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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 NTRS1983

The effect of volcanic aerosols on the thermal infrared budget of the lower stratosphere

The thermal IR heating of the stratosphere due to volcanic aerosols such as those released by the eruption of El Chichon is investigated by means of clear-sky model computations using a LOWTRAN5 radiance code (Kneizys et al., 1980) modified by Charlock (1983) to increase its vertical resolution. The results are presented graphically for 4-km-thick aerosol layers at altitudes 18, 22, and 25 km and at latitudes 0 deg and 35 deg N, and the effects of tropospheric cloud height (0-10 km) are taken into account. The aerosol-induced IR divergence is shown to depend on aerosol height and to be highly and nonlinearly sensitive to the location of underlying water clouds.

Charlock, T. P.↗
NASA NTRS1983

Influence of clouds on the earth's radiation budget determined from GOES data

Estimates of the cloud radiative effects on the earth's regional and zonal radiation budgets derived from GOES data during November 1978 are presented. The diurnal cloud cover variability is shown to affect both the radiation-budget measurements and the estimation of the overall effect of clouds on the net flux. For this data set, the cloud cover causes a decrease in the net flux from the clear-sky value. Thus, the cloud albedo effect outweights the greenhouse effect of the clouds. It is found that the value of the change in the radiation balance is closely related to the amount of incident solar radiation and to the zonal distributions of low, middle, and high cloud cover.

Harrison, E. F.↗
NASA NTRS1986

Development of algorithms for understanding the temporal and spatial variability of the earth's radiation balance

A brief description is given of how temporal and spatial variability in the earth's radiative behavior influences the goals of satellite radiation monitoring systems and how some previous systems have addressed the existing problems. Then, results of some simulations of radiation budget monitoring missions are presented. These studies led to the design of the Earth Radiation Budget Experiment (ERBE). A description is given of the temporal and spatial averaging algorithms developed for the ERBE data analysis. These algorithms are intended primarily to produce monthly averages of the net radiant exitance on regional, zonal, and global scales and to provide insight into the regional diurnal variability of radiative parameters such as albedo and long-wave radiant exitance. The algorithms are applied to scanner and nonscanner data for up to three satellites. Modeling of dialy shortwave albedo and radiant exitance with satellite samling that is insufficient to fully account for changing meteorology is discussed in detail. Studies performed during the ERBE mission and software design are reviewed. These studies provide quantitative estimates of the effects of temporally sparse and biased sampling on inferred diurnal and regional radiative parameters. Other topics covered include long-wave diurnal modeling, extraction of a regional monthly net clear-sky radiation budget, the statistical significance of observed diurnal variability, quality control of the analysis, and proposals for validating the results of ERBE time and space averaging.

Brooks, D. R.↗
NASA NTRS1986

Radiation fluctuation statistics in satellites and GCM's Cross correlations of albedo and IR with temperature, moisture, and dynamics

Cross-correlations were calculated between the radiation emitted and reflected from the top of the atmosphere and the temperature, horizontal wind and precipitable water in the middle troposphere. The study was extended to the time domain by filtering data for 1-2 and 2.5-6 day periods. The effects of cloud radiation were quantified by comparisons of IR full-sky and clear-sky values. Significant correlations were obtained between the middle atmospheric physical and dynamical parameters and the top of the atmosphere radiation.

Charlock, T. P.↗
NASA NTRS1987

The role of earth radiation budget studies in climate and general circulation research

The use of earth radiation budget (ERB) data for climate and general circulation research is studied. ERB measurements obtained in the 1960's and 1970's have provided data on planetary brightness, planetary global energy balances, the greenhouse effect, solar insolation, meridional heat transport by oceans and atmospheres, regional forcing, climate feedback processes, and the computation of albedo values in low latitudes. The role of clouds in governing climate, in influencing the general circulation, and in determining the sensitivity of climate to external perturbations needs to be researched; a procedure for analyzing the ERB data, which will address these problems, is described. The approach involves estimating the clear-sky fluxes from the high spatial resolution scanner measurement and defining a cloud radiative forcing; the global average of the sum of the solar and long-wave cloud forcing yields the net radiative effect of clouds on the climate.

Ramanathan, V.↗
NASA NTRS1987

Relationships between vegetation indices, radiation absorption, and net photosynthesis evaluated by a sensitivity analysis

A two-stream approximation to the radiative-transfer equation is used to calculate the vegetation indices (simple ratio and normalized difference), the fraction of incident photosynthetically active radiation (PAR) absorbed by the canopy, and the daily mean canopy net photosynthesis under clear-sky conditions. The model calculations are tested against field observations over wheat, cotton, corn, and soybean. The relationships between the vegetation indices and radiation absorption or net photosynthesis are generally found to be curvilinear, and changes in the soil reflectance affected these relationships. The curvilinearity of the relationship between normalized differences and PAR absorption decreases as the magnitude of soil reflectance increases. The vegetation indices might provide the fractional radiation absorption with some a priori knowledge about soil reflectance. The relationship between the vegetation indices and net photosynthesis must be distinguished for C3 and C4 crops. Effects of spatial heterogeneity are discussed.

Choudhury, Bhaskar J.↗
NASA NTRS1987

Generation of liquid water on Mars through the melting of a dusty snowpack

An optical/thermal model for dusty snowpacks at temperate Martian latitudes is used to investigate the possibility of valley network formation by liquid water that was provided by snowmelts, assuming insolation absorption under clear-sky conditions. The mean-annual surface temperatures for snow and the atmospheric exchange terms of the surface energy balance are constrained by global climate model results. Under favorable conditions, liquid water is generated at atmospheric pressures as low as 30-100 mbar, provided that the substrate is composed of regolith; this condition is in keeping with the cratered terrain expected in an ancient Martian surface.

Clow, Gary D.↗
NASA NTRS1988

The budget of biologically active ultraviolet radiation in the earth-atmosphere system

This study applies the concept of a budget to describe the interaction of solar ultraviolet (UV) radiation with the earth-atmosphere system. The wavelength ranges of interest are the biologically relevant UV-B between 280 and 320 nm and the UV-A from 32000 to 400 nm. The Nimbus 7 solar backscattered ultraviolet (SBUV) instrument provides measurements of total column ozone and information concerning cloud cover which, in combination with a simple model of radiation transfer, define the fractions of incident solar irradiance absorbed in the atmosphere, reflected to space, and absorbed at the ground. Results for the month of July quantify the contribution of fractional cloud cover and cloud optical thickness to the radiation budget's three components. Scattering within a thick cloud layer makes the downward radiation field at the cloud base more isotropic than is the case for clear skies. For small solar zenith angles, typical of summer midday conditions, the effective pathlength of this diffuse irradiance through tropospheric ozone is greater than that under clear-sky conditions. The result is an enhanced absorption of UV-B radiation in the troposphere during cloud-covered conditions. Major changes in global cloud cover or cloud optical thicknesses could alter the ultraviolet radiation received by the biosphere by an amount comparable to that predicted for long-term trends in ozone.

Frederick, John E.↗
NASA NTRS1987

Atmospheric general circulation and its low frequency variance - Radiative influences

The possible effects of radiation on the evolution of the atmosphere on time scales ranging from about a week to about 90 days are examined with reference to the available observational and modeling studies. The clear-sky and cloud radiative processes are shown to exert significant vertical, latitudinal, and longitudinal gradients in the diabatic heating within the troposphere and the stratosphere. The meridional heating gradient, which drives the general circulation, is altered significantly by clouds. The major conclusion of the study is that the observed negative anomalies in the outgoing IR radiation following intense warm episodes of tropicl sea-surface temperature (El Nino) are indeed anomalies in the cloud-radiative forcing.

Ramanathan, V.↗
NASA NTRS1988

The Nimbus-7 Global Cloud Climatology

The Nimbus-7 Global Cloud Climatology (N7GCC) has been produced from measurements made between April 1979 and March 1985 using the Temperature Humidity IR Radiometer and the Total Ozone Mapping Spectrometer on the Nimbus-7 satellite. The N7GCC gives, near local noon and midnight, the fractional area covered by high-level, middle-level, and low-altitude clouds, and the total fractional area covered by all clouds. Statistics for cirrus, deep convective, and warm low-altitude clouds and the cloud and clear-sky radiances with correlative surface temperatures are also included. The N7GCC is compared with other cloud data sets, including the International Satellite Cloud Climatology Project.

Hwang, Paul H.↗
NASA NTRS1988

Comparison of cloud amounts derived using GOES and Landsat data

A hybrid bispectral threshold method (HBTM) is presently used to compare cloud amounts derived from Landsat digital data over 22 regions having various cloud types with cloudiness information obtained from collocated, nearly-simultaneous 4 x 8-km GOES visible and IR data. A sensitivity analysis indicates that an rms underestimation of about 0.01 in clear sky reflectance by the HBTM increased the GOES cloud amount by 0.06, which is more than twice the decrese in cloud amount obtained by an equivalent increase in clear-sky reflectance. Landsat imagery and cloud properties derived from the Landsat data are used to explain how the partially cloud-filled GOES pixels were treated by the HBTM. It is found that the HBTM accounts for the effects of partially cloud-filled FOVs in most cases of the present study.

Minnis, Patrick↗
NASA NTRS1988

Fluctuation statistics of outgoing longwave radiation in a general circulation model and in satellite data

Fluctuation statistics of Northern-Hemisphere-winter outgoing longwave radiation (OLR) obtained from data collected by Nimbus 7 and NOAA AVHRR are compared with those computed by a general circulation model (GCM). It was found that the GCM OLR has more variance than does the satellite, but that the GCM clear-sky OLR has less variance than the satellite OLR. The variance of the GCM outgoing full-sky OLR was found to be forced by clouds. While the standard deviation of the GCM full OLR is larger than that of the satellite OLR, the geographical patterns of both are similar. The autocorrelations of the modeled and the observed OLR also display similar geographical distributions, and they are in turn correlated with the dynamics.

Charlock, Thomas P.↗
NASA NTRS1988

First estimates of the diurnal variation of longwave radiation from the multiple-satellite Earth Radiation Budget Experiment (ERBE)

First results for diurnal cycles derived from the Earth Radiation Budget Experiment are presented for the combined Earth Radiation Budget Satellite and NOAA-9 spacecraft for April 1985. Regional scale longwave radiation data are analyzed to determine diurnal variations for the total scene (including clouds) and for clear-sky conditions. The longwave diurnal range was found to be greatest for clear desert regions (up to about 70 W/sq m) and smallest for clear oceans (less than 5 W/sq m). Local time of maximum longwave radiation occurs at a wide range of times throughout the day and night over oceans, but generally occurs from noon to early afternoon over land and desert regions.

Harrison, Edwin F.↗
NASA NTRS1989

Earth radiation budget and cloudiness simulations with a general circulation model

A GCM with new parameterizations of solar and terrestrial radiation, parameterized cloud optical properties, and a simple representation of the cloud liquid water feedback is used with several observational data sets to analyze the effects of cloudiness on the earth's radiation budget. The January and July results from the model are in reasonable agreement with data from Nimbus-7. It is found that the simulated cloudiness overpredicts subtropical and midlatitude cloudiness. The simulated atmospheric cloud radiative forcing is examined. The clear-sky radiation fields obtained by two methods of Cess and Potter (1987) are compared. Also, a numerical experiment was performed to determine the effects of the water vapor continuum on the model results.

HARSHVARDHAN↗
NASA NTRS1989

Nimbus-7 global cloud climatology. II - First year results

Results are presented on the analysis of the Nimbus-7 satellite data set obtained on regional and seasonal variations in global cloud cover. Four midseason months (April, July, and October 1979 and January 1980) were analyzed for the total cloud amount, the cloud amounts at high, middle, and low altitudes, the cirrus and deep convective clouds, and the cloud and clear-sky 11.5 micron-derived radiances; in addition, noon versus midnight cloud amounts were examined. The Nimbus-7 data are compared with three previously published cloud climatologies, and the differences among these data sets are discussed.

Stowe, Larry L.↗
NASA NTRS1990

Stratocumulus cloud height variations determined from surface and satellite observations

Determination of cloud-top heights from satellite-inferred cloud-top temperatures is a relatively straightforward procedure for a well-behaved troposphere. The assumption of a monotonically decreasing temperature with increasing altitude is commonly used to assign a height to a given cloud-top temperature. In the hybrid bispectral threshold method, or HBTM, Minnis et al. (1987) assume that the lapse rate for the troposphere is -6.5/Kkm and that the surface temperature which calibrated this lapse rate is the 24 hour mean of the observed or modeled clear-sky, equivalent blackbody temperature. The International Satellite Cloud Climatology Project (ISCCP) algorithm (Rossow et al., 1988) attempts a more realistic assignment of height by utilizing interpolations of analyzed temperature fields from the National Meteorological Center (NMC) to determine the temperature at a given level over the region of interest. Neither these nor other techniques have been tested to any useful extent. The First ISCCP Regional Experiment (FIRE) Intensive Field Observations (IFO) provide an excellent opportunity to assess satellite-derived cloud height results because of the availability of both direct and indirect cloud-top altitude data of known accuracy. The variations of cloud-top altitude during the Marine Stratocumulus IFO (MSIFO, June 29 to July 19, 1987) derived from surface, aircraft, and satellite data are examined.

Minnis, Patrick↗
NASA NTRS1989

Results from the Earth Radiation Budget Experiment (ERBE)

The Earth Radiation Budget Experiment (ERBE) has been observing the earth during the past 4 years from three satellites. Numerous validation procedures have been applied to the data. Particularly important have been intercomparisons between three channels of scanning radiometers and wide and medium field-of-view radiometers. These intercomparisons and onboard calibration targets have provided assurance of high data quality. In addition to the classic radiation budget parameters: global absorbed and emitted energy, ERBE is producing fluxes on scales of 250 km that can significantly increase understanding of the earth's climate. Of particular interest are ERBE measurements of clear-sky albedos and longwave fluxes, which are part of the ERBE data products. Use of data from the precessing ERBE satellite together with data from the sun-synchronous NOAA-9 and NOAA-10 satellites also provides information on the diurnal cycle of shortwave and longwave fluxes.

Barkstrom, Bruce R.↗
NASA NTRS1989

Why is there a diurnal cycle of precipitation over the oceans?

Using the Colorado State University general circulation model, simulated diurnal and semidiurnal variability of precipitation has been analyzed. At least four mechanisms have been proposed to account for the observed daily oscillations of precipitations over the ocean: direct radiation convection, radiation-dynamics-convection interactions, remote influence of the continents, and atmospheric tidal forces. Results indicate that neither land-sea contrasts nor cloudiness are necessary to produce daily variations of precipitations over the oceans. Clear-sky radiative effects, cloud-radiative effects, and the remote influence of the continents all turn out to play a role.

Randall, David A.↗