Search results for "oceanic"
showing 10 items of 642 documents
Sensitivity of aerosol extinction to new mixing rules in the AEROPT submodel of the ECHAM5/MESSy1.9 atmospheric chemistry (EMAC) model
2014
Abstract. The modelling of aerosol radiative forcing is a major cause of uncertainty in the assessment of global and regional atmospheric energy budgets and climate change. One reason is the strong dependence of the aerosol optical properties on the mixing state of aerosol components like black carbon and sulphates. Using a new column version of the aerosol optical properties and radiative transfer code of the atmospheric chemistry-climate model EMAC, we study the radiative transfer applying various mixing states. The aerosol optics code builds on the AEROPT submodel which assumes homogeneous internal mixing utilising the volume average refractive index mixing rule. We have extended the sub…
Determination of eddy diffusivity in the lowermost stratosphere
2005
[1] We present a 2D-advection-diffusion model that simulates the main transport pathways influencing tracer distributions in the lowermost stratosphere (LMS). The model describes slow diabatic descent of aged stratospheric air, vertical (cross-isentropic) and horizontal (along isentropes) diffusion within the LMS and across the tropopause using equivalent latitude and potential temperature coordinates. Eddy diffusion coefficients parameterize the integral effect of dynamical processes leading to small scale turbulence and mixing. They were specified by matching model simulations to observed CO distributions. Interestingly, the model suggests mixing across isentropes to be more important tha…
Proposal and Validation of an Emissivity-Dependent Algorithm to Retrieve Sea-Surface Temperature From MSG-SEVIRI Data
2010
A frequent and accurate determination of sea-surface temperature (SST) would permit an improvement in both the forecasting of natural hazards and the monitoring of the effects of climate change. The Meteosat Second Generation (MSG) spinning enhanced visible and infrared imager (SEVIRI) (MSG-SEVIRI) offers this possibility, since it has a temporal resolution of 15 min. Current algorithms for SST retrieval from MSG-SEVIRI data use angular-dependent coefficients, but they do not use sea-surface emissivity (SSE) as an explicit input. This letter proposes a both angular- and emissivity-dependent split-window equation, together with simple equations to estimate SSE and atmospheric water-vapor con…
Hyperspectral solar spectral measurements and applications
2007
Measurements of hyperspectral solar irradiance from aircraft and satellite are applied to a variety of cloud and aerosol remote sensing, and radiative energy budget applications.
Irradiance in polluted cumulus fields: Measured and modeled cloud-aerosol effects
2009
[1] We present a new strategy to validate modeled spectral irradiance of shallow cumulus cloud fields in a polluted background with airborne measurements. The concept is based on a spectral distinction of effects associated with heterogeneous clouds, aerosol particles, and surface albedo. We use measurements from the Gulf of Mexico Atmospheric Composition and Climate Study, conducted in the urban-industrial Houston area. Modeled irradiance fields were obtained from extensive three-dimensional radiative transfer calculations applied to the output of large eddy simulations. We show that the measurements below clouds or cloud gaps can only be reproduced by the calculations when including the a…
Observed versus simulated mountain waves over Scandinavia – improvement by enhanced model resolution?
2016
Abstract. Two mountain wave events, which occured over northern Scandinavia in December 2013 are analysed by means of airborne observations and global and mesoscale numerical simulations with horizontal mesh sizes of 16 km, 7.2 km, 2.4 km and 0.8 km. During both events westerly cross-mountain flow induced upward propagating waves in the troposphere and stratosphere and trapped waves in the lee of the mountains. Despite similar forcing conditions gravity wave breaking occured during the first event at altitudes between 25 km to 30 km due to weak stratospheric background winds, while waves propagated to altitudes above 30 km during the second event. In the lower troposphere trapped lee waves …
Coherent neutrino scattering
2009
We present a microscopic model for coherent pion production off nuclei induced by neutrinos. This model is built upon a model for single nucleon processes that goes beyond the usual Delta dominance by including non resonant background contributions. We include nuclear medium effects: medium corrections to Delta$ properties and outgoing pion absortion via an optical potential. This results in major modifications to cross sections for low energy experiments when compared with phenomenological models like Rein-Sehgal's.
Effect of cholesterol on the physical properties of pulmonary surfactant films: Atomic force measurements study
2006
International audience; Atomic force measurements were performed on supported pulmonary surfactant (PS) films to address the effect of cholesterol on the physical properties of lung surfactant films. We recently found that cholesterol in excess of a physiological proportion abolishes surfactant function, and is the reason that surfactant fails to lower the surface tension upon compression. In this study, we investigated how the loss of mechanical stability observed earlier is related to the local mechanical properties of the film by local force measurements. The presence of 20% of cholesterol in bovine lipid extract surfactant (BLES) resulted in a decrease of the observed adhesive interacti…
Drying of shrinking cylinder-shaped bodies
1998
Abstract A mathematical model has been developed for the prediction of sample temperature, average moisture and moisture distribution in a cylinder-shaped solid during the drying process. The effect of shrinkage was taken into account. The macroscopic heat balance and the microscopic mass balance combined with Fick's law were simultaneously solved using the Runge-Kutta-Merson method and a numerical finite difference method. The effective diffusion coefficient was expressed as a function of sample temperature and local moisture content. Using an experimental drying curve determined at 90 °C, the diffusional equation was identified for broccoli stems, and was used to predict the average and l…
Non-Isothermal Mathematical Model of Wood and Paper Drying
2002
A mathematical model of wood or paper drying based on a detailed consideration of both heat and moisture transport phenomena is proposed. By averaging we express the model as a sequence of initial value problems for systems of two first order nonlinear ordinary differential equations. This mathematical model makes it possible to efficiently investigate the drying process of a thin wood plate or paper sheet for varying temperature and humidity conditions in the surroundings. In particular, we have considered the optimization of the heat regime over a series of steam-heated cylinders in a papermaking machine.