Search results for "Ocean"
showing 10 items of 2919 documents
The transport history of two Saharan dust events archived in an Alpine ice core
2005
Mineral dust from the Saharan desert can be transported across the Mediterranean towards the Alpine region several times a year. When coinciding with snowfall, the dust can be deposited on Alpine glaciers and then appears as yellow or red layers in ice cores. Two such significant dust events were identified in an ice core drilled at the high-accumulation site Piz Zupó in the Swiss Alps (46°22' N, 9°55' E, 3850 m a.s.l.). From stable oxygen isotopes and major ion concentrations, the events were approximately dated as October and March 2000. In order to link the dust record in the ice core to the meteorological situation that led to the dust events, a novel methodology based on b…
A theoretical study of the wet removal of atmospheric pollutants. Part I: the redistribution of aerosol particles captured through nucleation and imp…
1985
Abstract A theoretical model is formulated which allows the processes that control the wet deposition of atmospheric pollutants to be included in cloud dynamic models. The model considers the condensation process and the collision-coalescence process which, coupled together, control the fate of atmospheric aerosol particles removed by clouds and precipitation through nucleation scavenging and impaction scavenging. The model was tested by substituting a simple parcel model for the dynamic framework. In this form the model was used to determine the time evolution of the aerosol particle mass scavenged by drops as well as the aerosol particle mass left unactivated in air as “drop-interstitial”…
In-Situ observation of New Particle Formation in the upper troposphere/lower stratosphere of the Asian Monsoon Anticyclone
2020
Abstract. During the monsoon season of the year 2017 the airborne StratoClim mission took place in Kathmandu, Nepal with eight mission flights of the M-55 Geophysica in the upper troposphere/lower stratosphere (UT/LS) of the Asian Monsoon Anticyclone (AMA) over northern India, Nepal and Bangladesh. More than hundred events of New Particle Formation (NPF) were observed. In total, more than two hours of flight time were spent under NPF conditions as indicated by the abundant presence of ultrafine aerosols, i.e. with particle diameters dp smaller than 15 nm, which were in-situ detected by means of condensation nuclei counting techniques. Mixing ratios of ultrafine particles (nuf) of up to ~ 50…
Étude multi-échelles des précipitations et du couvert végétal au Cameroun : Analyses spatiales, tendances temporelles, facteurs climatiques et anthro…
2011
Due to its shape and location (2°N-13°N - 8°E-16°E; proximity of the Atlantic Ocean), Cameroon is characterized by a panel of cross-regional climate encountered widely in tropical Africa. Over the region, the decrease rainfall during the second half of the last century has been shown to be associated with stronger recurrence of drier periods, specifically in the core of the rainy season. These conditions have favored the degradation of vegetation cover, driven by socioeconomic and demographic constraints. The substantial impacts on human activities and local society highlight the need to better understand how climate and environmental dynamics do interact locally. The aim of this study is t…
Prévision et spatialisation des concentrations en ozone troposphérique en Bourgogne
2006
This PhD done in the Centre de Recherche de Climatologie, UMR 5210 CNRS of University of Burgundy has been supported by the Conseil Régional de Bourgogne, and the AASQA of Burgundy (Atmosf'Air). The ozone, a poison gas, is the core of this research because it is considered as one of the major worrying atmospheric pollutants in this region. We have conducted a study focused on hourly concentrations of measured ozone over several years for 12 stations. Their spatial and temporal variability are related to some features outside of the region (ground-level ozone, synoptic-scale conditions) and inside of the region (physical properties, land cover, meteorological features and precursor potential…
A numerical study of tropical cross-tropopause transport by convective overshoots
2007
Abstract. Observations obtained during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) golden day have revealed the presence of ice particles up to 410 K (18.2 km) 2 km above the local tropopause. The case was investigated using a three-dimensional quadruply nested non-hydrostatic simulation and Meteosat Second Generation (MSG) observations. The simulation reproduced the measurements along the flight track fairly well. A reasonable agreement with MSG observations was also achieved: the 10.8-μm brightness temperature (BT) minimum of 187 K was reproduced (a value 6 K colder than the environmental cold-point temperature) as was the positive BT difference between the 6.2- and 10…
Recent extreme drought events in the Amazon rainforest: assessment of different precipitation and evapotranspiration datasets and drought indicators
2022
Over the last decades, the Amazon rainforest has been hit by multiple severe drought events. Here, we assess the severity and spatial extent of the extreme drought years 2005, 2010 and 2015/16 in the Amazon region and their impacts on the regional carbon cycle. As an indicator of drought stress in the Amazon rainforest, we use the widely applied maximum cumulative water deficit (MCWD). Evaluating nine state-of-the-art precipitation datasets for the Amazon region, we find that the spatial extent of the drought in 2005 ranges from 2.2 to 3.0 (mean =2.7) ×106 km2 (37 %–51 % of the Amazon basin, mean =45 %), where MCWD indicates at least moderate drought conditions (relative MCWD anomaly <-0…
THE TROPOSPHERIC PROCESSING OF ACIDIC GASES AND HYDROGEN SULPHIDE IN VOLCANIC GAS PLUMES AS INFERRED FROM FIELD AND MODEL INVESTIGATIONS
2007
International audience; Improving the constraints on the atmospheric fate and depletion rates of acidic compounds persistently emitted by non-erupting (quiescent) volcanoes is important for quantitatively predicting the environmental impact of volcanic gas plumes. Here, we present new experimental data coupled with modelling studies to investigate the chemical processing of acidic volcanogenic species during tropospheric dispersion. Diffusive tube samplers were deployed at Mount Etna, a very active open-conduit basaltic volcano in eastern Sicily, and Vulcano Island, a closed-conduit quiescent volcano in the Aeolian Islands (northern Sicily). Sulphur dioxide (SO2), hydrogen sulphide (H2S), h…
Investigation of marine and continental layers in a stalactite older than 1 million years (Custonaci, north-western sector of Sicily)
2012
Questo lavoro si basa sul ritrovamento, in una grotta carsica, a 100 metri di quota a Custonaci in provincia di Trapani, di una stalattite di notevole interesse paleo climatico, ricoperta da coralli marini, la cui sezione rivela la presenza di 3 Iatus che denotano una interruzione della deposizione di carbonato continentale presumibilmente in seguito a trasgressioni marine. Il carbonato, datato attraverso la metodologia 230Th/U MC-ICPMS (NeptunePlus), ha fornito una età più antica del limite temporale massimo di applicabilità del metodo ( 600 ka). I coralli, che ricoprono il livello continentale più giovane, analizzati usando il rapporto 87Sr/86Sr, hanno fornito una età di 1.1±0.2 Myrs. Al…
An Inverse Modeling Approach to Investigate Past Lead Atmospheric Deposition in Southern Greenland
2013
International audience