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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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At least 199 records · Page 11
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NASA NTRS1985

Difference methods for problems with different time scales

The use of difference methods for weakly nonlinear systems of ordinary differential equations with rapidly oscillating solutions is considered, and a general approach which depends only on the smoothness of the coefficients and the nonlinearities is developed. In particular, one is led to a strategy which is suitable for the detection and resolution of turning points in such systems. A computational example is presented.

Scheid, R. E., Jr.↗
NASA NTRS1985

On-three time scale analysis

In the present consideration of a three-timescale system, a block diagonalization employing three-stage linear transformations is used to decouple the original system into slow, fast, and faster subsystems. A numerical algorithm is given to solve the resulting Ricatti-type equations, and the technique is verified for the case of a ninth-order example. The technique yields substantial computational requirment reductions, since it involves subsystems that are of a lower order than the original system.

Naidu, D. S.↗
NASA NTRS1986

Prediction of geomagnetic activity on time scales of one to ten years

The long-term prediction of geomagnetic indices that characterize the state of the magnetosphere is discussed. While a prediction of the yearly average sunspot number is simultaneously a prediction of the yearly number of sudden-commencement storms, it is not a prediction of the number of disturbed or quiet half days. Knowledge of the sunspot cycle phase leads to a good estimate of the correlation expected between activity during one 27-day solar rotation period and the next.

Feynman, J.↗
NASA NTRS1986

The intercomparison of ozone measured from the SME and Nimbus-7 satellites on short and long time scales

The spatial and temporal characteristics of ozone density measured from the SBUV (Solar Backscatter Ultraviolet) spectrometer on Nimbus-7 and the UV and the UV and the IR spectrometers on SME (Solar Mesosphere Explorer) are compared in the altitude region near 50 km where the three data sets overlap. Their temporal characteristics, when averaged over the same longitude range, are remarkably similar with respect to seasonal variations and short term fluctuations induced by transient planetary waves. The long term trends in the three data sets, however, differ significantly with each other. Over the three year period after 1982 ozone mixing ratio at 1 mb decreased by about 10 percent based on SEUV measurements but increased by 12 and 30 percent respectively based on SME-IR and SME-UV measurements. None of these estimates are consistent with the predicted decrease of about 2 percent based on solar UV flux and temperature changes during this period.

Chandra, S.↗
NASA NTRS1987

A comparison of the Mercury and earth magnetospheres - Electron measurements and substorm time scales

The present search for similarities between earth and Mercury plasma electron distribution and large-scale dynamics notes that both spectral shapes are similar to a kappa-distribution. A model distribution of this type which incorporates convective flow is used to simulate the observed plasma electron spectral variations near the Mariner 10-Mercury 1 A event; convection appears to be stronger before, rather than during, the A event, in contradiction to the Baker (1986) convective injection model for Mercury's two relativistic electron flux enhancements. Mercury's postmidnight energetic electron B and B-prime events seem to be multiple onsets in the course of a substorm.

Christon, S. P.↗
NASA NTRS1987

Emission-line variability and the broad-line region of quasi-stellar objects. I - Time scales and photon densities

Spectroscopic data for five low-redshift QSOs taken over several years are presented as evidence for emission-line variability in QSOs. The broad hydrogen emission lines in the QSOs 0026 + 129, 1202 + 281, 1612 + 261, and 2141 + 175 are found to vary in step with their underlying continua. Another QSO, 2135 - 147, shows an increase in the intensities of its hydrogen lines five years after the increase in its continuum level. The inferred upper limit to the size of the broad emission line region is smaller than 3 lt-yr, probably as small as 0.4 lt-yr for 0026 + 129, if the line-emitting region is spherically distributed. Such a small size implies a very high density of ionizing photons, of the order of 10 to the 10th/cu cm. A very high nucleon density must then be assumed in order to obtain a value of the ionization parameter consistent with current photoionization models.

Zheng, Wei↗
NASA NTRS1989

Cretaceous-tertiary boundary event - Evidence for a short time scale

The origin of the 'As, Sb, Zn anomaly' in Cretaceous-Tertiary boundary sites is investigated using data on 11 K-T boundary sites for which comprehensive trace element analyses were available. It was found that the proportions As/Ir, Sb/Ir, and Zn/Ir were remarkably constant over about 100-fold range in concentration. The correlation persisted in sublayers of boundary clay and extended to soot from burned land biomass, indicating that all the components, despite their diverse origin, became associated in a single global component prior to deposition. Data relating the amounts of As, Sb, and Zn and the amounts of marine and land biomass to the steady-state global inventory suggest a catastrophic, rather than a gradualist scenario.

Gilmour, Iain↗
NASA NTRS1989

Middle and high latitude Southern Hemispheric oscillations on the 35-60 day time scale

The low-frequency geopotential height fluctuations in the Southern Hemisphere were examined on the basis of one-point correlation maps. Results indicate that the 35-60 day fluctuations in the Southern-Hemisphere geopotential heights exhibit wavetrainlike characteristics. Correlations between a midlatitude reference point and tropical microwave temperature data were found to be weak, suggesting that the midlatitude wavetrain is not strongly coupled to the Madden and Julian (1971) 40-50 day oscillation.

Graves, Charles E.↗
NASA NTRS1993

Physical properties and evolutionary time scales of disks around solar-type and intermediate mass stars

Recent observations of circumstellar disks and their evolutionary timescales are reviewed. It is concluded that disks appear to be a natural outcome of the star-formation process. The disks surrounding young stars initially are massive, with optically thick structures comprised of gas and micron-sized grains. Disk masses are found to range from 0.01 to 0.2 solar masses for solar-type PMS stars, and from 0.01 to 6 solar masses for young, intermediate mass stars. Massive, optically thick accretion disks have accretion rates between 10 exp -8 and 10 exp -6 solar masses/yr for solar type PMS stars and between 10 exp -6 and 10 exp -4 solar masses/yr for intermediate stars. The results suggest that a significant fraction of the mass comprising the star may have passed through a circumstellar accretion disk.

Strom, Stephen E.↗
NASA NTRS1998

GCM Studies on the Interactions Between Photosynthesis and Climate at Diurnal to Decadal Time Scales

Transpiration, a major component of total evaporation from vegetated surfaces, is an unavoidable consequence of photosynthetic carbon fixation. Because of limiting soil moisture and competition for solar radiation plants invest most of their fixed carbon into structural and hydraulic functions (roots and stems) and solar radiation absorption (leaves). These investments permit individuals to overshadow competitors and provide for transport of water from the soil to the leaves where photosynthesis and transpiration occur. Often low soil moisture or high evaporative demand limit the supply of water to leaves reducing photosynthesis and thus transpiration. The absorption of solar radiation for photosynthesis and dissipation of this energy via radiation, heat, mass and momentum fluxes represents the link between photosynthesis and climate. Recognition of these relationships has led to the development of hydro/energy balance models that are based on the physiological ecology of photosynthesis. We discuss an approach to study vegetation-climate interactions using photosynthesis-centric models embedded in a GCM. The rate at which a vegetated area transpires and photosynthesizes is determined by the physiological state of the vegetation, its amount and its type. The latter two are specified from global satellite data collected since 1982. Climate simulations have been carried out to study how this simulated climate system responds to changes in radiative forcing, physiological capacity, atmospheric CO2, vegetation type and variable vegetation cover observed from satellites during the 1980's. Results from these studies reveal significant feedbacks between the vegetation activity and climate. For example, vegetation cover and physiological activity increases cause the total latent heat flux and precipitation to increase while mean and maximum air temperatures decrease. The reverse occurs if cover or activity'decreases. In general climate response of a particular region was dominated by local processes but we also find evidence that plausible climate-vegetation scenarios lead to changes in global atmospheric circulation and strong non-local influences in some cases.

Collatz, G. James↗
NASA NTRS2000

Predictability of the 1997 and 1998 South Asian Summer Monsoons on the Intraseasonal Time Scale Based on 10 AMIP2 Model Runs

Predictability of the 1997 and 1998 South Asian summer monsoons is examined using National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses, and 100 two-year simulations with ten different Atmospheric General Circulation Models (AGCMs) with prescribed sea surface temperature (SST). We focus on the intraseasonal variations of the south Asian summer monsoon associated with the Madden-Julian Oscillation (MJO). The NCEP/NCAR reanalysis shows a clear coupling between SST anomalies and upper level velocity potential anomalies associated with the MJO. We analyze several MJO events that developed during the 1997 and 1998 focusing of the coupling with the SST. The same analysis is carried out for the model simulations. Remarkably, the ensemble mean of the two-year AGCM simulations show a signature of the observed MJO events. The ensemble mean simulated MJO events are approximately in phase with the observed events, although they are weaker, the period of oscillation is somewhat longer, and their onset is delayed by about ten days compared with the observations. Details of the analysis and comparisons among the ten AMIP2 (Atmospheric Model Intercomparison Project) models will be presented in the conference.

Wu, Man Li C.↗
NASA NTRS2001

Are US Great Plains Droughts Predictable on Seasonal and Longer Time Scales?

The United States has experienced numerous episodes of unusually dry conditions lasting anywhere from months to several years. In this talk, I will examine the predictability of such episodes and the physical mechanisms controlling the variability of the summer climate of the continental United States. The analysis is based on ensembles of multi-year simulations and seasonal hindcasts generated with the NASA Seasonal-to-Interannual Prediction Project (NSIPP-1) General Circulation Model.

Schubert, Siegfried↗
NASA NTRS2001

Are Droughts in the United States Great Plains Predictable on Seasonal and Longer Time Scales?

The United States Great Plains has experienced numerous episodes of unusually dry conditions lasting anywhere from months to several years, In this presentation, we will examine the predictability of such episodes and the physical mechanisms controlling the variability of the summer climate of the continental United States. The analysis is based on ensembles of multi-year simulations and seasonal hindcasts generated with the NASA Seasonal to-Interannual Prediction Project (NSIPP-1) General Circulation Model.

Schubert, Siegfried D.↗