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Computations are presented for a Lambda = 75 deg delta wing in a supersonic freestream under two conditions which lead to leading-edge vortices. For one condition, analysis of the computed vortical flow reveals a closed streamline in the core. From varying computational parameters, it appears that this is due to truncation error of the convective derivatives. For the other condition, comparisons are made with wind-tunnel data, and good agreement is noted for pitot pressure distributions, flow angles on the symmetry plane, and the position of an embedded shock. Many of the aerodynamic parameters are shown to be insensitive to grid spacing.
The absolute cross sections for the production of N(+) and N2(+) have been measured from the dissociative ionization threshold to 115 A. In addition, the absolute photoabsorption and photoionization cross sections are tabulated between 114 and 796 A. The ionization efficiencies are also given at several discrete wavelengths between 660 and 790 A. The production of N(+) fragment ions are discussed in terms of the doubly excited N2(+) states with binding energies in the range 24 to 44 eV.
TEC values calculated with the Bent model were used instead of actual data for the Madrid Deep Space Communications Complex during most of the Voyager Uranus approach and encounter. These values were used from December 1, 1985 to January 16, 1986 for Voyager Uranus, and for March 1986 to support the Pathfinder mission; thus, the Halley flybys of Vega 1 and 2 and Giotto were included. Provided sunspot numbers are below 130, the Bent model can be used with confidence to calculate TEC values for midlatitude stations when actual TEC data or monthly averages are not available.
Explicit second-order accurate finite-difference schemes for the approximation of hyperbolic conservation laws are presented. These schemes are nonlinear even for the constant coefficient case. They are based on first-order upwind schemes. Their accuracy is enhanced by locally replacing the first-order one-sided differences with either second-order one-sided differences or central differences or a blend thereof. The appropriate local difference stencils are selected such that they give TVD schemes of uniform second-order accuracy in the scalar, or linear systems, case. Like conventional TVD schemes, the new schemes avoid a Gibbs phenomenon at discontinuities of the solution, but they do not switch back to first-order accuracy, in the sense of truncation error, at extrema of the solution. The performance of the new schemes is demonstrated in several numerical tests.
The mechanisms responsible for the observed H2O/H2 mixing ratio (HMR) in the Jovian troposphere are analyzed, with a focus on the relationship between HMR and O2 abundance and the abundance of the nonequilibrium trace gases CO and SiH4. The results of computations using a Jupiter atmosphere model consistent with recent observations (Bjoraker et al., 1986) are presented graphically and discussed in detail. It is found that the observed mixing ratios of CO (about 10 to the -9th) and SiH4 (upper limit 2-4 x 10 to the -9th) preclude O2 depletion and the presence of significant global H2O. The low observed HMRs (0.00003 at 6 bar) are tentatively attributed to local condensation in cloud-forming regions.
This paper describes the SPICE model of a transformer-rectified-filter (TRF) circuit and the Micro-CAP (Microcomputer Circuit Analysis Program) model and their application. The models were used to develop an actual circuit with reduced input current THD. The SPICE analysis consistently predicted the THD improvements in actual circuits as various designs were attempted. In an effort to predict and verify load regulation, the incorporation of saturable inductor models significantly improved the fidelity of the TRF circuit output voltage.
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The cavity pyrheliometer sensor aboard Nimbus 7 is now in its tenth year of operation. Results for 9 1/2 years show a decreasing trend through the end of solar cycle 21 of approximately -0.015 percent per year, a leveling off near solar minimum and an increasing irradiance for the beginning of cycle 22. Through April 1988, the irradiance has increased about 0.06 percent above the minimum value which was about 0.08 percent below the highest values obtained near solar maximum. The rise appears more rapid than the decline.
The unsteady flowfield about an airfoil-shaped inlet temperature sensor has been investigated using the thin-layer and full Navier-Stokes equations. A finite-volume formulation of the governing equations was used in conjunction with a Runge-Kutta time stepping scheme to analyze the flow about the sensor. Flow characteristics for this configuration were established at Mach numbers of 0.5 and 0.8 for different Reynolds numbers. The results were obtained for configurations of increasing complexity; important physical phenomena such as shock formation, boundary-layer separation, and unsteady wake formation were noted. Based on the computational results, recommendations for further study and refinement of the inlet temperature sensor were made.
The principal features of the thermodynamic regime of the stratosphere are governed by the development of the winter stratospheric low and the Aleutian and Atlantic heights. These are fed by the influx of the eddy energy transported into the stratosphere by the planetary waves. The intensity and variability of planetary waves and vortices associated with the waves determine the conditions of low-to-high latitudes ozone transport in the winter hemisphere. The ozone distributions are zonally inhomogeneous. The planetary wave dynamics are affected by solar activity variations during solar cycles. The 20th solar cycle maximum was accompanied by decreases of stratospheric planetary wave amplitudes, the 21st cycle was accompanied by increases of amplitudes.
Absolute absorption and photoionization cross sections of methane have been measured with an accuracy of about 2 or 3 percent over most of the wavelength range from 950 to 110 A. Also, dissociative photoionization cross sections were measured for the production of CH4(+), CH3(+), CH2(+), CH(+), and C(+) from their respective thresholds to 159 A, and for H(+) and H2(+) measurements were made down to 240 A. Fragmentation was observed at all excited ionic states of CH4.
A method for calculating daily evapotranspiration from the daily surface energy budget using remotely sensed surface temperature and several meteorological variables is presented. Vaules of the coefficients are determined from simulations with a one-dimensional boundary layer model with vegetation cover. Model constants are obtained for vegetation and bare soil at two air temperature and wind speed levels over a range of surface roughness and wind speeds. A different means of estimating the daily evapotranspiration based on the time rate of increase of surface temperature during the morning is also considered. Both the equations using our model-derived constants and field measurements are evaluated, and a discussion of sources of error in the use of the formulation is given.
Nimbus 7 solar irradiance values have been made available to the scientific community through the open literature (e.g., Hickey et al., 1988) and through NASA data centers. A comparison of these measurements to the Solar Maximum Mission/Active Cavity Radiometer Irradiance Monitor (SSM/ACRIM) time series indicated differences which might be caused in part by the method of converting the Nimbus 7 raw data counts to solar irradiance values. In an effort to see if the derivation of the solar irradiance could be improved, the raw counts were extracted from the tapes and analyzed to see how a new algorithm could be constructed. The basic form of the calibration remains the same as in the previous solar irradiance derivations. However, the input values to the equation differ from what was used before. In particular, improved values of the Earth-sun distance are incorporated and new temperature sensitivities were derived. Several problems with the instrument were uncovered which previously had not been noticed. The sun did not appear to cross the center of field of the radiometer but was systematically off by 1.5 to 2.5 degrees. The analog to digital convertor changed its properties in July 1980. The gain of the electronics apparently increased by 0.03 percent in September 1987. Applying these and other changes in the processing, the day to day variations appear much more like the SMM observations. In fact, the Nimbus 7 observations are sufficiently stable that a problem with the SSM observations in the spin mode period of 1981 to 1984 can be detected when the two time series are compared.
Computer simulations of orbital scenarios were performed to examine the effects of orbital altitude, equator crossing time, attitude uncertainty, and orbital eccentricity on ozone observations by future satellites. These effects were assessed by determining changes in solar and viewing geometry and earth daytime coverage loss. The importance of these changes on ozone retrieval was determined by simulating uncertainties in the TOMS ozone retrieval algorithm. The major findings are as follows: (1) Drift of equator crossing time from local noon would have the largest effect on the quality of ozone derived from TOMS. The most significant effect of this drift is the loss of earth daytime coverage in the winter hemisphere. The loss in coverage increases from 1 degree latitude for + or - 1 hour from noon, 6 degrees for + or - 3 hours from noon, to 53 degrees for + or - 6 hours from noon. An additional effect is the increase in ozone retrieval errors due to high solar zenith angles. (2) To maintain contiguous earth coverage, the maximum scan angle of the sensor must be increased with decreasing orbital altitude. The maximum scan angle required for full coverage at the equator varies from 60 degrees at 600 km altitude to 45 degrees at 1200 km. This produces an increase in spacecraft zenith angle, theta, which decreases the ozone retrieval accuracy. The range in theta was approximately 72 degrees for 600 km to approximately 57 degrees at 1200 km. (3) The effect of elliptical orbits is to create gaps in coverage along the subsatellite track. An elliptical orbit with a 200 km perigee and 1200 km apogee produced a maximum earth coverage gap of about 45 km at the perigee at nadir. (4) An attitude uncertainty of 0.1 degree in each axis (pitch, roll, yaw) produced a maximum scan angle to view the pole, and maximum solar zenith angle).
An analytical treatment of the effect of thermal molecular velocity on spacecraft atomic oxygen (AO) flux is presented. The analysis leads to a closed form equation that incorporates the effect of atmospheric temperature, number density, spacecraft velocity, and incidence angle on AO flux. The effects of atmospheric rotation, solar activity, and geomagnetic index on AO flux are also included on the computer model. Data developed with the model are presented for the Long Duration Exposure Facility (LDEF). The results incorporate variations in the defining environmental and orbital parameters of the spacecraft over its six year orbital flight. Cumulative ultraviolet solar and albedo exposures were calculated .
Techniques are developed for quantitative retrievals of high spatial resolution column atmospheric water vapor that is largely contained in the lower portion of the troposphere. One method consists of curve fitting observed spectra with simulated spectra in the 1.14 microns or the 0.94 micron water vapor band absorption region. The other method is a simple band ratioing technique, which requires less computer time than the curve fitting method. The advantage of the technique over humidity sounding by IR emission measurements is that the retrieved column water vapor amounts over land surfaces have significantly higher precision.
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