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At least 1,243 records · Page 69
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NASA NTRS1994

Periodic intensity variations in sulfur emissions from the Io plasma torus

In November and December 1988, we acquired 157 spectra of (S II) lambda 6731 emissions from the Io plasma torus with a Fabry-Perot interferometer at the McMath-Pierce Solar Telescope facility on Kitt Peak. A major goal of this experiment was to extend our earlier studies of intensity variations in the plasma torus. Our earlier analysis (F. L. Roesler, F. Scherb, and R. J. Oliversen, 1984, of (S III) lambda 9531 emission spectra acquired in April 1982 had shown that the intensity of torus emissions varied periodically with a period of 10.20 +/- 0.06 hr (1-sigma uncertainty level), slightly longer than Jupiter's System 3 rotational period of 9.925 hr. We present here an reanalysis of our 1982 data revealing, in addition to the 10.20-hr period, a clear secondary periodicity at 9.95 +/- 0.906 hr. By constrast, we show that our new (S II) lambda 6731 data have a single period of 10.14 +/- 0.03 hr. which is neither the System 3 period nor the proposed 'System 4' period of 10.224 hr.

Woodward, R. Carey, Jr.↗
NASA NTRS1995

An extended plasma model for Saturn

The Saturn magnetosphere model of Richardson and Sittler (1990) is extended to include the outer magnetosphere. The inner magnetospheric portion of this model is updated based on a recent reanalysis of the plasma data near the Voyager 2 ring plane crossing. The result is an axially symmetric model of the plasma parameters which is designed to provide accurate input for models needing either in situ or line-of-sight data and to be a useful tool for Cassini planning.

Richardson, John D.↗
NASA NTRS1994

Energetic electrons in the magnetosphere of Saturn

The energy spectra and angular distributions of electrons observed by Pioneer 11 as a function of radial distance in the inner magnetosphere of Saturn are reanalyzed and phase space densities are then calculated. The radial dependence of phase space density requires a distributed loss process. The loss is greatest in the region of the E ring (5.5 less than L less than 8.5) and is attributed to collisions with the ring particles in agreement with earlier work by Van Allen et al. (1980). Quantitative analysis yields the following properties of the E ring: the particle radii are in the range of 4 x 10(exp -5) to 3.2 x 10(exp -4) cm and the thickness of the ring is approximately 3 R(sub s). Between the inner edge of the E ring (5.5 R(sub s)) and the outer edge of the A ring (2.3 R(sub s)) there are more energetic electrons than can be supplied by radial diffusion from an external source. Detailed calculations show that a cosmic ray albedo neutron decay (CRAND) source in the A and B rings is a plausible source for this excess. The radial diffusion coefficient required to explain the E ring absorption and CRAND source for electrons is 1 x 10(exp -12) greater than D(sub 0) greater than 3 x 10(exp -12) R(exp 2, sub s)/s, assuming that D(sub LL) = D(sub 0)L(exp 3). As part of the reanalysis program, a method for the deconvolution of pitch angle distributions observed by simple detectors on a rotating spacecraft is developed. This process removes the instrumental response and rotational smear due to finite sampling periods and yields true angular distributions.

Randall, B. A.↗
NASA NTRS1996

Analysis of IUE Observations of Supernovae

This program supported the analysis of IUE observations of supernovae. One aspect was a Target-of-Opportunity program to observe bright supernovae which was applied to SN 1993J in M81, and another was continuing analysis of the IUE data from SN 1987A. Because of its quick response time, the IUE satellite has continued to provide useful data on the ultraviolet spectra of supernovae. Even after the launch of the Hubble Space Telescope, which has much more powerful ultraviolet spectrometers, the IUE has enabled us to obtain early and frequent measurements of ultraviolet radiation: this information has been folded in with our HST data to create unique observations of supernova which can be interpreted to give powerful constraints on the physical properties of the exploding stars. Our chief result in the present grant period was the completion of a detailed reanalysis of the data on the circumstellar shell of SN 1987A. The presence of narrow high-temperature mission lines from nitrogen-rich gas close to SN 1987A has been the principal observational constraint on the evolution of the supernova's progenitor. Our new analysis shows that the onset of these lines, their rise to maximum, and their subsequent fading can be understood in the context of a model for the photoionization of circumstellar matter.

Kirshner, Robert P.↗
NASA NTRS1995

Observation of local cloud and moisture feedbacks over high ocean and desert surface temperatures

New data on clouds and moisture, made possible by reanalysis of weather satellite observations, show that the atmosphere reacts to warm clusters of very high sea surface temperatures in the western Pacific Ocean with increased moisture, cloudiness, and convection, suggesting a negative feedback limiting the sea surface temperature rise. The reverse was observed over dry and hot deserts where both moisture and cloudiness decrease, suggesting a positive feedback perpetuating existing desert conditions. In addition, the observations show a common critical surface temperature for both oceans and land; the distribution of atmospheric moisture is observed to reach a maximum value when the daily surface temperatures approach 304 +/- 1 K. These observations reveal complex dynamic-radiative interactions where multiple processes act simultaneously at the surface as well as in the atmosphere to regulate the feedback processes.

Chahine, Moustafa T.↗
NASA NTRS1997

Studies of the Earth Energy Budget and Water Cycle Using Satellite Observations and Model Analyses

During this research period we have utilized the ERBE data set in comparisons to surface properties and water vapor observations in the atmosphere. A relationship between cloudiness and surface temperature anomalies was found. This same relationship was found in a general circulation model, verifying the model. The attempt to construct a homogeneous time series from Nimbus 6, Nimbus 7 and ERBE data is not complete because we are still waiting for the ERBE reanalysis to be completed. It will be difficult to merge the Nimbus 6 data in because its observations occurred when the average weather was different than the other periods, so regression adjustments are not effective.

Campbell, G. G.↗
NASA NTRS1995

Photochemistry of Triton's Atmosphere and Ionosphere

The photochemistry of 32 neutral and 21 ion species in Triton's atmosphere is considered. Parent species N2, CH4, and CO (with a mixing ratio of 3 x 10(exp -4) in our basic model) sublime from the ice with rates of 40, 208, and 0.3 g/sq cm/b.y., respectively. Chemistry below 50 km is driven mostly by photolysis of methane by the solar and interstellar medium Lyman-alpha photons, producing hydrocarbons C2H4, C2H6, and C2H2 which form haze particles with precipitation rates of 135, 28, and 1.3 g/sq cm/b.y., respectively. Some processes are discussed which increase the production of HCN (by an order of magnitude to a value of 29 g/sq cm/b.y.) and involve indirect photolysis of N2 by neutrals. Reanalysis of the measured methane profiles gives an eddy diffusion coefficient K = 4 x 10(exp 3)sq cm/s above the tropopause and a more accurate methane number density near the surface, (3.1 +/- 0.8)x IO(exp 11)/cu cm. Chemistry above 200 km is driven by the solar EUV radiation (lambda less than 1000 A) and by precipitation of magnetospheric electrons with a total energy input of 10(exp 8) W (based on thermal balance calculations). The most abundant photochemical species are N, H2, H, 0, and C. They escape with the total rates of 7.7 x 10(exp 24)/ s, 4.5 x 10(exp 25)/s, 2.4 x 10(exp 25)/s, 4.4 x 10(exp 22)/s, and 1.1 x 10(exp 24), respectively. Atomic species are transported to a region of 50-200 km and drive the chemistry there. Ionospheric chemistry explains the formation of an E region at 150-240 km with HCO(+) as a major ion, and of an F region above 240 km with a peak at 320 km and C(+) as a major ion. The ionosphere above 500 km consists of almost equal densities of C(+) and N(+) ions. The model profiles agree with the measured atomic nitrogen and electron density profiles. A number of other models with varying rate coefficients of some reactions, differing properties of the haze particles (chemically passive or active), etc., were developed. These models show that there are four basic unknown values which have strong impacts on the composition and structure of the atmosphere and ionosphere. These values and their plausible ranges are the CO mixing ratio f(sub co) = 10(exp -4) - 10(exp -3), the magnetospheric electron energy input (1 +/- 0.5) x 10(exp 8) W, the rate coefficient of charge-exchange reaction N2(+) + C(kappa) = 10(exp -11) - 10(exp -10)cu cm/s, and the ion escape velocity upsilon(sub i) approx. equals 150 cm/s.

Krasnopolsky, Vladimir A.↗
NASA NTRS1995

Photochemistry of Triton's Atmosphere and Ionosphere

The photochemistry of 32 neutral and 21 ion species in Triton's atmosphere is considered. Parent species N2, CH4, and CO (with a mixing ratio of 3 x 10(exp -4) in our basic model) sublime from the ice with rates of 40, 208, and 0.3 g/sq cm/b.y., respectively. Chemistry below 50 km is driven mostly by photolysis of methane by the solar and interstellar medium Lyman-alpha photons, producing hydrocarbons C2H4, C2H6, and C2H2 which form haze particles with precipitation rates of 135, 28, and 1.3 g/sq cm/b.y., respectively. Some processes are discussed which increase the production of HCN (by an order of magnitude to a value of 29 g/sq cm/b.y.) and involve indirect photolysis of N2 by neutrals. Reanalysis of the measured methane profiles gives an eddy diffusion coefficient K = 4 x 10(exp 3) sq cm/s above the tropopause and a more accurate methane number density near the surface, (3.1 +/- 0.8) x 10(exp 11)/cc cm. Chemistry above 200 km is driven by the solar EUV radiation (lambda less than 1000 A)) and by precipitation of magnetospheric electrons with a total energy input of 10(exp 8) W (based on thermal balance calculations). The most abundant photochemical species are N, H2, H, O, and C. They escape with the total rates of 7.7 x 10(exp 24)/ s, 4.5 x 10(exp 25)/ s, 2.4 x 10(exp 25)/ s, 4.4 x 10(exp 22)/ s, and 1.1 x 10(exp 24)/ s, respectively. Atomic species are transported to a region of 50-200 km and drive the chemistry there. Iono- spheric chemistry explains the formation of an E region at 150-240 km with HCO(+) as a major ion, and of an F region above 240 km with a peak at 320 km and C(+) as a major ion. The ionosphere above 500 km consists of almost equal densities of C(+) and N(+) ions. The model profiles agree with the measured atomic nitrogen and electron density profiles. A number of other models with varying rate coefficients of some reactions, differing properties of the haze particles (chemically passive or active), etc., were developed. These models show that there are four basic unknown values which have strong impacts on the composition and structure of the atmosphere and ionosphere. These values and their plausible ranges are the CO mixing ratio f(sub co) = 10(exp -4)- 10(exp -3), the magnetospheric electron energy input (1 +/- 0.5) x 10(exp 8) W, the rate coefficient of charge-exchange reaction N2(+) + Ck = 10(exp -11)-10(exp -10)cc cm/s, and the ion escape velocity upselon(sub i) approx. 150 cm/s.

Krasnopolsky, Vladimir A.↗
NASA NTRS1997

Diagnostic Studies with GLA Fields

Assessments of the NASA Goddard Earth Observing System-1 Data Assimilation System(GEOS-1 DAS), regarding heating rates, energetics, and angular momentum quantities were made. These diagnostics can be viewed as measures of climate variability. Comparisons with the NOAA/NCEP reanalysis system of momentum and energetics diagnostics are included. Water vapor and angular momentum are diagnosed in many models, including those of NASA, as part of the Atmospheric Model Intercomparison Project. 'Me GEOS-I and NOAA/NCEP global atmospheric angular momentum values are coherent on time scales down to about three days. Furthermore, they agree with the series of Earth angular momentum, as measured by tiny fluctuations in the rotation rate of the Earth, as variations in the length of day. The torques that effect such changes in atmospheric and Earth momentum are dominated by the influence of particular mountain systems, including the Rockies, Himalayas, and Andes, upon mountain torques on time scales shorter than about two weeks. Other project areas included collaboration with Goddard Space Flight Center to examine the impact of mountainous areas and the treatments of parameterizations on diagnoses of the atmosphere. Relevant preprints are included herein.

Salstein, David A.↗
NASA NTRS1995

Millimeter and Submillimeter Spectroscopy of Molecules of Atmospheric Importance

In our proposal we laid out work in three areas of relevance to atmospheric science: millimeter and submillimeter spectroscopy, variable temperature pressure broadening, and band and intensity measurements in the FIR. Below we will briefly discuss our progress during the second year of this project. In our millimeter and submillimeter (mm/submm) spectroscopic work, one of our goals has been to work towards the unification of the rotational (primarily obtained by mm/submm techniques) and rotational-vibrational (primarily obtained by infrared techniques) data sets in the context of theoretically well founded models which take advantage of the strengths of the data from each experimental technique. From the point of view of the development of the optimal data base for atmospheric observations, this is clearly a desirable goal. During the first year of this project we did an analysis of a weighted, mixed infrared and mm/submm data set of the n = 0, 1, and 2 torsional states of the ground vibrational state of HOOH. The purpose of this work is to provide a unified understanding of the spectrum, which is applicable in both the rotational and rotational - vibrational regimes. We have succeed in doing this in the context of a single weighted fit which accounts for both data sets to their respective experimental uncertainty (-0.1 and 10 MHz, respectively). Additionally, we have now done a similar analysis on the n = 0 torsional state of v(sub 3) and begun a similar analysis on v(sub 6). For several years we have been working on the mm/submm rotational spectra of the many excited vibrational states of HNO3, again with particular emphasis on the relationships between the mm/submm and infrared spectra. During the first year of this project we were able to use mm/submm spectroscopy to fully resolve the torsional splittings in 2 v(sub 9) and v(sub 5), establish a theoretically well founded quantitative relation between them, and show that both have their physical origin in the torsional motion of the v(sub 9) mode.This result has now been incorporated in a recent reanalysis of the infrared spectrum and has resulted in improved fits - eliminating what was in retrospect a systematic error associated with this previously unknown effect.

DeLucia, Frank C.↗
NASA NTRS1997

Diagnostic Studies With GLA Fields

Assessments of the NASA Goddard Earth Observing System-1 Data Assimilation System (GEOS-1 DAS) regarding heating rates, energetics and angular momentum quantities were made. These diagnostics can be viewed as measures of climate variability. Comparisons with the NOAA/NCEP reanalysis system of momentum and energetics diagnostics are included. Water vapor and angular momentum are diagnosed in many models, including those of NASA, as part of the Atmospheric Model Intercomparison Project. Relevant preprints are included herein.

Salstein, David A.↗
NASA NTRS1997

Attitudinal Responses to Changes in Noise Exposure in Residential Communities

The purpose of this study is (1) to investigate the current body of knowledge encompassing two related topics: (a) to what extent can we reliably predict the change in people's attitudes in response to an abrupt change in noise exposure, and (b) after the change, is there a decay in the abrupt-change effect whereby people's attitudes slowly shift from their initial reaction to a steady-state value? and (2) to provide recommendations for any future work that may be needed. The literature search located 23 studies relating to one or both of the above topics. These prior studies shed considerable light on the current ability to predict initial reaction and decay effects. The literature makes one point very clear: Great care in both experimental design and data analysis is necessary to produce credible, convincing findings, both in the reanalysis of existing data and for planning future data acquisition and analysis studies. New airport studies must be designed to minimize nuisance variables and avoid past design features that may have introduced sufficient unexplained variance to mask sought after effects. Additionally, the study must be designed to tie in with previous investigations by incorporating similar survey questions and techniques.

Horonjeff, Richard D.↗
NASA NTRS1998

Gamma-Ray Observations of the Interstellar Clouds in Cepheus

During the last six months of the period of performance, the diffuse gamma-ray emission from the Monoceros region was reanalyzed and one of the important conclusions was revised as a result. The reanalysis incorporated newly-available data from recent EGRET viewing periods and revealed a previously-uncataloged gamma-ray point source near the plane in Monoceros. The effect of incorporating this source in the diffuse emission model was significant, as its flux was comparable to that from a large interstellar cloud complex in the Perseus arm. In the updated model, a greatly reduced gamma-ray emissivity was found in the Perseus arm. This finding alters the previous conclusion that we had found evidence for an enhanced emissivity in the arm, which had supported the hypothesis that cosmic rays are coupled to the interstellar medium on the scale of spiral arms. Our updated findings are consistent with our previous results for the emissivity toward the Cepheus region (Digel et al. 1996), where a monotonic gradient of emissivity in the outer Galaxy was found. The updated analysis of Monoceros was presented at the June, 1998 meeting of the American Astronomical Society, and a journal publication should be ready for submission soon.

Digel, S.↗
NASA NTRS1999

Interannual and Decadal Variability of Summer Rainfall over South America

Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the Goddard Earth Observing System reanalysis and the Climate Analysis Center sea surface temperature (SST) data, we conduct a diagnostic study of the interannual and decadal scale variability of summer rainfall over South America. Results show three leading modes of rainfall variation identified with interannual, decadal, and long-term trend variability. Together, these modes explain more than half the total variance. The first mode is highly correlated with El Nino/southern oscillation (ENSO), showing severe drought over Northeast Brazil and copious rainfall over the Ecuador coast and the area of Uruguay-Southern Brazil in El Nino years. This pattern is attributed to the large scale zonal shift of the Walker circulation and local Hadley cell anomaly induced by positive (negative) SST anomaly over the eastern (western) equatorial Pacific. In El Nino years, two convective belts indicated by upper tropospheric velocity potential trough and mid-tropospheric rising motion, which are somewhat symmetric about the equator, extend toward the northeast and the southeast into the tropical North and South Atlantic respectively. Sandwiched between the ascent is a region of descending motion over Northeast Brazil. The southern branch of the anomalous Hadley cell is dynamically linked to the increase of rainfall over Uruguay-Southern Brazil. The regional response of anomalous circulation shows a stronger South American summer monsoon and an enhanced (weakened) subtropical high over the South Atlantic (South Pacific) Ocean. The decadal variation displays a meridional shift of the Intertropical Convergence Zone (ITCZ), which is tie to the anomalous cross-equatorial SST gradient over the Atlantic and the eastern Pacific. In conjunction with this mode is a large scale mass swing between the polar regions and midlatitudes in both hemispheres. Over the South Atlantic and the South Pacific, the changes of the strength of the subtropical high and the associated surface wind are dynamically consistent with the distribution of local SST anomalies, suggesting the importance of the atmospheric forcing in the decadal time scale. The decadal mode also presents a weak summer monsoon in its positive phase, which reduces the moisture supply from the equatorial Atlantic and the Amazon Basin and results in negative rainfall anomalies over the central Andes and Gran Chaco. The long-term trend shows decrease of rainfall from the northwest coast to the southeast subtropical region and a southward shift of Atlantic ITCZ that leads to increased rainfall over northern and eastern Brazil. Our result shows a close link of this mode to the observed SST warming trend over the subtropical South Atlantic and a remote connection to the interdecadal SST variation over the extratropical North Atlantic found in previous studies.

Zhou, Jiayu↗
NASA NTRS1999

Parallel Grid Manipulations in Earth Science Calculations

The National Aeronautics and Space Administration (NASA) Data Assimilation Office (DAO) at the Goddard Space Flight Center is moving its data assimilation system to massively parallel computing platforms. This parallel implementation of GEOS DAS will be used in the DAO's normal activities, which include reanalysis of data, and operational support for flight missions. Key components of GEOS DAS, including the gridpoint-based general circulation model and a data analysis system, are currently being parallelized. The parallelization of GEOS DAS is also one of the HPCC Grand Challenge Projects. The GEOS-DAS software employs several distinct grids. Some examples are: an observation grid- an unstructured grid of points at which observed or measured physical quantities from instruments or satellites are associated- a highly-structured latitude-longitude grid of points spanning the earth at given latitude-longitude coordinates at which prognostic quantities are determined, and a computational lat-lon grid in which the pole has been moved to a different location to avoid computational instabilities. Each of these grids has a different structure and number of constituent points. In spite of that, there are numerous interactions between the grids, e.g., values on one grid must be interpolated to another, or, in other cases, grids need to be redistributed on the underlying parallel platform. The DAO has designed a parallel integrated library for grid manipulations (PILGRIM) to support the needed grid interactions with maximum efficiency. It offers a flexible interface to generate new grids, define transformations between grids and apply them. Basic communication is currently MPI, however the interfaces defined here could conceivably be implemented with other message-passing libraries, e.g., Cray SHMEM, or with shared-memory constructs. The library is written in Fortran 90. First performance results indicate that even difficult problems, such as above-mentioned pole rotation- a sparse interpolation with little data locality between the physical lat-lon grid and a pole rotated computational grid- can be solved efficiently and at the GFlop/s rates needed to solve tomorrow's high resolution earth science models. In the subsequent presentation we will discuss the design and implementation of PILGRIM as well as a number of the problems it is required to solve. Some conclusions will be drawn about the potential performance of the overall earth science models on the supercomputer platforms foreseen for these problems.

Sawyer, W.↗
NASA NTRS1999

I/O Parallelization for the Goddard Earth Observing System Data Assimilation System (GEOS DAS)

The National Aeronautics and Space Administration (NASA) Data Assimilation Office (DAO) at the Goddard Space Flight Center (GSFC) has developed the GEOS DAS, a data assimilation system that provides production support for NASA missions and will support NASA's Earth Observing System (EOS) in the coming years. The DAO's support of the EOS project along with the requirement of producing long-term reanalysis datasets with an unvarying system levy a large I/O burden on the future system. The DAO has been involved in prototyping parallel implementations of the GEOS DAS for a number of years and is now converting the production version from shared-memory parallelism to distributed-memory parallelism using the portable Message-Passing Interface (MPI). If the MPI-based GEOS DAS is to meet these production requirements, we must make I/O from the parallel system efficient. We have designed a scheme that allows efficient I/O processing while retaining portability, reducing the need for post-processing, and producing data formats that are required by our users, both internal and external. The first phase of the GEOS DAS Parallel I/O System (GPIOS) will expand upon the common method of gathering global data to a Single PE for output. Instead of using a PE also tasked with primary computation, a number of PEs will be dedicated to I/O and its related tasks. This allows the data transformations and formatting required prior to output to take place asynchronously with respect to the GEOS DAS assimilation cycle, improving performance and generating output data sets in a format convenient for our users. I/O PEs can be added as needed to handle larger data volumes or to meet user file specifications. We will show I/O performance results from a prototype MPI GCM integrated with GPIOS. Phase two of GPIOS development will examine ways of integrating new software technologies to further improve performance and build scalability into the system. The maturing of MPI-IO implementations and other supporting libraries such as parallel HDF should provide performance gains while retaining portability.

Lucchesi, R.↗
NASA NTRS1998

Wind Stress Forcing of the North Sea "Pole Tide"

We conducted numerical simulations of the wind-forcing of the sea level variations in the North Sea using a barotropic ocean model with realistic geography, bathymetry, and boundary conditions, to examine the forcing of the 14-month "pole tide" which is known to be strong along the Denmark- Netherlands coast. The simulation input is the monthly-mean surface wind stress field from the National Centers for Environmental Prediction (NCEP) reanalysis for the 40-year period 1958-1997. The output sea level response was then compared with 10 coastal tide gauge records from the Permanent Service for Mean Sea Level (PSMSL). Besides the strong seasonal variations, several prominent quasi-periodicities exist at around 7 years, 3 years, 14 months, 9 months, and 6.5 months. Correlation and spectral analyses show remarkable agreement between the model output and the observations, particularly in the 14-month, or Chandler period band. The latter indicates that the enhanced pole tide found in the North Sea along the Denmark-Netherlands coast is actually the coastal setup response to wind stress forcing with a periodicity of 14 months. We find no need to invoke a geophysical explanation involving resonance-enhancement of pole tide in the North Sea to explain the observations.

OConnor, William P.↗
NASA NTRS1998

Prediction of Particle Number Density and Particle Properties in the Flow Field Observed by the Nephelometer Experiment on the Galileo Probe

This report summarizes the work performed to assist in the analysis of data returned from the Galileo Probe's Nephelometer instrument. A computation of the flow field around the Galileo Probe during its descent through the Jovian atmosphere was simulated. The behavior of cloud particles that passed around the Galileo probe was then computed and the number density in the vicinity of the Nephelometer instrument was predicted. The results of our analysis support the finding that the number density of cloud particles was not the same in each of the four sampling volumes of the Nephelometer instrument. The number densities calculated in this study are currently being used to assist in the reanalysis of the data returned from the Galileo Probe.

Naughton, Jonathan W.↗