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At least 1,045 records · Page 58

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NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study - Cirrus parameter relationships derived from satellite and lidar data

Cirrus cloud radiative and physical characteristics are determined using a combination of ground-based, aircraft, and satellite measurements taken as part of the First ISCCP Regional Experiment (FIRE) Cirrus Intensive Field Observations (IFO) during October and November 1986. Lidar backscatter data are used to define cloud base, center, and top heights and the corresponding temperatures. Coincident GOES 4 km visible (0.65 microns) and 8 km infrared window (11.5 microns) radiances are analyzed to determine cloud emittances and reflectances. Infrared optical depth is computed from the emittance results. Visible optical depth is derived from reflectance using a theoretical ice crystal scattering model and an empirical bidirectional reflectance mode. No clouds with visible optical depths greater than 5 or infrared optical depths less than 0.1 were used in the analysis. Average cloud thickness ranged from 0.5 km to 8 km for the 71 scenes. An average visible scattering efficiency of 2.1 was found for this data set. The results reveal a significant dependence of scattering efficiency on cloud temperature.

Minnis, Patrick↗

NASA NTRS1991

Inferring the abundances of ClO and HO2 from Spacelab 3 atmospheric trace molecule spectroscopy observations

The vertical distributions of the important highly reactive stratospheric species, ClO and HO2, have been inferred from Spacelab 3 (May 1985) Atmospheric Trace Molecule Spectroscopy (ATMOS) measurements of more detectable radical and reservoir species. A simple steady state algebraic expression for ClO, utilizing the observed ClONO2/NO2 abundance ratio, approximates the ClO results of a time-dependent photochemical model at sunset (30 deg N). Balloon measurements of ClO and comparisons of time-dependent photochemical model calculations of ClONO2 and HCl with the corresponding ATMOS profiles suggest that the actual ClO values are less than the time-dependent model profiles for ClO at sunset and sunrise (47 deg S). Errors in the current model simulation of the partitioning among the principal free chlorine species (HCl, ClONO2, and ClO) are indicated. The accuracy of the time-dependent model calculations of HO2 is suggested by the agreement between model results and ATMOS observations for HO2NO2 and balloon measurements of HO2. This confirms for the first time the procedure suggested previously by a number of authors of deriving HO(x) abundances from observed fields of O3 and H2O.

Allen, Mark↗

NASA NTRS1991

Multipolar magnetic fields in neutron stars

The small periods and period derivatives of millisecond pulsars permit interesting upper bounds to be placed on the strength of multipole components in their magnetic fields if the loss of rotational energy may be approximated by vacuum electromagnetic radiation formulas. The surface field strength of millisecond pulsars may be as high as about 10 to the 12th G if the dominant multipole component is l not less than 3. Significant multipole moments may help explain the unusual pulse morphology of millisecond pulsars. If the magnetic fields in gamma-ray burst sources (old neutron stars?) have the same evolutionary history as in millisecond pulsars, the about 10 to the 12th G local fields observed in several gamma-ray bursts must be due to multipole moments with l not less than 3.

Krolik, Julian H.↗

NASA NTRS1991

Diurnal variation of marine stratocumulus over San Nicolas Island during July 1987

A study is presented of surface measurements made at San Nicolas Island during the intensive field observation marine stratocumulus phase of the First International Satellite Cloud Climatology Program Regional Experiment, July 1987, to retrieve the average diurnal variation of marine stratocumulus and associated surface variables. The diurnal behavior of the cloud base appears to be consistent with model-predicted uncoupling of the cloud layer and the subcloud layer as the turbulent flux of moisture is limited by solar heating close to the cloud base. Also, variation in surface air temperature is consistent with the limitation of the turbulent flux of heat between the two layers, screening the surface from the effect of longwave cooling from the cloud top.

Blaskovic, Miriam↗

NASA NTRS1991

Interaction of the sea breeze with a river breeze in an area of complex coastal heating

The interaction of the sea-breeze circulation with a river-breeze circulation in an area of complex coastal heating (east coast of Florida) was studied using a 3D finite-element mesoscale model. The model simulations are compared with temperature and wind fields observed on a typical fall day during the Kennedy Space Center Atmospheric Boundary Layer Experiment. The results from numerical experiments designed to isolate the effect of the river breeze indicate that the convergence in the sea-breeze front is suppressed when it passes over the cooler surface of the rivers.

Zhong, Shiyuan↗

NASA NTRS1991

Turbomachinery noise

Summarized here are key advances in experimental techniques and theoretical applications which point the way to a broad understanding and control of turbomachinery noise. On the experimental side, the development of effective inflow control techniques makes it possible to conduct, in ground based facilities, definitive experiments in internally controlled blade row interactions. Results can now be valid indicators of flight behavior and can provide a firm base for comparison with analytical results. Inflow control coupled with detailed diagnostic tools such as blade pressure measurements can be used to uncover the more subtle mechanisms such as rotor strut interaction, which can set tone levels for some engine configurations. Initial mappings of rotor wake-vortex flow fields have provided a data base for a first generation semiempirical flow disturbance model. Laser velocimetry offers a nonintrusive method for validating and improving the model. Digital data systems and signal processing algorithms are bringing mode measurement closer to a working tool that can be frequently applied to a real machine such as a turbofan engine. On the analytical side, models of most of the links in the chain from turbomachine blade source to far field observation point have been formulated. Three dimensional lifting surface theory for blade rows, including source noncompactness and cascade effects, blade row transmission models incorporating mode and frequency scattering, and modal radiation calculations, including hybrid numerical-analytical approaches, are tools which await further application.

Groeneweg, John F.↗

NASA NTRS1988

Interpreting measurements obtained with the cloud absorption radiometer

The software developed for the analysis of data from the Cloud Absorption Radiometer (CAR) is discussed. The CAR is a multichannel radiometer designed to measure the radiation field in the middle of an optically thick cloud (the diffusion domain). It can also measure the surface albedo and escape function. The instrument currently flies on a C-131A aircraft operated by the University of Washington. Most of this data was collected during the First International satellite cloud climatology project Regional Experiment (FIRE) Marine Stratocumulus Intensive Field Observation program off San Diego during July 1987. Earlier flights of the CAR have also been studied.

Source record↗

NASA NTRS1991

Reflectivities of uniform and broken layered clouds

Differences between the reflectivities of uniform layered clouds and of broken clouds taken from the same layers of the Californian coast were investigated using 1 km data obtained by the AVHRRs on the NOAA-9 and -10 satellites during the FIRE Marine Stratocumulus Intensive Field Observations (June 29 - July 18, 1987). The reflectivities are compared at 0.63 micron, where cloud droplets are nonabsorbing, and at 3.7 micron, where the cloud droplets absorb and the single-scattering albedo is about 0.9. It was found that, at visible wavelengths, the reflectivities of broken clouds were only 80-85 percent of those of the same clouds where they formed regions of extensive uniform layers. The radiation not reflected was transmitted to the surface. The results suggest that the presatellite estimates of the planetary albedo may be too large because they failed to allow for the effects of cloud boundaries on cloud reflectivities.

Coakley, James A., Jr.↗

NASA NTRS1990

A climatology of satellite-derived cloud properties over marine stratocumulus regions

Satellite data on cloud properties obtained during the First ISCCP Regional Experiment (FIRE) (where ISCCP stands for Interantional Satellite Cloud Climatology Project) were analyzed using a methodology used in the 1987 FIRE Intensive Field Observations (IFO) measurements, in order to link the small-scale IFO results to the ISCCP large-scale bulk cloud properties and to provide a detailed climatology for climate modeling. The preliminary results of the analysis delineated some of the features common to all four major subtropical marine stratus areas analyzed. The differences observed between the areas were greatest for the values of cloud optical depths.

Heck, Patrick W.↗

NASA NTRS1990

Retrieval of cirrus cloud properties from comparative analyses of aircraft and satellite measurements made during the 1986 FIRE IFO

Results are presented of a comparison of cirrus cloud properties obtained from aircraft measurements made during the FIRE Intensive Field Observations and Landsat 5 and NOAA-9 observations carried out during several near coincident overpasses by these satellites. Results of the analyses of these measurements and a comparison between measurements and model calculations were used to determine particle sizes within cirrus clouds and the IR optical depths.

Hammer, Philip D.↗

NASA NTRS1991

Planetary-scale waves in the Southern Hemisphere winter and early spring stratosphere - Stability analysis

A barotropic stability model linearized about a zonally symmetric flow is used to examine the stability characteristics of horizontal zonal-mean flow profiles representative of the Southern Hemisphere middle stratosphere during winter and early spring, with emphasis on periods when planetary wave growth appears confined to the stratosphere. Unstable modes of eastward-travelling waves 2 and 3 are found to have period sand spatial structures, similar to observations. Wave-2 and wave-3 momentum fluxes are similar in observations and model results and are consistent with the transfer of kinetic energy from the zonal-mean flow to the wave. When a barotropic model with a zonally symmetric basic flow is used, wave 3 is usually most unstable. Including a stationary wave 1 in the basic flow destabilizes both wave 2 and wave 3, but has little effect on their periods or spatial structures. The similarity between observed fields and model results in a number of cases when wave 2 appears to grow within the stratosphere suggests that in situ instabilities play a role in the evolution of the eastward-traveling wave-2 characteristic of the Southern Hemisphere winter and early spring stratosphere.

Manney, G. L.↗

NASA NTRS1991

Statistical problems of wind-generated gravity waves arising in microwave remote sensing of surface winds

The basic geometric features of a developed sea surface affecting the accuracy of wind speed measurements by satellite instruments are reviewed. Error trends in the satellite winds are shown to be correlated with various measures of wave development. For a developed sea, the influence of the equilibrium range parameters characterizing the spectrum of wind-generated waves are derived and compared with field observations. Fluctuations in the actual number of steep wavelet events which occur within a finite surface area are shown to be an important factor of the radar backscatter if the surface area, i.e., the resolution cell, is much smaller than 1 sq km. The inner scale of the equilibrium range caused by energy dissipation by breaking waves is considered to be a major factor in determining the surface's statistical geometry and, hence, its microwave returns for all satellite sensors.

Glazman, Roman E.↗

NASA NTRS1990

Comparison of stratocumulus cloud properties derived from simultaneous satellite and surface-based instrumentation

Data from the First ISCCP Regional Experiment Marine Stratocumulus Intensive Field Observation period are used here to evaluate the cloud properties derived from the GOES in the vicinity of San Nicolas Island. Comparisons of island observations with satellite cloud parameter retrievals show that the hybrid bispectral threshold method provides a reliable and relatively accurate depiction of the diurnal variations of cloud amount, height, albedo, and thickness over this region. The level of agreement obtained here is very encouraging for simple method of extracting cloud parameters from operational meteorological satellite data. It is found that dissipating stratocumulus clouds tend to become thin enough to become nonblack in the infrared spectrum. The decrease in emissivity corresponds to 100 m or more in satellite-retrieved cloud-top height.

Minnis, Patrick↗

NASA NTRS1992

Landsat-TM identification of Amblyomma variegatum (Acari: Ixodidae) habitats in Guadeloupe

The feasibility of identifying specific habitats of the African bont tick, Amblyomma variegatum, from Landsat-TM images was investigated by comparing remotely sensed images of visible farms in Grande Terre (Guadeloupe) with field observations made in the same period of time (1986-1987). The different tick habitates could be separated using principal component analysis. The analysis clustered the sites by large and small variance of band values, and by vegetation and moisture indexes. It was found that herds in heterogeneous sites with large variances had more ticks than those in homogeneous or low variance sites. Within the heterogeneous sites, those with high vegetation and moisture indexes had more ticks than those with low values.

Hugh-Jones, M.↗

NASA NTRS1990

A 2 1/2-dimensional magnetic field model of plasmoids

The traditional 2D picture of plasmoid formation predicts the creation of closed loops, field lines closed on themselves, which are called magnetic islands. Examination of plasmoid formation in three dimensions led Hughes and Sibeck (1987) to the conclusion that a flux rope is formed instead of a magnetic island. A 2 1/2-dimensional flux rope model is here used to study the magnetic topology of plasmoids and examine the ability to distinguish between the two models using magnetometer data from a single satellite pass. Spacecraft data is simulated by sampling the magnetic field along a path through the model. The principal axis directions are strongly dependent on the path of a satellite through the structure. ISEE 3 magnetic field observations of plasmoids can be reproduced using a model of a flux rope with a significant axial component. It appears that principal axis analysis of magnetometer data of a single satellite pass is insufficient to differentiate between magnetic island and flux rope models, and can give misleading indications of the real axes of symmetry of the structure.

Moldwin, Mark B.↗

NASA NTRS1992

Stratocumulus cloud properties derived from simultaneous satellite and island-based instrumentation during FIRE

Cloud parameters derived from visible and infrared window data from the Geostationary Operational Environmental Satellite (GOES) are compared to corresponding properties determined from instrumentation on San Nicolas Island off the coast of California during the First ISCCP Regional Experiment marine stratocumulus intensive field observations period in July 1987. Examination of the satellite imagery revealed that the apparent bias can be explained by the persistence of the clouds over the northwest part of the island during periods of clearing around the island. Diurnal variations in the cloud cover were very significant; minimum cloudiness occurred during the late afternoon and maximum cloudiness early in the morning. Relationships were established between the satellite-derived cloud optical depth and two surface-observed quantities: cloud liquid water path and cloud thickness. Simultaneous observations of liquid water path and satellite-derived cloud optical depth were used to infer effective cloud-droplet radius, resulting in good agreement with correlative data. The diurnal variations in cloud amount are accompanied by changes in cloud thickness, cloud-top height, cloud liquid water path, and effective droplet size. These observations provide the most complete picture, to date, of the diurnal cycle of marine stratocumulus clouds, confirming previous satellite-based inferences of the diurnal behavior of marine stratocumulus at larger scales.

Minnis, Patrick↗

NASA NTRS1992

The photochemistry of manganese and the origin of banded iron formations

The origin of the deposition of superior-type Precambrian banded iron formations (BIFs) is investigated in experiments where the effect of UV radiation on dissolved manganese was studied to determine if the commonly accepted photochemical model for BIF formation is consistent with the distribution of Mn in BIFs. Solutions containing 0.56 M NaCl and about 180 microM MnCl2, with or without 3 to 200 microM FeCl2 were irradiated with filtered and unfiltered UV light for up to 8 hrs; the solutions were deaerated and buffered to a pH of 7, and the experiments were conducted under oxygen-free atmosphere. Data on the rate of manganese photooxidation confirmed that a photochemical model for the origin of oxide facies BIFs is consistent with field observations.

Anbar, A. D.↗

NASA NTRS1992

Rock fraction effects on the interpretation of microwave emission from soils

The effect of the rock fraction of soil on emissivity is presently investigated through a combination of laboratory dielectric measurements and field observation of emissivity from soils with and without rocks. The rock fraction reduced the range of emissivity; beyond this, it appears to be important only in determining the moisture in the soil component. Data gathered at 6 cm indicate that the presence of rocks renders this and shorter wavelengths useless as soil-moisture sensors. Modeling of the 21-cm case suggest that rock-fraction effects on soil dielectric properties can be compensated for by the greater surface roughness.

Jackson, Thomas J.↗