink for CH4. The first part of this thesis examines the OH interannual variation, using results from a "full-chemistry" simulation that accounts for interannual variations in emissions of the main O3 precursors (including carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons) as well as the year-to-year variation in meteorology (e.g. atmospheric water vapor content), lightning emissions, and overhead O3 column. We calculated a global OH concentration of 1.22×106 molec cm-3 averaged over the period. We find that global OH concentrations steadily increased during the early 90's by 8% and reached a maximum in 1997. Afterward, concentrations decrease by 5%. We find that changes in water vapor concentrations, anthropogenic emissions of CO and NOx, lightning NOx emissions, and overhead ozone column all play a role in driving the OH year-to-year variations. The relative contributions of these parameters depend on the latitudinal and altitudinal regions of the troposphere. We examine in particular the influence of the 1997-1998 ENSO on the global OH concentrations. We find that the 1997-1998 ENSO resulted in a large increase in OH in the tropical areas and in the extra-tropical areas of the northern hemisphere (largely driven by an increase in water vapor) while it leads to a decrease in OH in the extra-tropical region of the southern hemisphere (that results from changes in the transport pathways that bring CO in the most southern latitudes and deplete OH). Our results (in terms of OH variability) are in contradiction to those found by other methods, especially those using inverse modeling approaches that are based on methyl chloroform (CH3CCl3) observations. This may results from poorly constrained sources. We then seek to implement a comprehensive set of CH4 emissions in our global model. We used anthropogenic CH4 emission data set of anthropogenic emissions from the International Institute of Technology (IIASA) whose emissions vary between 250 and 290 Tg/year between 1990 and 2000. We estimated biomass burning emissions, derived from an inventory of the total annual biomass burned area and emission factors that we constrained with measurements of the isotopic composition of atmospheric methane. This results in a global emissions rate of 60 Tg/year, which is much stronger than most of previous studies. We also developed a wetland scheme that accounts for soil carbon content, wetland fraction areas, soil temperature and humidity (with the three latter parameters varying interannually) and we evaluated the wetland areas with satellite-based estimates. Our global wetland emissions amount to about 150 Tg/year. We find a global CH4 lifetime of 10.6 years, which is in the range of values reported in previous studies. Comparing our results with different set of measurements gives promising results. The model reproduces well the year-to-year variation even if it slightly overestimates concentrations after 2000. By conducting different set of sensitivity simulations, we investigated the role of different parameters on the CH4 variations. We find that the long-term trend in CH4 is driven by a competition between anthropogenic emissions and tropospheric decay. Peaks of growth rate are driven by biomass burning emissions and to a lesser extend, wetland emissions. We find that even if we used increasing anthropogenic emissions during the 90s (that is in contradiction with some previous studies), reconstructing the observed year-to-year variation of CH4 concentrations was possible if one considers an increasing in OH during the 90s.

EPFL2008

Modeling study of the interannual variability in global tropospheric hydroxyl radical and methane concentrations over the last two decades

Jérôme Drevet

EPFL2008