Fast Adjustments of the Asian Summer Monsoon to Anthropogenic Aerosols
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Xiaoqiong Li↗
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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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Predictability and prediction of persistent cool states of the Tropical Pacific Ocean
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Nandini Ramesh↗
An outburst and FU Ori-type disc of a former low-luminosity protostar
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Mizna Ashraf↗
The JCMT BISTRO Survey: multiwavelength polarimetry of bright regions in NGC 2071 in the far-infrared/submillimetre range, with POL-2 and HAWC+
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Lapo Fanciullo↗
Traveling neutral disturbances
The coupling of acoustic-gravity waves in the main atmosphere to acoustic waves characteristic of individual minor species in the atmosphere is postulated. Such coupling would exist as a result of resonances in the response of the minor species, and its likelihood depends on the mass of the atmospheric particle relative to the major species mass, the diffusion of the minor species, and the direction of propagation of the main disturbance. These minor-species disturbances may explain some AE-C measurements in the thermosphere and could possibly play a role in the distribution of minor species and their chemistry in the mesosphere.
Gross, S. H.↗
Ionospheric disturbances and gravity waves
The response of ionization to a gravity wave moving through the ionosphere is studied. Hydrodynamic equations are used, and local thermodynamic equilibrium is imposed for simplicity. The treatment involves a perturbation analysis, and the background medium is assumed to be time stationary, horizontally stratified, and known. It is shown that ionization may be locally resonant at each level for certain frequencies and directions, for which condition neutral and ionized particles are considered closely or critically coupled. The phase direction for this critical coupling is always downward in the absence of a magnetic field. A magnetic field results in two resonant directions for the same frequency, and these directions are mostly downward. Observed TID's associated with gravity waves may be indicative of such resonances. It is also noted that strong coupling may occur to neutral acoustic waves at high altitudes. Previous investigations restrict their use of momentum equations to the diffusion equation. The analysis also shows that such restrictions result in the neglect of terms arising from momentum transport due to any background ambipolar diffusion velocity and wave motion. These terms are mostly relevant at higher altitudes.
Eun, H.↗
Resonant coupling of ionization waves and acoustic gravity waves in the presence of a magnetic field
The nature of the two resonant directions that occur for a single frequency in the presence of a magnetic field is demonstrated, along with the manner in which the resonances change with the dip angle and the angle of propagation from the meridian plane. The conditions under which acoustic branch resonances may occur are outlined. It is found that the calculated frequencies and directions for resonance are in the range of observed values for TID's obtained from ground and satellite measurements. This result is indicative of a possible connection between TID's and the resonance phenomenon. It is shown that a strong resonance type of response may be possible in the F region at a particular frequency from a region that can be as great as 100 km in altitude.
Eun, H.↗
Travelling neutral disturbances and minor constituent particle mass
The mass cut-offs for critical or resonant coupling of minor species acoustic waves (so-called travelling neutral disturbances) and acoustic-gravity waves in the main atmosphere are shown and explained. The effects of vertical temperature gradients and the diffusion of the minor species on the mass cut-offs are also demonstrated. The wave characteristics of these minor species waves are examined. The wave number surface is shown to be such that energy and group velocity directions are more nearly vertical than those of gravity waves for the same phase velocity direction. It is expected that these coupled waves, when properly excited, will act to damp gravity waves and redistribute energy vertically. Implications for the thermosphere and mesosphere are discussed. Under ordinary conditions such resonant coupling is judged more likely for lighter mass species, such as helium and hydrogen.
Gross, S. H.↗
A spectral search for Lyman-Birge-Hopfield band nightglow from Spacelab 1
Huffman et al. (1980) have reported the observation of significant intensities of the N2 Lyman-Birge-Hopfield (LBH) bands at midlatitudes at night. During the course of the 10-day Spacelab 1 mission, spectral observations were made of the atmosphere on both the dayside and nightside of the earth with the vehicle in various attitudes. The present investigation is concerned with an examination of selected data for evidence of the LBH nightglow. The considered data include far ultraviolet observations which were made on the nocturnal atmosphere at low latitudes and midlatitudes. The investigation confirms that the earlier reported LBH nightglow does appear to be generally present at the time of the Spacelab 1 mission.
Torr, M. R.↗
The natural background at Shuttle altitudes
In order to make astronomical observations from the Shuttle, the observer needs good information on the intensities and spectral characteristics of various sources. This paper presents a model spectrum for the natural airglow background. The spectrum is modeled over a wavelength range extending from the extreme ultraviolet to the near-infrared. This model is based on the present knowledge of the upper atmosphere. The effect of different viewing configurations is illustrated, together with day-to-night variations. The results synthesized here assume an ideal vehicle in the sense that no contaminant emissions are induced by the Shuttle and payload. These spectra therefore represent a baseline which can be used to locate unanticipated or nonambient features.
Torr, Marsha R.↗
Plasma-puff initiation of high Coulomb transfer switches
The plasma-puff triggering mechanism based on a hypocycloidal pinch geometry was investigated to determine the optimal operating conditions for an azimuthally uniform surface flashover which initiates plasma-puff under wide ranges of fill gas pressures of Ar, He and N2. The optimal fill gas pressures for the azimuthally uniform plasma-puff were about 120 mTorr less than P(sub opt) less than 450 Torr for He and N2. For Argon 20 mTorr is less than P(sub opt) is less than 5 Torr. The inverse pinch switch was triggered with the plasma-puff and the switching capability under various electrical parameters and working gas pressures of Ar, He and N2 was determined. It was also shown that the azimuthally uniform switching discharges were dependent on the type of fill gas and its fill pressure. A new concept of plasma-focus driven plasma-puff was also discussed in comparison with hypocycloidal pinch plasma-puff triggering. The main discharge of the inverse pinch switch with the plasma-focus driven plasma-puff trigger is found to be more azimuthally uniform than that with the hypocycloidal pinch plasma-puff trigger in a gas pressure region between 80 mTorr and 1 Torr. In order to assess the effects of plasma current density on material erosion of electrodes, emissions from both an inverse-pinch plasma switch (INPIStron) and from a spark gap switch under test were studied with an optical multichannel analyzer (OMA). The color temperature of the argon plasma was approximately 4,000 K which corresponded with the peak continuum emission near 750 nm. There are the strong line emissions of argon in the 650 - 800 nm range and a lack of line emissions of copper and other solid material used in the switch. This indicates that the plasma current density during closing is low and the hot spot or hot filament in the switch is negligible. This result also indicates considerable reduction of line emission with the INPIStron switch over that of a spark-gap switch. However, a strong carbon line emission exists due to vaporization of the plastic insulator used. In order to reduce the vaporization of the insulator, the plexiglass insulating material of INPIStron was replaced with Z-9 material. A comparative study of the INPIStron and a spark gap also reveals that the INPIStron, with a low impedance of Z = 9 ohms, can transfer a high voltage pulse with a superior pulse-shape fidelity over that of a spark gap with Z = 100 ohms.
Han, Kwang S.↗
Characteristics of plasma-puff trigger for a inverse-pinch plasma switch
The plasma-puff triggering mechanism based on a hypocycloidal pinch geometry was investigated to determine the optimal operating conditions for the azimuthally uniform surface flashover which initiates plasma-puff under wide ranges of fill gas pressure of Ar, He and N2. The optimal fill-gas pressure range for the azimuthally uniform plasma-puff was about 120 mTorr less than or equal to P(sub op) less than or equal to 450 Torr for He and N2. For Argon 120 mTorr is less than or equal to P(sub op) is less than or equal to 5 Torr. The inverse-pinch switch was triggered with the plasma-puff and the switching capability under various electrical parameters and working gas pressures of Ar, He and N2 was determined. The azimuthally uniform switching discharges were dependent on the type of fill gas and its fill pressure. A new concept of plasma-focus driven plasma-puff will be discussed in comparison with the current hypocycloidal-pinch plasma-puff triggering.
Choi, Eun H.↗
Superconductor-Magnet Bearings With Inherent Stability and Velocity-Independent Drag Torque
A hybrid superconductor magnet bearing system has been developed based on passive magnetic levitation and the flux pinning effect of high-temperature superconductivity. The rationale lies in the unique capability of a high-temperature superconductor (HTS) to enhance system stability passively without power consumption. Characterization experiments have been conducted to understand its dynamic behavior and to estimate the required motor torque for its driving system design. These experiments show that the hybrid HTS-magnet bearing system has a periodic oscillation of drag torque due mainly to the nonuniform magnetic field density of permanent magnets. Furthermore, such a system also suffers from a small superimposed periodic oscillation introduced by the use of multiple HTS disks rather than a uniform annulus of HTS material. The magnitude of drag torque is velocity independent and very small. These results make this bearing system appealing for high-speed application. Finally, design guidelines for superconducting bearing systems are suggested based on these experimental results.
Lee, Eun-Jeong↗
A Discussion of Upper Stratospheric Ozone Asymmetry and Ozone Trend Changes
Analyses from SAGE I/II version 6.0 data exhibit upper stratospheric ozone trends which are not significantly different from those in version 5.96 data. Trend calculations show larger downward trends at mid-high latitudes in the Southern Hemisphere than in the Northern Hemisphere, particularly in 1980s. There are also indications of decreasing downward trends with time from 1979 to 1999. We have used a chemical box model and the UARS measurements of long lived gases, CH4, H2O, NO(x), and temperature to show that, with a constant Cl(sub y) trend, a hemispheric ozone trend asymmetry of 1%/decade at 45 deg. around 43 km is expected due to the hemispheric differences of temperature and CH4 during late winter/early. Also ozone trends should have been approximately 1%/decade more negative from 1979-1989 than from 1989-1999 because of the chemical feedbacks. The model results further indicate that both the reported decrease in CH4 and the increase in H2O in HALOE measurements will result in a larger downward ozone trend and a decrease in the hemispheric ozone trend asymmetry.
Li, Jinlong↗
Computational modeling of cardiovascular response to orthostatic stress
The objective of this study is to develop a model of the cardiovascular system capable of simulating the short-term (< or = 5 min) transient and steady-state hemodynamic responses to head-up tilt and lower body negative pressure. The model consists of a closed-loop lumped-parameter representation of the circulation connected to set-point models of the arterial and cardiopulmonary baroreflexes. Model parameters are largely based on literature values. Model verification was performed by comparing the simulation output under baseline conditions and at different levels of orthostatic stress to sets of population-averaged hemodynamic data reported in the literature. On the basis of experimental evidence, we adjusted some model parameters to simulate experimental data. Orthostatic stress simulations are not statistically different from experimental data (two-sided test of significance with Bonferroni adjustment for multiple comparisons). Transient response characteristics of heart rate to tilt also compare well with reported data. A case study is presented on how the model is intended to be used in the future to investigate the effects of post-spaceflight orthostatic intolerance.
Flight Experiment↗
Attribution of Recovery in Lower-Stratospheric Ozone
Multiple satellite and ground-based observations provide consistent evidence that the thickness of Earth's protective ozone layer has stopped declining since 1997, close to the time of peak stratospheric halogen loading. Regression analyses with Effective Equivalent Stratospheric Chlorine (EESC) in conjunction with further analyses using more sophisticated photochemical model calculations constrained by satellite data demonstrate that the cessation of ozone depletion between 18-25 km altitude is consistent with a leveling off of stratospheric abundances of chlorine and bromine, due to the Montreal Protocol and its amendments. However, ozone increases in the lowest part of the stratosphere, from the tropopause to 18 km, account for about half of the improvement in total column ozone during the past 9 years at northern hemisphere mid-latitudes. The increase in ozone for altitudes below 18 km is most likely driven by changes in transport, rather than driven by declining chlorine and bromine. Even with this evidence that the Montreal Protocol and its amendments are having the desired, positive effect on ozone above 18 km, total column ozone is recovering faster than expected due to the apparent transport driven changes at lower altitudes. Accurate prediction of future levels of stratospheric ozone will require comprehensive understanding of the factors that drive temporal changes at various altitudes, and partitioning of the recent transport-driven increases between natural variability and changes in atmospheric structure perhaps related to anthropogenic climate change.
Yang, Eun-Su↗
Evidence for slowdown in stratospheric ozone loss: First stage of ozone recovery
Global ozone trends derived from the Stratospheric Aerosol and Gas Experiment I and II (SAGE I/II) combined with the more recent Halogen Occultation Experiment (HALOE) observations provide evidence of a slowdown in stratospheric ozone losses since 1997. This evidence is quantified by the cumulative sum of residual differences from the predicted linear trend. The cumulative residuals indicate that the rate of ozone loss at 35- 45 km altitudes globally has diminished. These changes in loss rates are consistent with the slowdown of total stratospheric chlorine increases characterized by HALOE HCI measurements. These changes in the ozone loss rates in the upper stratosphere are significant and constitute the first stage of a recovery of the ozone layer.
Newchurch, M. J.↗
Attribution of Recovery in Lower-stratospheric Ozone
Multiple satellite and ground-based observations provide consistent evidence that the thickness of Earth's protective ozone layer has stopped declining since 1997, close to the time of peak stratospheric halogen loading. Regression analyses with Effective Equivalent Stratospheric Chlorine (EESC) in conjunction with further analyses using more sophisticated photochemical model calculations constrained by satellite data demonstrate that the cessation of ozone depletion between 18-25 km altitude is consistent with a leveling off of stratospheric abundances of chlorine and bromine, due to the Montreal Protocol and its amendments. However, ozone increases in the lowest part of the stratosphere, from the tropopause to 18 km, account for about half of the improvement in total column ozone during the past 9 years at northern hemisphere mid-latitudes. The increase in ozone for altitudes below 18 km is most likely driven by changes in transport, rather than driven by declining chlorine and bromine. Even with this evidence that the Montreal Protocol and its amendments are having the desired, positive effect on ozone above 18 km, total column ozone is recovering faster than expected due to the apparent transport driven changes at lower altitudes. Accurate prediction of future levels of stratospheric ozone will require comprehensive understanding of the factors that drive temporal changes at various altitudes, and partitioning of the recent transport-driven increases between natural variability and changes in atmospheric structure perhaps related to anthropogenic climate change.
Yang, Eun-Su↗