Search results for "Processes"

Column-integrated aerosol optical properties in Sodankylä (Finland) during the Solar Induced Fluorescence Experiment (SIFLEX-2002).

2006

[1] A study has been made of the column aerosols using solar irradiance extinction measurements at ground level in a boreal region (Sodankyla, Finland) during spring 2002. The aerosol properties have been related to air mass origin. In general, the aerosol levels were observed to be very low, independent of the air mass origin, with an aerosol optical depth (AOD) value at 500 nm of less than 0.09 ± 0.03. Two characteristic patterns were observed depending on whether the air masses originated in the north and west or from the south and east. In the first case (north and west origins) the aerosol load was very small, with very low optical depths in the range 0.03 ± 0.02 to 0.09 ± 0.03 for 500…

Surface temperature retrieval from Along Track Scanning Radiometer 2 data: Algorithms and validation

2004

[1] A study has been carried out using MODTRAN 3.5 simulations of the Along Track Scanning Radiometer 2 (ATSR-2) data at 3.7, 11, and 12 μm wavelengths to give a range of algorithms for estimating surface. Making use of the dual-angle feature of the ATSR-2, algorithms based on dual-angle, split-window, and mixed structure have been considered. The coefficients of the algorithms are derived by regression analysis using the MATLAB code. The evaluation of the sensitivity of each algorithm shows that in general, dual-angle algorithms provide smaller errors in the estimation of surface temperature than the split-window algorithms and that the algorithms with water vapor dependence give an improv…

Flux retrieval optimization with a nonscanner along-track broadband radiometer

2003

[1] The theoretical behavior of broadband flux retrieval is analyzed with the aid of a radiance field database. Several angular inversion models are developed for different viewing configurations, with special emphasis in a nonscanner along-track design concept. Results show that the performance of these angular models depends on the viewing zenith angle (VZA). When cloud cover is predominant within the observed scene, VZAs around 55° (shortwave) and 50° (longwave) minimize the error when deriving fluxes. These results might help in the design of future missions where the main idea is to obtain accurate instantaneous measurements of top of atmosphere reflected and emitted fluxes. Such measu…

Evaluation of split-window and dual-angle correction methods for land surface temperature retrieval from Envisat/Advanced Along Track Scanning Radiom…

2006

[1] Land surface temperature (LST) can be derived from thermal infrared remote sensing data provided that atmospheric and emissivity effects are corrected for. In this paper, two correction methods were evaluated using a database of ground LST measurements and concurrent Envisat/Advanced Along Track Scanning Radiometer (AATSR) data. They were the split-window (SW) method, which uses two channels at 11 and 12 μm, and the dual-angle (DA) method, using one single channel (11 μm) at two observation angles (close to nadir and around 55° forward). The ground LST measurements were performed in a large, flat, and thermally homogeneous area of rice fields during the summers of 2002–2005, when the cr…

Hygroscopic properties and water-soluble volume fraction of atmospheric particles in the diameter range from 50 nm to 3.8 μm during LACE 98

2002

[1] Hygroscopic properties of atmospheric aerosol particles in the Aitken, large, and giant particle range were studied during the Lindenberg Aerosol Characterization Experiment (LACE 98) in a rural area 80 km southeast of Berlin. The hygroscopic behavior of Aitken particles were determined in situ in four size classes (50, 100, 150, 250 nm) with a Hygroscopic Tandem Differential Mobility Analyzer for relative humidities (RH) of 60% and 90%. Measurements at 60% RH served as reference data used by other LACE 98 investigators for mass closure and radiative transfer calculations. In most cases, at 90% RH, the atmospheric particles could be classified into two groups (“more” and “less” hygrosco…

Regional Saharan dust modelling during the SAMUM 2006 campaign

2011

The regional dust model system LM-MUSCAT-DES was developed in the framework of the SAMUM project. Using the unique comprehensive data set of near-source dust properties during the 2006 SAMUM field campaign, the performance of the model system is evaluated for two time periods in May and June 2006. Dust optical thicknesses, number size distributions and the position of the maximum dust extinction in the vertical profiles agree well with the observations. However, the spatio-temporal evolution of the dust plumes is not always reproduced due to inaccuracies in the dust source placement by the model. While simulated winds and dust distributions are well matched for dust events caused by dry syn…

2015

Abstract. During the winter of 2013 and 2014 measurements of cloud microphysical properties over a 5-week period at the high-alpine site Jungfraujoch, Switzerland, were carried out as part of the Cloud Aerosol Characterisation Experiments (CLACE) and the Ice Nucleation Process Investigation and Quantification project (INUPIAQ). Measurements of aerosol properties at a second, lower site, Schilthorn, Switzerland, were used as input for a primary ice nucleation scheme to predict ice nuclei concentrations at Jungfraujoch. Frequent, rapid transitions in the ice and liquid properties of the clouds at Jungfraujoch were identified that led to large fluctuations in ice mass fractions over temporal s…

Sudan-Sahel rainfall onset: Definition of an objective index, types of years, and experimental hindcasts

2006

Using rainfall estimates from the 5-day version of CPC Merged Analysis of Precipitation (CMAP) and Global Precipitation Climatology Project data along with multiscale spatial key descriptors of atmospheric dynamics from National Center for Environmental Prediction/Department of Energy reanalysis 2 (NCEP/DOE), we first define a West African monsoon onset index to determine its successive dates of occurrence over the period 1979-2004 (28-29 June in mean with a standard deviation of 8.5 days). Then we focus on the three main types of time evolutions of that index at the moment of the monsoon onset in terms of precipitation, pressure, temperature, and winds at different levels to detect the mos…

An analysis of VLF electric field spectra measured in Titan's atmosphere by the Huygens probe

2009

[1] A numerical simulation of Titan's electromagnetic cavity in the VLF band is carried out using the Transmission Line Matrix (TLM) method, with the aim of assessing the VLF electric field spectra sent by the Huygens probe. In an Earth-like model, successive peaks would be expected in the spectra, associated with multiple reflections of the electromagnetic wave on the external surfaces of Titan's electromagnetic cavity, formed by the ionosphere and a conductive ground or underground surface. However, owing to high losses conferred by the electrical conductivity to Titan's atmosphere, the direct numerical and experimental spectra are decreasing functions of the frequency without resonances …

Summertime columnar content of atmospheric water vapor from ground-based Sun-sky radiometer measurements through a new in situ procedure

2010

[1] A new in situ technique for the retrieval of atmospheric water vapor content (i.e., precipitable water content) from Sun photometric direct solar irradiance measurements, taken at the 940 nm wavelength during clear‐sky conditions, is presented. The procedure is applied to summer data recorded in 2007, 2008, and 2009 with a Sun‐sky radiometer at the San Pietro Capofiume station in the Po valley, Italy. It is a preliminary development of the retrieval procedure providing the columnar water vapor content from measurements performed with PREDE Sun‐sky radiometers. The technique brings improvement and innovation by retrieving the best values of constants (a and b), characterizing atmospheric…