Mois | EPFL Graph Search

Le mois est une unité de temps utilisée dans les calendriers, correspondant à une division de l'année. Dans les calendriers solaires occidentaux, un mois est défini comme un douzième de l'année, elle-même basée sur l'année tropique, chacun des mois comptant un nombre variable de jours. D'autres types de calendrier utilisent des définitions différentes, comme les calendriers lunaires, basés sur les lunaisons. D'autres découpent le temps de façon arbitraire sans correspondance avec des phénomènes astronomiques comme certains calendriers aztèques. Sauf dans le cas d'une date évoquant un événement historique, le mois s'écrit normalement, c'est-à-dire en minuscule : on écrira ainsi « le » (une date courante), mais « le » (date de la fête nationale française). Le mois peut se diviser en trois parties :

la première (1-10) est le début du mois, qu'on divise communément en deux parties : ** la première (1-5) est le début du début du mois ; ** la deuxième (6-10) est la fin du début du m

Towards understanding the characteristics of new particle formation in the Eastern Mediterranean

Lubna Dada

To quantify the contribution of new particle formation (NPF) to ultrafine particle number and cloud condensation nuclei (CCN) budgets, one has to understand the mechanisms that govern NPF in different environments and its temporal extent. Here, we study NPF in Cyprus, an Eastern Mediterranean country located at the crossroads of three continents and affected by diverse air masses originating from continental, maritime, and desert-dust source areas. We performed 1-year continuous measurements of aerosol particles down to ∼ 1 nm in diameter for the first time in the Eastern Mediterranean and Middle East (EMME) region. These measurements were complemented with trace gas data, meteorological variables, and retroplume analysis. We show that NPF is a very frequent phenomenon at this site and has higher frequencies of occurrence during spring and autumn. NPF events were both of local and regional origin, and the local events occurred frequently during the month with the lowest NPF frequency. Some NPF events exhibited multiple onsets, while others exhibited apparent particle shrinkage in size. Additionally, NPF events were observed during the nighttime and during episodes of high desert-dust loadings. Particle formation rates and growth rates were comparable to those in urban environments, although our site is a rural one. Meteorological variables and trace gases played a role in explaining the intra-monthly variability of NPF events, but they did not explain why summer months had the least NPF frequency. Similarly, pre-existing aerosol loading did not explain the observed seasonality. The months with the least NPF frequency were associated with higher H2SO4 concentrations but lower NO2 concentrations, which is an indicator of anthropogenic influence. Air masses arriving from the Middle East were not observed during these months, which could suggest that precursor vapors important for nucleation and growth are transported to our site from the Middle East. Further comprehensive measurements of precursor vapors are required to prove this hypothesis.

2021

Snow cover variations and spring snowmelt runoff modelling in the source region of the Yellow River, China

Léo Zhou Ficheux

This study aims to assess the snow cover spatial and temporal variation in the Source Region of the Yellow River, to understand the effect of snowmelt on the hydrology and to evaluate the potential impact of increasing temperature on the spring snowmelt runoff. The Snowmelt Runoff Model (SRM) developed by Rango and Martinec was used and improved by adding diurnal temperature computation and snow storage computation to model the runoff for 2013, 2014, 2016 and 2017. The snow cover assessment was done using Tera-MODIS satellite images between 2001 and 2017. Results showed that spring snowmelt produces 38% of direct runoff before July and 15% of annual runoff in average. The snow cover is very sensitive to temperature and to winter precipitation. There is a significant decrease of snow cover in May since 2001 in parallel to a significant increase of temperature. The snow cover duration has decreased by more than 15 days (20%) in the permafrost area in 15 years. Simulation suggests that a temperature increase of 2°C or 4°C will reduce the spring snowmelt by at least 20% and 30% respectively, and spring peak runoff will occur up to 15 days and one month earlier. Future investigations should focus on the interaction between snow, frozen ground and ground water recharge in order to extend the knowledge on snowmelt impact to soil related processes which play a key role on the ecosystem degradation in the region.

2018

A comparison of hydrological models with different level of complexity in Alpine regions in the context of climate change

Mathias Thierry Pierre Bavay, Francesca Carletti, Michael Lehning, Adrien Michel

This study compares the ability of two degree-day models (Poli-Hydro and a degree-day implementation of Alpine3D) and one full energy-balance melt model (Alpine3D) to predict the discharge on two partly glacierized Alpine catchments of different size and intensity of exploitation, under present conditions and climate change as projected at the end of the century. For present climate, the magnitude of snow melt predicted by Poli-Hydro is sensibly lower than the one predicted by the other melt schemes, and the melting season is delayed by one month. This difference can be explained by the combined effect of the reduced complexity of the melting scheme and the reduced computational temporal resolution. The degree-day implementation of Alpine3D reproduces a melt season closer to the one obtained with its full solver; in fact, the onset of the degree-day mode still depends upon the full energy-balance solver, thus not bringing any particular benefit in terms of inputs and computational load, unlike with Poli-Hydro. Under climate change conditions, Alpine3D is more sensitive than Poli-Hydro, reproducing discharge curves and volumes shifted by one month earlier as a consequence of the earlier onset of snow melt. Despite their benefits, the coarser temporal computational resolution and the fixed monthly degree-days of simpler melt models like Poli-Hydro make them controversial to use for climate change applications with respect to energy-balance ones. Nevertheless, under strong river regulation, the influence of calibration might even overshadow the benefits of a full energy-balance scheme.

2021

Towards understanding the characteristics of new particle formation in the Eastern Mediterranean

Lubna Dada

2021