21 research outputs found
Constraining the aerosol influence on cloud liquid water path
The impact of aerosols on cloud properties is one of the largest uncertainties in the anthropogenic radiative forcing of the climate. In recent years, significant progress has been made in constraining this forcing using observations, but uncertainty still remains, particularly in the adjustments of cloud properties to aerosol perturbations. Cloud liquid water path (LWP) is the leading control on liquid-cloud albedo, making it important to observationally constrain the aerosol impact LWP. Previous modelling and observational studies have shown that multiple processes play a role in determining the LWP response to aerosol perturbations, but that the aerosol effect can be difficult to isolate. Following previous studies using mediating variables, this work investigates use of the relationship between cloud droplet number concentration (Nd) and LWP for constraining the role of aerosols. Using joint probability histograms to account for the non-linear relationship, this work finds a relationship that is broadly consistent with previous studies. There is significant geographical variation in the relationship, partly due to role of meteorological factors (particularly relative humidity) in the relationship. However, the Nd-LWP relationship is negative in the majority of regions, suggesting that aerosol induced LWP reductions could offset a significant fraction of the radiative forcing from aerosol-cloud interactions (RFaci). However, variations in the Nd-LWP relationship in response to volcanic and shipping aerosol perturbations indicate that the Nd-LWP relationship overestimates the Nd impact on LWP. As such, the estimate of LWP changes due to aerosol in this work provides an upper bound to the radiative forcing from aerosol-induced changes in the LWP
Ice crystal number concentration estimates from lidar-radar satellite retrievals. Part 2: Controls on the ice crystal number concentration
The ice crystal number concentration (Ni) is a keyproperty of ice clouds, both radiatively and microphysically.Due to sparse in situ measurements of ice cloud properties,the controls on theNihave remained difficult to determine.As more advanced treatments of ice clouds are included inglobal models, it is becoming increasingly necessary to de-velop strong observational constraints on the processes in-volved.This work uses the DARDAR-NiceNiretrieval describedin Part 1 to investigate the controls on theNiat a globalscale. The retrieved clouds are separated by type. The ef-fects of temperature, proxies for in-cloud updraft and aerosolconcentrations are investigated. Variations in the cloud topNi(Ni(top)) consistent with both homogeneous and hetero-geneous nucleation are observed along with differing rela-tionships between aerosol andNi(top)depending on the pre-vailing meteorological situation and aerosol type. Away fromthe cloud top, theNidisplays a different sensitivity to thesecontrolling factors, providing a possible explanation for thelowNisensitivity to temperature and ice nucleating particles(INP) observed in previous in situ studies.This satellite dataset provides a new way of investigat-ing the response of cloud properties to meteorological andaerosol controls. The results presented in this work increaseour confidence in the retrievedNiand will form the basis for further study into the processes influencing ice and mixedphase clouds
Ice crystal number concentration estimates from lidarâradar satellite remote sensing â Part 2: Controls on the ice crystal number concentration
The ice crystal number concentration (Ni) is a key property of ice clouds, both radiatively and microphysically. Due to sparse in situ measurements of ice cloud properties, the controls on the Ni have remained difficult to determine. As more advanced treatments of ice clouds are included in global models, it is becoming increasingly necessary to develop strong observational constraints on the processes involved. This work uses the DARDAR-Nice Ni retrieval described in Part 1 to investigate the controls on the Ni at a global scale. The retrieved clouds are separated by type. The effects of temperature, proxies for in-cloud updraft and aerosol concentrations are investigated. Variations in the cloud top Ni (Ni(top)) consistent with both homogeneous and heterogeneous nucleation are observed along with differing relationships between aerosol and Ni(top) depending on the prevailing meteorological situation and aerosol type. Away from the cloud top, the Ni displays a different sensitivity to these controlling factors, providing a possible explanation for the low Ni sensitivity to temperature and ice nucleating particles (INP) observed in previous in situ studies. This satellite dataset provides a new way of investigating the response of cloud properties to meteorological and aerosol controls. The results presented in this work increase our confidence in the retrieved Ni and will form the basis for further study into the processes influencing ice and mixed phase clouds
Ice crystal number concentration estimates from lidarâradar satellite remote sensing â Part 2: Controls on the ice crystal number concentration
The ice crystal number concentration (Ni) is a key property of
ice clouds, both radiatively and microphysically. Due to sparse
in situ measurements of ice cloud properties, the controls on the
Ni have remained difficult to determine. As more advanced
treatments of ice clouds are included in global models, it is becoming
increasingly necessary to develop strong observational constraints on the
processes involved.This work uses the DARDAR-Nice Ni retrieval described in Part 1
to investigate the controls on the Ni at a global scale. The
retrieved clouds are separated by type. The effects of temperature, proxies
for in-cloud updraft and aerosol concentrations are investigated.
Variations in the cloud top Ni (Ni(top))
consistent with both homogeneous and heterogeneous nucleation are observed
along with differing relationships between aerosol and
Ni(top) depending on the prevailing meteorological
situation and aerosol type. Away from the cloud top, the Ni
displays a different sensitivity to these controlling factors, providing a
possible explanation for the low Ni sensitivity to temperature
and ice nucleating particles (INP) observed in previous in situ studies.This satellite dataset provides a new way of investigating the response of
cloud properties to meteorological and aerosol controls. The results
presented in this work increase our confidence in the retrieved
Ni and will form the basis for further study into the processes
influencing ice and mixed phase clouds.</p
Constraining the Twomey effect from satellite observations: issues and perspectives
The Twomey effect describes the radiative forcing
associated with a change in cloud albedo due to an increase
in anthropogenic aerosol emissions. It is driven by the perturbation
in cloud droplet number concentration (1Nd; ant)
in liquid-water clouds and is currently understood to exert
a cooling effect on climate. The Twomey effect is the key
driver in the effective radiative forcing due to aerosolâcloud
interactions, but rapid adjustments also contribute. These
adjustments are essentially the responses of cloud fraction
and liquid water path to 1Nd; ant and thus scale approximately
with it. While the fundamental physics of the influence
of added aerosol particles on the droplet concentration
(Nd) is well described by established theory at the particle
scale (micrometres), how this relationship is expressed at the
large-scale (hundreds of kilometres) perturbation, 1Nd; ant,
remains uncertain. The discrepancy between process understanding
at particle scale and insufficient quantification at
the climate-relevant large scale is caused by co-variability of
aerosol particles and updraught velocity and by droplet sink
processes. These operate at scales on the order of tens of metres at which only localised observations are available and at
which no approach yet exists to quantify the anthropogenic
perturbation. Different atmospheric models suggest diverse
magnitudes of the Twomey effect even when applying the
same anthropogenic aerosol emission perturbation. Thus, observational
data are needed to quantify and constrain the
Twomey effect. At the global scale, this means satellite data.
There are four key uncertainties in determining 1Nd; ant,
namely the quantification of (i) the cloud-active aerosol â the
cloud condensation nuclei (CCN) concentrations at or above
cloud base, (ii) Nd, (iii) the statistical approach for inferring
the sensitivity of Nd to aerosol particles from the satellite
data and (iv) uncertainty in the anthropogenic perturbation
to CCN concentrations, which is not easily accessible from
observational data. This review discusses deficiencies of current
approaches for the different aspects of the problem and
proposes several ways forward: in terms of CCN, retrievals
of optical quantities such as aerosol optical depth suffer from
a lack of vertical resolution, size and hygroscopicity information,
non-direct relation to the concentration of aerosols,
difficulty to quantify it within or below clouds, and the problem
of insufficient sensitivity at low concentrations, in addition
to retrieval errors. A future path forward can include
utilising co-located polarimeter and lidar instruments, ideally
including high-spectral-resolution lidar capability at two
wavelengths to maximise vertically resolved size distribution
information content. In terms of Nd, a key problem is the lack
of operational retrievals of this quantity and the inaccuracy of
the retrieval especially in broken-cloud regimes. As for the
Nd-to-CCN sensitivity, key issues are the updraught distributions
and the role of Nd sink processes, for which empirical
assessments for specific cloud regimes are currently the best
solutions. These considerations point to the conclusion that past studies using existing approaches have likely underestimated
the true sensitivity and, thus, the radiative forcing due
to the Twomey effect
Bounding global aerosol radiative forcing of climate change
Aerosols interact with radiation and clouds. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the Earth's radiation budget caused by anthropogenic aerosols, called aerosol radiative forcing, but uncertainties remain large. This review provides a new range of aerosol radiative forcing over the industrial era based on multiple, traceable, and arguable lines of evidence, including modeling approaches, theoretical considerations, and observations. Improved understanding of aerosol absorption and the causes of trends in surface radiative fluxes constrain the forcing from aerosol-radiation interactions. A robust theoretical foundation and convincing evidence constrain the forcing caused by aerosol-driven increases in liquid cloud droplet number concentration. However, the influence of anthropogenic aerosols on cloud liquid water content and cloud fraction is less clear, and the influence on mixed-phase and ice clouds remains poorly constrained. Observed changes in surface temperature and radiative fluxes provide additional constraints. These multiple lines of evidence lead to a 68% confidence interval for the total aerosol effective radiative forcing of -1.6 to -0.6 W mâ2, or -2.0 to -0.4 W mâ2 with a 90% likelihood. Those intervals are of similar width to the last Intergovernmental Panel on Climate Change assessment but shifted toward more negative values. The uncertainty will narrow in the future by continuing to critically combine multiple lines of evidence, especially those addressing industrial-era changes in aerosol sources and aerosol effects on liquid cloud amount and on ice clouds
Molecular Effects of Doxycycline Treatment on Pterygium as Revealed by Massive Transcriptome Sequencing
Pterygium is a lesion of the eye surface which involves cell proliferation, migration, angiogenesis, fibrosis, and extracellular matrix remodelling. Surgery is the only approved method to treat this disorder, but high recurrence rates are common. Recently, it has been shown in a mouse model that treatment with doxycycline resulted in reduction of the pterygium lesions. Here we study the mechanism(s) of action by which doxycycline achieves these results, using massive sequencing techniques. Surgically removed pterygia from 10 consecutive patients were set in short term culture and exposed to 0 (control), 50, 200, and 500 ”g/ml doxycycline for 24 h, their mRNA was purified, reverse transcribed and sequenced through Illuminaâs massive sequencing protocols. Acquired data were subjected to quantile normalization and analyzed using cytoscape plugin software to explore the pathways involved. False discovery rate (FDR) methods were used to identify 332 genes which modified their expression in a dose-dependent manner upon exposure to doxycycline. The more represented cellular pathways included all mitochondrial genes, the endoplasmic reticulum stress response, integrins and extracellular matrix components, and growth factors. A high correlation was obtained when comparing ultrasequencing data with qRT-PCR and ELISA results
Acute and delayed sulfur mustard toxicity; novel mechanisms and future studies
Sulfur mustard (SM), also known as mustard gas, has been the most widely used chemical weapon. The toxicity of SM as an incapacitating agent is of much greater importance than its ability to cause lethality. Acute toxicity of SM is related to reactive oxygen and nitrogen species, DNA damage, poly(ADP-ribose) polymerase activation and energy depletion within the affected cell. Therefore melatonin shows beneficial effects against acute SM toxicity in a variety of manner. It scavenges most of the oxygen- and nitrogen-based reactants, inhibits inducible nitric oxide synthase, repairs DNA damage and restores cellular energy depletion. The delayed toxicity of SM however, currently has no mechanistic explanation. We propose that epigenetic aberrations may be responsible for delayed detrimental effects of mustard poisoning. Epigenetic refers to the study of changes that influence the phenotype without causing alteration of the genotype. It involves changes in the properties of a cell that are inherited but do not involve a change in DNA sequence. It is now known that in addition to genetic mutations, epimutations can also involve in the pathogenesis of a variety of human diseases. Several actions of melatonin are now delineated by epigenetic actions including modulation of histone acetylation and DNA methylation. Future studies are warranted to clarify whether epigenetic mechanisms are involved in pathogenesis of delayed sulfur mustard toxicity and melatonin alleviates delayed toxicity of this warfare agent
Ice crystal number concentration estimates from lidarâradar satellite remote sensing â Part 1: Method and evaluation
International audienceThe number concentration of cloud particles is a key quantity for understanding aerosolâcloud interactions and describing clouds in climate and numerical weather prediction models. In contrast with recent advances for liquid clouds, few observational constraints exist regarding the ice crystal number concentration (Ni). This study investigates how combined lidarâradar measurements can be used to provide satellite estimates of Ni, using a methodology that constrains moments of a parameterized particle size distribution (PSD). The operational liDARâraDAR (DARDAR) product serves as an existing base for this method, which focuses on ice clouds with temperatures Tcâ<ââ30°C.Theoretical considerations demonstrate the capability for accurate retrievals of Ni, apart from a possible bias in the concentration in small crystals when Tcâłâââ50°C, due to the assumption of a monomodal PSD shape in the current method. This is verified via a comparison of satellite estimates to coincident in situ measurements, which additionally demonstrates the sufficient sensitivity of lidarâradar observations to Ni. Following these results, satellite estimates of Ni are evaluated in the context of a case study and a preliminary climatological analysis based on 10 years of global data. Despite a lack of other large-scale references, this evaluation shows a reasonable physical consistency in Ni spatial distribution patterns. Notably, increases in Ni are found towards cold temperatures and, more significantly, in the presence of strong updrafts, such as those related to convective or orographic uplifts. Further evaluation and improvement of this method are necessary, although these results already constitute a first encouraging step towards large-scale observational constraints for Ni. Part 2 of this series uses this new dataset to examine the controls on Ni
Mitochondrial inside-out signalling during alkylating agent-induced anoikis
International audienc