Showing papers by "Kenneth Sassen published in 2001"
Washington University in St. Louis1, California Institute of Technology2, University of Washington3, Texas Tech University4, Pacific Northwest National Laboratory5, United States Geological Survey6, United States Naval Research Laboratory7, Goddard Space Flight Center8, University of Central Florida9, University of British Columbia10, University of San Diego11, University of Rhode Island12, University of Oregon13, Tokyo University of Marine Science and Technology14, University of Malta15, United States Environmental Protection Agency16, University of Utah17, National Institute for Environmental Studies18, Colorado State University19
TL;DR: In this paper, two intense dust storms were generated over the Gobi desert by springtime low-pressure systems descending from the northwest, and the windblown dust was detected and its evolution followed by its yellow color on SeaWiFS satellite images, routine surface-based monitoring and through serendipitous observations.
Abstract: On April 15 and 19, 1998, two intense dust storms were generated over the Gobi desert by springtime low-pressure systems descending from the northwest. The windblown dust was detected and its evolution followed by its yellow color on SeaWiFS satellite images, routine surface-based monitoring, and through serendipitous observations. The April 15 dust cloud was recirculating, and it was removed by a precipitating weather system over east Asia. The April 19 dust cloud crossed the Pacific Ocean in 5 days, subsided to the surface along the mountain ranges between British Columbia and California, and impacted severely the optical and the concentration environments of the region. In east Asia the dust clouds increased the albedo over the cloudless ocean and land by up to 10–20%, but it reduced the near-UV cloud reflectance, causing a yellow coloration of all surfaces. The yellow colored backscattering by the dust eludes a plausible explanation using simple Mie theory with constant refractive index. Over the West Coast the dust layer has increased the spectrally uniform optical depth to about 0.4, reduced the direct solar radiation by 30–40%, doubled the diffuse radiation, and caused a whitish discoloration of the blue sky. On April 29 the average excess surface-level dust aerosol concentration over the valleys of the West Coast was about 20–50 μg/m3 with local peaks >100 μg/m3. The dust mass mean diameter was 2–3 μm, and the dust chemical fingerprints were evident throughout the West Coast and extended to Minnesota. The April 1998 dust event has impacted the surface aerosol concentration 2–4 times more than any other dust event since 1988. The dust events were observed and interpreted by an ad hoc international web-based virtual community. It would be useful to set up a community-supported web-based infrastructure to monitor the global aerosol pattern for such extreme aerosol events, to alert and to inform the interested communities, and to facilitate collaborative analysis for improved air quality and disaster management.
795 citations
TL;DR: In this article, a cloud detection algorithm based on ground-based remote sensors has been developed that can differentiate among various atmospheric targets such as ice and water clouds, virga, precipitation, and aerosol layers.
Abstract: A cloud detection algorithm based on ground-based remote sensors has been developed that can differentiate among various atmospheric targets such as ice and water clouds, virga, precipitation, and aerosol layers. Standard cloud type and macrophysical properties are identified by combining polarization lidar, millimeter-wave radar, infrared radiometer, and dual-channel microwave radiometer measurements. These algorithms are applied to measurements collected during 1998 from the Atmospheric Radiation Measurement Program Cloud and Radiation Test Bed site in north-central Oklahoma. The statistical properties of clouds for this year are presented, illustrating how extended-time remote sensing datasets can be converted to cloud properties of concern to climate research.
258 citations
TL;DR: In this article, the information content of laser backscatter depolarization measurements in terms of cloud microphysical content is treated, based on scattering principles indicating that polarization lidar can be applied to identifying cloud phase, and describing ice particle shape and orientation.
Abstract: In Part II of this series of papers describing the results of the extended time observations of cirrus clouds from the University of Utah Facility for Atmospheric Remote Sensing (FARS), the information content of laser backscatter depolarization measurements in terms of cloud microphysical content is treated. The authors rely on scattering principles indicating that polarization lidar can be applied to identifying cloud phase, and describing ice particle shape and orientation. It is found that 0.694-μm lidar linear depolarization ratios δ obtained in the zenith display a steady increase with height. With respect to temperature, a minimum of δ = 0.25 is found at −17.5°C, where horizontally oriented planar ice crystals are to be expected, and the δ increase up to 0.45 at −77.5°C. This trend indicates a basic transition in cirrus ice crystal shape with temperature, likely reflecting not only the effects of crystal axis ratio (i.e., plate-to-column) but also internal and radial crystallographic featu...
217 citations
TL;DR: In this article, the visible and infrared radiative properties of midlatitude cirrus clouds over Salt Lake City, Utah, were examined using ∼860 h of combined ruby (0.694 μm) lidar and midinfrared (9.5-11.5μm) radiometer data collected between 1992 and 1999.
Abstract: In Part III of a series of papers describing the extended time high-cloud observations from the University of Utah Facility for Atmospheric Remote Sensing (FARS) supporting the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment, the visible and infrared radiative properties of cirrus clouds over Salt Lake City, Utah, are examined. Using ∼860 h of combined ruby (0.694 μm) lidar and midinfrared (9.5–11.5 μm) radiometer data collected between 1992 and 1999 from visually identified cirrus clouds, the visible optical depths τ and infrared layer emittance ϵ of the varieties of midlatitude cirrus are characterized. The mean and median values for the cirrus sample are 0.75 ± 0.91 and 0.61 for τ, and 0.30 ± 0.22 and 0.25 for ϵ. Other scattering parameters studied are the visible extinction and infrared absorption coefficients, and their ratio, and the lidar backscatter-to-extinction ratio, which has a mean value of 0.041 sr−1. Differences among cirrus clouds generated by g...
182 citations
TL;DR: In this paper, the authors examined the climatological properties of the cirrus clouds studied over Salt Lake City, Utah, ∼2200 h of data collected from 1986-96 is used to create a subset of 1389 hourly polarization ruby (0.694 μm) lidar measurements of cloud layer heights.
Abstract: A uniquely extensive high cloud dataset has been collected from the University of Utah Facility for Atmospheric Remote Sensing in support of the First (ISCCP) International Satellite Cloud Climatology Project Regional Experiment extended time observations satellite validation effort. Here in Part I of a series of papers examining the climatological properties of the cirrus clouds studied over Salt Lake City, Utah, ∼2200 h of data collected from 1986–96 is used to create a subset of 1389 hourly polarization ruby (0.694 μm) lidar measurements of cloud layer heights. These data were obtained within ±3 h of the local 0000 UTC National Weather Service radiosonde launches to provide reliable cloud temperature, pressure, and wind data. Future parts of this series will consider the inferred cirrus cloud microphysical and radiative properties. In addition to describing the cirrus macrophysical properties in terms of their yearly, seasonal, and monthly means and variabilities, the synoptic weather patterns...
163 citations
TL;DR: The University of Utah Facility for Atmospheric Remote Sensing (FARS) has been applied to the probing of the atmosphere, concentrating on the study of high-level clouds as discussed by the authors.
Abstract: Since October 1987, the University of Utah Facility for Atmospheric Remote Sensing (FARS) has been applied to the probing of the atmosphere, concentrating on the study of high–level clouds. Regular FARS measurements, which currently total ~3000 h of ruby lidar polarization data, have been directed toward basic cloud research, remote sensing techniques development, and to improving satellite cloud property retrieval methods and GCM predictions by providing climatologically representative cloud datasets and parameterizations. Although the initial studies involved mainly the ruby lidar, the facility has steadily evolved to include a range of visible, infrared, and microwave passive remote sensors, and state–of–the–art, high–resolution dual–wavelength scanning lidar and W–band Doppler radar systems. All three active systems display polarization diversity. In this paper are reviewed the specifications of FARS instrumentation and the research programs to which they have been applied. Four multiple remo...
62 citations
TL;DR: In this paper, a method for retrieval of cirrus macrophysical and radiative properties using combined ruby lidar and infrared radiometer measurements is explained in detail, including estimation of a variable backscatter-to-extinction ratio for each lidar profile, which accounts for changes in cloud microphysical properties with time.
Abstract: A method for retrieval of cirrus macrophysical and radiative properties using combined ruby lidar and infrared radiometer measurements is explained in detail. The retrieval algorithm includes estimation of a variable backscatter-to-extinction ratio for each lidar profile, which accounts for changes in cloud microphysical properties with time. The technique also utilizes a correlated K distribution radiative transfer model, where absorption coefficients K have been tabulated specifically for the bandwidth and filter function of the infrared radiometer. The radiative transfer model allows for estimation of infrared emission due to atmospheric water vapor, ozone, and carbon dioxide, which is essential for deriving cirrus radiative properties. Also described is an improved technique for estimation of upwelling IR radiation that is emitted by the surface of the earth and reflected by the cloud into the radiometer field of view. Derived cirrus cloud properties include base and top height and temperatur...
61 citations
01 Jan 2001
TL;DR: The Cirrus Parcel Model Comparison (CPM) project as mentioned in this paper is a project of the GEWEX Cloud System Study Working Group on Cirrus Cloud Systems (GCSS WG2).
Abstract: The Cirrus Parcel Model Comparison is a project of the GEWEX Cloud System Study Working Group on Cirrus Cloud Systems (GCSS WG2). The primary goal of this project is to identify and quantify cirrus model sensitivities to the state of our knowledge of nucleation and microphysics. These factors are key to understanding microphysical development in cirrus and for developing realistic treatments of such processes in larger-scale models. Phase 1 of the project will be described.
34 citations
TL;DR: In this article, a one-dimensional version of a cloud model with an explicit microphysics scheme was used to simulate a case study of middle and upper level cloud formation and evolution that was observed during the FIRE Arctic Clouds Experiment.
Abstract: A one-dimensional version of a cloud model with an explicit microphysics scheme is used to simulate a case study of middle and upper level cloud formation and evolution that was observed during the FIRE Arctic Clouds Experiment. In the simulations, the midlevel altostratus cloud is initially liquid phase, then partially freezes, and exists in mixed phase for several hours with a relative equilibrium between the rate of drop production by condensation and their depletion by freezing. The dominant mode of cirrus formation was periodic homogeneous freezing of deliquescent submicron haze particles. These crystal layers form near the tropopause and, subsequently, precipitate into the middle troposphere, causing seeding of the underlying altostratus cloud. Sensitivity tests are conducted varying the initial humidity and nucleation schemes.
33 citations
TL;DR: In this article, Wang et al. proposed a parameterization of visible optical depth and infrared layer emittance as functions of both cloud temperature and vertical thickness to facilitate climate modeling research.
Abstract: The clouds of the middle and upper troposphere are difficult to treat in models because of their variable optical properties. Based on extensive cirrus, altostratus, and altocumulus cloud remote sensing measurements and model simulations, we offer parameterizations of visible optical depth and infrared layer emittance as functions of both cloud temperature and vertical thickness to facilitate climate modeling research. We find significant differences in the emittance relations that depend on cloud phase, but quite similar optical depth versus emittance relations. In comparison to previous midlatitude cirrus results, our findings lead to lower atmospheric heating rates.
8 citations
13 Feb 2001
TL;DR: In this article, the authors report on findings from ongoing polarization lidar research at the University of Utah Facility for Atmospheric Remote Sensing (FARS), which has been applied to the climatological investigation of cirrus cloud properties for basic research and satellite measurement validation.
Abstract: We report on findings from ongoing polarization lidar research at the University of Utah Facility for Atmospheric Remote Sensing (FARS). This facility was established in 1987, and the current total of lidar and radiometric measurements is approx. 2,900-h. Research at FARS has been applied to the climatological investigation of cirrus cloud properties for basic research and satellite measurement validation (currently in its 13th year), and studies of contrails, mixed phase clouds, and volcanic and Asian dust aerosols. Among the techniques utilized for monitoring cloud and aerosol properties are triple-wave length linear depolarization measurements, and high (1.5-m by 10-Hz) resolution scanning observations. The usefulness of extended time lidar studies for atmospheric and climate research is illustrated.