Explore the vast range of titles available.

Warming in the Arctic is larger than the global average. A primary reason for this Arctic Amplification is the albedo feedback. The contrasting albedo of sea ice and dark melted surface areas is the key component of albedo feedback. Cloud coverage over the changing surface and the response of the clouds to the changing surface conditions will modify the change in planetary albedo when sea ice melts. Space-based lidar measurements provide a unique opportunity for cloud measurements in the Arctic. The response of clouds to the changing sea ice concentration was directly observed. Based on CALIPSO satellite observations of cloud properties, this study found that cloud coverage in ice-free regions in the Arctic linearly increased with the area of ice-free water during the melt seasons in the past 10 years, while sea ice coverage varies significantly year-to-year. The observations suggest that when sea-ice retreats, cloud fraction of the ice-free region remains fixed at nearly 81%. The high cloud coverage over melted areas significantly reduces the albedo feedback. These results indicate that space-based lidar cloud and surface observations of the Arctic can help constrain and improve climate models.

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) version 4.10 (V4) level 2 aerosol data products, released in November 2016, include substantial improvements to the aerosol subtyping and lidar ratio selection algorithms. These improvements are described along with resulting changes in aerosol optical depth (AOD). The most fundamental change in the V4 level 2 aerosol products is a new algorithm to identify aerosol subtypes in the stratosphere. Four aerosol subtypes are introduced for stratospheric aerosols: polar stratospheric aerosol (PSA), volcanic ash, sulfate/other, and smoke. The tropospheric aerosol subtyping algorithm was also improved by adding the following enhancements: (1) all aerosol subtypes are now allowed over polar regions, whereas the version 3 (V3) algorithm allowed only clean continental and polluted continental aerosols; (2) a new “dusty marine” aerosol subtype is introduced, representing mixtures of dust and marine aerosols near the ocean surface; and (3) the “polluted continental” and “smoke” subtypes have been renamed “polluted continental/smoke” and “elevated smoke”, respectively. V4 also revises the lidar ratios for clean marine, dust, clean continental, and elevated smoke subtypes. As a consequence of the V4 updates, the mean 532 nm AOD retrieved by CALIOP has increased by 0.044 (0.036) or 52 % (40 %) for nighttime (daytime). Lidar ratio revisions are the most influential factor for AOD changes from V3 to V4, especially for cloud-free skies. Preliminary validation studies show that the AOD discrepancies between CALIOP and AERONET–MODIS (ocean) are reduced in V4 compared to V3.

We quantify the seasonal and spatial variations of cloud radiative impacts in the tropical tropopause layer (TTL) by using cloud retrievals from Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), International Satellite Cloud Climatology Project (ISCCP) and CloudSat. Over the convective regions including Western Pacific, Africa, South America, and South Asia, we find pronounced solar heating and infrared cooling in the lower part of the TTL (<∼16 km). The solar heating weakens above 16 km and nearly diminishes at 18 km, whereas the infrared cooling extends vertically throughout the TTL. The net cloud radiative forcing, which is the summation of cloud solar and infrared radiative forcing, has heating below ∼16 km and turns to mostly cooling above 17 km. The net cloud radiative heating over the convective regions is mainly contributed from solar radiation, whereas the weak net cloud radiative heating surrounding these regions is due to infrared heating. To further examine the impacts of different cloud types in the TTL, we classified TTL clouds in terms of cloud optical depths (τ) as thin cirrus (τ < 0.3), thick cirrus (0.3 ≤ τ < 3), and opaque clouds (τ ≥ 3). In the solar part, thin and thick cirrus play a relatively small role and the impact of cloud‐free air above clouds is negligible. The solar heating is dominantly contributed from the solar absorption near the top of opaque clouds. In the infrared part, the thick cirrus heating is mainly confined over the convective regions in the lower part of TTL while the thin cirrus infrared heating is more prevalent both vertically and horizontally in the TTL, which is the dominant infrared heating source. The infrared cooling in cloud‐free air above clouds is dominant above 17 km, whereas the infrared cooling near the top of opaque clouds is dominant below. Despite the infrared heating effects of thin and thick cirrus clouds, the infrared cooling from the opaque cloud top and cloud‐free air above clouds outweighs the heating effects so that the ensemble mean cloud infrared radiative forcing is mostly cooling except outside the convective regions.

The strengthening mechanisms during mechanical surface treatment methods need to be understood to optimize material surface modification processes. This study combined experimental approaches and physics-based crystal plasticity finite element method to quantify the strengthening contributions of laser-peening-induced microstructural evolutions on the local tensile properties of AA2195-T6 friction stir welded joints. The model predicted the strengthening effects of near-surface compressive residual stresses, work hardening, and crystal morphology evolutions after laser peening application on the joint center. The simulated local joint tensile properties were then inserted into the joint macroscale model to predict the overall modifications in the joint global tensile properties after laser peening. The digital image correlation method was applied with tensile tests to observe local and overall evolutions in joint tensile properties and evaluate modeling results. The crystal plasticity model predicted the enhancements in the joint tensile properties after multiple laser peening applications. As identified by the model, the major laser peening strengthening contribution stemmed from the induced near-surface compressive residual stresses, followed by work hardening and crystal morphology evolutions. Local enhancements in the tensile strength at the joint center and modification in overall joint tensile property homogeneity improved joint mechanical properties after laser peening.

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) is a two-wavelength polarization lidar that performs global profiling of aerosols and clouds in the troposphere and lower stratosphere. CALIOP is the primary instrument on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, which has flown in formation with the NASA A-train constellation of satellites since May 2006. The global, multiyear dataset obtained from CALIOP provides a new view of the earth’s atmosphere and will lead to an improved understanding of the role of aerosols and clouds in the climate system. A suite of algorithms has been developed to identify aerosol and cloud layers and to retrieve a variety of optical and microphysical properties. CALIOP represents a significant advance over previous space lidars, and the algorithms that have been developed have many innovative aspects to take advantage of its capabilities. This paper provides a brief overview of the CALIPSO mission, the CALIOP instrument and data products, and an overview of the algorithms used to produce these data products.

Emission Trading System (ETS) is an innovative practice under the progress of green development in China. It is also an important method for China to achieve market-oriented environmental governance in ecological civilization construction. The ETS pilot policy has implemented for more than 10 years. However, the co-benefits of ETS pilot policy by the integration of energy consumption, carbon and sulfur dioxide emissions, and wastewater has not been evaluated. In order to fill this gap, we use the 2003–2017 annual data of 30 China’s provinces (municipalities and autonomous regions), and utilize the Difference-in-Differences (DID) model and Propensity Score Matching (PSM-DID) methodology to evaluate the co-benefits of ETS pilot policy on energy conservation and emission reduction. We find that the ETS pilot policy significantly promote energy conservation and emission reduction. Eastern and central China have significantly benefited from the policy, while the western China has not due to the limited technology and innovation as well as an imbalance of the industrial structure. The results provide the policy reference for China’s government and institutions as well as the governments and institutions around the world to fulfill their commitments to save energy and reduce emissions, and early achieve the carbon peaking and carbon neutralization.

Austenitic stainless steel was subjected to multiple laser peening (LP) with high coverages and the gradient structures and corresponding mechanical behaviors were investigated in detail. Body-centered cubic α′ phase and hexagonal-close packed ε phase martensite induced by peening deformation accumulate in multiple LPed 304 austenitic stainless steel surface layer with the increasing coverage. In samples with 240 layers multiple LP, high density martensite in block and twins can be observed. The EBSD results show that the γ → ε → α′ martensitic transformation can be noticed to occur in grain boundaries and twins. Martensitic transformation volume fraction, twin volume fraction and hardness of multiple LPed 304 SS exhibit gradient characteristic from the top surface to substrate. The hardness of the specimens increased with the peening coverage near the top layers, and the influence of laser peening on hardness gradually vanished until 2 mm in depth, the tensile strength increased while the tensile elongation decreased, resulting from a peak power density of 8.19 GW/cm 2 . Multiple laser peening can be utilized as a solution to modify the mechanical performances by tailoring the gradient structure. Among the investigating range, the optimal multiple LP layers is suggested as 80 where both a relative high strength and ductility can be obtained.

The change in planetary albedo due to aerosol–cloud interactions during the industrial era is the leading source of uncertainty in inferring Earth’s climate sensitivity to increased greenhouse gases from the historical record. The variable that controls aerosol–cloud interactions in warm clouds is droplet number concentration. Global climate models demonstrate that the present-day hemispheric contrast in cloud droplet number concentration between the pristine Southern Hemisphere and the polluted Northern Hemisphere oceans can be used as a proxy for anthropogenically driven change in cloud droplet number concentration. Remotely sensed estimates constrain this change in droplet number concentration to be between 8 cm−3 and 24 cm−3. By extension, the radiative forcing since 1850 from aerosol–cloud interactions is constrained to be −1.2 W·m−2 to −0.6 W·m−2. The robustness of this constraint depends upon the assumption that pristine Southern Ocean droplet number concentration is a suitable proxy for preindustrial concentrations. Droplet number concentrations calculated from satellite data over the Southern Ocean are high in austral summer. Near Antarctica, they reach values typical of Northern Hemisphere polluted outflows. These concentrations are found to agree with several in situ datasets. In contrast, climate models show systematic underpredictions of cloud droplet number concentration across the Southern Ocean. Near Antarctica, where precipitation sinks of aerosol are small, the underestimation by climate models is particularly large. This motivates the need for detailed process studies of aerosol production and aerosol–cloud interactions in pristine environments. The hemispheric difference in satellite estimated cloud droplet number concentration implies preindustrial aerosol concentrations were higher than estimated by most models.

The Southern Ocean’s vital carbon sink is driven by phytoplankton Net Primary Production (NPP). Winter phytoplankton seed spring algal blooms and regulate nutrient cycling and ecosystem dynamics, yet Antarctic winter NPP remains poorly constrained due to limited in situ data and passive satellite sensor challenges in low-light, ice-covered conditions. Here, we leverage spaceborne LiDAR (CALIOP), analyzing 16 years of data (16,236 tracks spanning 2006-2023), to reveal a significant, previously underestimated rise in winter NPP, increasing by ~2.2 Tg C yr⁻¹ ( P  < 0.01). Enhanced coverage with CALIOP boosts ice-free sea observations from 12.5% to 80.7%, exposing pronounced NPP gains in the seasonal sea-ice zone, notably the Weddell and Ross Seas, driven by declining sea ice, greater light penetration, and nutrient mixing. These shifts, modulated by climate modes like the Southern Annular Mode and El Niño-Southern Oscillation, highlight the Southern Ocean’s escalating role in global carbon dynamics. Integrating winter NPP into carbon models is essential to refine projections of polar carbon sequestration under climate change. The Antarctic winter phytoplankton production is experiencing an underestimated acceleration based on the spaceborne LiDAR. This trend is linked to the declining sea ice, highlighting the Southern Ocean’s escalating role in the global carbon cycle.

Reward is essential for shaping behavior. Using sensory cues to imply forthcoming rewards, previous studies have demonstrated powerful effects of rewards on behavior. Nevertheless, the impact of reward on the sensorimotor transformation, particularly when reward is linked to behavior remains uncertain. In this study, we investigated how reward modulates smooth pursuit eye movements in monkeys. Three distinct associations between reward and eye movements were conducted in independent blocks. Results indicated that reward increased eye velocity during the steady-state pursuit, rather than during the initiation. The influence depended on the particular association between behavior and reward: a faster eye velocity was linked with reward. Neither rewarding slower eye movements nor randomizing rewards had a significant effect on behavior. The findings support the existence of distinct mechanisms involved in the initiation and steady-state phases of pursuit, and contribute to a deeper understanding of how reward interacts with these two periods of pursuit.