Engineering topics

Spencer, N. W.

Publications and source records attributed to Spencer, N. W..

At least 73 records · Page 4

NASA NTRS1980

Correlations between neutral meridional winds and ion densities observed on AE-E

The southward directed neutral meridional wind and the nighttime ion density simultaneously measured on AE-E for altitudes from 250 to 290 km are compared and found to correlate when the magnetic field inclination is negative and anticorrelate when the inclination is positive. This effect is attributed to neutral winds transporting the ions up or down a field line depending upon the sign of the field-aligned wind and the inclination. Model calculations for the ion density in the presence of a field-aligned wind and ambipolar diffusion are presented. Six examples of this ionospheric response are analyzed and found to be in qualitative and approximate quantitative agreement with the theoretical results.

Wharton, L. E.↗

NASA NTRS1980

The semidiurnal and terdiurnal tides in the equatorial thermosphere from AE-E measurements

Measurements of neutral composition and temperature aboard the near-equatorial AE-E satellite are analyzed to determine the semidiurnal and terdiurnal variations from 145 to 295 km. The amplitudes and phases of the semidiurnal variation are approximately the same for N2, O, He, and Ar at the lowest altitude, and the amplitude increases with decreasing altitude. Except for He, the phase undergoes a 180 deg shift around 200 km. The behavior of the terdiurnal variation is in many respects similar to the behavior of the semidiurnal variation. These characteristics suggest that the semidiurnal tide and (to a lesser extent) the terdiurnal tide have an origin primarily in the lower thermosphere or below.

Hedin, A. E.↗

NASA NTRS1980

Atomic nitrogen in the upper atmosphere of Venus

Atomic nitrogen has been detected in the upper atmosphere of Venus by the Pioneer-Venus Orbiter Neutral Mass Spectrometer (ONMS). Surface recombination of atomic nitrogen with atomic oxygen to form nitric oxide in the ion source allows it to be detected at mass 30. The scale height temperature of the mass 30 peak agrees with the scale height temperatures of the other species if it is assumed to be derived from atomic nitrogen. The diurnal variation of atomic nitrogen is approximately proportional to that of atomic oxygen with an estimated N/O ratio of 1.5% at 150 km.

Kasprzak, W. T.↗

NASA NTRS1980

Pioneer Venus Orbiter neutral gas mass spectrometer experiment

The Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) is designed to measure the vertical and horizontal density variations of the major neutral constituents in the upper atmosphere of Venus. The mass spectrometer sensor includes a retarding potential ion source, hyperbolic quadrupole rod analyzer, and electron multiplier detector. The supporting electronic system consists of hybrid integrated circuits to reduce weight and power. The ONMS instrument was launched aboard the Pioneer Venus Orbiter on May 20, 1978, and turned on in orbit around Venus on December 4, 1978. It has operated flawlessly for over a Venus year (243 earth days) and has returned data of the composition of the major constituents in the Venus atmosphere between the altitudes of 150 and 350 km.

Niemann, H. B.↗

NASA NTRS1979

Venus upper atmosphere neutral gas composition - First observations of the diurnal variations

Measurements of the composition, temperature, and diurnal variations of the major neutral constituents in the thermosphere of Venus are being made with a quadrupole mass spectrometer on the Pioneer Venus Orbiter. Concentrations of carbon dioxide, carbon monoxide, molecular nitrogen, atomic oxygen, and helium are presented, in addition to an empirical model of the data. The concentrations of the heavy gases, carbon dioxide, carbon monoxide, and molecular nitrogen, rapidly decrease from the evening terminator toward the nightside; the concentration of atomic oxygen remains nearly constant and the helium concentration increases, an indication of a nightside bulge. The kinetic temperature inferred from scale heights drops rapidly from 230 K at the terminator to 130 K at a solar zenith angle of 120 deg, and to 112 K at the antisolar point.

Niemann, H. B.↗

NASA NTRS1979

An experimental and theoretical study of the mean diurnal variation of O/+/, NO/+/, O2/+/, and N2/+/ ions in the mid-latitude F1 layer of the ionosphere

A theoretical model of the diurnal variations in the compositions of the ions O(+), NO(+), O2(+) and N2(+) in the midlatitude F1 layer is presented and compared with measurements made by AE-C. The theoretical model includes the rate coefficients and branching ratios for the dissociative recombination of NO(+), O2(+) and N2(+) with electrons and the ion-atom interchanges of O(+) with N2 and N2(+) with O. Input parameters to the model comprise measurements of ion and electron temperatures, neutral atmosphere composition, the solar EUV flux and the photoelectron spectrum. In general, model calculations are found to agree with satellite measurements, confirming the major ion sources and sinks of the photochemical model, which has an accuracy of + or - 60%.

Torr, D. G.↗

NASA NTRS1979

Energy and mass transport in the thermosphere

Examples illustrating the effects of large scale energy and mass transport in the thermosphere discussed include: (1) The seasonal variations reveal temperature, composition, and ionospheric anomalies involving energy exchange between the thermosphere and mesosphere. (2) The midnight temperature maximum in the thermosphere is interpreted as a signature of tidal waves emanating from the mesosphere and momentum coupling associated with ion drag. (3) The ionospheric storm in the F region illustrates the intricate effects of large scale atmospheric winds driven by magnetospheric energization processes. (4) Atmospheric signatures of Joule heating and electric field momentum coupling are markedly different.

Mayr, H. G.↗

NASA NTRS1979

The midnight temperature maximum in the earth's equatorial thermosphere

The paper reports in situ direct measurements of regularly observed thermosphere neutral particle (i.e., N2) temperature maxima that occur predominantly after midnight. The measurements were made using the Neutral Atmosphere Temperature Instrument aboard Atmosphere Explorer-E in circular orbit (inclination 19 deg) at about 275 km. Hundreds of midnight temperature maxima were observed, some having values exceeding the well-known afternoon maximum. Simultaneous in situ direct measurements of the wind component normal to the orbit plane have also been obtained and observed to correlate in a systematic way with the temperature maxima.

Spencer, N. W.↗

NASA NTRS1979

Tides and the midnight temperature anomally in the thermosphere

Spectral analysis of the midnight temperature anomaly observed on Atmosphere Explorer-E indicates that the phenomenon can be adequately represented with wave numbers between 1 and 5. Results from a multiconstituent circulation model suggest that this feature and associated variations in composition are the result of a complex interaction between the semidiurnal tide generated in the lower atmosphere and ion-neutral momentum coupling associated with the diurnal variation of the ion density which, in turn, also generates higher order tidal models.

Mayr, H. G.↗

NASA NTRS1979

Auroral origin of medium scale gravity waves in neutral composition and temperature

The kinetic temperature and neutral composition data obtained from the Aeros B neutral atmosphere temperature experiment and the neutral and ion mass spectrometer show spatial structures characteristic of medium scale gravity waves with a wavelength in the range of several hundred kilometers. These waves are associated with auroral activity, and their spatial structure reflects the time history of the auroral electrojet. The medium scale gravity waves tend to propagate to mid-latitudes on the nightside. On the dayside their range is limited to high latitudes. Gravity waves are carriers of auroral energy to middle and low latitudes where they may cause irreversible changes in temperature via viscous dissipation. Since auroral activity occurs frequently, it is suggested that this energy reaches the mid-latitude region of the thermosphere much more frequently than is indicated by planetary magnetic indices.

Chandra, S.↗

NASA NTRS1979

Neutral atmospheric waves determined from Atmospheric Explorer measurements

A description is presented of the first observations of neutral gravity waves in which a sufficient number of wave parameters are detected to allow a specification of the neutral wave characteristics. In situ measurements of neutral wind, temperature, and composition from Atmospheric Explorer are used to obtain wave amplitudes and phases for N2 temperature and wind, and N2, O, and He densities. These amplitudes and phases along with the Doppler shifted wave frequency provide sufficient information to evaluate the wave frequency and the wave vector.

Hoegy, W. R.↗

NASA NTRS1979

Venus upper atmosphere neutral composition - Preliminary results from the Pioneer Venus orbiter

Measurements in situ of the neutral composition and temperature of the thermosphere of Venus are being made with a quadrupole mass spectrometer on the Pioneer Venus orbiter. The presence of many gases, including the major constituents CO2, CO, N2, O, and He has been confirmed. Carbon dioxide is the most abundant constituent at altitudes below about 155 kilometers in the terminator region. Above this altitude atomic oxygen is the major constituent, with O/CO2 ratios in the upper atmosphere being greater than was commonly expected. Isotope ratios of O and C are close to terrestrial values. The temperature inferred from scale heights above 180 kilometers is about 400 K on the dayside near the evening terminator at a solar zenith angle of about 69 deg. It decreases to about 230 K when the solar zenith angle is about 90 deg.

Niemann, H. B.↗

NASA NTRS1979

Global model of longitude/UT variations in thermospheric composition and temperature based on mass spectrometer data

Measurements of N2, O, He, and Ar densities from neutral gas mass spectrometers on four satellites and inferred O2 and H densities from an ion mass spectrometer have been combined to produce a model of longitude/UT variations in thermospheric neutral composition and temperature. The longitude/UT model is an extension of the mass spectrometer-incoherent scatter thermospheric model (Hedin et al., 1977) and uses spherical harmonic terms dependent on geographic latitude, longitude, and UT. The combined longitude and UT variations reflect the influence of the geomagnetic field but indicate that the variations may not simply be represented in magnetic coordinates.

Hedin, A. E.↗

NASA NTRS1979

Comparison of atmospheric density data from mass spectrometers and atmospheric drag on the Aeros satellites

The comparison of perigee density data near 230 km for satellite Aeros-A has been extended to the complete mission time. The average ratio between orbital drag derived density and mass spectrometer measurements is very near to 1 with a large scatter reflected by a standard deviation of the order of 20%. A method of comparison was developed and tested which uses the observed rate of change of orbital period in comparison with the orbital decay computed from the actual mass spectrometer data measured at discrete positions along the orbit. This method proves that deviations from the average ratio of 1 between perigee densities from drag and mass spectrometers are due to the smoothing and poor resolution of the orbital drag technique.

Roemer, M.↗

NASA NTRS1978

Some properties of upper atmosphere dynamics

A unifying description is provided of some important dynamic properties of the upper atmosphere in composition and temperature characteristic of a variety of phenomena, including diurnal and seasonal tides, magnetic storms, and momentum coupling with the magnetosphere. A theoretical multiconstituent model is used which can link the large-scale variations of composition and temperature to the dynamics and energetics of the thermosphere. Global mean properties of the thermosphere are reviewed, and an attempt is made to convey some understanding of the dynamic properties of energy and diffusive mass transport in the thermosphere. Attention is given to sources of energy for the thermosphere, the transport processes involved in the solar diurnal tide of the thermosphere, energy and particle sources for the annual tide, feedback from composition changes to wind-field and temperature variations, energy deposition in the thermosphere during magnetic storms and substorms, and momentum source signatures in the thermosphere.

Mayr, H. G.↗

NASA NTRS1978

Direct evidence of transport processes in the thermospheric diurnal tide

Measurements of neutral composition and temperature obtained between December 6, 1975, and September 17, 1976, with instruments aboard the near-equatorial AE-E satellite are analyzed to determine the diurnal variations at altitudes from 145 to 295 km. The general trends, including the shift in oxygen phase from afternoon at high altitudes to morning at low altitudes, are reproduced by circulation theories. The oxygen and helium variations show small departures from diffusive equilibrium below 200 km that are consistent with wind-induced diffusion and provide the first direct evidence of transport processes in the diurnal tide of the thermosphere.

Hedin, A. E.↗

NASA NTRS1978

Gas densities near 230 km from orbital drag and mass spectrometer measurements - A comparison

Perigee density data near 230 km for the Aeros satellite are analyzed for more than 1000 orbits. A comparison method for such data was developed which is based on the observed rate of change of orbital period as compared with the orbital decay computed from mass-spectrometer data obtained at discrete positions along the orbit. In general, the method confirms the good agreement of the average ratio of in-situ and orbit-drag-inferred perigee densities. In the case of Aeros, absolute densities measured by the NATE mass spectrometer are confirmed.

Roemar, M.↗

NASA NTRS1977

A global thermospheric model based on mass spectrometer and incoherent scatter data MSIS. I - N2 density and temperature

Measurements of neutral nitrogen density from mass spectrometers on five satellites (AE-B, Ogo 6, San Marco 3, Aeros A, and AE-C) and neutral temperatures inferred from incoherent scatter measurements at four ground stations are combined to produce a model of thermospheric neutral temperatures and nitrogen densities similar to the Ogo 6 empirical model (Hedin et al., 1974). This global model is designated MSIS (mass spectrometer and incoherent scatter). The global average temperature, the annual temperature variation, lower bound density, and lower bound temperature are discussed. The data set covers the time period from the end of 1965 to mid-1975 and also a wide range of solar activities. Diurnal and semidiurnal variations in lower bound density and temperature are considered, as is magnetic activity.

Hedin, A. E.↗