Engineering topics
Publications and source records attributed to Siskind, D. E..
An overview of two years of data obtained with a ground-based microwave instrument is given. Intercomparisons with data obtained by the co-located JPL lidar and by SAGE 2 during near overpasses of the site are discussed, as are comparisons with mesospheric data taken earlier by SME and LIMS. Observations of diurnal variations of mesospheric ozone are shown.
A 3D mechanistic, primitive-equation model of the stratosphere and mesosphere is coupled to an offline spectral transport model. The dynamics model is initialized with and forced by observations so that the coupled models may be used to study specific episodes. Results are compared with those obtained by transport online in the dynamics model. Although some differences are apparent, the results suggest that coupling of the models to a comprehensive photochemical package will provide a useful tool for studying the evolution of constituents in the middle atmosphere during specific episodes.
A rocket observation of nitric oxide in the lower thermosphere during a time of high solar activity is compared to the results of calculations from a one-dimensional photochemical model. A solar soft X-ray flux of 0.75 erg/sq cm/s is needed to explain the observed NO densities. This result supports the theory that the variation in the low-latitude thermospheric NO is caused by variation in solar soft X-rays.
An observation of the ultraviolet nightglow between 2670 A and 3040 A was conducted over White Sands Missile Range on October 22, 1984, at 0020 hours LST during the Orionids meteor shower. A 1/4-meter UV spectrometer operating at 3.5 A resolution viewed the earth's limb at tangent heights between 90 km and 110 km for 120 seconds. By inverting the observed limb intensities, a total zenith intensity of 1.4 kR is inferred for the Herzberg I system. Excess emission above the Herzberg I (7,3) band at 2852 A is identified as the Mg I resonance line. The intensity ratio of the Herzberg I band system to the 2972 A line from O(1S) was less than that predicted from the accepted O(1S) branching ratio and acceptable ratios of Herzberg I to 5577 A emissions. Arguments supporting the identification of the Herzberg III band system are also advanced.
The response of low- and mid-latitude NO to the September 19, 1984 magnetic storm is studied. In particular, the effect of variations in the temperature and composition of the lower thermosphere on NO is investigated. Much of the observed NO response is adequately explained by including these variations in a photochemical model. In particular, Joule heating at auroral latitudes can cause temperature enhancements at nonauroral latitudes, which in turn can lead directly to an increase in the NO. The NO is most directly sensitive to heating at altitude above 120 km. Below 120 km, NO increased through downward diffusion from above. Sensitivity studies were performed to investigate the effect that uncertainties in the NO chemical scheme and in the state of the neutral atmosphere can have on the comparison of the model to the data. It is shown that the best fit to the midlatitude American orbit data is for O/O2 ratio twice that in the original TGCM simulation and for an N(2D) quenching value of 5 x 10 to the -13th.
NOAA 6 and 7 particle measurements are used, in conjunction with a statistical model of the auroral particle precipitation, to study the response of auroral NO to the auroral storm of September 19, 1984. The results of a time-dependent photochemical calculation show that particle precipitation can more effectively produce NO than can Joule heating, in contrast to nonauroral latitudes where heating is important. Both the model and the NO data show NO increases as a result of the storm; however, the absolute magnitude of the NO in the model, as well as the amplitude of the increase, significantly exceeded what was observed. Two possible explanations for the this discrepancy are proposed.
A model is proposed in which the strong hydrodynamic shock forming around the Space Shuttle, and occasionally detaching, generates strong hydrodynamic turbulence downstream. The level of this turbulence is found to be sufficiently great to account for the heating of electrons that has been observed. A shock formed in front of the Orbiter is shown to satisfy the Rankine-Hugoniot momentum and pressure balance equations. The hydrodynamic turbulence is coupled through ion-neutral collisions to the O2(+) and N2(+) ions of outgas.
This paper presents an analysis of interactions between the Space Shuttle Orbiter and the ionosphere based on thermal plasma data obtained from a Spherical Retarding Potential Analyzer (SRPA) and a Langmuir Probe (LP) flown on the third Space Shuttle flight (STS-3) in March 1982. While previous work on spacecraft-plasma interactions has dealt with wake effects, the present work deals with effects that are seen in ram conditions that have not been previously discussed. One observation is a higher degree of plasma turbulence than has been reported from unmanned spacecraft measurements that manifests itself as a frequency component at 2.2 kHz in the SRPA signal. Also seen are unusually high number densities of what appear to be ions with a mass of at least 30 or 32 amu and a temperature in the range 2000-3000 K. Coincident with the enhanced molecular ion species, the temperature of the thermal electrons is seen elevated to above 5000 K. It is hypothesized that these measurements are evidence for a plasma instability resulting from the motion of the outgassing Orbiter through the ionosphere.
The paper presents some initial results on measurements of the thermal plasma environment obtained by a spherical retarding potential analyzer and a Langmuir probe flown on (STS-3) as part of the NASA Office of Space Science-1 payload in March 1982. One of the major effects observed is a higher degree of turbulence in the ambient plasma compared to what is observed from similar instruments flown on unmanned satellites. In addition we see the temperature of the thermal electrons elevated to values of 4000-5000 K. Associated with elevated electron temperatures are regions of enhanced plasma density resulting from the appearance of high densities of molecular ions. The thermal plasma data also show clear effects of an induced V x B.L potential at the location of the probes which matches that produced by an L vector linking the probes to the engine nozzles; thereby establishing the prime return current location on the Orbiter. The final observations discussed are the pronounced and complex wake effects resulting both from the main structure of the Orbiter and from the complex shapes of appendages attached to the Orbiter.