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NASA NTRS1999

Evaluation of Dust Absorption and Radiative Forcing of Climate Using Satellite and Ground Based Remote Sensing

Simultaneous spaceborne and ground based measurements of the scattered solar radiation, create a powerful tool for determination of dust absorption. Absorption of solar radiation is a key component in understanding dust impact on radiative forcing at the top of the atmosphere, on the temperature profile and on cloud formation. We use Landsat spaceborne measurements at seven spectral channels in the range of 0.47 to 2.2 microns over Senegal with corresponding measurements of the aerosol spectral optical thickness by ground based sunphotometers, to find that Saharan dust absorption of solar radiation is two to four times smaller than measured in situ and represented in models. Though dust was found to absorb in the blue (single scattering albedo wo = 0.88), almost no absorption, wo = 0.98, was found for 1 greater than 0.6 microns. The results are in agreement with dust radiative measurements reported in the literature, and explain some previously reported but unexplained dust radiative properties. Therefore, the new finding should be of general relevance. The new finding increases by 50% recently estimated solar radiative forcing by dust at the top of the atmosphere and decreases the estimated dust heating of the lower troposphere due to absorption of solar radiation. Dust transported from Asia shows slightly higher absorption for wavelengths under 1 @im, that can be explained by the presence of black carbon from urban/industrial pollution associated with the submicron size mode.

Kaufman, Yoram J.↗

NASA NTRS1990

R-matrix calculations for electron-impact excitation of C(+), N(2+), and O(3+) including fine structure

The new R-matrix package for comprehensive close-coupling calculations for electron scattering with the first three ions in the boron isoelectronic sequence, the astrophysically significant C(+), N(2+), and O(3+), is presented. The collision strengths are calculated in the LS coupling approximation, as well as in pair-coupling scheme, for the transitions among the fine-structure sublevels. Calculations are carried out at a large number of energies in order to study the detailed effects of autoionizing resonances.

Luo, D.↗

NASA NTRS2003

A Search for Impact Debris in the Pliocene Age Sirius Group, Transantarctic Mountains

The Sirius Group is a mixed sequence of interbedded diamictite and mudstone of Pliocene age found at scattered locations along the length of the Transantarctic Mountains. Sirius Group rocks are usually considered tillites, but contain some very "un-tillite" elements. Within section and from site to site, Sirius Group rocks vary considerably in terms of texture and relative abundance of clast lithologies, recording a history that includes shifting influences of glacial, lacustrine, fluvial and wetland processes. The colorful heritage of the Sirius Group has generated a lot of interest due to its potential as a record of changes in the behavior of the East Antarctic icesheet during a climatologically interesting period.

Harvey, Ralph P.↗

NASA NTRS1984

Infrared emission associated with chemical reactions on Shuttle and SIRTF surfaces

The infrared intensities which would be observed by the Shuttle Infrared Telescope Facility (SIRTF), and which are produced by surface chemistry following atmospheric impact on SIRTF and the shuttle are estimated. Three possible sources of reactants are analyzed: (1) direct atmospheric and scattered contaminant fluxes onto the shuttle's surface; (2) direct atmospheric and scattered contaminant fluxes onto the SIRTF sunshade; and (3) scattered fluxes onto the cold SIRTF mirror. The chemical reactions are primarily initiated by the dominent flux of reactive atomic oxygen on the surfaces. Using observations of the optical glow to constrain theoretical parameters, it is estimated for source (1) that the infrared glow on the SIRTF mirror will be comparable to the zodiacal background between 1 and 10 micron wavelengths. It is speculated that oxygen reacts with the atoms and the radicals bound in the organic molecules that reside on the shuttle and the Explorer surfaces. It is concluded that for source (2) that with suitable construction, a warm sunshade will produce insignificant infrared glow. It is noted that the atomic oxygen flux on the cold SIRTF mirror (3) is insufficient to produce significant infrared glow. Infrared absorption by the ice buildup on the mirror is also small.

Hollenbach, D. J.↗

NASA NTRS1996

Lidar Observations of the Optical Properties and 3-Dimensional Structure of Cirrus Clouds

The scientific research conducted under this grant have been reported in a series of journal articles, dissertations, and conference proceedings. This report consists of a compilation of these publications in the following areas: development and operation of a High Spectral Resolution Lidar, cloud physics and cloud formation, mesoscale observations of cloud phenomena, ground-based and satellite cloud cover observations, impact of volcanic aerosols on cloud formation, visible and infrared radiative relationships as measured by satellites and lidar, and scattering cross sections.

Eloranta, E. W.↗

NASA NTRSDate not supplied

Deep Space Observations of Cloud Glints: Spectral and Seasonal Dependence

From a distance of about one and a half million kilometers, the Earth Polychromatic Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) spacecraft takes about 13 or 22 images a day of the sunlit side of Earth. Several earlier studies showed that these images often feature sun glint from water surfaces and from ice crystals that float inside clouds in a horizontal orientation. This presentation expands on the earlier analyses of observed glints caused by clouds, focusing on the way the appearance of these glints varies with wavelength and season. The statistical analysis of all EPIC images taken in 2017 reveals that the wavelength dependence of glints is shaped predominantly by the Rayleigh scattering and gaseous absorption caused by the atmosphere above the cloud top. The analysis also reveals that the radiative impact of cloud glints displays seasonal variations that are consistent with seasonal changes in the amount and temperature of ice clouds that were observed independently by the Moderate resolution imaging spectroradiometer (MODIS).

ice cloud↗

NASA NTRS1983

Electron impact excitation from a 1 Delta g state of molecular oxygen

First measurements of electron impact excitation on the O2 a delta-one sub g metastable state to a higher bound state, pi-one sub u, is reported. The data were taken at an incident electron energy of 500 eV and scattering angles of 0 deg to 15 deg. A superelastic electron scattering experiment was performed on the pure oxygen target gas in order to establish the composition of the discharged oxygen and to confirm the existence of delta-one sub g molecules in the interaction region. The electron-impact energy loss spectrum obtained is shown. The electronic assignment of the upper state which produces the vibrational structure was determined to be pi-one sub u by examining the potential energy curves of O2 and applying the electric dipole selection rules. The relative line intensities were obtained and used to determine the Morse potential for the pi-one sub u state.

Khakoo, M. A.↗

NASA NTRS1995

One-dimensional hybrid satellite track model for the Dynamics Explorer 2 (DE 2) satellite

A one-dimensional hybrid satellite track model has been developed to calculate the high-latitude thermospheric/ionospheric structure below the satellite altitude using Dynamics Explorer 2 (DE 2) satellite measurements and theory. This model is based on Emery et al. (1985) satellite track code but also includes elements of Roble et al. (1987b) global mean thermosphere/ionosphere model. A number of parameterizations and data handling techniques are used to input satellite data from several DE 2 instruments into this model. Profiles of neutral atmospheric densities are determined from the Mass Spectrometer Incoherent Scatter 1990 (MSIS-90) model and measured neutral temperatures. Measured electron precipitation spectra are used in an auroral model to calculate particle impact ionization rates below the satellite. These rates are combined with a solar ionization rate profile and used to solve the O(+) diffusion equation, with the measured electron density as an upper boundary condition. The calculated O(+) density distribution, as well as the ionization profiles, are then used in a photochemical equilibrium model to calculate the electron and molecular ion densities. The electron temperature is also calculated by solving the electron energy equation with an upper boundary condition determined by the DE 2 measurement. The model enables calculations of altitude profiles of conductivity and Joule heating rate along and below the satellite track. In a first application of the new model, a study is made of thermospheric and ionospheric structure below the DE 2 satellite for a single orbit which occurred on October 25, 1981. The field-aligned Poynting flux, which is independently obtained for this orbit, is compared with the model predictions of the height-integrated energy conversion rate. Good quantitative agreement between these two estimates has been reached. In addition, measurements taken at the incoherent scatter radar site at Chatanika (65.1 deg N, 147.4 deg W) during a DE 2 overflight are compared with the model calculations. A good agreement was found in lower thermospheric conductivities and Joule heating rate.

Deng, Wei↗

NASA NTRS1976

Differential cross-section for positronium formation in electron-atomic hydrogen collisions

The L=0 and 1 partial wave amplitudes obtained by a two-state coupled static approximation with correlation with the L greater than or equal to 2 Born amplitudes were combined to obtain the differential cross section for positronium formation in electron-atomic hydrogen collisions. For positron energies of 0.64 and 0.75 ryd, minima at the scattering angles of 57 deg and 51 deg are found. Total cross sections for positronium formation for low and intermediate impact energies are given. Measurement of the differential cross section for the process positron + helium yields positronium + helium ion for the detection of possible minima is suggested.

Drachman, R. J.↗

NASA NTRS1981

Radiative properties of the background stratospheric aerosols and implications for perturbed conditions

A series of Mie scattering calculations has been performed to define the wavelength-dependent, single scattering properties of aerosols present in the stratosphere during July 1979. Additional radiative transfer computations were conducted to assess the impact of aerosols on the earth's radiation budget. For these purposes, an extensive set of measurements of aerosol characteristics that were obtained in Alaska from aircraft and satellite platforms was used. At that time, the optical depth was too small for aerosols to significantly impact earth's climate. But the optical depth of the stratospheric aerosol layer has been large enough during some volcanically perturbed periods for the aerosols to have caused a noticeable warming of the stratosphere and cooling of the troposphere.

Pollack, J. R.↗

NASA NTRS2003

Solar array development for the surface of Mars

JPL's missions to Mars have revealed factors that have an adverse impact on the performance of Mars Surface Solar Arrays. These factors included a spectrum shift toward the red wavelengths, atmospheric scattering and absorption and an accumulation of Mars surface dust on the arrays. All of these factors will reduce the power generated from state of the art triple junction solar cells used by earth orbiting satellites. This paper will report the results of JPL supported work conducted by US solar array manufacturers to increase the performance of solar arrays for future Mars surface missions. JPL awarded four vendors contracts to evaluate methods of improving power generation on the surface of Mars. These four contracts cover the redesign of the existing triple junction solar cell, modifying solar simulator output to match the Mars surface spectrum and techniques to control or remove dust from the surface of the arrays. The methodology and results of this evaluation will be presented in this paper.

Mars solar arrays↗

NASA NTRS2020

Radiative Heating from Biomass Burning Aerosol and its Impact on Cloud Structure in the Southeast Atlantic

Marine boundary layer clouds, including the transition from stratocumulus to cumulus, are poorly represented in numerical weather prediction and general circulation models. In many cases, the complex physical relationships between marine boundary cloud morphology and the environmental conditions in which the clouds exist are not well understood. Such uncertainties arise in the presence of biomass burning carbonaceous aerosol, as is the case over the southeast Atlantic Ocean. It is likely that the absorbing and heating properties of these aerosols influence the microphysical composition and macrophysical arrangement of marine stratocumulus and trade cumulus in this region; however, this has yet to be quantified. The deployment of the Atmospheric Radiation Measurement Mobile Facility #1 (AMF1) in support of LASIC (Layered Atlantic Smoke Interactions with Clouds) provided a unique opportunity to collect observations of cloud and aerosol properties during two consecutive biomass burning seasons during July through October of 2016 and 2017 over Ascension Island (7.96 S, 14.35 W). Thermodynamic profiles will be analyzed through the unique combination of sounding data from radiosonde launches and microwave profiling radiometers, giving observations of additional quantities important for cloud development such as CAPE and CIN at a fine temporal resolution. The thermodynamic profiles will be presented in conjunction with detailed observations of the cloud structure over the site from a K-band cloud radar, micropulse lidar, and laser ceilometer. The observed thermodynamic and cloud profiles will be used as input forcing, alongside aerosols from the Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA-2), for the Rapid Radiative Transfer Model (RRTM) to gain information regarding the radiative heating profiles. Idealized experiments using RRTM with and without aerosols will be used to quantify the impact of biomass burning carbonaceous aerosol plumes as they pass over the site. Due to documented discrepancies in the single scatter albedo (SSA) between models and observations, further sensitivity experiments will demonstrate the importance of the optical properties of biomass burning aerosol in accurately representing heating within the column. Finally, the heating rates will be put into context of the cloud structure over the site from the perspective of the mass flux closure from the University of Washington shallow convective scheme.

Collow, Allison↗

NASA NTRS2000

Global Analysis of the Effects of Dust on the Photodissociation Rates

Aerosols scatter and absorb UV radiation and consequently either enhance or reduce the actinic fluxes and photolysis rates. Mineral dust particles are known to absorb UV radiation, but the impact on the photolysis rates is complicated by the optical properties dependency on the particle size, composition and wavelength. The high spatial and temporal variabilities of the dust size distribution add difficulties to the global analysis. The Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model has been used to simulate several years of the global distribution of mineral dust in the troposphere. The optical parameters (extinction efficiency, single scattering albedo and asymmetry parameter) of the seven particle sizes (from 0.1 to 5 microns), transported by the model, have been inserted in the Tropospheric Ultraviolet-Visible (TUV) radiation model version 4. The photodissociation rates of J(N02) and J(03 to O(1D)) have been calculated with TUV-4 with and without dust particles on the global scale. The effects of dust on J(N02) and J(03) will be analyzed with an emphasis on the difference between major dust sources in Africa and Asia.

Ginoux, Paul↗

NASA NTRS1982

Elastic scattering of electrons from SO2

A crossed electron beam-molecular beam scattering geometry and the relative-flow technique are used to measure the ratios of the elastic differential cross sections of SO2 to those of He at electron impact energies of 12, 20, 50, 100, 150, and 200 eV. At each energy, an angular range of 15-150 deg is covered. The ratios are multiplied by previously known He elastic differential cross sections to obtain elastic differential cross sections for SO2. Integral and momentum transfer cross sections are then determined from a knowledge of differential cross sections. With the aid of the two-potential theory of e-molecule scattering, calculations are also performed and compared with the measurements.

Orient, O. J.↗

NASA NTRS1995

Impact of differences in the solar irradiance spectrum on surface reflectance retrieval with different radiative transfer codes

Surface reflectance retrieval from imaging spectrometer data as acquired with the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) has become important for quantitative analysis. In order to calculate surface reflectance from remotely measured radiance, radiative transfer codes such as 5S and MODTRAN2 play an increasing role for removal of scattering and absorption effects of the atmosphere. Accurate knowledge of the exo-atmospheric solar irradiance (E(sub 0)) spectrum at the spectral resolution of the sensor is important for this purpose. The present study investigates the impact of differences in the solar irradiance function, as implemented in a modified version of 5S (M5S), 6S, and MODTRAN2, and as proposed by Green and Gao, on the surface reflectance retrieved from AVIRIS data. Reflectance measured in situ is used as a basis of comparison.

Staenz, K.↗

NASA NTRS2000

Potential Applications of Satellite Based Low Frequency Microwave Measurements of Snow and Ice

In this presentation we will examine some potential applications of low frequency microwave radar and radiometer data to remote sensing of snow and ice conditions over land. We focus on the following low frequency bands; L-band (1.28 GHz), S-band (2.69 GHz), and C-band (5.0 GHz). To predict the effect of snow cover on microwave emission, we need to characterize the dielectric properties of the snow in terms of important physical parameters such as snow density, temperature, and wetness. For the case of dry snow, we use an empirical mixing formula which gives the effective complex permittivity of snow as a function of density, temperature, and frequency. For wet snow, we use another mixing formula which gives the effective complex permittivity as a function of snow wetness. With dry snow, the loss at low microwave frequencies is very small so the corresponding penetration depths are very large (eg., 100 m). Clearly seasonal snow covers are far too thin to have a direct scattering or emission effect on these low frequency bands. There are, however, indirect effects introduced because of altered reflection at the snow/soil boundary, and an extra reflecting interface at the snow/air boundary. For C-band, layers of snow with different densities can have an impact if the number of layers grows sufficiently large. (eg., many meters of snow pack with cm-scale density layering.) Wet snow poses a more difficult problem. Liquid water is much more effective than ice at scattering and absorbing L-band radiation, so even a small amount of wetness will greatly reduce penetration. For example, with a snow wetness of 1 percent (volume fraction), and a density of 300 kg/cu. m, the penetration depths for L-band, S-band, and C-band are about 1.6 m, 0.3 m, and 0.15 m respectively. Very wet snow has more than 10 percent liquid water, and the corresponding L-band penetration is less than 0.2 m. Because the penetration distance is a strong function of frequency, it may be possible to identify a particular class of snow where the wetness is a few percent, and the depth is around one meter by looking at the frequency gradient.

West, Richard D.↗

NASA NTRS1977

Electron-impact excitation of carbon and silicon in the distorted-wave approximation

The 3P to 1D electron-impact excitation cross section within the ground configuration of both neutral carbon and silicon is calculated in the distorted-wave approximation of the two-state Hartree-Fock coupled equations. An essential element of the present treatment is that orthogonality to core orbitals is not assumed in deriving equations for the scattering orbitals. A local adiabatic polarization potential is also added to the distorted-wave equations. Both elements are necessary in getting good agreement with close-coupling results for carbon to low impacting energies. The agreement is sufficiently good that predictions for silicon should be accurate to within a factor of 2.

Pindzola, M. S.↗

NASA NTRS2023

Long-Term Geospace Climate Monitoring

Climate change is characterized by global surface warming associated with the increase of greenhouse gas population since the start of the industrial era. Growing evidence shows that the upper atmosphere is experiencing appreciable cooling over the last several decades. The seminal modeling study by Roble and Dickinson (1989) suggested potential effects of increased greenhouse gases on the ionosphere and thermosphere cooling which appear consistent with some observations. However, several outstanding issues remain regarding the role of CO 2 , other important contributors, and impacts of the cooling trend in the ionosphere and thermosphere: for example, (1) what is the regional variability of the trends? (2) the very strong ionospheric cooling observed by multiple incoherent scatter radars that does not fit with the prevailing theory based on the argument of anthropogenic greenhouse gas increases, why? (3) what is the effect of secular changes in Earth’s main magnetic field? Is it visible now in the ionospheric data and can it explain some of the regional variability in the observed ionospheric trends? (4) what is the impact of long-term cooling in the thermosphere on operational systems? (5) what are the appropriate strategic plans to ensure the long-term monitoring of the critical space climate?

long-term trends↗