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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1989

Fast spectroscopic variations on rapidly-rotating, cool dwarfs. 3: Masses of circumstellar absorbing clouds on AB Doradus

New time-resolved H alpha, Ca II H and K and Mg II h and k spectra of the rapidly-rotating K0 dwarf star AB Doradus (= HD 36705). The transient absorption features seen in the H alpha line are also present in the Ca II and Mg II resonance lines. New techniques are developed for measuring the average strength of the line absorption along lines of sight intersecting the cloud. These techniques also give a measure of the projected cloud area. The strength of the resonance line absorption provides useful new constraints on the column densities, projected surface areas, temperatures and internal turbulent velocity dispersions of the circumstellar clouds producing the absorption features. At any given time the star appears to be surrounded by at least 6 to 10 clouds with masses in the range 2 to 6 x 10(exp 17) g. The clouds appear to have turbulent internal velocity dispersions of order 3 to 20 km/s, comparable with the random velocities of discrete filamentary structures in solar quiescent prominences. Night-to-night changes in the amount of Ca II resonance line absorption can be explained by changes in the amplitude of turbulent motions in the clouds. The corresponding changes in the total energy of the internal motions are of order 10(exp 29) erg per cloud. Changes of this magnitude could easily be activated by the frequent energetic (approximately 10(exp 34) erg) x ray flares seen on this star.

Cameron, A. Collier↗
NASA NTRS1984

Theoretical development of Monte Carlo codes for modeling cumulus cloud fields

Reflected fluxes are calculated for stratocumulus cloud fields as a function of skycover, cloud aspect ratio, and cloud shape. Cloud liquid water volume is held invariant as cloud shape is varied so that the results can be utilized more effectively by general circulation models and climate models. On the basis of required accuracy in the Earth Radiation Budget Experiment program, an order of magnitude value of 10 W/sq m is used to estimate significant differences between plane parallel and broken cloudiness. This limit is exceeded for cloud covers between 10% and 90%, indicating that plane paralel calculations are not satisfactory at most values of cloud cover. The choice of cloud shape also leads to large differences in reflected fluxes. These differences are traced to the anisotropic intensity pattern out the cloud sides, to the size and shape of the holes between clouds, and to variations in cloud area as viewed from the solar direction. An empirical relationship for effective cloud cover is given at solar zenith angle of theta = 60 deg. This relationship allows for the relatively accurate (delta F = 10 - 15 W/sq m.) computation of broken cloud field reflected fluxes from plane parallel calculations.

Welch, R. M.↗
NASA NTRS2019

Fusion of Surface Ceilometer Data and Satellite Cloud Retrievals in 2D Mesh Interpolating Model with Clustering

For accurate cloud ceiling information, a data fusion approach is proposed that utilizes satellite data to extend surface station information to much wider areas. Cloud base height (CBH) retrieved from satellite observations provides for much larger spatial coverage and higher resolution. The direct comparison of GOES-16 CBH with surface station ceiling yields a local bias that has to be corrected for in the initial GOES-16 cloud base information. This sparsely sampled bias correction presents an irregular 2D mesh of control points, which is then interpolated by constructing a continuous smooth field using polyharmonic splines. The influence of remote stations is restricted by grouping the control points into clusters depending on an effective distance. This cluster-based approach allows for constructing separate spline surfaces corresponding to physically different clouds. The obtained continuous bias correction function is then applied to the entire GOES-16 pixel level CBH except for areas far away from surface stations in data sparse regions such as offshore. The described method is currently being tested using daytime-only observations over the central and eastern United States. Overall, this approach has potential to provide more accurate, high spatial resolution cloud ceiling information for the aviation community.

Khlopenkov, Konstantin↗
NASA NTRS1992

The effect of spatial resolution upon cloud optical property retrievals. I - Optical thickness

High spectral and spatial resolution Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) imagery is used to study the effects of spatial resolution upon fair weather cumulus cloud optical thickness retrievals. As a preprocessing step, a variation of the Gao and Goetz three-band ratio technique is used to discriminate clouds from the background. The combination of the elimination of cloud shadow pixels and using the first derivative of the histogram allows for accurate cloud edge discrimination. The data are progressively degraded from 20 m to 960 m spatial resolution. The results show that retrieved cloud area increases with decreasing spatial resolution. The results also show that there is a monotonic decrease in retrieved cloud optical thickness with decreasing spatial resolution. It is also demonstrated that the use of a single, monospectral reflectance threshold is inadequate for identifying cloud pixels in fair weather cumulus scenes and presumably in any inhomogeneous cloud field. Cloud edges have a distribution of reflectance thresholds. The incorrect identification of cloud edges significantly impacts the accurate retrieval of cloud optical thickness values.

Feind, Rand E.↗
NASA NTRS1994

Microphysical modeling of cirrus. 2: Sensitivity studies

The one-dimensional cirrus model described in part 1 of this issue has been used to study the sensitivity of simulated cirrus microphysical and radiative properties to poorly known model parameters, poorly understood physical processes, and environmental conditions. Model parameters and physical processes investigated include nucleation rate, mode of nucleation (e.g., homogeneous freezing of aerosols and liquid droplets or heterogeneous deposition), ice crystal shape, and coagulation. These studies suggest that the leading sources of uncertainty in the model are the phase change (liquid-solid) energy barrier and the ice-water surface energy which dominate the homogeneous freezing nucleation rate and the coagulation sticking efficiency at low temperatures which controls the production of large ice crystals (radii greater than 100 mcirons). Environmental conditions considered in sensitivity tests were CN size distribution, vertical wind speed, and cloud height. We found that (unlike stratus clouds) variations in the total number of condensation nuclei (NC) have little effect on cirrus microphysical and radiative properties, since nucleation occurs only on the largest CN at the tail of the size distribution. The total number of ice crystals which nucleate has little or no relationship to the number of CN present and depends primarily on the temperature and the cooling rate. Stronger updrafts (more rapid cooling) generate higher ice number densities, ice water content, cloud optical depth, and net radiative forcing. Increasing the height of the clouds in the model leads to an increase in ice number density, a decrease in effective radius, and a decrease in ice water content. The most prominent effect of increasing cloud height was a rapid increase in the net cloud radiative forcing which can be attributed to the change in cloud temperature as well as change in cloud ice size distributions. It has long been recognized that changes in cloud height or cloud area have the greatest potential for causing feedbacks on climate change. Our results suggest that variations in vertical velocity or cloud microphysical changes associatd with cloud height changes may also be important.

Jensen, Eric J.↗
NASA NTRS1993

Surface areas and porosities of ices used to simulate stratospheric clouds

Surface areas, bulk densities, and porosities of ices formed at 85 or 200 K are measured to study the morphology of the vapor-deposited ices that have been used to simulate ice clouds in the laboratory. Surface areas are measured from the Brunauer, Emmett, and Teller (BET) analysis of absorption isotherms obtained at 72.2 K. Bulk densities and porosities are determined photogrammetrically. Results show that water ice and HNO3-H2O ice films deposited from the vapor at temperatures below 200 K exhibit large BET surface areas and are highly porous. For the ices annealed at temperatures above 200 K, external surface areas calculated from the observed particle sizes agree reasonably well with the BET areas, which indicates that the annealed ices are composed of nonporous particles and that the porosity of these ices is due to interstices among the particles.

Keyser, Leon F.↗
NASA NTRS1991

Fluctuations of high clouds and 500-mb geopotential heights in baroclinic waveguides

The spatial phase relationship between the atmospheric circulation and the bandpass fluctuations in cloudiness are investigated using satellite retrievals of high cloud areas reported by Stowe et al. (1988, 1989) NMC 500-mb geopotential heights in northern extratropics. Results of the analysis suggest that the high-cloud structures of baroclinic waves are less spatially coherent than the internal geopotential-height structures. It is shown that over the North Pacific, small-scale (latitudinal wavenumber 13-18) fluctuations in geopotential play a greater role in forcing high cloudiness than do medium-scale (latitudinal wavenumber 7-12) fluctuations in geopotential.

Charlock, Thomas P.↗
NASA NTRS1976

Infrared thermal mapping of the Martian surface and atmosphere - First results

The Viking infrared thermal mapper measures the thermal emission of the Martian surface and atmosphere and the total reflected sunlight. With the high resolution and dense coverage being achieved, planetwide thermal structure is apparent at large and small scales. The thermal behavior of the best-observed areas, the landing sites, cannot be explained by simple homogeneous models. The data contain clear indications for the relevance of additional factors such as detailed surface texture and the occurrence of clouds. Areas in the polar night have temperatures distinctly lower than the CO2 condensation point at the surface pressure. This observation implies that the annual atmospheric condensation is less than previously assumed and that either thick CO2 clouds exist at the 20-kilometer level or that the polar atmosphere is locally enriched by noncondensable gases.

Kieffer, H. H.↗
NASA NTRS1988

Simulation and diagnosis of water vapor imagery with mesoscale model output

The present simulation of 6.7-micron channel water vapor imagery employs March 6-7, 1982 soundings from the Limited Area Mesoscale Prediction System (LAMPS) mesoscale model as inputs to a radiative transfer scheme. A comparison of model-generated and observed brightness temperatures indicates that LAMPS was able to replicate major features of the VAS imagery, including the pronounced warm, dry development streak and a cold cloud area. The model was not, however, able to resolve such finer-scaled details as the double structure of the development portion of the streak.

Muller, Bradley M.↗
NASA NTRS1983

Rain estimation from satellites: An examination of the Griffith-Woodley technique

The Griffith-Woodley Technique (GWT) is an approach to estimating precipitation using infrared observations of clouds from geosynchronous satellites. It is examined in three ways: an analysis of the terms in the GWT equations; a case study of infrared imagery portraying convective development over Florida; and the comparison of a simplified equation set and resultant rain map to results using the GWT. The objective is to determine the dominant factors in the calculation of GWT rain estimates. Analysis of a single day's convection over Florida produced a number of significant insights into various terms in the GWT rainfall equations. Due to the definition of clouds by a threshold isotherm the majority of clouds on this day did not go through an idealized life cycle before losing their identity through merger, splitting, etc. As a result, 85% of the clouds had a defined life of 0.5 or 1 h. For these clouds the terms in the GWT which are dependent on cloud life history become essentially constant. The empirically derived ratio of radar echo area to cloud area is given a singular value (0.02) for 43% of the sample, while the rainrate term is 20.7 mmh-1 for 61% of the sample. For 55% of the sampled clouds the temperature weighting term is identically 1.0. Cloud area itself is highly correlated (r=0.88) with GWT computed rain volume. An important, discriminating parameter in the GWT is the temperature defining the coldest 10% cloud area. The analysis further shows that the two dominant parameters in rainfall estimation are the existence of cold cloud and the duration of cloud over a point.

Negri, A. J.↗
NASA NTRS1984

Rain estimation from satellites - An examination of the Griffith-Woodley Technique

The Griffith-Woodley Technique (GWT) is an approach to estimating precipitation using infrared observations of clouds from geosynchronous satellites. It is examined in three ways: an analysis of the terms in the GWT equations; a case study of infrared imagery portraying convective development over Florida; and the comparison of a simplified equation set and resultant rain map to results using the GWT. The objective is to determine the dominant factors in the calculation of GWT rain estimates. Analysis of a single day's convection over Florida produced a number of significant insights into various terms in the GWT rainfall equations. Due to the definition of clouds by a threshold isotherm the majority of clouds on this day did not go through an idealized life cycle before losing their identity through merger, splitting, etc. As a result, 85 percent of the clouds had a defined life of 0.5 or 1 h. For these clouds, the terms in the GWT which are dependent on cloud life history become essentially constant. The empirically derived ratio of radar echo area to cloud area is given a singular value (0.02) for 43 percent of the sample, while the rainrate term is 20.7 mmh-1 for 61 percent of the sample. For 55 percent of the sampled clouds, the temperature weighting term is identically 1.0. Cloud area itself is highly correlated (r = 0.88) with GWT computed rain volume. An important, discriminating parameter in the GWT is the temperature defining the coldest 10 percent cloud area. The analysis further shows that the two dominant parameters in rainfall estimation are the existence of cold cloud and the duration of cloud over a point. Previously announced in STAR as N84-13735

Negri, A. J.↗
NASA NTRS1973

Water and the Martian W cloud.

The diurnal brightening of the W cloud region of Mars during the flyby of Mariners 6 and 7 is likely due to the formation of water ice clouds. The water required in the cloud and as vapor in the atmosphere to produce the observed brightening is estimated to be roughly between 0.1 and 10 microns. Either a qualified local source with this daily production over the W cloud area or a more probable daily uplift and saturation of existing atmosphere are compatible with observations.

Peale, S. J.↗
NASA NTRS1974

The major Martian yellow storm of 1971

Extensive earth-based photography produced by the International Planetary Patrol has been used to map the positions of brightened areas (clouds) during the 1971 storm on Mars. The mapping was done on an hourly basis from two days prior to the onset of the storm through its twenty-second day. Summaries of these maps are presented to illustrate the changes that take place during the course of a Martian day, as well as the changes from one day to the next. It is shown that the storm goes through a daily cycle of regeneration, although each day it advances farther than it did the day before. The possible influence of Martian topography on the progress of the storm is examined. Comparisons between red- and blue-filter photographs of the storm are presented cartographically and are discussed.

Martin, L. J.↗
NASA NTRS1983

Impact of LANDSAT MSS sensor differences on change detection analysis

Differences in overall sensor response, due to both factors within the sensor system, and external factors such as atmospheric effects, must be dealt with before change detection techniques using image differencing can be successfully implemented. The approach used to be coregister data to a base, followed by between image scatterogram generation and evaluation, and image differencing. Data from LANDSAT 2 and 3 were registered to LANDSAT 4 data. The area was limited to a small protion of the scene near the City of Santa Cruz because this was the only area cloud and haze free on all the images. Visual examination of each image, as well as the between image scatterograms, provide information on radiometric characteristics of each sensor. The image differencing, after normalizing for radiometric differences, provides a visual depiction of geometric distortions.

Likens, W.↗
NASA NTRS1984

Validation of the Thematic Mapper radiometric and geometric correction algorithms

The radiometric and geometric correction algorithms for Thematic Mapper are critical to subsequent successful information extraction. Earlier Landsat scanners, known as Multispectral Scanners, produce imagery which exhibits striping due to mismatching of detector gains and biases. Thematic Mapper exhibits the same phenomenon at three levels: detector-to-detector, scan-to-scan, and multiscan striping. The cause of these variations has been traced to variations in the dark current of the detectors. An alternative formulation has been tested and shown to be very satisfactory. Unfortunately, the Thematic Mapper detectors exhibit saturation effects suffered while viewing extensive cloud areas, and is not easily correctable. The geometric correction algorithm has been shown to be remarkably reliable. Only minor and modest improvements are indicated and shown to be effective.

Fischel, D.↗
NASA NTRS1989

Simulation studies of improved sounding systems

Two instrument designs for indirect satellite sounding of the atmosphere in the infrared are represented by the High Resolution Infra-Red Sounder, Model 2 (HIRS-2) and by the Advanced Meteorological Temperature Sounder (AMTS). The relative capabilities of the two instruments were tested by simulating satellite measurements from a group of temperature soundings, allowing the two participants to retrieve the temperature profiles from the simulated data, and comparing the results with the original temperature profiles. Four data sets were produced from radiosondes data extrapolated to a suitable altitude, representing continents and oceans, between 30S and 30N. From the information available, temperature profiles were retrieved by two different methods, statistical regression and inversion of the radiative transfer equation. Results show the consequence of greater spectral purity, concomitant increase in the number of spectral intervals, and the better spatial resolution in partly clouded areas. At the same time, the limitation of the HIRS-2 without its companion instrument leads to some results which should be ignored in comparing the two instruments. A clear superiority of AMTS results is shown.

Yates, H.↗
NASA NTRS1992

Spatial resolution and cloud optical thickness retrievals

The impact of sensor spatial resolution and accurate cloud pixel identification on cloud property retrievals was investigated. Twelve fair weather cumulus (FWC) scenes of high spectral and spatial resolution Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) data are analyzed. A variation of the 3-band ratio technique of Gao and Goetz is used to discriminate clouds from the background, and then a discrete ordinate radiative transfer model is used to obtain optical thickness of cloudy regions for each scene. To study the effect of spatial resolution upon retrieved optical thickness, the 20 m AVIRIS data was spatially degraded to spatial resolutions ranging from 40 to 960 m. Cloud area, scene average optical thickness, and distribution of retrieved optical thickness are determined at each spatial resolution. Finally, a comparison between the 3-band ratio technique and monospectral reflectance thresholding, using 20 m spatial resolution data, is presented.

Feind, Rand E.↗