12,711 research outputs found
Space shuttle exhaust cloud properties
A data base describing the properties of the exhaust cloud produced by the launch of the Space Transportation System and the acidic fallout observed after each of the first four launches was assembled from a series of ground and aircraft based measurements made during the launches of STS 2, 3, and 4. Additional data were obtained from ground-based measurements during firings of the 6.4 percent model of the Solid Rocket Booster at the Marshall Center. Analysis indicates that the acidic fallout is produced by atomization of the deluge water spray by the rocket exhaust on the pad followed by rapid scavening of hydrogen chloride gas aluminum oxide particles from the Solid Rocket Boosters. The atomized spray is carried aloft by updrafts created by the hot exhaust and deposited down wind. Aircraft measurements in the STS-3 ground cloud showed an insignificant number of ice nuclei. Although no measurements were made in the column cloud, the possibility of inadvertent weather modification caused by the interaction of ice nuclei with natural clouds appears remote
Low cloud properties influenced by cosmic rays
The influence of solar variability on climate is currently uncertain. Recent
observations have indicated a possible mechanism via the influence of solar
modulated cosmic rays on global cloud cover. Surprisingly the influence of
solar variability is strongest in low clouds (<= 3km), which points to a
microphysical mechanism involving aerosol formation that is enhanced by
ionisation due to cosmic rays. If confirmed it suggests that the average state
of the Heliosphere is important for climate on Earth.Comment: 10 pages, 2 figure
Spatial scales of cirrus cloud properties
Research in studying the spatial scales of the cirrus, used data collected during the flight legs of the NCAR Sabreliner aircraft on four days during the FIRE Cirrus IFO to study the spatial scales of the cirrus, and will concentrate on the scales of horizontal wind. The spatial scales of the cloud features can be described by power spectra (or spectral density graphs) and cumulative variance graphs. The cumulative variance graphs were created by first using a Fast Fourier Transform (FFT) to create variance spectra. The variances were then summed in a cumulative fashion from the largest scalelengths (wavelengths) to the smallest. No detrending was done to the original data, and no smoothing or averaging was done to the spectral points. All the spectral points were included. This means that the values of the first five to ten spectral points of the large scalelengths should only be considered to be qualitatively correct. The cumulative variance at smaller scalelengths should be correct because a more accurate representation of the variance at the larger scalelengths should only redistribute the energy amongst the larger scalelengths
Bias-free Measurement of Giant Molecular Cloud Properties
(abridged) We review methods for measuring the sizes, line widths, and
luminosities of giant molecular clouds (GMCs) in molecular-line data cubes with
low resolution and sensitivity. We find that moment methods are robust and
sensitive -- making full use of both position and intensity information -- and
we recommend a standard method to measure the position angle, major and minor
axis sizes, line width, and luminosity using moment methods. Without
corrections for the effects of beam convolution and sensitivity to GMC
properties, the resulting properties may be severely biased. This is
particularly true for extragalactic observations, where resolution and
sensitivity effects often bias measured values by 40% or more. We correct for
finite spatial and spectral resolutions with a simple deconvolution and we
correct for sensitivity biases by extrapolating properties of a GMC to those we
would expect to measure with perfect sensitivity. The resulting method recovers
the properties of a GMC to within 10% over a large range of resolutions and
sensitivities, provided the clouds are marginally resolved with a peak
signal-to-noise ratio greater than 10. We note that interferometers
systematically underestimate cloud properties, particularly the flux from a
cloud. The degree of bias depends on the sensitivity of the observations and
the (u,v) coverage of the observations. In the Appendix to the paper we present
a conservative, new decomposition algorithm for identifying GMCs in
molecular-line observations. This algorithm treats the data in physical rather
than observational units, does not produce spurious clouds in the presence of
noise, and is sensitive to a range of morphologies. As a result, the output of
this decomposition should be directly comparable among disparate data sets.Comment: Accepted to PASP (19 pgs., 12 figures). The submission describes an
IDL software package available from
http://cfa-www.harvard.edu/~erosolow/cprops
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Combined CloudSat-CALIPSO-MODIS retrievals of the properties of ice clouds
In this paper, data from spaceborne radar, lidar and infrared radiometers on the “A-Train” of satellites are combined in a variational algorithm to retrieve ice cloud properties. The method allows a seamless retrieval between regions where both radar and lidar are sensitive to the regions where one detects the cloud. We first implement a cloud phase identification method, including identification of supercooled water layers using the lidar signal and temperature to discriminate ice from liquid. We also include rigorous calculation of errors assigned in the variational scheme. We estimate the impact of the microphysical assumptions on the algorithm when radiances are not assimilated by evaluating the impact of the change in the area-diameter and the density-diameter relationships in the retrieval of cloud properties. We show that changes to these assumptions affect the radar-only and lidar-only retrieval more than the radar-lidar retrieval, although the lidar-only extinction retrieval is only weakly affected. We also show that making use of the molecular lidar signal beyond the cloud as a constraint on optical depth, when ice clouds are sufficiently thin to allow the lidar signal to penetrate them entirely, improves the retrieved extinction. When infrared radiances are available, they provide an extra constraint and allow the extinction-to-backscatter ratio to vary linearly with height instead of being constant, which improves the vertical distribution of retrieved cloud properties
Masses, Radii, and Cloud Properties of the HR 8799 Planets
The near-infrared colors of the planets directly imaged around the A star HR
8799 are much redder than most field brown dwarfs of the same effective
temperature. Previous theoretical studies of these objects have concluded that
the atmospheres of planets b, c, and d are unusually cloudy or have unusual
cloud properties. Some studies have also found that the inferred radii of some
or all of the planets disagree with expectations of standard giant planet
evolution models. Here we compare the available data to the predictions of our
own set of atmospheric and evolution models that have been extensively tested
against observations of field L and T dwarfs, including the reddest L dwarfs.
Unlike some previous studies we require mutually consistent choices for
effective temperature, gravity, cloud properties, and planetary radius. This
procedure thus yields plausible values for the masses, effective temperatures,
and cloud properties of all three planets. We find that the cloud properties of
the HR 8799 planets are not unusual but rather follow previously recognized
trends, including a gravity dependence on the temperature of the L to T
spectral transition--some reasons for which we discuss. We find the inferred
mass of planet b is highly sensitive to whether or not we include the H and K
band spectrum in our analysis. Solutions for planets c and d are consistent
with the generally accepted constraints on the age of the primary star and
orbital dynamics. We also confirm that, like in L and T dwarfs and solar system
giant planets, non-equilibrium chemistry driven by atmospheric mixing is also
important for these objects. Given the preponderance of data suggesting that
the L to T spectral type transition is gravity dependent, we present an
exploratory evolution calculation that accounts for this effect. Finally we
recompute the the bolometric luminosity of all three planets.Comment: 52 pages, 12 figures, Astrophysical Journal, in press. v2 features
minor editorial updates and correction
Satellite-derived cloud fields during the FIRE cirrus IFO case study
The First ISCCP Regional Experiment (FIRE) Cirrus Intensive Field Observation (IFO) program measured cirrus cloud properties with a variety of instruments from the surface, aircraft, and satellites. Surface and aircraft observations provide a small scale point and line measurements of different micro- and macro-physical properties of advecting and evolving cloud systems. Satellite radiance data may be used to measure the areal variations of the bulk cloud characteristics over meso- and large scales. Ideally, the detailed cloud properties derived from the small scale measurements should be tied to the bulk cloud properties typically derived from the satellite data. Full linkage of these data sets for a comprehensive description of a given cloud field, one of the goals of FIRE, should lead to significant progress in understanding, measuring, and modeling cirrus cloud systems. The relationships derived from intercomparisons of lidar and satellite data by Minnis et al. are exploited in a mesoscale analysis of the satellite data taken over Wisconsin during the Cirrus IFO case study
Intercomparisons of GOES-derived cloud parameters and surface observations over San Nicolas Island
The spatial sampling limitations of surface measurement systems necessitate the use of satellite data for the investigation of large-scale cloud processes. Understanding the information contained in the satellite-observed radiances, however, requires a connection between the remotely sensed cloud properties and those more directly observed within the troposphere. Surface measurements taken during the First ISCCP Regional Experiment (FIRE) Marine Stratocumulus Intensive Field Observations (IFO) are compared here to cloud properties determined from Geostationary Operational Environmental Satellite (GOES) data in order to determine how well the island measurements represent larger areas and to verify some of the satellite-measured parameters
Cloud properties as deduced from satellite observation
The three major accomplishments of this project are presented. The first was the simultaneous observations from both satellite and in situ aircraft of the effects of ship exhaust on cloud microphysics and the consequent changes in cloud reflectivity. Second, the satellite observations collected during the FIRE marine stratocumulus intensive field operation (IFO) were analyzed to reveal differences in the reflectivities of uniform and broken clouds. Third, the relationship between liquid water path and cloud reflectivity was examined
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