Research funded by the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) program has led to significant improvements in longwave radiative transfer modeling over the last decade. ...These improvements, which have generally come in small incremental changes, were made primarily in the water vapor self- and foreign-broadened continuum and the water vapor absorption line parameters. These changes, when taken as a whole, result in up to a 6 W m-2 improvement in the modeled clear-sky downwelling longwave radiative flux at the surface and significantly better agreement with spectral observations. This paper provides an overview of the history of ARM with regard to clear-sky longwave radiative transfer, and analyzes remaining related uncertainties in the ARM state-of-the-art Line-by-Line Radiative Transfer Model (LBLRTM). A quality measurement experiment (QME) for the downwelling infrared radiance at the ARM Southern Great Plains site has been ongoing since 1994. This experiment has three objectives: 1) to validate and improve the absorption models and spectral line parameters used in line-by-line radiative transfer models, 2) to assess the ability to define the atmospheric state, and 3) to assess the quality of the radiance observations that serve as ground truth for the model. Analysis of data from 1994 to 1997 made significant contributions to optimizing the QME, but is limited by small but significant uncertainties and deficiencies in the atmospheric state and radiance observations. This paper concentrates on the analysis of QME data from 1998 to 2001, wherein the data have been carefully selected to address the uncertainties in the 1994-97 dataset. Analysis of this newer dataset suggests that the representation of self-broadened water vapor continuum absorption is 3%-8% too strong in the 750-1000 cm-1 region. The dataset also provides information on the accuracy of the self- and foreign-broadened continuum absorption in the 1100-1300 cm-1 region. After accounting for these changes, remaining differences in modeled and observed downwelling clear-sky fluxes are less than 1.5 W m-2 over a wide range of atmospheric states.
The ISLSCP Workshop was held in Columbia, Maryland, 23–26 June 1992 with over 240 scientists and science managers attending. The goal was to assess the progress of the last decade in the areas of ...modeling, satellite data algorithm development, and field experiments. This article includes:
1.
1. A review of the state and direction of biosphere-atmosphere model development and an assessment of the data needs of the models. Models covering a large range of timescales were considered: energy-water-carbon (seconds to seasons); carbon cycles and biogeochemistry (days to years); and ecological structure and function (years to millennia).
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2. A reference to current satellite data algorithms and other global data sources. The areas covered in the workshop were: near-surface meteorology, surface radiation budget, precipitation, runoff, snow and ice, soils and soil moisture, and land cover type and land cover attributes. These are discussed in detail in other articles in this issue.
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3. A review of completed and planned major field experiments. The major experiments of the last decade are summarized and the lessons noted.
The participating scientists agreed on the need to rapidly assemble and circulate global data sets of variables and parameters required to initialize, force, and validate the global biosphere-atmosphere models. A prioritized list of data sets required to meet this need is set out and discussed. Lastly, initiatives taken by ISLSCP to satisfy these requirements are reviewed:
Initiative I. Immediate Generation of High Priority Global Data Sets
Some essential global data sets are to be put together within 2 years and released to the community by mid-1994. These data sets will be mapped to a common spatial resolution (1° × 1°) and will cover the period 1987–1988.
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1.
Vegetation: Global sets of vegetation-related parameters are to be generated with a monthly time resolution. Available AVHRR data sets are to be used as the basis for this effort, and algorithms will be applied to calculate fields of cover type, phenology, FPAR, and leaf area index. These fields can then in turn be used to infer other surface parameters such as roughness, albedo, biomass, etc.
2.
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Hydrometeorology: Global meteorological fields retrieved from numerical reanalysis will be manipulated to provide near-surface forcing data sets for temperature, humidity, windspeed, etc. Observations of precipitation, runoff, and snow cover are to be worked up into easily accessible forms.
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Radiation Budget: A closer interface with the International Satellite Cloud Climatology Project (ISCCP) and related projects will be pursued to obtain surface radiation budget components at higher spatial resolutions, as well as fields of incident PAR.
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Soils: A small project was set in place with the goal of providing a useful soil type and properties data set for use by global modelers.
Initiative II: Improved, Follow-on Data Sets
The data sets specified in Initiative I are to be generated within a 2-year period. However, it is clear that great improvements could be made over this first data release which must rely on preexisting data sets and robust, available algorithms. Work was started to scope out what needs to be done to produce improved versions of all the Initiative I data sets within 5 years, by mid-1997.
Initiative III: Improved Communications within the Land Science Community
Future discussions within ISLSCP and between ISLSCP and other bodies will focus on the need to coordinate different research thrusts within the land science community, particularly the modeling, algorithm and field experiment work.
The Advanced Very High Resolution Radiometer (AVHRR) outgoing longwave radiation (OLR) product, which NOAA has been operationally generating since 1979, is a very long data record that has been used ...in many applications, yet past studies have shown its limitations and several algorithm-related deficiencies. Ellingson et al. have developed the multispectral algorithm that largely improved the accuracy of the narrowband-estimated OLR as well as eliminated the problems in AVHRR. NOAA has been generating High Resolution Infrared Radiation Sounder (HIRS) OLR operationally since September 1998. In recognition of the need for a continuous and long OLR data record that would be consistent with the earth radiation budget broadband measurements in the National Polar-orbiting Operational Environmental Satellite System (NPOESS) era, and to provide a climate data record for global change studies, a vigorous reprocessing of the HIRS radiance for OLR derivation is necessary. This paper describes the development of the new HIRS OLR climate dataset. The HIRS level 1b data from the entire Television and Infrared Observation Satellite N-series (TIROS-N) satellites have been assembled. A new radiance calibration procedure was applied to obtain more accurate and consistent HIRS radiance measurements. The regression coefficients of the HIRS OLR algorithm for all satellites were rederived from calculations using an improved radiative transfer model. Intersatellite calibrations were performed to remove possible discontinuity in the HIRS OLR product from different satellites. A set of global monthly diurnal models was constructed consistent with the HIRS OLR retrievals to reduce the temporal sampling errors and to alleviate an orbital-drift-induced artificial trend. These steps significantly improved the accuracy, continuity, and uniformity of the HIRS monthly mean OLR time series. As a result, the HIRS OLR shows a comparable stability as in the Earth Radiation Budget Satellite (ERBS) nonscanner OLR measurements. HIRS OLR has superb agreement with the broadband observations from Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth's Radiant Energy System (CERES) in the ENSO-monitoring regions. It shows compatible ENSO-monitoring capability with the AVHRR OLR. Globally, HIRS OLR agrees with CERES with an accuracy to within 2 W msup -2 and a precision of about 4 W msup -2. The correlation coefficient between HIRS and CERES global monthly mean is 0.997. Regionally, HIRS OLR agrees with CERES to within 3 W msup -2 with precisions better than 3 W msup -2 in most places. HIRS OLR could be used for constructing climatology for applications that plan to use NPOESS ERBS and previously used AVHRR OLR observations. The HIRS monthly mean OLR data have high accuracy and precision with respect to the broadband observations of ERBE and CERES. It can be used as an independent validation data source. The uniformity and continuity of HIRS OLR time series suggest that it could be used as a reliable transfer reference for the discontinuous broadband measurements from ERBE, CERES, and ERBS. PUBLICATION ABSTRACT
Earth loses energy to space in the form of longwave (or infrared) radiation. Much of this energy is radiated through the transparent portion of the water vapor rotational band from 17 to 33 μm (300 ...to 600 cm−1). Very few measurements have been made in this spectral region to characterize how water vapor absorbs and emits longwave radiation. An Atmospheric Emitted Radiance Interferometer (AERI) with extended longwave spectral coverage has been deployed at the Surface Heat Budget of the Arctic Ocean (SHEBA) ice station 300 miles north of the Alaskan coast to measure downwelling radiances at wavelengths of 3 to 26 μm (380 to 3000 cm−1). The spectral and radiometric performance of the instrument, installation at the ice station, and initial observations are shown. Comparisons to line‐by‐line radiative transfer calculations for selected clear‐sky cases are presented, and air‐broadened water vapor continuum absorption coefficients are determined in the wing of the pure rotational band from 17 to 26 μm (380 to 600 cm−1). Comparisons of the coefficients with the widely used Clough Kneizys Davies (CKD) water vapor continuum model suggest empirical modifications to this model are necessary. Comparisons to laboratory measurements of Burch et al. 1974 made at room temperature suggests little or no temperature dependence of the continuum from 400 to 550 cm−1. Implications of these modifications on top‐of‐atmosphere and surface fluxes, as well as atmospheric cooling rates, are discussed.
The Average Mass Profile of Galaxy Clusters Carlberg, R. G; Yee, H. K. C; Ellingson, E ...
Astrophysical journal/The Astrophysical journal,
08/1997, Letnik:
485, Številka:
1
Journal Article
Galaxy Cluster Virial Masses and Omega Carlberg, R. G.; Yee, H. K. C.; Ellingson, E. ...
The Astrophysical journal,
05/1996, Letnik:
462
Journal Article
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