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- Author or Editor: John A. Reagan x
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Abstract
A multiple wavelength solar radiometer designed for the purpose of measuring atmospheric optical depth at discrete wavelengths through the visible region is described. Experimental techniques including sample observations, are presented for obtaining atmospheric optical depth from radiometer measurements. These techniques apply for conditions where the optical depth is either temporally variant or invariant during the course of a day. The influence of the aerosol she distribution on optical depth is investigated. Theoretical calculations of the wavelength dependency of the aerosol optical depth contribution are presented for several representative aerosol size distributions. Methods are also presented for estimating the aerosol size distribution and aerosol man loading from multi-wavelength optical depth measurements.
Abstract
A multiple wavelength solar radiometer designed for the purpose of measuring atmospheric optical depth at discrete wavelengths through the visible region is described. Experimental techniques including sample observations, are presented for obtaining atmospheric optical depth from radiometer measurements. These techniques apply for conditions where the optical depth is either temporally variant or invariant during the course of a day. The influence of the aerosol she distribution on optical depth is investigated. Theoretical calculations of the wavelength dependency of the aerosol optical depth contribution are presented for several representative aerosol size distributions. Methods are also presented for estimating the aerosol size distribution and aerosol man loading from multi-wavelength optical depth measurements.
Abstract
A new analytic solution to the lidar equation is presented, which realistically considers the scattering properties of the aerosols and the molecular atmosphere individually. With this solution, it is shown, in turbid atmospheres where the aerosols dominate the scattering properties, that accurate vertical profiles of the volume extinction cross section can be obtained with an uncalibrated lidar, provided that the total transmittance of the atmospheric layer being investigated is known. This solution is applied to data samples collected under very clear and under very dusty conditions.
Abstract
A new analytic solution to the lidar equation is presented, which realistically considers the scattering properties of the aerosols and the molecular atmosphere individually. With this solution, it is shown, in turbid atmospheres where the aerosols dominate the scattering properties, that accurate vertical profiles of the volume extinction cross section can be obtained with an uncalibrated lidar, provided that the total transmittance of the atmospheric layer being investigated is known. This solution is applied to data samples collected under very clear and under very dusty conditions.
Abstract
It can be shown, theoretically, that the polarization properties of laser light scattered by a volume of air containing aerosols include considerable information as to the size distribution of the aerosols. A theoretical inversion model, utilizing the above information, is developed, which uses the Stokes parameters of the angularly scattered laser light as input data. These input data are generated theoretically from assumed size distribution functions of the aerosols. Both “perfect” measurements and measurements into which random errors are introduced are employed. These data are then used in the inversion model to generate predicted size distribution functions. Numerical experiments are performed with 0, 1 and 2% random error in the observations, in order to determine what accuracy is required in the lidar measurements. Comparisons between the actual and predicted functions are then made in order to assess the accuracy of the model.
Abstract
It can be shown, theoretically, that the polarization properties of laser light scattered by a volume of air containing aerosols include considerable information as to the size distribution of the aerosols. A theoretical inversion model, utilizing the above information, is developed, which uses the Stokes parameters of the angularly scattered laser light as input data. These input data are generated theoretically from assumed size distribution functions of the aerosols. Both “perfect” measurements and measurements into which random errors are introduced are employed. These data are then used in the inversion model to generate predicted size distribution functions. Numerical experiments are performed with 0, 1 and 2% random error in the observations, in order to determine what accuracy is required in the lidar measurements. Comparisons between the actual and predicted functions are then made in order to assess the accuracy of the model.
Abstract
The distribution of a climate model across homogeneous and heterogeneous computer environments with nodes that can reside at geographically different locations is investigated. This scientific application consists of an atmospheric general circulation model (AGCM) coupled to an oceanic general circulation model (OGCM).
Three levels of code decomposition are considered to achieve a high degree of parallelism and to mask communication with computation. First, the domains of both the gridpoint AGCM and OGCM are divided into subdomains for which calculations an carded out concurrently (domain decomposition). Second, the model is decomposed based on the diversity of tasks performed by its major components (task decompositions). Three such components are identified: (a) AGCM/physics which computes the effects on the grid-scale flow of subgrid-scale processes such as convection and turbulent mixing; (b) AGCM/dynamics, which computes the evolution of the flow governed by the primitive equations; and (c) the OGCM. Task decomposition allows the AGCM/dynamics and OGCM calculations to be carried out concurrently. Last, computation and communication are organized in such a way that the exchange of data between different tasks is carded out in subdomains of the model domain (110 decomposition). In a dedicated computer network environment, the wall-clock time required by the resulting distributed application is reduced to that for the AGCMJ physics, with the other two components and interprocess communications running in parallel.
The network bandwidth requirements for the distributed application are analyzed. It is assumed that the wall-clock time required to run the AGCM/physics for the model atmosphere in a dedicated computer environment is fixed at a value corresponding to high network efficiency. The analysis shows that, for computer environments based an nodes equivalent to the Intel Touchstone Delta, a bandwidth approaching that of the Gigabit Network is required for an efficient operation of the distributed application with model resolution double that used in current studies of the climate system if output is visualized in real time.
It is argued that distribution of a climate model based on domain, task, and 110 decomposition has the potential for significant and eventually superlinear speedup in model execution, which will facilitate performance of the long integrations required by climate studies.
Abstract
The distribution of a climate model across homogeneous and heterogeneous computer environments with nodes that can reside at geographically different locations is investigated. This scientific application consists of an atmospheric general circulation model (AGCM) coupled to an oceanic general circulation model (OGCM).
Three levels of code decomposition are considered to achieve a high degree of parallelism and to mask communication with computation. First, the domains of both the gridpoint AGCM and OGCM are divided into subdomains for which calculations an carded out concurrently (domain decomposition). Second, the model is decomposed based on the diversity of tasks performed by its major components (task decompositions). Three such components are identified: (a) AGCM/physics which computes the effects on the grid-scale flow of subgrid-scale processes such as convection and turbulent mixing; (b) AGCM/dynamics, which computes the evolution of the flow governed by the primitive equations; and (c) the OGCM. Task decomposition allows the AGCM/dynamics and OGCM calculations to be carried out concurrently. Last, computation and communication are organized in such a way that the exchange of data between different tasks is carded out in subdomains of the model domain (110 decomposition). In a dedicated computer network environment, the wall-clock time required by the resulting distributed application is reduced to that for the AGCMJ physics, with the other two components and interprocess communications running in parallel.
The network bandwidth requirements for the distributed application are analyzed. It is assumed that the wall-clock time required to run the AGCM/physics for the model atmosphere in a dedicated computer environment is fixed at a value corresponding to high network efficiency. The analysis shows that, for computer environments based an nodes equivalent to the Intel Touchstone Delta, a bandwidth approaching that of the Gigabit Network is required for an efficient operation of the distributed application with model resolution double that used in current studies of the climate system if output is visualized in real time.
It is argued that distribution of a climate model based on domain, task, and 110 decomposition has the potential for significant and eventually superlinear speedup in model execution, which will facilitate performance of the long integrations required by climate studies.
Abstract
A multi-wavelength solar radiometer has been used to monitor the directly transmitted solar radiation at discrete wavelengths spaced through the visible and near-infrared wavelength regions. The relative irradiance of the directly transmitted sunlight at each wavelength was measured during the course of each cloud-free day, from which the total optical depth of the atmosphere was determined using the Bouguer-Langley method. From the spectral variation of total optical depth the ozone absorption optical depths, and hence total ozone content of the atmosphere, have been derived. By subtracting the molecular scattering and estimated ozone absorption contributions from the total optical depth, the aerosol optical depth for each day and wavelength can be determined provided the wavelengths selected have no additional molecular absorption bands. Results of this analysis for 133 clear stable days at Tucson, Arizona are presented for a 29-month period between August 1975 and December 1977. Monthly averages of the total and aerosol optical depths are presented for five wavelengths between 0.4400 and 0.8717 μm. The aerosol optical depth obtains a maximum in July and August with a secondary maximum in April and May. The median aerosol optical depth for the entire data set decreases with wavelength from 0.0508 (λ = 0.4400 μm) to 0.0306 (λ = 0.8717 μm). Also presented are daily values of total ozone content which exhibit the characteristic seasonal cycle with peak values in early May and an annual mean value of 275 m atm-cm.
Abstract
A multi-wavelength solar radiometer has been used to monitor the directly transmitted solar radiation at discrete wavelengths spaced through the visible and near-infrared wavelength regions. The relative irradiance of the directly transmitted sunlight at each wavelength was measured during the course of each cloud-free day, from which the total optical depth of the atmosphere was determined using the Bouguer-Langley method. From the spectral variation of total optical depth the ozone absorption optical depths, and hence total ozone content of the atmosphere, have been derived. By subtracting the molecular scattering and estimated ozone absorption contributions from the total optical depth, the aerosol optical depth for each day and wavelength can be determined provided the wavelengths selected have no additional molecular absorption bands. Results of this analysis for 133 clear stable days at Tucson, Arizona are presented for a 29-month period between August 1975 and December 1977. Monthly averages of the total and aerosol optical depths are presented for five wavelengths between 0.4400 and 0.8717 μm. The aerosol optical depth obtains a maximum in July and August with a secondary maximum in April and May. The median aerosol optical depth for the entire data set decreases with wavelength from 0.0508 (λ = 0.4400 μm) to 0.0306 (λ = 0.8717 μm). Also presented are daily values of total ozone content which exhibit the characteristic seasonal cycle with peak values in early May and an annual mean value of 275 m atm-cm.
Abstract
Columnar aerosol size distributions have been inferred by numerically inverting particulate optical depth measurements as a function of wavelength. An inversion formula which explicitly includes the magnitude of the measurement variances is derived and applied to optical depth measurements obtained in Tucson with a solar radiometer. It is found that the individual size distributions of the aerosol particles (assumed spherical), at least for radii ≳ 0.1 μm, fall into one of three distinctly different categories. Approximately 50% of all distributions examined thus far can best be represented as a composite of a Junge distribution plus a distribution of relatively monodispersed larger particles centered at a radius of about 0.5 μm. Scarcely 20% of the distributions yielded Junge size distributions, while 30% yielded relatively monodispersed distributions of the log-normal or gamma distribution types. A representative selection of each of these types will be presented and discussed. The sensitivity of spectral attenuation measurements to the radii limits and refractive index assumed in the numerical inversion will also be addressed.
Abstract
Columnar aerosol size distributions have been inferred by numerically inverting particulate optical depth measurements as a function of wavelength. An inversion formula which explicitly includes the magnitude of the measurement variances is derived and applied to optical depth measurements obtained in Tucson with a solar radiometer. It is found that the individual size distributions of the aerosol particles (assumed spherical), at least for radii ≳ 0.1 μm, fall into one of three distinctly different categories. Approximately 50% of all distributions examined thus far can best be represented as a composite of a Junge distribution plus a distribution of relatively monodispersed larger particles centered at a radius of about 0.5 μm. Scarcely 20% of the distributions yielded Junge size distributions, while 30% yielded relatively monodispersed distributions of the log-normal or gamma distribution types. A representative selection of each of these types will be presented and discussed. The sensitivity of spectral attenuation measurements to the radii limits and refractive index assumed in the numerical inversion will also be addressed.
Abstract
Coordinated observational data of atmospheric aerosols were collected over a 24-h period between 2300 mountain daylight time (MDT) on 27 August 2009 and 2300 MDT on 28 August 2009 at Bozeman, Montana (45.66°N, 111.04°W, elevation 1530 m) using a collocated two-color lidar, a diode-laser-based water vapor differential absorption lidar (DIAL), a solar radiometer, and a ground-based nephelometer. The optical properties and spatial distribution of the atmospheric aerosols were inferred from the observational data collected using the collocated instruments as part of a closure experiment under dry conditions with a relative humidity below 60%. The aerosol lidar ratio and aerosol optical depth retrieved at 532 and 1064 nm using the two-color lidar and solar radiometer agreed with one another to within their individual uncertainties while the scattering component of the aerosol extinction measured using the nephelometer matched the scattering component of the aerosol extinction retrieved using the 532-nm channel of the two-color lidar and the single-scatter albedo retrieved using the solar radiometer. Using existing aerosol models developed with Aerosol Robotic Network (AERONET) data, a thin aerosol layer observed over Bozeman was most likely identified as smoke from forest fires burning in California; Washington; British Columbia, Canada; and northwestern Montana. The intrusion of the thin aerosol layer caused a change in the atmospheric radiative forcing by a factor of 1.8 ± 0.5 due to the aerosol direct effect.
Abstract
Coordinated observational data of atmospheric aerosols were collected over a 24-h period between 2300 mountain daylight time (MDT) on 27 August 2009 and 2300 MDT on 28 August 2009 at Bozeman, Montana (45.66°N, 111.04°W, elevation 1530 m) using a collocated two-color lidar, a diode-laser-based water vapor differential absorption lidar (DIAL), a solar radiometer, and a ground-based nephelometer. The optical properties and spatial distribution of the atmospheric aerosols were inferred from the observational data collected using the collocated instruments as part of a closure experiment under dry conditions with a relative humidity below 60%. The aerosol lidar ratio and aerosol optical depth retrieved at 532 and 1064 nm using the two-color lidar and solar radiometer agreed with one another to within their individual uncertainties while the scattering component of the aerosol extinction measured using the nephelometer matched the scattering component of the aerosol extinction retrieved using the 532-nm channel of the two-color lidar and the single-scatter albedo retrieved using the solar radiometer. Using existing aerosol models developed with Aerosol Robotic Network (AERONET) data, a thin aerosol layer observed over Bozeman was most likely identified as smoke from forest fires burning in California; Washington; British Columbia, Canada; and northwestern Montana. The intrusion of the thin aerosol layer caused a change in the atmospheric radiative forcing by a factor of 1.8 ± 0.5 due to the aerosol direct effect.
