Search results for "electromagnetic [current]"
showing 10 items of 1008 documents
Black and brown carbon over central Amazonia: long-term aerosol measurements at the ATTO site
2018
The Amazon rainforest is a sensitive ecosystem experiencing the combined pressures of progressing deforestation and climate change. Its atmospheric conditions oscillate between biogenic and biomass burning (BB) dominated states. The Amazon further represents one of the few remaining continental places where the atmosphere approaches pristine conditions during occasional wet season episodes. The Amazon Tall Tower Observatory (ATTO) has been established in central Amazonia to investigate the complex interactions between the rainforest ecosystem and the atmosphere. Physical and chemical aerosol properties have been analyzed continuously since 2012. This paper provides an in-depth analysis of t…
Contrast in column-integrated aerosol optical properties during heating and non-heating seasons at Urumqi — Its causes and implications
2017
Abstract Aerosol optical properties were retrieved from two years' worth of Sunphotometer measurements at Urumqi, an urban station in western China. Distinct seasonal variations of aerosol optical properties were revealed. During the heating season, mean aerosol optical depth at 550 nm (τ a ), Angstrom exponent calculated from aerosol optical depth at wavelength of 440 and 870 nm (α) as well as PM 2.5 concentration were 0.58 ± 0.33, 1.11 ± 0.34 and 79.5 ± 69.6 μg m − 3 , respectively, which contrasted their counterparts during the non-heating season of 0.32 ± 0.22, 0.79 ± 0.26, and 35.0 ± 20.1 μg m − 3 . Seasonal variations of τ a and PM 2.5 at Urumqi contrasted with corresponding values in…
Determination and analysis of in situ spectral aerosol optical properties by a multi-instrumental approach
2014
Continuous in situ measurements of aerosol optical properties were conducted from 29 June to 29 July 2012 in Granada (Spain) with a seven-wavelength Aethalometer, a Multi-Angle Absorption Photometer, and a three-wavelength integrating nephelometer. The aim of this work is to describe a methodology to obtain the absorption coefficients (babs) for the different Aethalometer wavelengths. In this way, data have been compensated using algorithms which best estimate the compensation factors needed. Two empirical factors are used to infer the absorption coefficients from the Aethalometer measurements: C – the parameter describing the enhancement of absorption by particles in the filter matrix due …
The optical constants of atmospheric aerosol particles in the 7.5–12 ?m spectral region
2011
Thin films of atmospheric aerosol particles which have been collected by an automatic jet impactor are used to obtain the real and imaginary part of the mean complex refractive index of aerosol particles of various types in the 7.5–12 ?m spectral region. A dispersion analysis of the measured ir-spectra of absorption of the particle films is performed. By applying the Lorentz theory of continuous dielectrics to the particle films a mathematical relation between the optical constants of the particle films and those of the aerosol particles themselves is obtained. The resulting complex refractive indices are applied to Mie computations to indicate the importance of scattering and absorbing aer…
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: …
Bayesian dynamic modeling of time series of dengue disease case counts
2017
The aim of this study is to model the association between weekly time series of dengue case counts and meteorological variables, in a high-incidence city of Colombia, applying Bayesian hierarchical dynamic generalized linear models over the period January 2008 to August 2015. Additionally, we evaluate the model’s short-term performance for predicting dengue cases. The methodology shows dynamic Poisson log link models including constant or time-varying coefficients for the meteorological variables. Calendar effects were modeled using constant or first- or second-order random walk time-varying coefficients. The meteorological variables were modeled using constant coefficients and first-order …
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 …
A study on the sensitivities of simulated aerosol optical properties to composition and size distribution using airborne measurements
2014
We present a flexible framework to calculate the optical properties of atmospheric aerosols at a given relative humidity based on their composition and size distribution. The similarity of this framework to climate model parameterisations allows rapid and extensive sensitivity tests of the impact of uncertainties in data or of new measurements on climate relevant aerosol properties. The data collected by the FAAM BAe-146 aircraft during the EUCAARI-LONGREX and VOCALS-REx campaigns have been used in a closure study to analyse the agreement between calculated and measured aerosol optical properties for two very different aerosol types. The agreement achieved for the EUCAARI-LONGREX flights is…
Examining the Effects of Dust Aerosols on Satellite Sea Surface Temperatures in the Mediterranean Sea Using the Medspiration Matchup Database
2011
Abstract Dust aerosol plumes from the Sahara cover the Mediterranean Sea regularly during the summer months (June–August) and occasionally during other seasons. Dust can absorb infrared longwave radiation, thus causing a drop in sea surface temperature (SST) retrievals from satellite. To quantify the magnitude of this absorption and to understand the sources of the biases that might be introduced when trying to validate SST algorithms with in situ bulk temperatures, the effects of the dust absorption are studied using the Medspiration Match-up Database. This database provides in situ and satellite SSTs derived from the Advanced Very High Resolution Radiometer (AVHRR) and the Advanced Along-…
Sensitivity of the atmospheric temperature profile to the aerosol absorption in the presence of dust
2014
Abstract Radiative transfer simulations in the shortwave (SW) and longwave (LW) spectral regions have been carried out to investigate the time evolution of the atmospheric heating/cooling rates and their influence on the temperature profiles under different vertical distributions of the aerosol absorption. The case study is based on measurements made at Rome, Italy, on 20 June 2007, when a dust layer was present above the urban boundary layer (BL) and the column aerosol optical depth at 550 nm was about 0.37. Column-integrated aerosol optical depth and single scattering albedo, as well as vertical profiles of aerosol extinction and meteorological variables have been derived from observation…