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Radiative Transfer Model (radiative + transfer_model)
Selected AbstractsA simple device for the evaluation of the UV radiation indexMETEOROLOGICAL APPLICATIONS, Issue 2 2003Giuseppe Rocco Casale The solar ultraviolet radiation (UV) flux density at the earth's surface depends on the incoming solar energy and the transmission properties of the atmosphere. UV radiation is strongly absorbed by ozone in the spectral range 200,310 nm, while the attenuation is increasingly weaker at longer wavelengths. Following the discovery of the Antarctic ozone hole in 1985, the risk of a possible UV increase at ground level, due to the observed stratospheric ozone depletion, has heightened the interest within the scientific community given the potentially harmful effects on terrestrial and aquatic ecosystems. Spectroradiometers, broad-band meters and dosimeters may be used for measurements of solar UV. In addition, radiation transfer models can be used to quantify UV irradiances at various times and locations, provided that the extraterrestrial solar radiation and the state of the atmosphere are known. Information about UV radiation at the earth's surface is given by the ultraviolet index ,UVI', which is defined as the effective integrated irradiance (280,400 nm) weighted by the erythemal action spectrum. The UV Index is widely used by many international weather services as an indicator of UV levels at the earth's surface providing public awareness of the effects of prolonged exposure to the sun's rays. The aim of this paper is to present a device capable of estimating the UV Index. This device is a compact disc, used as a sundial, and is based on modelled UV irradiances derived from the STAR radiative transfer model (System for Transfer of Atmospheric Radiation). The device was tested in an urban setting under clear sky conditions. Copyright © 2003 Royal Meteorological Society [source] Analytic Formula for the Clear-sky UV IndexPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2007Sasha Madronich An approximate formula for the UV Index (UVI) under cloud-free, unpolluted, low surface albedo conditions is: where ,o is the cosine of the solar zenith angle and , is the total vertical ozone column (in Dobson Units, DU). The dependence on ,o and , is based on a simple physical model of biologically weighted atmospheric transmission in the UV-B and UV-A spectral bands, with coefficients tuned to a detailed radiative transfer model, and is accurate to 10% or better over 0,60° and 200,400 DU. Other factors (clouds, haze, ground, etc.) mostly conserve this dependence and scale simply. [source] Standard Ultraviolet Daylight for Nonextreme Exposure Conditions,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2005François J. Christiaens ABSTRACT The skin is exposed to ultraviolet radiation (UVR) from natural or artificial sources on a daily basis. The effects of chronic low dose exposure merit investigation, even when these effects are neither conspicuous nor clinically assessable. The purpose of the present study was to define a relative spectral UV irradiance that is representative of frequent nonextreme sun exposure conditions and therefore more appropriate for studies of the long-term and daily effects of solar UV on the skin. Solar spectral UV irradiance values were calculated for different dates and locations by using a radiative transfer model. The spectral irradiance values obtained when the solar elevation is lower than 45° were averaged. An important feature is the dUVA (320,400 nm) to dUVB (290,320 nm) irradiance values ratio, which was found to be 27.3 for the overall average. When the months corresponding to extreme irradiance values (low or high) were excluded from the calculations, the dUVA to dUVB ratio ranged from 27.2 to 27.5. The mean spectral irradiance of the model presented here represents environmental UV exposure conditions and can be used both as a standard to investigate the biological effects of a nonextreme UVR and to assess the effectiveness of products for daily skin protection. [source] Toward a consistent reanalysis of the upper stratosphere based on radiance measurements from SSU and AMSU-ATHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 645 2009Shinya Kobayashi Abstract Radiance measurements from the Stratospheric Sounding Unit (SSU) and the Advanced Microwave Sounding Unit (AMSU-A) are the primary source of information for stratospheric temperature in reanalyses of the satellite era. To improve the time consistency of the reanalyses, radiance biases need to be properly understood and accounted for in the assimilation system. The investigation of intersatellite differences between SSU and AMSU-A radiance observations shows that these differences are not accurately reproduced by the operational version of the radiative transfer model for the TIROS Operational Vertical Sounder (RTTOV-8). We found that this deficiency in RTTOV was mainly due to the treatment of the Zeeman effect (splitting of the oxygen absorption lines at 60 GHz) and to changes in the spectral response function of the SSU instrument that are not represented in RTTOV. On this basis we present a revised version of RTTOV that can reproduce SSU and AMSU-A intersatellite radiance differences more accurately. Assimilation experiments performed with the revised version of RTTOV in a four-dimensional variational analysis system (4D-Var) show some improvements in the stratospheric temperature analysis. However, significant jumps in the stratospheric temperature analysis still occur when switching satellites, which is due to the fact that systematic errors in the forecast model are only partially constrained by observations. Using a one-dimensional retrieval equation, we show that both the extent and vertical structure of the partial bias corrections must inevitably change when the nature of the radiance measurement changes with the transition from SSU to AMSU-A. Copyright © 2009 Royal Meteorological Society [source] Reproducing cloud microphysical and irradiance measurements using three 3D cloud generatorsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 624 2007K. Sebastian Schmidt Abstract Using three cloud generators, three-dimensional (3D) cloud fields are reproduced from microphysical cloud data measured in situ by aircraft. The generated cloud fields are used as input to a 3D radiative transfer model to calculate the corresponding fields of downward and upward irradiance, which are then compared with airborne and ground-based radiation measurements. One overcast stratocumulus scene and one broken cumulus scene were selected from the European INSPECTRO field experiment, which was held in Norwich, UK, in September 2002. With these data, the characteristics of the three different cloud reproduction techniques are assessed. Besides vertical profiles and histograms of measured and modelled liquid water content and irradiance, the horizontal structure of these quantities is examined in terms of power spectra and autocorrelation lengths. 3D radiative transfer calculations are compared with the independent pixel approximation, and their differences with respect to domain-averaged quantities and 3D fields are interpreted. Copyright © 2007 Royal Meteorological Society [source] Effects of CO2 and dust on present-day solar radiation and climate on MarsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 611 2005Hannu Savijärvi Abstract A comprehensive spectrum-resolving radiative transfer model (SRM) was used to simulate the average, present-day, solar radiation field on Mars. A CO2 -only 6 hPa Martian atmosphere absorbs about 1% of zenith solar radiation, producing a modest heating rate of 4,5 K day,1 in the lowest 10 km. The trace gases have an insignificant effect but airborne dust reduces the downwelling solar flux effectively, and the reflected flux somewhat less. This produces an anti-greenhouse trend (cooling at the surface, warming within the atmosphere, reflection at the top), which increases strongly with the dust load. For instance, with dust visible optical depth of unity and sun in zenith, the surface solar irradiation is attenuated by 26% and the solar heating rate increases to about 70 K day,1 in the lowest 25 km. The numbers are however strongly dependent on the optical properties of the dust, which are not known very well. Several fast two-stream methods for dust were compared with the SRM results. Their common systematic errors were reduced by a simple, physically-based correction. The global albedo of Mars was then studied as a function of dust load, dust optics and surface albedo. The crossover from added airborne dust tending to make the whole planet look whiter or darker occurred at surface albedo of about 35%, nearly independently of the dust load. We demonstrate, however, that this value is sensitive to the optical properties of the assumed dust. Copyright © 2005 Royal Meteorological Society [source] | ||||||||||