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NASA NTRS1974

Observations and calculations of atmospheric helium 10830 emission

Observations and computer model calculations of helium excitation and transport were carried out. The following conclusions can be drawn: (1) the dawn helium density in the thermosphere is greater than the dusk helium density by 50 per cent or more, in contrast to the static diffusion models but in agreement with the dynamic models; (2) the computed He 10830 intensities are inconsistent with the observations when use of the new Penning ionization cross section for loss of atomic oxygen is used; (3) conjugate photoelectron precipitation is responsible for excitation of atmospheric helium at middle latitudes, but it is not evident in the observations at the equator or Brazil (L equals 1.1); (4) the computations predict greater conjugate effects than observed, leading to the possibility of strong interhemispheric absorption.

Christensen, A. B.↗

NASA NTRS1976

Satellite measurements of high-altitude twilight Mg/plus/ emission

Observations made by the ultraviolet spectrometer on board the orbiting geophysical observatory OGO 4 confirmed the presence of resonance scattering at 2800 A of Mg(plus) ions in the twilight subtropical ionosphere. The column density reached 4 billion ions/sq cm above 160 km. Photometric measurements by the ESRO TD 1 satellite revealed a maximum of the Mg(plus) abundance at equinoxes in the top side F region. The interhemisphere asymmetries observed in the intensity distribution are essentially attributed to the effect of eastward thermospheric winds. The 2800-A doublet was also detected by OGO 4 at middle and high latitudes from 110 to 250 km. The brightness of the emission and other evidence indicate that evaporation of meteoritic matter cannot explain the abundance of ions at 200 km. Therefore Mg(plus) ions are probably transported upward from the 100-km permanent source layer.

Gerard, J.-C.↗

NASA NTRS1977

Characteristics of southern hemisphere 200-mbar flow as determined from satellite data

Characteristics of southern hemisphere (SH) 200-mbar flow are examined by using geopotential height fields constructed with the aid of a satellite-based thermal structure. Similar northern hemisphere (NH) satellite-based fields are developed in order to make interhemispheric comparisons. Results indicate that both zonal and meridional components of the SH eddy kinetic energy are as large as their NH counterparts. The SH flow is in general more dependent on transient eddies, especially with regard to the meridional flow. In winter the difference in standing eddy magnitude is apparent only in the north-south component. In summer both zonal and meridional components have smaller standing eddy contributions in the SH. The meridional spectra show a preference for intermediate size (k = 4, 5) transient waves. Ratios of zonal to meridional energies indicate that, especially at intermediate wavelengths, the SH waves are 'more meridional' than those in the NH.

Adler, R. F.↗

NASA NTRS1978

Helium ion outflow from the terrestrial ionosphere

For situations where ion outflow occurs from the topside ionosphere, steady-state solutions for the He(+) continuity, momentum, and energy equations have been obtained self-consistently, yielding density, velocity, and temperature profiles of He(+) from 200 to 2000 km altitude. The study indicates that the outflowing He(+) has density profiles of similar shape to those of H(+), for basically different reasons; the effect of the perpendicular electric field differs considerably for H(+) and He(+); the fractional heating of He(+) due to the He(+)-O(+) relative flow is not as effective in heating He(+) as the flow is in heating H(+); during magnetospheric disturbances the He(+) peak density decreases only by approximately a factor of 2; and the He(+) escape flux over the winter pole is approximately a factor of 20 greater than the He(+) escape flux over the summer pole. The possibility of interhemispheric He(+) flux from winter to summer on high-latitude closed field lines is considered.

Raitt, W. J.↗

NASA NTRS1978

Photoelectrons in the upper atmosphere - A formulation incorporating effects of transport

A technique for solving the problem of photoelectron spatial transport and spectral degradation is presented. The developed model, which allows for a relatively complete description of the relevant transport and collisional physics, can be applied to study processes at either low or high altitude, and may be used to investigate interhemispheric transport. The technique involves dividing the spatial dimension into a set of discrete ordinates and calculating the photoelectron intensity for a specific energy at each point in space and at a set of angle points. The selected range of the energy spectrum was covered completely by a set of energy bins, and the photoelectron intensity in the highest energy bin was calculated first by assuming that the only source term was derived from photoionization. The method is similar to a method used in radiative transfer theory. Spatial and angular redistribution of electrons play a dominant role at heights above 400 km.

Prather, M. J.↗

NASA NTRS1978

Global and regional N2O measurements

Real-time N2O measurements have been made in situ at the South Pole, Antarctica, north and south of the equator from on board the Alpha Helix and over the Pacific Ocean on several aircraft flights from the U.S. to New Zealand, Australia and 90 deg S. In addition, an automated EC-GC has been operated for the past year intermittently monitoring N2O in surface air at a rural site in the wheatlands of eastern Washington state. The data obtained are consistent and in agreement with the data obtained from the analyses of a large number of samples collected both from ground stations and a variety of aircraft flights made in the southern and northern hemisphere. The observed global data show no interhemispheric differences. The present concentration of N2O in the troposphere is measured to be 330 + or - 3 ppbv. Its vertical distribution in the troposphere is very uniform. A small decrease (2-3 percent) across the tropopause is characteristically observed in the high-altitude flights.

Rasmussen, R. A.↗

NASA NTRS1978

Currents and electric fields in the ionosphere due to field-aligned auroral currents

Birkeland (1908, 1913) did a detailed analysis of the upper atmospheric current system in the high-latitude region, and suggested that field-aligned currents flowing into and out of the auroral ionosphere were the driving mechanism for this current system. In the present paper, static electric field and current patterns due to the field-aligned Birkeland currents are examined, using a model in which currents approximating those reported by Iijima and Potemra (1976) are used as input to a global model of the ionospheric conductivities, in which interhemispheric coupling along field lines is included. The model reproduces the main features of the high-latitude current and voltage system and the penetration of these currents within the plasmasphere.

Nisbet, J. S.↗

NASA NTRS1979

A summary of research on the NASA-Global Atmospheric Sampling Program performed by the Atmospheric Sciences Research Center

The annual variations of ozone near the tropopause are derived from aircraft exhibit year-to-year differences which are not explicitly accounted for by the simple, classical ozone transport theory. Phenomena such as tropopause lifting, interannual variations in the rates of stratospheric-tropospheric exchange and meridional mixing, contribute differently to the distribution of ozone in this altitude region. Ozone encounter climatologies have been represented by global maps which show the probabilities of exceeding ambient ozone levels of 200, 300, and 400 ppbV along flight routes during the year. Continuous ozone records obtained from the GASP system revealed the presence of gravity waves whose wavelength is of the order 20 km. The GASP data cannot, however, be utilized for the evaluation of horizontal fluxes of such quantities as ozone, sensible heat, and zonal momentum; the data are too sparsely and irregularly distributed for the computation of stable correlations. Multiple species data from the unique circumglobal flight of a Pan American airliner on 28-30 October 1977 are discussed with particular regard to the apparent interhemispheric differences in tropospheric species concentrations, variation between the Arctic and Antarctic stratospheres, to possible covariations between species, and to potential source regions for various constituents.

Falconer, P. D.↗

NASA NTRS1979

F layer positive response to a geomagnetic storm - June 1972

A circulation model of neutral thermosphere-ionosphere coupling is used to interpret in situ spacecraft measurements taken during a topside midlatitude ionospheric storm. The data are measurements of electron density taken along the circular polar orbit of Ariel 4 at 550 km during the geomagnetically disturbed period June 17-18, 1972. It is inferred that collisional momentum transfer from the disturbed neutral thermosphere to the ionosphere was the dominant midday process generating the positive F-layer storm phase in the summer hemisphere. In the winter hemisphere the positive storm phase drifted poleward in the apparent response to magnetospheric E x B drifts. A summer F-layer positive phase developed at the sudden commencement and again during the geomagnetic main phase; a winter F-layer positive phase developed only during the geomagnetic main phase. The observed seasonal differences in both the onsets and the magnitudes of the positive phases are attributed to the interhemispheric asymmetry in thermospheric dynamics.

Miller, N. J.↗

NASA NTRS1980

The solar ultraviolet heating efficiency of the midlatitude thermosphere

In this paper we quantify the major channels by which solar UV energy is transferred to the atmosphere, and determine the UV heating efficiency for the thermosphere. Current knowledge of the solar ultraviolet fluxes, thermospheric chemistry and neutral atmosphere is used in a steady state, interhemispheric solution of the ionospheric continuity, momentum and energy equations. The heating efficiency is found to be a strong function of altitude, and peaks near the altitude of maximum EUV deposition at a value of approximately 50%.

Torr, M. R.↗

NASA NTRS1981

The distribution of carbon monoxide and ozone in the free troposphere

The two-dimensional distributions of CO and O3 in the free troposphere during July and August, 1974, are discussed. The data confirm the previous findings that both of these gases are considerably more abundant in the northern hemisphere, but the degree of the asymmetry is somewhat different from what had been reported previously, especially for CO. When examined with respect to other available data sets, the conclusion is drawn that a pronounced seasonal cycle exists for CO in both hemispheres which may be driven by the likely seasonal cycle of the OH radical. The data also indicate that CO concentrations exhibit significant variability with height in the northern hemisphere, whereas southern hemispheric concentrations are quite constant with altitude except in cases where interhemispheric exchange of air may be occurring. A discussion on the vertical and horizontal transport processes inferred from the CO and O3 measurements is presented. The possible interdependence of the photochemical cycles of these two trace gases is also discussed.

Seiler, G.↗

NASA NTRS1981

Implications of Titan's north-south brightness asymmetry

Voyager 1 images of Titan, when normalized to remove limb darkening, reveal an axially symmetric brightness pattern with significant north-south asymmetry. This interhemispheric contrast seems to be a response to seasonal solar heating variations resulting from Titan's inclined spin axis. The contrast significantly lags the solar forcing, indicating that its production involves the atmosphere well below the unit optical depth level. The contrast has a significant effect on Titan's disk-integrated brightness as seen from earth, and probably accounts for most of the observed long term variation, with solar UV variations accounting for the remainder.

Sromovsky, L. A.↗

NASA NTRS1982

Plasmaspheric helium ion distribution from satellite observations of He II 304-A

High sensitivity and spatial resolution observations of the He II 304-A emission line intensity in the earth's nightglow have been carried out by the extreme ultraviolet telescope on the Apollo-Soyuz mission in July, 1975. The data, obtained over a wide range of plasmasphere parameters, are compared to the predictions of a kinetic equilibrium model of plasmaspheric ion density. Excellent agreement between observation and theory is found using as inputs a temperature model, solar flux and H(+) and O(+) number densities determined by extrapolating nearly simultaneous Atmospheric Explorer C measurements at 300 km. The observations in the Northern Hemisphere are well fit by a model having 285 He(+) ions/cu cm at 500 km independent of latitude or longitude, while those in the south require 430 He(+) ions/cu cm at the same altitude. This result is consistent with available information on the interhemispheric asymmetry of He(+) observed by a mass spectrometer on Explorer 32 and on the winter neutral helium bulge.

Chakrabarti, S.↗

NASA NTRS1983

Large-scale counterstreaming of H(+) and He(+) along plasmaspheric flux tubes

An interhemispheric plasma transport model is used to study the flow characteristics of H(+), He(+), and O(+) along closed geomagnetic field lines for solstice conditions. The model corresponds to a time-dependent solution of the coupled continuity, momentum, and energy equations for the ions and electrons. The equations are solved along an entire flux tube from 120 km in one hemisphere to 120 km in the other hemisphere. The calculations are carried out for noon conditions for the flux tube passsing through Millstone Hill, at L = 3.2. The main conclusion is that H(+)-He(+) counterstreaming can be expected along a large segment of a plasmaspheric flux tube at solstice. For both symmetric and asymmetric wind patterns, the He(+) flow is from the winter to the summer ionosphere not only in the steady state, but during flux tube refilling due to the winter helium bulge and the depletion of N2.

Richards, P. G.↗

NASA NTRS1984

The concentration of the large-scale solar magnetic field by a meridional surface flow

Analytical and numerical solutions to the magnetic flux transport equation in the absence of new bipolar sources of flux are calculated for several meridional flow profiles and a range of peak flow speeds. It is found that a poleward flow with a broad profile and a nominal 10 m/s maximum speed concentrates the large-scale field into very small caps of less than 15 deg half-angle, with average field strengths of several tens of gauss, contrary to observations. A flow which reaches its peak speed at a relatively low latitude and then decreases rapidly to zero at higher latitudes leads to a large-scale field pattern which is consistent with observations. For such a flow, only lower latitude sunspot groups can contribute to interhemispheric flux annihilation and the resulting decay and reversal of the polar magnetic fields.

Devore, C. R.↗

NASA NTRS1984

Theoretical Modeling for Numerical Weather Prediction

The goal is to utilize predictability theory and numerical experimentation to identify and understand some of the dynamical processes which must be modeled more realistically if large-scale numerical weather predictions are to be improved. The emphasis is on the use of relatively simple models to exlore the properties of physically comprehensive general circulation models (GCM's). A global linear quasi-geostrophic model and the Goddard Laboratory for Atmospheric Sciences (GLAS) GCM were used to investigate several mechanisms which are responsible for the decay of large-scale forecast skill in mid-latitude numerical weather predictions. Five-day forecasts for an ensemble of cases were made using First GARP Global Experiment data. It was found that forecast skill depends crucially on the specification of the stationary forcing. A lack of stationary forcing leads to spurious westwad propagation of the ultralong waves. Forecasts made with stationary forcings derived from climatological data are superior to those using forcings inferred from observations immediately preceding the forecast period. Interhemispheric forecast differences were analyzed, and the model errors were compared to errors of a simple persistence-damped-to-climatology scheme and to errors of the GLAS GCM.

Somerville, R. C. J.↗

NASA NTRS1985

A research in support of NASA's space science

Thirty-nine papers on cosmic ray anisotropies, law energy auroral particles, helium and hydrogen airglow, ionospheric irregularities, thermospheric winds, interhemisphere ion transport, ion cyclotron heating, ion temperature morphology, ion chemistry, ion convection, and spacecraft interactions with the atmosphere and ionosphere are described.

Hanson, W. B.↗

NASA NTRS1985

Bottomside sinusoidal irregularities in the equatorial F region. II - Cross-correlation and spectral analysis

Equatorial bottomside sinusoidal (BSS) irregularities have been studied by applying techniques of cross-correlation and spectral analysis to the Atmosphere Explorer data set. The phase of the cross-correlations of the plasma number density is discussed and the two drift velocity components observed using the retarding potential analyzer and ion drift meter on the satellite are discussed. Morphology is addressed, presenting the geographical distributions of the occurrence of BSS events for the equinoxes and solstices. Physical processes including the ion Larmor flux, interhemispheric plasma flows, and variations in the lower F region Pedersen conductivity are invoked to explain the findings.

Cragin, B. L.↗