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Fesen, C. G.

Publications and source records attributed to Fesen, C. G..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Database of theoretical thermosphere/ionosphere predictions

The National Center for Atmospheric Research (NCAR) thermosphere-ionosphere general circulation model has performed a series of self-consistent calculations of the thermosphere/ionosphere structure for a variety of geophysical conditions. The model simulates March, June, and December periods for solar cycle minimum and maximum for three levels of geomagnetic activity representing quiet, moderate, and disturbed conditions. The calculations include predictions of N2, O2, O, N(sup 4)S, N(sup 2)D, NO, N2(+), O2(+), O(+), NO(+), and N(+), along with the ion, electron, and neutral temperatures and three components of the neutral winds. The model simulations are available from the authors or through the Coupling, Energetic, and Dynamics of Atmospheric Regions database at NCAR.

Fesen, C. G.↗
NASA NTRS1994

Solar activity variations in midlatitude thermospheric meridional winds

Upper thermospheric meridional wind data at midlatitudes and for low magnetic activity are examined for solar activity variations following an analysis scheme suggested by a Coordinated Analysis of the Thermosphere workshop. Wind data from incoherent scatter, Fabry-Perot, and F2 peak heights show decreasing diurnal amplitudes with increasing solar activity during all seasons, except for Saint Santin data, which show a slight increase in summer. Equivalent winds from F2 peak height data have strong decreases in diurnal amplitude in all seasons. The coupled thermosphere ionosphere model and thermosphere ionosphere global circulation model predictions of diurnal amplitude, while differing considerably in magnitude, also show decreasing amplitudes during all seasons except summer, while the HWM90 empirical model amplitudes increase slightly with solar activity during all seasons. The diurnal mean wind trends with solar activity are fairly weak, except for Millstone Hill incoherent scatter radar, which shows a shift from strong southward to near zero or northward wind with increasing activity. Model results for the mean generally fall within the band of measurements. Near midnight, most of the data also show that the typically southward winds weaken with increasing solart activity in all seasons except summer, when results are mixed. There are significant differences between the trends and between absolute values for the various data sets and models which need further investigation.

Hedin, A. E.↗
NASA NTRS1993

Mars mesosphere and thermosphere coupling - Semidiurnal tides

The Mars thermospheric general circulation model (MTGCM) is modified to examine the impact of a prescribed semidiurnal tidal wave upon Martian thermospheric fields corresponding to near solar minimum (Mariner 9) and solar maximum (Mariner 6-7) observational periods. The effects of upward propagating tides are introduced into the Mars Thermospheric General circulation Model (MTGCM) by appropriately specifying its lower boundary condition according to classical tidal theory. Estimates of the amplitude and phase of the likely dominant semidiurnal (2,2) mode at the mesopause (about 100 km) are specified for a range of possible lower atmosphere dust conditions. MTGCM simulations contrasting tidally driven fields with solar-only forced ones exhibit a dramatic change in the horizontal and vertical wind patterns, whereby the global temperature and oxygen distributions are also modified significantly.

Bougher, S. W.↗
NASA NTRS1993

On the coupling between the lower and the upper thermosphere during the first lower thermosphere coupling study

The study reports simultaneous observations of the neutral winds and temperatures and electron densities in the upper and lower thermosphere. The measurements were made at Arecibo and Millstone Hill during the first Lower Thermosphere Coupling Study (LTCS 1) campaign in September 1987. The observations show much day-to-day variability, possibly due to the geomagnetic activity which occurred during the period; storm effects are discernible in the data at low altitudes even at low latitudes. Simulations of the low and midlatitudes did not substantially improve with the use of lower boundary conditions derived from the measurements. The model predicts that diurnal waves are not negligible in analysis of lower thermosphere data; near 100 km the diurnal wave amplitudes of the meridional waves were predicted to be greater than the semidiurnal.

Fesen, C. G.↗
NASA NTRS1992

Atomic oxygen in the Martian thermosphere

The Mariner 9 Ultraviolet Spectrometer (UVS) made extensive observations of air-glow emissions from the thermosphere of Mars throughout the nominal mission (November 1971 - February 1972), during late summer in the southern hemisphere. Limb and disc measurements of the 130 nm triplet emission from thermospheric atomic oxygen were modelled by Strickland et al. Recently, the thermospheric general circulation models (TGCMs) developed for the Earth and Venus have been applied to Mars; we refer to it as the MTGCM. Our analysis shows that the oxygen mixing ratio is the fundamental unknown controlling the 130 nm brightness. Our radiative transport calculation shows that the emergent intensity at 130 nm is not very sensitive to variations in thermospheric temperature. The pattern of diurnal variation derived from our analysis is roughly the same as Strickland et al. although with somewhat lower values for the O mixing ratio. The main reasons for this difference are the more important role played by the photoelectron source in our model, and the somewhat larger 130 nm solar flux; thus, we require less oxygen to match the observed brightnesses. Strickland et al. also found that the OI 130 nm emission on Mars is correlated with solar activity. We find that the correlation is virtually non-existent during the early orbits when the planet was covered with a thick global dust storm, but later orbits, during the clearing of the storm, show a persistent correlation.

Stewart, A. I. F.↗
NASA NTRS1992

Atomic oxygen in the Martian thermosphere

Modern models of thermospheric composition and temperature and of excitation and radiative transfer processes are used to simulate the O I 130-nm emission from Mars measured by the Mariner 9 ultraviolet spectrometer. This paper uses the Mars thermospheric general circulation model calculations (MTGCM) of Bougher et al. (1988) and the Monte Carlo partial frequency redistribution multiple scattering code of Meier and Lee (1982). It is found that the decline in atomic oxygen through the daylight hours predicted by the MTGCM cannot be reconciled with the excess afternoon brightness seen in the data. Oxygen concentrations inferred from the data show a positive gradient through the day, in agreement with the original analysis by Strickland et al. (1973). In addition, the data suggest that the oxygen abundance increases toward high southerly latitudes, in contrast with the MTGCM prediction of high values in the Northern Hemisphere. It appears that solar forcing alone cannot account for the observed characteristics of the Martian thermosphere and that wave and tidal effects may profoundly affect the structure, winds, and composition.

Stewart, A. I. F.↗
NASA NTRS1990

The latitudinal gradient of the NO peak density

Results are presented from SME observations of the latitudinal gradients of peak NO densities at about 110-km altitude during the solstice and equinox periods from 1982 through 1985. It is shown that the response of the peak NO densities to the declining level of solar activity varies with latitude, with the polar regions exhibiting low sensitivity and the low-latitude regions responding strongly. The SME data also revealed marked asymmetries in the latitudinal structure of the two hemispheres for each season and considerable day-to-day variations in the NO densities. The solar cycle minimum data for June were simulated using a two-dimensional model; results of sensitivity studies performed with varied quenching rate and eddy diffusion coefficient are presented.

Fesen, C. G.↗
NASA NTRS1990

Solar cycle variation of thermospheric nitric oxide at solstice

A coupled, two-dimensional, chemical-diffusive model of the thermosphere is used to study the role of solar activity in the global distribution of nitric oxide. The model calculates self-consistently the zonally averaged temperature, circulation, and composition for solstice under solar maximum and solar minimum conditions. A decrease of the NO density by a factor of three to four in the E region is predicted from solar maximum to solar minimum. It is found that the main features of the overall morphology and the changes induced by the solar cycle are well reproduced in the model, although some details are not satisfactorily predicted. The sensitivity of the NO distribution to eddy transport and to the quenching of metastable N(2D) atoms by atomic oxygen is also described.

Gerard, J.-C.↗
NASA NTRS1990

Low-latitude thermospheric neutral winds determined from AE-E measurements of the 6300-A nightglow at solar maximum

Atmosphere Explorer E (AE-E) measurements of the O(1D) 6300-A emission in the nighttime equatorial thermosphere are used to infer the height of the F2 layer peak as a function of latitude and local time. The investigation is conducted both for northern hemisphere winter solstice and for spring equinox, under solar maximum conditions. The layer heights are used to derive magnetic meridional components of the transequatorial neutral wind, in conjunction with the MSIS-86 model and previous Jicamarca incoherent scatter measurements of the zonal electric field. The AE-E wind estimates indicate a predominant summer to winter flow for the winter solstice case. Comparisons are made with the empirical horizontal wind model HWM87 and with winds generated by the thermospheric general circulation model. The model predictions and experimental results are generally in good agreement, confirming the applicability of visible airglow data to studies of the global neutral wind pattern.

Burrage, M. D.↗
NASA NTRS1990

The Venus nitric oxide night airglow - Model calculations based on the Venus Thermospheric General Circulation Model

The mechanism responsible for the Venus nitric oxide (0,1) delta band nightglow observed in the Pioneer Venus Orbiter UV spectrometer (OUVS) images was investigated using the Venus Thermospheric General Circulation Model (Dickinson et al., 1984), modified to include simple odd nitrogen chemistry. Results obtained for the solar maximum conditions indicate that the recently revised dark-disk average NO intensity at 198.0 nm, based on statistically averaged OUVS measurements, can be reproduced with minor modifications in chemical rate coefficients. The results imply a nightside hemispheric downward N flux of (2.5-3) x 10 to the 9th/sq cm sec, corresponding to the dayside net production of N atoms needed for transport.

Bougher, S. W.↗
NASA NTRS1989

Rapid deactivation of N(2D) by O - Impact on thermospheric and mesospheric odd nitrogen

One- and two-dimensional models of thermospheric odd nitrogen are used to explore the consequences of the recently measured fast quenching of N(2D) by O. A large rate coefficient for this reaction profoundly affects the odd-nitrogen chemistry by removing N(2D) as a source of NO and increasing the concentration of N(4S), which destroys NO. The model calculations show that, as the quenching rate increases, the NO and N(2D) densities decrease, while N(4S) densities increase. Comparisons with Atmosphere Explorer and Solar Mesosphere Explorer satellite observations are made. Use of the fast quenching rate in the models causes the NO peak altitude, typically observed near 110 km, to rise to 140 km.

Fesen, C. G.↗
NASA NTRS1983

Theoretical modeling of low-latitude Mg

The appearance of metal ions at altitudes near 100 km has long been known. The interest in metal ions arises from the contributions they can make towards understanding atmospheric dynamics. A description is presented of the results of a theoretical investigation of Mg(+) using an ionospheric model which incorporates realistic geomagnetic and electric fields. In particular, longitudinal effects can be included. The data base for comparison is the altitude profiles and latitude-local time cross sections of Mg(+) densities at fixed altitudes from the Visual Airglow Experiment on Atmospheric Explorer 'E' (AE-E), which was in equatorial orbit. Mg(+) number densities were found as functions of dip latitude, altitude, and local time in three longitudinal regions.

Fesen, C. G.↗
NASA NTRS1982

Mg/+/ morphology from visual airglow experiment observations

Observations of low-latitude Mg(+) by the Visual Airglow Experiment on Atmosphere Explorer E were analyzed by a two-dimensional inversion technique. Number density profiles as functions of geographic position were obtained in the F2 region. The profiles represent daytime northern winter, solar maximum conditions and reveal frequent occurrences of large number densities (50-100 per cu cm) at altitudes up to 475 km. Maximum densities are usually found near the equator at 1200-1400 LT. The equatorial density then decreases as the peak concentrations shift to higher latitudes. Longitudinal differences in the time development of the metal ion density appear in the afternoon. These seem to be due to the increasing importance of zonal winds and/or to longitudinal differences in the vertical ion drift velocity.

Fesen, C. G.↗
NASA NTRS1982

Two-dimensional inversion technique for satellite airglow data

A technique is described which inverts satellite airglow data producing volume emission rates as functions of altitude and position. The inversion is applied to data obtained when the spacecraft spins in the orbital plane. The altitude and height resolutions are constrained by the geometry chosen to simplify the inversion. The limitations of the method and its implementation on data from the Visual Airglow Experiment onboard the Atmosphere Explorer satellite are discussed. Sample maps of brightness and volume emission rates are shown.

Fesen, C. G.↗