Satellite quantification of aerosol effects on clouds relies on
aerosol optical depth (AOD) as a proxy for aerosol concentration or cloud
condensation nuclei (CCN). However, the lack of error ...characterization of
satellite-based results hampers their use for the evaluation and improvement
of global climate models. We show that the use of AOD for assessing
aerosol–cloud interactions (ACIs) is inadequate over vast oceanic areas in
the subtropics. Instead, we postulate that a more physical approach that
consists of matching vertically resolved aerosol data from the Cloud-Aerosol
Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite at
the cloud-layer height with Moderate Resolution Imaging
Spectroradiometer (MODIS) Aqua cloud retrievals reduces uncertainties in
satellite-based ACI estimates. Combined aerosol extinction coefficients
(σ) below cloud top (σBC) from the Cloud-Aerosol Lidar
with Orthogonal Polarization (CALIOP) and cloud droplet number
concentrations (Nd) from MODIS Aqua yield high correlations across a
broad range of σBC values, with σBC quartile
correlations ≥0.78. In contrast, CALIOP-based AOD yields correlations
with MODIS Nd of 0.54–0.62 for the two lower AOD quartiles. Moreover,
σBC explains 41 % of the spatial variance in MODIS Nd,
whereas AOD only explains 17 %, primarily caused by the lack of spatial
covariability in the eastern Pacific. Compared with σBC,
near-surface σ weakly correlates in space with MODIS Nd,
accounting for a 16 % variance. It is concluded that the linear regression
calculated from ln(Nd)–ln(σBC) (the standard method for
quantifying ACIs) is more physically meaningful than that derived from the
Nd–AOD pair.
The radiative effects of the large‐scale air traffic slowdown during April and May 2020 due to the international response to the COVID‐19 pandemic are estimated by comparing the coverage (CC), ...optical properties, and radiative forcing of persistent linear contrails over the conterminous United States and two surrounding oceanic air corridors during the slowdown period and a similar baseline period during 2018 and 2019 when air traffic was unrestricted. The detected CC during the slowdown period decreased by an area‐averaged mean of 41% for the three analysis boxes. The retrieved contrail optical properties were mostly similar for both periods. Total shortwave contrail radiative forcings (CRFs) during the slowdown were 34% and 42% smaller for Terra and Aqua, respectively. The corresponding differences for longwave CRF were 33% for Terra and 40% for Aqua. To account for the impact of any changes in the atmospheric environment between baseline and slowdown periods on detected CC amounts, the contrail formation potential (CFP) was computed from reanalysis data. In addition, a filtered CFP (fCFP) was also developed to account for factors that may affect contrail formation and visibility of persistent contrails in satellite imagery. The CFP and fCFP were combined with air traffic data to create empirical models that estimated CC during the baseline and slowdown periods and were compared to the detected CC. The models confirm that decreases in CC and radiative forcing during the slowdown period were mostly due to the reduction in air traffic, and partly due to environmental changes.
Plain Language Summary
Contrails produced by aircraft flying in cold but humid air both warm the atmosphere by reducing infrared radiation emitted back into space and cool it by increasing reflected sunlight. Due to the decrease in air traffic during the first months of the COVID pandemic, fewer satellite‐detectable contrails were produced compared to pre‐pandemic times, and thus the radiative effects of contrails were also diminished. But changes in the overall temperature and humidity at aircraft cruise altitudes also affect contrail formation and might explain at least some of the observed decrease in contrail coverage during April and May 2020. Analysis of satellite imagery showed that the thickness and ice‐crystal size of the contrails during the COVID period did not change much from pre‐pandemic contrails. The regional contrail coverage was accurately simulated from a combination of the estimated air traffic activity at cruise altitude and the probable frequency of when atmospheric conditions were favorable for contrail formation. This simulation confirms that most of the decrease in contrails and their radiative effects during the COVID‐related slowdown period were due to the reduction in air traffic, and to a lesser extent to changes in temperature and humidity at cruise altitude during April and May 2020.
Key Points
Contrail coverage during the start of the COVID pandemic was reduced significantly over the study area, mostly due to less air traffic
Monthly mean coverage was accurately estimated from a simple relation between air traffic and contrail formation probability
The relation confirms that the decrease in contrail radiative effects is greater than that expected from the decrease in air traffic alone
Drawbacks of current carbon dioxide capture methods include corrosivity, evaporative losses and fouling. Separating the capture solvent from infrastructure and effluent gases via microencapsulation ...provides possible solutions to these issues. Here we report carbon capture materials that may enable low-cost and energy-efficient capture of carbon dioxide from flue gas. Polymer microcapsules composed of liquid carbonate cores and highly permeable silicone shells are produced by microfluidic assembly. This motif couples the capacity and selectivity of liquid sorbents with high surface area to facilitate rapid and controlled carbon dioxide uptake and release over repeated cycles. While mass transport across the capsule shell is slightly lower relative to neat liquid sorbents, the surface area enhancement gained via encapsulation provides an order-of-magnitude increase in carbon dioxide absorption rates for a given sorbent mass. The microcapsules are stable under typical industrial operating conditions and may be used in supported packing and fluidized beds for large-scale carbon capture.
Visible-near infrared (VIS-NIR) and thermal infrared (TIR) methods have long been used for ice cloud property retrievals based on satellite observations. Both retrieval methods are sensitive to the ...assumed ice particle models, which can significantly impact the accuracy of the retrieved microphysical and radiative properties of ice clouds. The two-habit model (THM) is considered a suitable ice particle model for passive remote sensing of global ice clouds, as confirmed by spectral consistency in cloud optical thickness (COT), which refers to the agreement between VIS-NIR and TIR COT retrievals. However, the ratio of COTs retrieved from these two methods using the THM varies with the scattering angle, indicating the potential influence of atmospheric and cloud properties on the spectral consistency of the inferred COT. The present study investigates potential factors affecting the angular dependence of the COT ratio based on observations made by the Advanced Baseline Imager (ABI) sensors on the 17th Geostationary Operational Environmental Satellite (GOES-17). For optically thin clouds (COT < 1) illuminated at a solar zenith angle (SZA) <inline-formula> <tex-math notation="LaTeX"> < 20^{\circ } </tex-math></inline-formula>, the heterogeneous particle combination of mixed-phase clouds is the dominant factor that produces an angular-dependent negative bias in COT spectral consistency. At greater SZAs, cloud 3-D radiative effects are presumed to be a dominant factor. Negative biases in the cloud top temperature (CTT) and sea surface temperature contribute to negative biases in the COT ratio. This study suggests that the angular dependence of the COT ratio could help identify mixed-phase clouds and estimate their impact on the spectral consistency in retrieving ice cloud COT.
An artificial neural network (ANN) algorithm, employing several Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) channels, the retrieved cloud phase and total cloud visible optical depth, ...and temperature and humidity vertical profiles is trained to detect multilayer (ML) ice-over-water cloud systems identified by matched 2008 CloudSat and CALIPSO (CC) data. The trained multilayer cloud-detection ANN (MCANN) was applied to 2009 MODIS data resulting in combined ML and single layer detection accuracies of 87 % (89 %) and 86 % (89 %) for snow-free (snow-covered) regions during the day and night, respectively. Overall, it detects 55 % and ∼ 30 % of the CC ML clouds over snow-free and snow-covered surfaces, respectively, and has a relatively low false alarm rate. The net gain in accuracy, which is the difference between the true and false ML fractions, is 7.5 % and ∼ 2.0 % over snow-free and snow/ice-covered surfaces. Overall, the MCANN is more accurate than most currently available methods. When corrected for the viewing-zenith-angle dependence of each parameter, the ML fraction detected is relatively invariant across the swath. Compared to the CC ML variability, the MCANN is robust seasonally and interannually and produces similar distribution patterns over the globe, except in the polar regions. Additional research is needed to conclusively evaluate the viewing zenith angle (VZA) dependence and further improve the MCANN accuracy. This approach should greatly improve the monitoring of cloud vertical structure using operational passive sensors.
Linear contrail coverage, optical property, and radiative
forcing data over the Northern Hemisphere (NH) are derived from a year
(2012) of Terra and Aqua Moderate-resolution Imaging Spectroradiometer ...(MODIS)
imagery and compared with previously published 2006 results (Duda et al.,
2013; Bedka et al., 2013; Spangenberg et al., 2013) using a consistent
retrieval methodology. Differences in the observed Terra-minus-Aqua screened contrail
coverage and patterns in the 2012 annual-mean air traffic estimated with
respect to satellite overpass time suggest that most contrails detected by
the contrail detection algorithm (CDA) form approximately 2 h before
overpass time. The 2012 screened NH contrail coverage (Mask B) shows a
relative 3 % increase compared to 2006 data for Terra and increases by almost
7 % for Aqua, although the differences are not expected to be statistically
significant. A new post-processing algorithm added to the contrail mask
processing estimated that the total contrail cirrus coverage visible in the
MODIS imagery may be 3 to 4 times larger than the linear contrail
coverage detected by the CDA. This estimate is similar in magnitude to the
spreading factor estimated by Minnis et al. (2013). Contrail property
retrievals of the 2012 data indicate that both contrail optical depth and
contrail effective diameter decreased approximately 10 % between 2006 and
2012. The decreases may be attributed to better background cloudiness
characterization, changes in the waypoint screening, or changes in contrail
temperature. The total mean contrail radiative forcings (TCRFs) for all 2012
Terra observations were −6.3, 14.3, and 8.0 mW m−2 for the shortwave
(SWCRF), longwave (LWCRF), and net forcings, respectively. These values are
approximately 20 % less than the corresponding 2006 Terra estimates. The
decline in TCRF results from the decrease in normalized CRF, partially
offset by the 3 % increase in overall contrail coverage in 2012. The TCRFs
for 2012 Aqua are similar, −6.4, 15.5, and 9.0 mW m−2 for shortwave,
longwave, and net radiative forcing. The strong correlation between the
relative changes in both total SWCRF and LWCRF between 2006 and 2012 and the
corresponding relative changes in screened contrail coverage over each air
traffic region suggests that regional changes in TCRF from year to year are
dominated by year-to-year changes in contrail coverage over each area.
This study examined associations of maternal glycemia during pregnancy with childhood glucose outcomes in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) cohort.
HAPO was an observational ...international investigation that established associations of maternal glucose with adverse perinatal outcomes. The HAPO Follow-up Study included 4,832 children ages 10-14 years whose mothers had a 75-g oral glucose tolerance test (OGTT) at ∼28 weeks of gestation. Of these, 4,160 children were evaluated for glucose outcomes. Primary outcomes were child impaired glucose tolerance (IGT) and impaired fasting glucose (IFG). Additional outcomes were glucose-related measures using plasma glucose (PG), A1C, and C-peptide from the child OGTT.
Maternal fasting plasma glucose (FPG) was positively associated with child FPG and A1C; maternal 1-h and 2-h PG were positively associated with child fasting, 30 min, 1-h, and 2-h PG, and A1C. Maternal FPG, 1-h, and 2-h PG were inversely associated with insulin sensitivity, whereas 1-h and 2-h PG were inversely associated with disposition index. Maternal FPG, but not 1-h or 2-h PG, was associated with child IFG, and maternal 1-h and 2-h PG, but not FPG, were associated with child IGT. All associations were independent of maternal and child BMI. Across increasing categories of maternal glucose, frequencies of child IFG and IGT, and timed PG measures and A1C were higher, whereas insulin sensitivity and disposition index decreased.
Across the maternal glucose spectrum, exposure to higher levels in utero is significantly associated with childhood glucose and insulin resistance independent of maternal and childhood BMI and family history of diabetes.
Recent studies have found that flight through deep convective storms and ingestion of high mass concentrations of ice crystals, also known as high ice water content (HIWC), into aircraft engines can ...adversely impact aircraft engine performance. These aircraft engine icing events caused by HIWC have been documented during flight in weak reflectivity regions near convective updraft regions that do not appear threatening in onboard weather radar data. Three airborne field campaigns were conducted in 2014 and 2015 to better understand how HIWC is distributed in deep convection, both as a function of altitude and proximity to convective updraft regions, and to facilitate development of new methods for detecting HIWC conditions, in addition to many other research and regulatory goals. This paper describes a prototype method for detecting HIWC conditions using geostationary (GEO) satellite imager data coupled with in-situ total water content (TWC) observations collected during the flight campaigns. Three satellite-derived parameters were determined to be most useful for determining HIWC probability: 1) the horizontal proximity of the aircraft to the nearest overshooting convective updraft or textured anvil cloud, 2) tropopause-relative infrared brightness temperature, and 3) daytime-only cloud optical depth. Statistical fits between collocated TWC and GEO satellite parameters were used to determine the membership functions for the fuzzy logic derivation of HIWC probability. The products were demonstrated using data from several campaign flights and validated using a subset of the satellite-aircraft collocation database. The daytime HIWC probability was found to agree quite well with TWC time trends and identified extreme TWC events with high probability. Discrimination of HIWC was more challenging at night with IR-only information. The products show the greatest capability for discriminating TWC ≥ 0.5 g m
. Product validation remains challenging due to vertical TWC uncertainties and the typically coarse spatio-temporal resolution of the GEO data.
A variety of satellite and ground-based observations are used to study how diurnal variations of cloud radiative heating affect the life cycle of anvil clouds over the tropical western Pacific Ocean. ...High clouds thicker than 2 km experience longwave heating at cloud base, longwave cooling at cloud top, and shortwave heating at cloud top. The shortwave and longwave effects have similar magnitudes during midday, but only the longwave effect is present at night, so high clouds experience a substantial diurnal cycle of radiative heating. Furthermore, anvil clouds are more persistent or laterally expansive during daytime. This cannot be explained by variations of convective intensity or geographic patterns of convection, suggesting that shortwave heating causes anvil clouds to persist longer or spread over a larger area. It is then investigated if shortwave heating modifies anvil development by altering turbulence in the cloud. According to one theory, radiative heating drives turbulent overturning within anvil clouds that can be sufficiently vigorous to cause ice nucleation in the updrafts, thereby extending the cloud lifetime. High-frequency air motion and ice-crystal number concentration are shown to be inversely related near cloud top, however. This suggests that turbulence depletes or disperses ice crystals at a faster rate than it nucleates them, so another mechanism must cause the diurnal variation of anvil clouds. It is hypothesized that radiative heating affects anvil development primarily by inducing a mesoscale circulation that offsets gravitational settling of cloud particles.
Birth weight variation is influenced by fetal and maternal genetic and non-genetic factors, and has been reproducibly associated with future cardio-metabolic health outcomes. In expanded genome-wide ...association analyses of own birth weight (n = 321,223) and offspring birth weight (n = 230,069 mothers), we identified 190 independent association signals (129 of which are novel). We used structural equation modeling to decompose the contributions of direct fetal and indirect maternal genetic effects, then applied Mendelian randomization to illuminate causal pathways. For example, both indirect maternal and direct fetal genetic effects drive the observational relationship between lower birth weight and higher later blood pressure: maternal blood pressure-raising alleles reduce offspring birth weight, but only direct fetal effects of these alleles, once inherited, increase later offspring blood pressure. Using maternal birth weight-lowering genotypes to proxy for an adverse intrauterine environment provided no evidence that it causally raises offspring blood pressure, indicating that the inverse birth weight-blood pressure association is attributable to genetic effects, and not to intrauterine programming.
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