Mountain Scholar :: Browsing by Author "Cox, Stephen K., author"

Browsing by Author "Cox, Stephen K., author"

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Open Access
A case study of radiative forcing upon a tropical cloud cluster
(Colorado State University. Libraries, 1980-11) Byrd, Gregory P., author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher
Tropospheric radiative convergence profiles from Cox and Griffith (1978) are used to assess the radiative forcing upon a tropical cloud cluster located in the vicinity of the GATE A/B-scale array during 4-6 September 1974. "Slab" and cross sectional analyses are carried out in order to present a three dimensional view of the radiative convergence field within the cluster and its surrounding regions. Next, a simple vertical motion profile is constructed to investigate the potential effects of radiative forcing upon cluster scale dynamical interactions with the large scale circulation. The model is tested on a daytime and a nighttime case within the cluster life cycle. The ensuing discussion evaluates the analysis and expands upon the possible roles of radiative forcing upon cluster scale and large-scale dynamics. Radiative forcing is strongest during the initial stages of cluster development. Throughout the cluster life cycle, the radiative forcing is consistently strongest in the middle troposphere (400-700 mb). With the intensification of the cluster system, a substantial weakening of horizontal gradients of radiative convergence occurs as a result of SW warming superimposed upon LW cooling during the daylight hours. Increased amounts of middle and high cloud remnants in regions surrounding the maturing cluster also contribute to the observed weakening of radiative forcing. The cross sectional analyses reveal that E-W gradients of radiative convergence between the cluster and its surroundings are comparable in magnitude to the N-S gradients. The maximum in cluster precipitation intensity is observed to lag the incidence of strong radiative forcing by some 6-8 hours, in general agreement with GATE composite observations. Continental-oceanic differential heating plays a significant role in modulating the cluster and large scale dynamical interactions, accounting for-the anomalously large precipitation lag observable in the GATE cluster. The radiatively derived vertical motion model yields a qualitatively realistic total area of cluster influence for the nighttime period. The model assumption of a closed mass system breaks down during the daytime period, yielding an unreasonably large total area of influence. This suggests the occurrence of significant cluster scale interactions with large scale circulations during the daytime period. Radiative forcing appears to play a more significant role in dynamical interactions at night, when circulations appear to be somewhat more localized.
Open Access
A climate index derived from satellite measured special infrared radiation
(Colorado State University. Libraries, 1981) Abel, Michael David, author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher
Open Access
A laboratory investigation of radiative transfer in cloud fields
(Colorado State University. Libraries, 1978) Kuenning, James Alexander, author; Cox, Stephen K., author; McKee, Thomas B., author; Department of Atmospheric Science, Colorado State University, publisher
Open Access
A modeling study of visibility in the Grand Canyon
(Colorado State University. Libraries, 1986-08) Weissbluth, Michael Jeffrey, author; Cox, Stephen K., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
Using a backward version of the Monte Carlo Radiative Transfer model, radiance values in the Grand Canyon were simulated to within the precision of ten percent. The contiguous spectral contrast was introduced to distinguish between adjacent areas of the same target and compared to the apparent spectral contrast. The contiguous spectral contrast is a valuable tool in evaluating visibility because in some cases, the target became more distinguishable when viewed against the sky while the target features became less distinguishable. Average equilibrium radiance values were calculated and incorporated into the Koschmieder estimate; the Koschmieder estimate was deemed to be of limited value in the Grand Canyon because of the violation of the assumptions used to derive the estimate. It was shown that first order scattering results alone could be used to estimate apparent spectral contrast to within a 10% accuracy; higher order scattering must be considered when radiance values are calculated for the Grand Canyon scene.
Open Access
A polynomial representation of 6.3 μm water vapor and 4.3 μm CO2 atmospheric transmissivities
(Colorado State University. Libraries, 1976) Minnis, Patrick, author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher
The research reported in this paper describes a polynomial model formulated for the depiction of 6.3 μm H2O and 4.3 μm CO2 transmissivities in the atmosphere. A six degree function utilizing a corrected optical path is found sufficient for expressing convolved tabulated transmittance data of 10 cm-1 resolution, with an RMS error of about one percent transmission. With this model transmissivities may be calculated for many spectral intervals in a relatively small amount of time with the precision required for most atmospheric problems.
Open Access
An analysis of the GATE aircraft pyrgeometer instrumentation
(Colorado State University. Libraries, 1976) Albrecht, Bruce A., author; Cox, Stephen K., author; Prokofyev, Mikhail Alekseevich, author; Department of Atmospheric Science, Colorado State University, publisher
Significant differences in US and USSR aircraft measurements of hemispherical infrared irradiance were noted during GATE in-flight intercomparisons. In specific instances the downward irradiance measured by the USSR instrument (a Kozyrev pyrgeometer) was as much as 1.5 times greater than the irradiance measured with the US instrument (an Eppley pyrgeometer). A post-GATE intercomparison at Colorado State University verified these differences; the pyrgeometer measurements were compared with independent measurements obtained with an infrared bolometer and with a radiative transfer calculation. The differences noted during GATE and post-GATE intercomparisons may be attributed to differences in calibration techniques and the accurate determination of the temperature of the instrument's thermopile cold junctions. When corrections based upon this analysis were applied to the USSR data, the maximum intercomparison differences were less than 5 percent.
Open Access
An investigation into the effects of particle nonsphericity in cirrus cloud radiative properties
(Colorado State University. Libraries, 1994) Withrow, John R., author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher
Open Access
An investigation of the radiative boundary conditions during the development of the southwest monsoon Saudi Arabian heat low
(Colorado State University. Libraries, 1981-07) Smith, Eric A., author; Sakkal, M. Marwan, author; Ackerman, Steven A., author; Cox, Stephen K., author; Vonder Haar, Thomas H., author
Progress report no. 1 on the cooperative research project between the Department of Atmospheric Science at Colorado State University and the Faculty of Meteorology and Environmental Science at King Abdul-Aziz University in accordance with the CID-ARME TED Project of the University of Arizona. Period covered February 15 to August 15, 1981.
Open Access
Analysis of boundary layer sounding data from the FIRE Marine Stratocumulus Project
(Colorado State University. Libraries, 1987-10) Schubert, Wayne H., author; Ciesielski, Paul, E., author; McKee, Thomas B., author; Kleist, John D., author; Cox, Stephen K., author; Johnson-Pasqua, Christopher, author; Smith, William L., Jr., author
We present an analysis of the boundary layer thermodynamic data obtained by the CLASS radiosonde system during the marine boundary layer experiment on San Nicolas Island in the summer of 1987. The analysis procedure retains the highest possible vertical resolution in the data. Plots of temperature, dew point temperature, potential temperature, equivalent potential temperature and saturation equivalent potential temperature are presented for each of the sixty-nine soundings taken during FIRE. Conditions were mostly cloudy with fifty-five of the sixty-nine soundings being released with stratocumulus overhead. For the fifty-live cloudy soundings, cloud top Jumps of equivalent potential temperature i, and total water mixing ratio r were also determined. Each of these soundings is then represented by a point in the (~11., ~r) plane. Fifteen of these soundings are on the unstable aide of the evaporative instability line, and there appears to be some tendency for break-up under these conditions.
Open Access
Analysis of Colorado precipitation
(Colorado State University. Libraries, 1975) Kuo, Marie Siew Man, author; Cox, Stephen K., author; Environmental Resources Center, Colorado State University, publisher
The objectives of the research proposal 'Anlaysis of Colorado Precipitation' fall into two categories. Firstly, 56 years of precipitation history were used to determine if there are any significant trends in regional and statewide precipitation in Colorado. This portion of the research is complementary to the work of Sellers (1960) who used the 90 year running mean of annual precipitation for 18 stations of Arizona and western New Mexico. Secondly, 20 years of Colorado hourly precipitation data were used to represent precipitation events, called 'storms'. and the data were examined to find storm frequency, length and yield. The storms were divided into size categories and were used to determine the contribution of each size of precipitation event to the annual total. Data from the western part of the state has been studied extensively because it is part of the upper Colorado River Basin which supplies water to the arid southwestern United States. Marlatt and Riehl (1963) found that most of the precipitation is produced in a few days and the amount of precipitation is correlated with the fraction of area receiving precipitation. In a comparison paper by Riehl and Elsberry (1964), consecutive days with precipitation were grouped together to form storms. The precipitation derived from medium size storms of 0.3 to 1.2 inches were found to be most closely related to the annual precipitation in the basin, and the size of storms roughly corresponds to the duration of the episode.
Open Access
Analysis of sounding data from Porto Santo island during ASTEX
(Colorado State University. Libraries, 1992-11-07) Schubert, Wayne H., author; Cox, Stephen K., author; McKee, Thomas B., author; Randall, David A., author; Ciesielski, Paul E., author; Kleist, John D., author; Stevens, Eric L., author
We present an analysis of the ASTEX radiosonde data obtained on Porto Santo Island during 1-28 June 1992. The data consists of 203 soundings and is available in two forms-Level I and Level II. The Level I data is the raw data produced by the real time software of the AIR radiosonde system. This data is at irregular pressure and height levels. Level II data consists of processed thermodynamic and wind data at a uniform vertical resolution of 10m, which essentially retains the highest possible vertical resolution in the original raw data. Plots of temperature and dew point temperature are presented for each of the 203 soundings taken during ASTEX. Plots of the 28 day means and of the diurnal variations are also presented. Accessibility of this data via anonymous ftp is also discussed.
Open Access
Anisotropy of reflected solar radiation from fields of finite clouds
(Colorado State University. Libraries, 1987-11) Alberta, Timothy L., author; Cox, Stephen K., author
Anisotropy of reflected solar radiation from simulated cloud fields is examined using a laboratory device known as the Cloud Field Optical Simulator (CFOS). Reflectance data from 20 cloud fields, each composed of a different random distribution of simulated clouds covering 30% of the target area, were collected. One hundred sixty-nine detector locations, each representing a different local zenith and azimuth angle, describe a hemispherical solid angle encompassing the cloud field. Radiances measured at these detector locations were numerically integrated, and locations were found where irradiances determined by assuming isotropy underestimated and overestimated the numerically integrated irradiances. Overestimates were found exclusively at large local zenith angles while the detector measured backscattered radiation. Underestimates were found primarily while the detector measured forward scattered radiation . Results of this comparison are presented in the form of frequency distributions, which also show increasing anisotropy with increasing incident zenith angle. Seven different incident zenith angles were analyzed for variations in reflected irradiance arising from different cloud field geometries. Results show irradiance differences as great as 107% at small incident zenith angles. Variations in irradiances were shown to be smaller at larger incident zenith angles. Also indicated are increased irradiance values at larger incident zenith angles. Fourier series analysis was performed on selected portions of the data set to examine the azimuthal dependence of irradiances. It was found that the number of terms required to produce an accurate representation of the intensity field at a specific local zenith angle was highly dependent on the number of azimuthal measurements available. The importance of both amplitude functions involved in the Fourier series calculations were also examined. Results indicate the increased importance of the sine term when assuming azimuthal dependence.
Open Access
Assessment of the extent of the contamination of measurements taken on Porto Santo during ASTEX
(Colorado State University. Libraries, 1994-02) Lappen, Cara-lyn, author; Cox, Stephen K., author
The object of the Atlantic Stratocumulus Experiments(ASTEX) was to measure and examine properties of the marine atmosphere. Since instruments were placed on the island of Porto Santo, however, some degree of contamination of pure marine conditions was experienced due to the local effects of island topography. In order to assess the expected differences between a pure marine environment and measurements taken on the island of Porto Santo, a numerical model- the Regional Atmospheric Modelling System (RAMS) was used in direct comparison with observational data for the case of June 10, 1992. Specifically, this study focuses on the mean wind fields simulated by RAMS and compares them to the winds measured by the United Kingdom's C130 Meteorological Research Flight, a 400Mhz wind profiler, and rawinsondes. The model's inability to resolve a 100m cliff on the windward side of the island was found to cause a phase shift between the model-produced and the actual wind fields. This was determined to be a l-2km upward phase shift and a 300m to 500m windward phase shift for the RAMS data. After applying this correction, and comparing these four sources of data, the extent of the island's effects in the horizontal as well as the vertical was determined. In the horizontal, the effects decrease with distance from the island until approximately 2km upwind or downwind where the effect was minimal. In the vertical, the effect of the island was detectable up to 3.5km, but not felt continuously. The maximum effect was found at the ground and at approximately 1.2km. Wind data taken at Porto Santo must be filtered at the ground, and near the 1.2km and 3.5km levels. In between these levels, wind measurements taken on the island would appear to provide an accurate representation of the pure marine environment.
Open Access
Broadband radiative properties of cirrus clouds deduced from aircraft measurements during fire
(Colorado State University. Libraries, 1989-10) Smith, William L., Jr., author; Cox, Stephen K., author
The bulk radiative and microphysical properties of five cirrus clouds sampled via the NCAR Sabreliner on four days during the FIRE first cirrus IFO are described. These cirrus systems, which developed under a variety of synoptic weather conditions, occurred at various altitudes and ranged in geometric thickness from about 2.0 to 4.5 km. A broadband, infrared radiative transfer model is employed to deduce the impact of the cirrus layers on infrared radiation. This model isolates the effect of the atmospheric gases from that of the cloud ice water permitting retrieval of the cloud emittance ( £c1d) and profiles of the mass absorption coefficient (K). For the five cirrus cloud cases, the total cloud emittance, £c1d, ranged from about 0.4 to 0.8 and the deduced emittance profiles appear as similar functions of ice water path (IWP) Furthermore, the mass absorption coefficient, K, is found to decrease with increasing particle size ranging from about 0.48 m2g-1 in the top of one layer to about 0.007 m2g-3 near the base of another. This relationship is somewhat dissimilar from one cirrus system to the next suggesting the significant effect of some unmeasured microphysical property. Small particles, which have been shown by other authors to be prevalent in cirrus clouds via the spectral characteristics remotely sensed in the 8-12 μm window region, are a likely suspect. Broadband, infrared absorption coefficients (u) are also computed and found to exhibit a similar temperature dependence as data recently presented by other authors. The horizontal variabilities in the shortwave and infrared properties of these cirrus systems are explored. The range of variation in the shortwave properties are found to be similar to the observed range in the infrared. Good correlation was found between the shortwave albedo (p) and upward effective emittance (c• i). A scatter plot of these two parameters agreed well with theoretical calculations assuming an asymmetry parameter of 0.7. Downward effective emittances (c• !) were found to range from about 0.4 to 0.8, while the shortwave effective extinction (~) ranged from 0 to 0.45. c• ! and were not well correlated owing to cloud heterogeneities. Finally, the current state of cirrus radiation parameterizations was briefly assessed in relation to this data set and there appears to be sufficient observational evidence to support the initial development of parameterization schemes for general circulation and climate models.
Open Access
Case study of convection lines during GATE
(Colorado State University. Libraries, 1977) Mower, R. N. (R. Neil), author; Betts, Alan K., author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher
Open Access
Characteristics of middle and upper tropospheric clouds as deduced from rawinsonde data
(Colorado State University. Libraries, 1980) Starr, David O'C., author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher
Characterizes the static environment of middle and upper tropospheric clouds as deduced from rawinsonde data from 24 locations in the contiguous U.S. for 1977.
Open Access
Cloud analysis from bi-spectral satellite data
(Colorado State University. Libraries, 1978) Mendola, Christopher, author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher
Open Access
Colorado State University radiation instrumentation and data reduction procedures for the Convail 990 during summer MONEX
(Colorado State University. Libraries, 1980) Ackerman, Steven A., author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher
Describes the basic system design and the radiative instrumentation maintained by Colorado State University on board the Convail 990 jet aircraft during the Summer Monsoon Experiment (MONEX). Discusses calibration procedures and gives the derived constraints used to convert instrument output to engineering units. Also discusses specific problems encountered during data reduction and the methods used to overcome them.
Open Access
Comparison of a thermopile broadband detector and a photon detector for the measurement of solar radiation
(Colorado State University. Libraries, 1976) Silva Dias, Maria Assunção Faus da, author; Cox, Stephen K., author; Davis, John Moulton, 1938-, author; Department of Atmospheric Science, Colorado State University, publisher
Open Access
Computer simulation of irradiance measurements from aircraft
(Colorado State University. Libraries, 1975) Poellot, Michael R., author; Cox, Stephen K., author; Department of Atmospheric Science, Colorado State University, publisher