Spatial scales of cirrus cloud properties

Research in studying the spatial scales of the cirrus, used data collected during the flight legs of the NCAR Sabreliner aircraft on four days during the FIRE Cirrus IFO to study the spatial scales of the cirrus, and will concentrate on the scales of horizontal wind. The spatial scales of the cloud features can be described by power spectra (or spectral density graphs) and cumulative variance graphs. The cumulative variance graphs were created by first using a Fast Fourier Transform (FFT) to create variance spectra. The variances were then summed in a cumulative fashion from the largest scalelengths (wavelengths) to the smallest. No detrending was done to the original data, and no smoothing or averaging was done to the spectral points. All the spectral points were included. This means that the values of the first five to ten spectral points of the large scalelengths should only be considered to be qualitatively correct. The cumulative variance at smaller scalelengths should be correct because a more accurate representation of the variance at the larger scalelengths should only redistribute the energy amongst the larger scalelengths

Radiative properties of cirrus clouds inferred from broadband measurements during FIRE

It is well known that clouds are significant modulators of weather and climate because of their effects on the radiation field and thus on the energy balance of the earth atmosphere system. As a result, the accurate prediction of weather and climate depends to a significant degree on the accuracy with which cloud radiation interactions can be described. The broadband radiative and microphysical properties of five cirrus cloud systems are reported, as observed from the NCAR Sabreliner during the FIRE first Cirrus IFO, in order to better understand cirrus cloud-radiation interactions. A broadband infrared (BBIR) radiative transfer model is used to deduce BBIR absorption coefficients in order to assess the impact of the cirrus clouds on infrared radiation. The relationships of these absorption coefficients to temperature and microphysical characteristics are explored

Temperature sensitivity of Eppley broadband radiometers

Broadband radiometers manufactured by Eppley Laboratories Inc. are commonly used to measure irradiance from both ground-based and aircraft platforms. Namely, the pyranometer (Model PSP) measures irradiance in the .3 to 3.0 micron spectral region while the pyrgeometer (Model PIR) senses energy in the 4 to 50 micron region. The two instruments have a similar thermopile construction but different filters to achieve the appropriate spectral selection. During the fall of 1986, the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) commenced with the first cirrus Intensive Field Observation (IFO) conducted in Central Wisconsin. Due to the nature of this field project, pyranometers and pyrgeometers manufactured by Eppley were flown on NCAR's high altitude research aircraft, the Sabreliner. Inherent in the construction of these radiometers is temperature compensation circuitry designed to make the instrument sensitivity nominally constant over a temperature range from -20 to +40 C. Because the Sabreliner flew at high altitudes where temperatures were as cold as -70 C, it was necessary to determine the radiometers relative sensitivity to temperatures below -20 C and apply appropriate corrections to the FIRE radiation data set. A procedure to perform this calibration is outlined. It is meant to serve as a supplement to calibration procedures

Downwelled longwave surface irradiance data from five sites for the FIRE/SRB Wisconsin Experiment from October 12 through November 2, 1986

Tables are presented which show data from five sites in the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE)/Surface Radiation Budget (SRB) Wisconsin experiment regional from October 12 through November 2, 1986. A discussion of intercomparison results is also included. The field experiment was conducted for the purposes of both intensive cirrus-cloud measurements and SRB algorithm validation activities

Finite cloud effects in longwave radiative transfer

November 1994.Sponsored by National Aeronautics and Space Administration NAG-1-1146.Sponsored by Office of Naval Research N00014-91-J-1422

Radiative properties of Cirrus clouds: FIRE IFO case October 28, 1986

A description of the radiative properties of two cirrus clouds sampled on 10/28/88 in the FIRE cirrus IFO is presented. The clouds are characterized in terms of the broadband infrared effective emittance, cloud fractional absorptance, shortwave heating rate, cloud albedo and vertical velocity. The broadband fluxes used in these calculations were obtained from measurements made by pyranometers and pyrgeometers. The shortwave irradiances were corrected to a horizontal plane and normalized to the same time by taking into account Sabreliner flight information (i.e., pitch, roll, heading and angle of attack), as well as sun-earth geometry considerations. Since only one aircraft was used, broadband fluxes at different levels in the cloud were not measured simultaneously. As a result, sampling errors may occur due to the nonsteady state of the cloud field or due to the possibility that the flight legs were not flown directly above or below each other. To minimize these errors and to simplify the analysis, the necessary variables were averaged and the averages used in the calculations. The downwelling shortwave and longwave irradiances were used as selection criteria to remove cloud free data encountered along the data sampling leg

Vertical velocity observations of a FIRE II cirrus event

July 1994.Includes bibliographical references.The development of doppler radar wind profilers and their subsequent deployment have dramatically improved the spatial and temporal resolutions of wind observations. While the horizontal winds deduced from these observations are generally reliable, serious questions remain on the ability to reliably observe the vertical wind component. In an upper tropospheric cirrus cloud environment often characterized by weak backscatter signal strength, small magnitude vertical motions, high altitude and short life cycle, this problem is especially difficult. A review of the echo generating mechanisms for a 400 MHz radar system is presented. This study further examines the feasibility of determining reliable vertical motion fields from both individual and a network of wind profiler observations. Data employed in this research were collected during the FIRE II experiment in November and December of 1991. Vertical motions were calculated in three ways: directly from the doppler radial velocity observations, from a quasi-V AD method utilizing the four non-zenith profiler beams, and by applying the kinematic method to profiler network data. The deduced vertical wind fields from each method are compared. This research also includes a diagnostic study of a jet streak system observed on 26 November 1991; this study emphasizes the thermal and dynamic instability structures, the vertical forcing the ageostrophic circulation. Results from the diagnostic and previous theoretical studies are compared with the vertical velocity fields deduced from wind profiler observations.Sponsored by the National Aeronautics and Space Administration NAG 1-1146, and the Department of Energy DE-FG02-90ER60970

Observation and parameterization of solar irradiance in marine stratocumulus and cumulus regimes

December 1995.Bibliography: pages 100-104.Sponsored by National Aeronautics and Space Administration NAG 1-1704.Sponsored by Office of Naval Research N00014-91-J-1422, P00006.Sponsored by Office of Naval Research N00014-95-1-1188

Radiative energy budget estimates for the 1979 Southwest Summer Monsoon

November, 1986.Includes bibliographical references

Tracking errors and optical scatter in a solar tracker with linear regression error correction

March 1998.Also issued as Norman Bryce Wood's thesis (M.S.) -- Colorado State University, 1998.Includes bibliographical references.Tracking errors were assessed for a computer controlled solar tracker. The effects of optical scattering on radiometric measurements performed with the tracker were also evaluated. As the position of the tracker is iteratively corrected over time, linear regression is used to calculate a best-fit correction for tracking error. The performance of the tracker was found to be sensitive to the timing of the iterative corrections and to the errors associated with those corrections. Using an optimized scheme for iterative corrections in a field test, the average tracking error was found to be 0.11 ± 0.05 degrees for 48 hours following the final iterative correction. The solar tracker may be fitted with a mirror which can reflect the image of a target into an instrument. Because the mirror is exposed to multiple sources of illumination (direct sunlight, skylight, and light from surrounding objects) the scattering properties of the mirror are important. The intensity of light scattered from the mirror was compared with the intensity of diffuse skylight. Scatter from the diffuse field incident on the mirror (background scatter) was found to be more significant than scatter from the direct solar beam, and both were significant compared to the intensity of diffuse skylight. Background scatter ranged from 20% to 70% of the total measured signal, depending on scattering geometry and wavelength. Solar scatter ranged from 1% to 20%, also depending on scattering geometry and wavelength. The scattering properties of the mirror, as measured by the bidirectional reflectance distribution function, appeared to be anisotropic, possibly because of surface defects. For the wavelengths examined, the scattering properties did not follow the wavelength scaling law predicted by Rayleigh-Rice theory for clean, smooth, front-surface reflectors.Sponsored by the National Aeronautics and Space Administration (grant no. NAG1-1704); the Office of Naval Research (contract no. N00014-91-J-1422); and the Department of Defense Center for Geoscience Phase II (contract no. DAAH04-94-G-0420)