2,586 research outputs found
Middle atmosphere modeling
Breaking gravity waves generate and maintain a background level of turbulence which is capable of producing substantial cooling and/or heating in the upper mesosphere and lower thermosphere. The net thermodynamic effect of breaking gravity waves is critically dependent on the eddy Prandt number (P sub t) applicable to mesospheric turbulence. When P sub t is approximately 1, the calculations of the heat budget for the mesopause region imply that the globally averaged eddy or turbulent diffusion coefficient cannot exceed .000001 sq cm/s. This upper limit on turbulant diffusion applies to both potential temperature transport and chemically inert tracer transport when radiative damping is neglible. For chemically active species larger diffusion coefficients are permitted, because the effective eddy diffusion coefficient is increased by an additive term L/2 gamma (sup 2), where L is the chemical loss rate and gamma is the vertical wavenumber. For P sub t is approximately 4 to 6, the turbulent diffusion of momentum (D sub M) is sufficiently greater than the turbulent diffusion of heat (D sub H) that the conversion of gravity wave energy to heat with high efficiency nearly balances the divergence of the downward eddy heat flux in the wave breaking zone. Therefore the heat budget of the mesopause region would no longer provide a powerful and useful constraint on D sub H. If P sub t exceeds 6 with high efficiency for energy conversion to heat, gravity waves would heat the mesosphere throughout the wave breaking region
Aeronomy of Saturn and Titan
The Saturn system presents exciting and unique objects for planetary aeronomy. The photochemistry of H2 and He leads to the formation of an ionosphere. Methane photolysis results in the formation of spectroscopically detectable amounts of C2H6 and C2H2 and in the case of Titan, C2H4. Density profiles of C2H6, C2H2, and PH3 should be indicative of the strength of atmospheric mixing processes
Neutron star properties in the Thomas-Fermi model
The modern nucleon-nucleon interaction of Myers and Swiatecki, adjusted to
the properties of finite nuclei, the parameters of the mass formula, and the
behavior of the optical potential is used to calculate the properties of
--equilibrated neutron star matter, and to study the impact of this
equation of state on the properties of (rapidly rotating) neutron stars and
their cooling behavior. The results are in excellent agreement with the outcome
of calculations performed for a broad collection of sophisticated
nonrelativistic as well as relativistic models for the equation of state.Comment: 23 pages, LaTeX, 15 ps-figure
Empirical determination of the effects of clouds on the Earth's Radiation Budget over the Pacific Ocean
The main objectives of this research has been to learn how clouds interact with the Earth's Radiation Budget (ERB). This broad goal has been approached in three distinct ways. The first has been to analyze the direct effect cloud amount has on the radiative components of the ERB. The second has been to investigate the indirect effects clouds and water vapor may have on the climate as a feedback mechanism. And finally an attempt has been made to simulate the findings in a simple radiative-convective climate model. This report will summarize these three phases of the research
The effect of clouds on the earth's radiation budget
The radiative fluxes from the Earth Radiation Budget Experiment (ERBE) and the cloud properties from the International Satellite Cloud Climatology Project (ISCCP) over Indonesia for the months of June and July of 1985 and 1986 were analyzed to determine the cloud sensitivity coefficients. The method involved a linear least squares regression between co-incident flux and cloud coverage measurements. The calculated slope is identified as the cloud sensitivity. It was found that the correlations between the total cloud fraction and radiation parameters were modest. However, correlations between cloud fraction and IR flux were improved by separating clouds by height. Likewise, correlations between the visible flux and cloud fractions were improved by distinguishing clouds based on optical depth. Calculating correlations between the net fluxes and either height or optical depth segregated cloud fractions were somewhat improved. When clouds were classified in terms of their height and optical depth, correlations among all the radiation components were improved. Mean cloud sensitivities based on the regression of radiative fluxes against height and optical depth separated cloud types are presented. Results are compared to a one-dimensional radiation model with a simple cloud parameterization scheme
The structure and kinematics of the the Galaxy thin gaseous disc outside the solar orbit
The rotation curve of the Galaxy is generally thought to be flat. However,
using radial velocities from interstellar molecular clouds, which is common in
rotation curve determination, seems to be incorrect and may lead to incorrectly
inferring that the rotation curve is flat indeed. Tests basing on photometric
and spectral observations of bright stars may be misleading. The rotation
tracers (OB stars) are affected by motions around local gravity centers and
pulsation effects seen in such early type objects. To get rid of the latter a
lot of observing work must be involved. We introduce a method of studying the
kinematics of the thin disc of our Galaxy outside the solar orbit in a way that
avoids these problems. We propose a test based on observations of interstellar
CaII H and K lines that determines both radial velocities and distances. We
implemented the test using stellar spectra of thin disc stars at galactic
longitudes of 135{\degr} and 180{\degr}. Using this method, we constructed the
rotation curve of the thin disc of the Galaxy. The test leads to the obvious
conclusion that the rotation curve of the thin gaseous galactic disk,
represented by the CaII lines, is Keplerian outside the solar orbit rather than
flat.Comment: 33 pages, 18 figures, accepted for publication in Publications of the
Astronomical Society of the Pacific, 2015. February
The PASTEL catalogue of stellar parameters
The PASTEL catalogue is an update of the [Fe/H] catalogue, published in 1997
and 2001. It is a bibliographical compilation of stellar atmospheric parameters
providing (Teff,logg,[Fe/H]) determinations obtained from the analysis of high
resolution, high signal-to-noise spectra, carried out with model atmospheres.
PASTEL also provides determinations of the one parameter Teff based on various
methods. It is aimed in the future to provide also homogenized atmospheric
parameters and elemental abundances, radial and rotational velocities. A web
interface has been created to query the catalogue on elaborated criteria.
PASTEL is also distributed through the CDS database and VizieR. To make it as
complete as possible, the main journals have been surveyed, as well as the CDS
database, to find relevant publications. The catalogue is regularly updated
with new determinations found in the literature. As of Febuary 2010, PASTEL
includes 30151 determinations of either Teff or (Teff,logg,[Fe/H]) for 16649
different stars corresponding to 865 bibliographical references. Nearly 6000
stars have a determination of the three parameters (Teff,logg,[Fe/H]) with a
high quality spectroscopic metallicity.Comment: 5 pages, accepted for publication in A&A. The PASTEL catalogue can be
queried at http://pastel.obs.u-bordeaux1.fr/ or
http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/paste
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