Determining the effects of the formation of contrails within natural cirrus clouds has proven to be challenging. Quantifying any such effects is necessary if we are to properly account for the ...influence of aviation on climate. Here we quantify the effect of aircraft on the optical thickness of already-existing cirrus clouds by matching actual aircraft flight tracks to satellite lidar measurements. We show that there is a systematic, statistically significant increase in normalized cirrus cloud optical thickness inside mid-latitude flight tracks compared with adjacent areas immediately outside the tracks.
Beware the impact factor Noone, Kevin J.
Ambio,
09/2016, Letnik:
45, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The research community is under increasing pressure to document the impact of its activities. Done judiciously, an ongoing assessment of the impact of research would be a good thing for all involved: ...society, funding agencies, and the research community itself.
Long-term Aqua and Terra MODIS (MODerate resolution Imaging Spectroradiometer) Collections 5.1 and 6.1 (c051 and c061, respectively) aerosol data have been combined with AERONET (AERosol RObotic ...NETwork) ground-based sun photometer observations to examine trends in aerosol optical thickness (AOT, at 550 nm) over Northern Europe for the months April to September. For the 1927 and 1559 daily coincident measurements that were obtained for c051 and c061, respectively, MODIS AOT varied by 86 and 90%, respectively, within the predicted uncertainty of one standard deviation of the retrieval over land (ΔAOT = ±0.05 ± 0.15·AOT). For the coastal AERONET site Gustav Dalen Tower (GDT), Sweden, larger deviations were found for MODIS c051 and c061 (79% and 75%, respectively, within predicted uncertainty). The Baltic Sea provides substantially better statistical representation of AOT than the surrounding land areas and therefore favours the investigations of trends in AOT over the region. Negative trends of 1.5% and 1.2% per year in AOT, based on daily averaging, were found for the southwestern Baltic Sea from MODIS c051 and c061, respectively. This is in line with a decrease of 1.2% per year in AOT at the AERONET station Hamburg. For the western Gotland Basin area, Sweden, negative trends of 1.5%, 1.1% and 1.6% per year in AOT have been found for MODIS c051, MODIS c061 and AERONET GDT, respectively. The strongest trend of -1.8% per year in AOT was found for AERONET Belsk, Poland, which can be compared to -1.5% per day obtained from MODIS c051 over central Poland. The trends in MODIS and AERONET AOT are nearly all statistically significant at the 95% confidence level. The strongest aerosol sources are suggested to be located southwest, south and southeast of the investigation area, although the highest prevalence of pollution events is associated with air mass transport from southwest.
Using a large amount of aircraft measurements of cloud droplet size distributions, the relationship between cloud spectral relative dispersion (ɛ) and cloud droplet number concentration (Nc) is ...studied. The results indicate that the value of ɛ varies between 0.2 to 0.8 when the cloud droplet number concentration is low (about 50 cm−3), and converges toward a narrow range of 0.4 to 0.5 when the cloud number concentration is higher. Because the distribution of the cloud droplet size is an important parameter in estimating the first indirect radiative effect of aerosols on the climate system, the uncertainty in the corresponding radiative forcing can be reduced by 10–40% (depending on cloud droplet number density) under high aerosol loading. This finding is important for improving climate change projections, especially for the regions where aerosol loading is high and continues to increase.
Primary marine aerosol (PMA)‐cloud interactions off the coast of California were investigated using observations of marine aerosol, cloud condensation nuclei (CCN), and stratocumulus clouds during ...the Eastern Pacific Emitted Aerosol Cloud Experiment (E‐PEACE) and the Stratocumulus Observations of Los‐Angeles Emissions Derived Aerosol‐Droplets (SOLEDAD) studies. Based on recently reported measurements of PMA size distributions, a constrained lognormal‐mode‐fitting procedure was devised to isolate PMA number size distributions from total aerosol size distributions and applied to E‐PEACE measurements. During the 12 day E‐PEACE cruise on the R/V Point Sur, PMA typically contributed less than 15% of total particle concentrations. PMA number concentrations averaged 12 cm−3 during a relatively calmer period (average wind speed 12 m/s1) lasting 8 days, and 71 cm−3 during a period of higher wind speeds (average 16 m/s1) lasting 5 days. On average, PMA contributed less than 10% of total CCN at supersaturations up to 0.9% during the calmer period; however, during the higher wind speed period, PMA comprised 5–63% of CCN (average 16–28%) at supersaturations less than 0.3%. Sea salt was measured directly in the dried residuals of cloud droplets during the SOLEDAD study. The mass fractions of sea salt in the residuals averaged 12 to 24% during three cloud events. Comparing the marine stratocumulus clouds sampled in the two campaigns, measured peak supersaturations were 0.2 ± 0.04% during E‐PEACE and 0.05–0.1% during SOLEDAD. The available measurements show that cloud droplet number concentrations increased with >100 nm particles in E‐PEACE but decreased in the three SOLEDAD cloud events.
Key Points
New method of analyzing primary marine aerosol (PMA) number size distributions
PMA <15% of aerosol number concentrations, <58% of CCN in E–PEACE
CDNC increased with increasing >100 nm particles in E-PEACE but not SOLEDAD
Meteorology and microphysics affect cloud formation, cloud droplet distributions, and shortwave reflectance. The Eastern Pacific Emitted Aerosol Cloud Experiment and the Stratocumulus Observations of ...Los‐Angeles Emissions Derived Aerosol‐Droplets studies provided measurements in six case studies of cloud thermodynamic properties, initial particle number distribution and composition, and cloud drop distribution. In this study, we use simulations from a chemical and microphysical aerosol‐cloud parcel (ACP) model with explicit kinetic drop activation to reproduce observed cloud droplet distributions of the case studies. Four cases had subadiabatic lapse rates, resulting in fewer activated droplets, lower liquid water content, and higher cloud base height than an adiabatic lapse rate. A weighted ensemble of simulations that reflect measured variation in updraft velocity and cloud base height was used to reproduce observed droplet distributions. Simulations show that organic hygroscopicity in internally mixed cases causes small effects on cloud reflectivity (CR) (<0.01), except for cargo ship and smoke plumes, which increased CR by 0.02 and 0.07, respectively, owing to their high organic mass fraction. Organic hygroscopicity had larger effects on droplet concentrations for cases with higher aerosol concentrations near the critical diameter (namely, polluted cases with a modal peak near 0.1 µm). Differences in simulated droplet spectral widths (k) caused larger differences in CR than organic hygroscopicity in cases with organic mass fractions of 60% or less for the cases shown. Finally, simulations from a numerical parameterization of cloud droplet activation suitable for general circulation models compared well with the ACP model, except under high organic mass fraction.
Key Points
Using distributions of updraft velocity and lapse rate increases droplet spectral width
Organic hygroscopicity changes cloud drop only for high concentrations near critical diameter
Changes in drop spectral width cause larger reflectivity differences than organic hygroscopicity
Size-resolved observations of aerosol particles and cloud droplet residuals were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, San Diego, California, during 2012. A ...counterflow virtual impactor (CVI) was used as the inlet to sample cloud residuals while a total inlet was used to sample both cloud residuals and interstitial particles. Two cloud events totaling 10 h of in-cloud sampling were analyzed. Based on bulk aerosol particle concentrations, mass concentrations of refractory black carbon (rBC), and back trajectories, the two air masses sampled were classified as polluted marine air. Since the fraction of cloud droplets sampled by the CVI was less than 100%, the measured activated fractions of rBC should be considered as lower limits to the total fraction of rBC activated during the two cloud events. Size distributions of rBC and a coating analysis showed that sub-100 nm rBC cores with relatively thick coatings were incorporated into the cloud droplets (i.e., 95 nm rBC cores with median coating thicknesses of at least 65 nm were incorporated into the cloud droplets). Measurements also show that the coating volume fraction of rBC cores is relatively large for sub-100 nm rBC cores. For example, the median coating volume fraction of 95 nm rBC cores incorporated into cloud droplets was at least 0.9, a result that is consistent with κ-Köhler theory. Measurements of the total diameter of the rBC-containing particles (rBC core and coating) suggest that the total diameter of rBC-containing particles needed to be at least 165 nm to be incorporated into cloud droplets when the core rBC diameter is ≥ 85 nm. This result is consistent with previous work that has shown that particle diameter is important for activation of non-rBC particles. The activated fractions of rBC determined from the measurements ranged from 0.01 to 0.1 for core rBC diameters ranging from 70 to 220 nm. This type of data is useful for constraining models used for predicting rBC concentrations in the atmosphere.
The Monterey Area Ship Track experiment DURKEE, P. A; NOONE, K. J; BLUTH, R. T
Journal of the atmospheric sciences,
08/2000, Letnik:
57, Številka:
16
Journal Article
Recenzirano
Odprti dostop
In June 1994 the Monterey Area Ship Track (MAST) experiment was conducted off the coast of California to investigate the processes behind anthropogenic modification of cloud albedo. The motivation ...for the MAST experiment is described here, as well as details of the experimental design. Measurement platforms and strategies are explained, and a summary of experiment operations is presented.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Aerosol optical thickness (AOT) has decreased substantially in Europe in the summer half year (April–September) since 1980, with almost a 50% reduction in Central and Eastern Europe, according to ...Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) reanalysis. At the same time, strong positive trends in ERA5 reanalysis surface solar radiation downward for all‐sky and clear‐sky conditions (SSRD and SSRDc, respectively) and temperature at 2 m are found for Europe in summer during the period 1979–2020. The GEBA observations show as well strong increases in SSRD during the latest four decades. Estimations of changes in SSRDc, using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model, show similarly strong increases when fed by MERRA‐2 AOT. The estimates of warming in this study, caused by increases in SSRD and SSRDc, are based on energy budget approximations and the Stefan Boltzmann law. The increases in near surface temperature, estimated both for clear‐sky and all‐sky conditions, are up to about 1°C for Central and Eastern Europe. The total warming over large parts of this region for clear‐sky conditions is however nearly double the global mean temperature increase of 1.1°C, while somewhat less for all‐sky conditions. The effects of aerosols on warming over the southerly Iberian Peninsula are weaker compared to countries further north. The rapid total warming over the Iberian Peninsula is probably caused by greenhouse warming, drier surface conditions, and to some degree decline in aerosols. Reduced cloud cover is found for large parts of Europe in summer during the latest four decades.
Plain Language Summary
Aerosol particles cool the planet, but this effect is short‐lived in comparison with human impact on the greenhouse effect. This study shows that the greatest cooling effect in Europe has taken place in Central and Eastern Europe over the past four decades. The average temperature for the period April–September has increased by around 1°C due to reduced levels of aerosol particles. This is relevant for other areas of the Earth where the levels of aerosol particles are elevated today. This means that aerosol particles mask future warming if emissions begin to decrease, for example, in Eastern China and India. The total warming over large parts of Europe is however twice as large, and then also to the global average temperature increase of about 1.1°C. Positive feedbacks, by way of dryer surface conditions and reduced cloud cover, due to enhanced greenhouse effect have highly contributed to the rapid warming observed. Human emissions of carbon dioxide are the major threat, as the greenhouse gase affects the climate for hundreds to thousands of years.
Key Points
Substantial increase in near surface temperature was found during decline in aerosols for Central and Eastern Europe
Total warming for clear‐sky summer conditions over large parts of Europe since 1979 is nearly double the global mean temperature record
Rapid warming over Iberian Peninsula is likely caused by enhanced greenhouse effect, dryer surfaces, and to some degree decline in aerosols
The expanding field of community science offers the possibility to augment the way science is done, making closer, two‐way connections between researchers, communities, and community members. It ...enriches and improves science through broadening the scope of problem and hypothesis formulation to include practitioners who will use the results of scientific investigation. It enriches the communities involved through access to and participation in scientific investigations aimed at their own challenges. In this article, we describe a new facility—the Community Science Exchange—that offers venues for both researchers and community practitioners to publish and share their work to the benefit of both science and communities.
Plain Language Summary
We are in a new epoch in which society needs to deal with “wicked” problems—such as sustainably producing healthy, nutritious, affordable, and attractive food for everyone on the planet while enhancing ecosystem resilience, dealing with climate change, transforming our energy and transport sectors, and ensuring just and equitable access to resources. Dealing with these sorts of problems challenge the research community to become more connected to society, and to more holistically involve communities and practitioners in the process of science. In this article, we describe a new facility that offers venues for publishing, promoting and rewarding science done with, not for, communities.
Key Points
Community science—new knowledge co‐produced by researchers and community members—has the potential to enrich science through broadening our research perspectives, help communities respond to their pressing challenges, increase equitable access to science, and increase the understanding of and support for science in society
The grammar of science is important; while we currently focus mainly on nouns and verbs (i.e., our results and methods), we need to augment our grammatical treasure chest with prepositions (science "with" society, not "for" or "on"), prefixes (i.e., trans‐disciplinary science is different from inter‐ and multi‐disciplinary science), and adverbs describing how we work (e.g., collaboratively)
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