4,093 research outputs found
Time dependent correlations in marine stratocumulus cloud base height records
The scaling ranges of time correlations in the cloud base height records of
marine boundary layer stratocumulus are studied applying the Detrended
Fluctuation Analysis statistical method. We have found that time dependent
variations in the evolution of the exponent reflect the diurnal
dynamics of cloud base height fluctuations in the marine boundary layer. In
general, a more stable structure of the boundary layer corresponds to a lower
value of the - indicator, i.e. larger anti-persistence, thus a set of
fluctuations tending to induce a greater stability of the stratocumulus. In
contrast, during periods of higher instability in the marine boundary, less
anti-persistent (more persistent like) behavior of the system drags it out of
equilibrium, corresponding to larger values. From an analysis of the
frequency spectrum, the stratocumulus base height evolution is found to be a
non-stationary process with stationary increments. The occurrence of these
statistics in cloud base height fluctuations suggests the usefulness of similar
studies for the radiation transfer dynamics modeling.Comment: 12 pages, 6 figures; to appear in Int. J. Mod. Phys. C, Vol. 13, No.
2 (2002
Comparison of cloud models for Brown Dwarfs
A test case comparison is presented for different dust cloud model approaches
applied in brown dwarfs and giant gas planets. We aim to achieve more
transparency in evaluating the uncertainty inherent to theoretical modelling.
We show in how far model results for characteristic dust quantities vary due to
different assumptions. We also demonstrate differences in the spectral energy
distributions resulting from our individual cloud modelling in 1D substellar
atmosphere simulationsComment: 5 pages, Proceeding to "Exoplantes: Detection, Formation, Dynamics",
eds. Ferraz-Mello et
Constraining the Inflationary Equation of State
We explore possible constraints on the inflationary equation state: p=w\rho.
While w must be close to -1 for those modes that contribute to the observed
power spectrum, for those modes currently out of experimental reach, the
constraints on w are much weaker, with only w<-1/3 as an a priori requirement.
We find, however, that limits on the reheat temperature and the inflationary
energy scale constrain w further, though there is still ample parameter space
for a vastly different (accelerating) equation of state between the end of
quasi-de Sitter inflation and the beginning of the radiation-dominated era. In
the event that such an epoch of acceleration could be observed, we review the
consequences for the primordial power spectrum.Comment: 12 pages, 2 figur
The efficacy of aerosolâcloud radiative perturbations from near-surface emissions in deep open-cell stratocumuli
Aerosolâcloud radiative effects are determined and quantified in simulations
of deep open-cell stratocumuli observed during the VAMOS Ocean-Cloud-Atmosphere-Land
Study Regional Experiment (VOCALS-REx) campaign off
the west coast of Chile. The cloud deck forms in a boundary
layer 1.5 km deep, with cell sizes reaching 50 km in diameter. Global databases of ship
tracks suggest that these linear structures are seldom found in boundary
layers this deep. Here, we quantify the changes in cloud radiative properties
to a continuous aerosol point source moving along a fixed emission line
releasing 1017 particles per second. We show that a spatially coherent
cloud perturbation is not evident along the emission line. Yet our model
simulates an increase in domain-mean all-sky albedo of 0.05, corresponding to
a diurnally averaged cloud radiative effect of 20 Wâmâ2, given the
annual mean solar insolation at the VOCALS-REx site. Therefore, marked
changes in cloud radiative properties in precipitating deep open cells may be
driven by anthropogenic near-surface aerosol perturbations, such as those
generated by ships.
Furthermore, we demonstrate that these changes in cloud radiative properties
are masked by the naturally occurring variability within the organised cloud
field. A clear detection and attribution of cloud radiative effects to a
perturbation in aerosol concentrations becomes possible when sub-filtering of
the cloud field is applied, using the spatio-temporal distribution of the
aerosol perturbation. Therefore, this work has implications for the detection
and attribution of effective cloud radiative forcing in marine stratocumuli,
which constitutes one of the major physical uncertainties within the climate
system. Our results suggest that ships may sometimes have a substantial
radiative effect on marine clouds and albedo, even when ship tracks are not
readily visible.</p
Aerosol single-scattering albedo and asymmetry parameter from MFRSR observations during the ARM Aerosol IOP 2003
International audienceMulti-filter Rotating Shadowband Radiometers (MFRSRs) provide routine measurements of the aerosol optical depth (?) at six wavelengths (0.415, 0.5, 0.615, 0.673, 0.870 and 0.94 ?m). The single-scattering albedo (?0) is typically estimated from the MFRSR measurements by assuming the asymmetry parameter (g). In most instances, however, it is not easy to set an appropriate value of g due to its strong temporal and spatial variability. Here, we introduce and validate an updated version of our retrieval technique that allows one to estimate simultaneously ?0 and g for different types of aerosol. We use the aerosol and radiative properties obtained during the Atmospheric Radiation Measurement (ARM) Program's Aerosol Intensive Operational Period (IOP) to validate our retrieval in two ways. First, the MFRSR-retrieved optical properties are compared with those obtained from independent surface, Aerosol Robotic Network (AERONET), and aircraft measurements. The MFRSR-retrieved optical properties are in reasonable agreement with these independent measurements. Second, we perform radiative closure experiments using the MFRSR-retrieved optical properties. The calculated broadband values of the direct and diffuse fluxes are comparable (~5 W/m2) to those obtained from measurements
Itâs not too late to do the right thing:: Moral motivations for climate change action
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordWhile it is too late to avert some dangerous consequences of climate change, it is not âall-ornothingâ and our actions can still make a difference. Building on social psychology research
showing the importance of seeing oneâs group as moral, one reason people act on climate
change is to help create a more moral and caring society. Considering climate change action
through this lens gives rise to several challenges, including how people respond to moral
threats, who has moral standing as advocates, the consequences of promoting a moral cause
through âimmoralâ actions (e.g., breaking the law), and moral âblindspotsâ where some
emitting behaviours are excluded from scrutiny. Reviewing social psychological bases for
these issues suggests potential responses to these challenges, including the importance of
engaging people with diverse views and backgrounds (e.g., through citizensâ assemblies),
advisory personal carbon budgets, and broad-based policies that aim to secure the social
wellbeing of communities as well as the protect the environment (e.g., a Green New Deal).
Encouragingly, a recent study suggests that many people are more ready than we might
assume to accept the types of changes urgently needed
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