Search results for "Radiative Transfer"
showing 10 items of 551 documents
Simulation of a biomass-burning plume: Comparison of model results with observations
2002
[1] We have simulated the dynamical evolution of the plume from a prescribed biomass fire, using the active tracer high- resolution atmospheric model (ATHAM). Initialization parameters were set to reflect the conditions during the fire. The model results are compared with airborne remote-sensing and in situ measurements of the plume. ATHAM reproduces the injection height (250-600 m) and the horizontal extent of the plume (similar to4 km) with good accuracy. The aerosol mass concentrations are underestimated but still in the range of the observations. Remaining differences between the model results and the measurements are attributed to limited meteorological and fire emission information. A…
Altitude effect in UV radiation during the Evaluation of the Effects of Elevation and Aerosols on the Ultraviolet Radiation 2002 (VELETA-2002) field …
2008
[1] The Evaluation of the Effects of Elevation and Aerosols on the Ultraviolet Radiation 2002 (VELETA-2002) field campaign was designed to study the influence of aerosols and altitude on solar UV irradiance. The altitude effect (AE) was evaluated for UV irradiance under cloudless conditions by taking spectral and broadband measurements in SE Spain in the summer of 2002 at three nearby sites located at different heights (680 m, 2200 m, and 3398 m). A spectral radiative transfer model (Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART)) was also applied, mainly to evaluate the tropospheric ozone impact on AE. Results are related to the optical properties and air mass origin of the a…
Three-dimensional solar radiation effects on the actinic flux field in a biomass-burning plume
2003
[1] Three-dimensional (3-D) solar radiative transfer models describe radiative transfer under inhomogeneous atmospheric conditions more accurately than the commonly used one-dimensional (1-D) radiative transfer models that assume horizontal homogeneity of the atmosphere. Here results of 3-D radiative transfer simulations for a biomass-burning plume are presented and compared with local one-dimensional (l-1-D) simulations, i.e., 1-D simulations in every column of the model domain. The spatial distribution of the aerosol particles was derived from a 3-D atmospheric transport simulation. We studied the impact of 3-D radiative effects on the actinic flux within the plume center. The differences…
Modeling the outdoor cooling impact of highly radiative “super cool” materials applied on roofs
2021
Abstract Highly reflective “cool materials” are commonly used to reduce temperatures in the urban environment. Recently developed “super cool” materials feature an even higher albedo and emissivity (both above 0.95) than traditional cool materials. To examine the impacts of super cool roofing materials on outdoor air temperature compared to traditional cool roofs and green roofs, we conduct a sensitivity study with the microclimate model ENVI-met. Simulated surface temperature of super cool roofs remained around 6 K below ambient air temperature during high solar irradiation, which is consistent with observations. Super cool roofs – with an averaged street-level air temperature cooling of a…
A new method to retrieve the aerosol layer absorption coefficient from airborne flux density and actinic radiation measurements
2010
A new method is presented to derive the mean value of the spectral absorption coefficient of an aerosol layer from combined airborne measurements of spectral net irradiance and actinic flux density. While the method is based on a theoretical relationship of radiative transfer theory, it is applied to atmospheric radiation measurements for the first time. The data have been collected with the Spectral Modular Airborne Radiation Measurement System (SMARTA¢ÂÂAlbedometer), the Solar Spectral Flux Radiometer (SSFR), and the Actinic Flux Spectroradiometer (AFSR) during four field campaigns between 2002 and 2008 (the Saharan Mineral Dust Experiment (SAMUM), the Influence of Clouds on the Spectra…
Effects of ice crystal habit on thermal infrared radiative properties and forcing of cirrus
2007
[1] The impact of assumed ice crystal morphology on thermal infrared (IR) radiative properties of subtropical cirrus is quantified. In particular, the crystal-shape-dependent profiles of downwelling and upwelling thermal IR (broadband and spectral) irradiances and the radiative forcing of cirrus (at the top and bottom of the atmosphere) are investigated. For this purpose, airborne measurements of ice crystal size distribution (in terms of ice crystal maximum dimension) from the CRYSTAL-FACE campaign and a recently published library of thermal IR optical properties of nonspherical ice crystal habits are implemented into radiative transfer simulations. Two cirrus cases are studied in detail: …
Ground-based measured and calculated spectra of actinic flux density and downward UV irradiance in cloudless conditions and their sensitivity to aero…
2003
Ground-based spectral measurements of actinic flux density (300–660 nm wavelength) and downward UV irradiance (300–324 nm) under cloudless conditions have been compared with the results of one-dimensional radiative transfer calculations employing concurrent airborne vertical profile measurements of aerosol particle size distributions. Good agreement (within ±10%) between measured and calculated spectra was found. The remaining differences were explained by uncertainties inherent in the aerosol particle microphysical input data and the column ozone content. A respective sensitivity analysis of the calculated spectra, which was based on the observed variability of microphysical properties, ha…
The effects of different radiation parametrizations on cloud evolution
1997
With the use of the microphysical stratus model (MISTRA), investigations into the effects of variations in the radiative-transfer parametrizations on cloud development have been undertaken. Two radiative-transfer schemes were coupled with the microphysical-thermodynamical section of MISTRA, one based on the exponential sumfitting method and the other based on the correlated k-distribution method of determining gaseous absorption properties. Model runs were initiated with parameter values in accordance with measurements made over the North Sea and comparisons made between model runs where only the radiation schemes were altered. Results indicated that differences between the two schemes had …
On the direct and semidirect effects of Saharan dust over Europe: A modeling study
2007
[1] On the basis of a new regional dust model system, the sensitivity of radiative forcing to dust aerosol properties and the impact on atmospheric dynamics were investigated. Uncertainties in optical properties were related to uncertainties in the complex spectral refractive index of mineral dust. The climatological-based distribution of desert-type aerosol in the radiation scheme of the nonhydrostatic regional model LM was replaced by dust optical properties from spectral refractive indices, derived from in situ measurements, remote sensing, bulk measurements, and laboratory experiments, employing Mie theory. The model computes changes in the solar and terrestrial irradiance from a spatia…
A Simple method for estimating the latent heat flux over grass from radiative bowen ratio
1998
Abstract The evaluation of crop evapotranspiration from infrared temperature is usually calculated as the residual component of the surface energy balance. This method has given good results over a full grass canopy cover with unstressed transpiration, in spite of the not well understood meaning of the aerodynamic resistance needed. A simple and more accurate method, which determines the Bowen ratio (β) and the latent heat flux (λE) over a reference grass area without knowledge of surface resistances, is proposed. The proportionality between β and a radiative Bowen ratio βs is shown. The radiative Bowen ratio is derived from surface and air temperatures and vapor pressure. This relationship…