63 research outputs found
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
Mesospheric dynamics and chemistry from SME data
A fast Curtis matrix calculation of cooling rates due to the 15 micron band of CO2 is modified to parameterize the detailed calculations by Dickinson (1984) of infrared cooling by CO2 in the mesosphere and lower thermosphere. The calculations included separate NLTE treatment of the different 15 micron bands likely to be important for cooling. The goal was to compress the detailed properties of the different bands into a modified Curtis matrix, which represents one composite band with appropriate averaged radiative properties to allow for a simple and quick calculation of cooling rates given a temperature profile. Vertical constituent transport in the mesosphere was also studied
Hydrocarbon photochemistry and Lyman alpha albedo of Jupiter
A combined study of hydrocarbon and atomic hydrogen photochemistry is made to calculate self-consistently the LÉ‘ albedo of Jupiter. It is shown that the LÉ‘ emissions observed by Voyagers I and II can be explained by resonance scattering of sunlight. Precipitation-of energetic particles
from the magnetosphere can provide the large required source of atomic hydrogen, although the contribution of direct particle excitation to the disk-averaged brightness is insignificant. The variability of the LÉ‘ brightness inferred from many observations in recent years is examined. The large difference in the brightness of the He 584 Ã… resonance line observed by Pioneer and Voyager is briefly discussed. Driving the photochemistry by solar ultraviolet radiation alone yields a maximum mixing ratio of C_2H_6 + C_2H_2 at 10^(-2) atm of about 4 x 10^(-6). The possibility of additional CH_4 dissociation from precipitation of magnetospheric particles is discussed. The
photochemistry of C_2H_2 and C_2H_3 is sufficiently uncertain not to permit accurate calculations of their densities and the ratio C_2H_6/C_2H_2
Aurora on Ganymede
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98774/1/jgra50122.pd
Observations and modeling of H_2 fluorescence with partial frequency redistribution in giant planet atmospheres
Partial frequency redistribution (PRD), describing the formation of the line
profile, has negligible observational effects for optical depths smaller than
~10^3, at the resolving power of most current instruments. However, when the
spectral resolution is sufficiently high, PRD modeling becomes essential in
interpreting the line shapes and determining the total line fluxes. We
demonstrate the effects of PRD on the H_2 line profiles observed at high
spectral resolution by the Far-Ultraviolet Spectroscopic Explorer (FUSE) in the
atmospheres of Jupiter and Saturn. In these spectra, the asymmetric shapes of
the lines in the Lyman (v"- 6) progression pumped by the solar Ly-beta are
explained by coherent scattering of the photons in the line wings. We introduce
a simple computational approximation to mitigate the numerical difficulties of
radiative transfer with PRD, and show that it reproduces the exact radiative
transfer solution to better than 10%. The lines predicted by our radiative
transfer model with PRD, including the H_2 density and temperature distribution
as a function of height in the atmosphere, are in agreement with the line
profiles observed by FUSE. We discuss the observational consequences of PRD,
and show that this computational method also allows us to include PRD in
modeling the continuum pumped H_2 fluorescence, treating about 4000 lines
simultaneously.Comment: 17 pages, accepted for publication in Ap
HST/STIS Ultraviolet Imaging of Polar Aurora on Ganymede
We report new observations of the spectrum of Ganymede in the spectral range
1160 - 1720 A made with the Space Telescope Imaging Spectrograph (STIS) on HST
on 1998 October 30. The observations were undertaken to locate the regions of
the atomic oxygen emissions at 1304 and 1356 A, previously observed with the
GHRS on HST, that Hall et al. (1998) claimed indicated the presence of polar
aurorae on Ganymede. The use of the 2" wide STIS slit, slightly wider than the
disk diameter of Ganymede, produced objective spectra with images of the two
oxygen emissions clearly separated. The OI emissions appear in both
hemispheres, at latitudes above 40 degrees, in accordance with recent Galileo
magnetometer data that indicate the presence of an intrinsic magnetic field
such that Jovian magnetic field lines are linked to the surface of Ganymede
only at high latitudes. Both the brightness and relative north-south intensity
of the emissions varied considerably over the four contiguous orbits (5.5
hours) of observation, presumably due to the changing Jovian plasma environment
at Ganymede. However, the observed longitudinal non-uniformity in the emission
brightness at high latitudes, particularly in the southern hemisphere, and the
lack of pronounced limb brightening near the poles are difficult to understand
with current models. In addition to observed solar HI Lyman-alpha reflected
from the disk, extended Lyman-alpha emission resonantly scattered from a
hydrogen exosphere is detected out to beyond two Ganymede radii from the limb,
and its brightness is consistent with the Galileo UVS measurements of Barth et
al. (1997).Comment: 7 pages, 4 figures, accepted for publication in ApJ, June 1, 200
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