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At least 199 records · Page 11

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NASA NTRS1979

Relationship between the growth of the ring current and the interplanetary quantity

Akasofu (1979) has reported that the interplanetary parameter epsilon correlates reasonably well with the magnetospheric substorm index AE; in the first approximation, epsilon represents the solar wind coupled to the magnetosphere. The correlation between the interplanetary parameter, the auroral electrojet index and the ring current index is examined for three magnetic storms. It is shown that when the interplanetary parameter exceeds the amount that can be dissipated by the ionosphere in terms of the Joule heat production, the excess energy is absorbed by the ring current belt, producing an abnormal growth of the ring current index.

Akasofu, S.-I.↗

NASA NTRS1979

Nuclear pumped electronic transition laser studies

An experiment is proposed that should yield unambiguous absolute results on the production efficiency of rare gas excimers from fission fragments. Laser threshold efficiency is parameterized and calculations indicate that some lasers can be operated using relatively simple experimental apparatus adjacent to GODIVA. Operation of a KrF excimer laser adjacent to GODIVA appears to be possible, although the neutron pulse width is not well matched to the laser pulse duration. However, calculation indicates that KrF excimer laser output on the order of a joule may be possible.

Hughes, W. M.↗

NASA NTRS1980

Atmospheric lidar multi-user instrument system definition study

A spaceborne lidar system for atmospheric studies was defined. The primary input was the Science Objectives Experiment Description and Evolutionary Flow Document. The first task of the study was to perform an experiment evolutionary analysis of the SEED. The second task was the system definition effort of the instrument system. The third task was the generation of a program plan for the hardware phase. The fourth task was the supporting studies which included a Shuttle deficiency analysis, a preliminary safety hazard analysis, the identification of long lead items, and development studies required. As a result of the study an evolutionary Lidar Multi-User Instrument System (MUIS) was defined. The MUIS occupies a full Spacelab pallet and has a weight of 1300 kg. The Lidar MUIS laser provides a 2 joule frequency doubled Nd:YAG laser that can also pump a tuneable dye laser wide frequency range and bandwidth. The MUIS includes a 1.25 meter diameter aperture Cassegrain receiver, with a moveable secondary mirror to provide precise alignment with the laser. The receiver can transmit the return signal to three single and multiple photomultiple tube detectors by use of a rotating fold mirror. It is concluded that the Lidar MUIS proceed to program implementation.

Greco, R. V.↗

NASA NTRS1979

The heating of the temperature minimum region in solar flares - A reassessment

The paper discusses and evaluates the suggestions made by Machado et al. (1978) on how to reconcile the observed temperature enhancements at temperature-minimum levels in solar flares with some theoretical heating mechanism. The objective is to gain deeper insight into the nature of the photospheric flare. The discussion focuses on the validity of the assumption of H(-) LTE at temperature-minimum levels, as well as on EUV irradiation and Joule heating by steady currents as heating mechanisms. It is found that, unless there are strong inhomogeneities associated with either heating mechanism, neither can reasonably be reconciled with observations. It is concluded that detailed high-resolution (both spatial and temporal) measurements are necessary to further the present understanding of the flare process at temperature-minimum levels.

Emslie, A. G.↗

NASA NTRS1980

What is a magnetospheric substorm

The paper suggests that if the solar wind-magnetosphere energy coupling increases above about 10 to the 18th erg/sec, the magnetosphere suddenly develops a more efficient energy dissipation process than that operating during periods of less than 10 to the 18th erg/sec. Discussion covers the appearance that the magnetosphere achieves this enhanced energy dissipation by interrupting the cross-tail current in the magnetotail and diverting it into the ionosphere, causing an enhanced Joule heat production in the ionosphere.

Akasofu, S.-I.↗

NASA NTRS1980

Mesoscale mapping of available solar energy at the earth's surface by use of satellites

A method is presented for use of cloud images in the visual spectrum from the SMS/GOES geostationary satellites to determine the hourly distribution of sunshine on the mesoscale. Cloud coverage and density as a function of time of day and season are evaluated through the use of digital data processing techniques. Seasonal geographic distributions of cloud cover/sunshine are converted to joules of solar radiation received at the earth's surface through relationships developed from long-term measurements of these two parameters at six widely distributed stations. The technique can be used to generate maps showing the geographic distribution of total solar radiation on the mesoscale which is received at the earth's surface.

Hiser, H. W.↗

NASA NTRS1980

Mechanical energy transport

The properties, generation, and dissipation mechanisms of acoustic, gravity and Alfven waves are described, whose restoring forces are pressure, buoyancy, and magnetic tension, respectively. For acoustic waves, generation by turbulent convective motions and by the Eddington Valve thermal overstability is discussed, considering the 'five-minute' oscillation; dissipation is possible either by radiation or shocks. Generation of gravity waves by penetrative convective motions and by shear arising from supergranule motions is reviewed, and dissipation due to wave breaking, interaction with the mean horizontal fluid flow, and very severe radiative damping is considered. Attention is given to Alfven wave generation by convective motions and thermal overstability, and to dissipation by mode coupling, wave decay, current dissipation, and particle collisions producing Joule or viscous heating.

Stein, R. F.↗

NASA NTRS1980

Rocket observations at the northern edge of the eastward electrojet

The paper discusses a Nike-Tomahawk rocket launched north over quiet, late evening auroral arcs in March 1975. A northward magnetic disturbance was observed on the ground under the rocket trajectory; south of the arcs the northward electric field was 60 mV/m, indicating strong westward plasma flow. An eastward electrojet current layer was penetrated in the upward flight, and precipitating electrons were observed over each arc. Using the observed electron flux and a model of the ionosphere, the Hall and Pedersen conductivities were calculated which were used to compute the eastward and northward components of the horizontal ionospheric currents. The joule power decreased abruptly in the auroral arcs, as the precipitating electron power increased; the total dissipated power was the same inside the arcs, between them and southward. North of the aurora the electric field and dissipated power remained low; field-aligned currents carried by the observed electrons were about a factor of 3 lower than those inferred from the magnetic field measurements.

Cahill, L. J., Jr.↗

NASA NTRS1981

Crystal growth of device quality GaAs in space

Experimental and theoretical efforts in the development of crystal growth approaches, effective techniques for electronic characterization on a macro and microscale, and in the discovery of phenomena and processes relevant to GaAs device applications are reported. The growth of electron trap-free bulk GaAS with extremely low density of dislocations is described. In electroepitaxy, growth configuration which eliminates the substrate back-contact was developed. This configuration can be extended to the simultaneous growth on many substrates with a thin solution layer sandwiched between any two of them. The significant reduction of Joule heating effects in the configuration made it possible to realize the in situ measurement of the layer thickness and the growth velocity. Utilizing the advantages of electroepitaxy in achieving abrupt acceleration (or deceleration) of the growth it was shown that recombination centers are formed as a result of growth acceleration.

Lagowski, J.↗

NASA NTRS1981

Ultimate limits to error probabilities for ionospheric models based on solar geophysical indices and how these compare with the state of the art

An ideal model based on a given set of geophysical indices is defined as a model that provides a least squares fit to the data set as a function of the indices considered. Satellite measurements of electron content for three stations at different magnetic latitudes were used to provide such data sets which were each fitted to the geophysical indices. The magnitude of the difference between the measured value and the derived equation for the data set was used to estimate the probability of making an error greater than a given magnitude for such an ideal model. Atmospheric Explorer C data is used to examine the causes of the fluctuations and suggestions are made about how real improvements can be made in ionospheric forecasting ability. Joule heating inputs in the auroral electrojets are related to the AL and AU magnetic indices. Magnetic indices based on the time integral of the energy deposited in the electrojets are proposed for modeling processes affected by auroral zone heating.

Nisbet, J. S.↗

NASA NTRS1981

Theoretical investigation of the generation and injection of electromagnetic waves in space plasma by means of a long-orbiting tether

Analysis of the various mechanisms of electromagnetic wave generation by the shuttle-borne orbiting tether of the T.S.S. Facility shows that significant electrodynamic power levels are available even when overestimating the loss mechanisms expected to intervene. This electrodynamic power is in part dissipated by Joule losses in the tether, in part goes to accelerate electrons through the sheath surrounding the balloon (when in a downward deployment), and in part goes into e.m. wave generation. A preliminary estimate shows that a 100 km tether in orbit would produce ULF/ELF signals that are detectable on the ground with state-of-the-art magnetometric instrumentation.

Dobrowolny, M.↗

NASA NTRS1980

Improving the Mach number capabilities of arc driven shock tubes

New systematic trends in one of the performance parameters of pressure loaded arc driven shock tubes have been determined. For a given configuration, the Mach number increases with the cube root of capacitor energy; however, the initial driver gas pressure is relatively unimportant. A qualitative model based on the assumption of Joule-preheating by the arc discharge is discussed.

Johnson, J. A., III↗

NASA NTRS1980

Model calculations of the dayside ionosphere of Venus - Energetics

A model of the energy balance of the dayside ionosphere of Venus is presented. Calculations of the dayside electron and ion temperature profiles are carried out and compared with data from experiments on the Pioneer Venus orbiter. The coupled heat conduction equations for electrons and ions are solved for several values of the solar zenith angle. It is shown that thermal conductivities are inhibited by the presence of a horizontal magnetic field. A realistic model of the magnetic field that includes fluctuations is employed in deriving an appropriate expression for the thermal conductivity. The contributions of photoelectrons, ion chemistry, Joule heating, and solar wind heating to the energy balance of the ionosphere are considered.

Cravens, T. E.↗

NASA NTRS1981

Anomalous heating of the polar E region by unstable plasma waves. II - Theory

It is found that anomalous electron temperatures in the disturbed high-latitude E region can be quantitatively explained in terms of heating by unstable plasma waves. The electron temperatures at 110 km have been measured to be as high as 1500 K instead of the expected value of about 300 K. It is shown that by using quasi-linear theory there is an ample source of heat in the unstable waves and that the measured electron temperature profiles have a shape very similar to what is expected from plasma wave heating by the modified two-stream instability. It is found that there is even more heating going to the ion gas, but that the resulting effect on the ion temperature may be difficult to measure. The best estimate of the wave heating rates leads to the conclusion that wave heating can be as much as 50% of the Joule heating for dc electric field strengths of the order of 45 mV/m or greater.

St.-Maurice, J. P.↗

NASA NTRS1981

Neutral winds and electric fields in the dusk auroral oval. I - Measurements

Two rockets carrying an upleg and downleg trimethyl aluminum chemical trail release and three barium cannisters were launched from Poker Flat, Alaska on Feb. 28, 1978 and Mar. 2, 1978 in order to study neutral winds and electric fields in the dusk auroral oval. Electric field measurements were also made with a radar system to supplement the barium cloud data. The barium cloud drifts on both days showed intense poleward electric fields in the subauroral region. The drifts were nearly latitude-independent and were equivalent to electric fields of 60 mV/m of February 2 and 40 mV/m on March 2. The data indicate that the Lorentz force and Joule heating had a strong influence on the observed neutral winds.

Mikkelsen, I. S.↗

NASA NTRS1981

Quantitative simulation of a magnetospheric substorm. II - Comparison with observations

Results of the computer simulation of the behavior of the inner magnetosphere during the substorm-type event of September 19, 1976, are discussed. The computed electric fields are found to compare satisfactorily with electric fields measured from S3-2, although there are detailed differences. The three general features on which the model and observations are in good agreement are (1) the magnitude and direction of the high-latitude electric field, (2) the degree to which the low-latitude ionosphere is shielded from the high-latitude convection electric field, and (3) the fact that the poleward electric field on the duskside is significantly larger, on the average, than the equatorward electric field on the dawnside. Simple formulas are presented that give rough estimates of global Joule heating rates from observable parameters.

Harel, M.↗

NASA NTRS1981

Upper atmosphere of Jupiter - A post Voyager perspective

Some significant upper atmosphere features of Jupiter are discussed with reference to the Voyager observations of 1979. From the time of Pioneer observations in 1973-1974, the Jovian upper atmospheric temperature has increased by about 30%, the eddy diffusion coefficient at the homopause decreased by a factor of 100, the equatorial disk Lyman alpha intensity increased by a factor of 30, and the equatorial ionosphere became more extensive and showed diurnal variation. Important potential candidates for upper atmosphere energetics are thought to be the penetration of the magnetospheric soft electrons, Joule heating mechanism, and auroral electrons.

Atreya, S. K.↗

NASA NTRS1981

Solar EUV energy budget of the thermosphere

The considered study represents an extension of investigations reported by Torr et al. (1980). The earlier investigations are concerned with a quantification of thermospheric UV energy partitions for steady state conditions. The heating efficiency was determined as a function of altitude for selected conditions. Its value was found to vary dynamically as a function of altitude, season, latitude, and solar cycle. The steady state solution reported earlier is extended in the current study to a time dependent solution over a diurnal cycle. It is pointed out that the reported results will make necessary a significant revision of thermospheric models. Thus, estimates of additional sources such as Joule heating obtained from global thermospheric circulation models will require reevaluation.

Torr, M. R.↗