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1. Axisymmetric Radiative Transfer Models of Kilonovae

   https://doi.org/10.3847/1538-4357/abe1b5  

   Korobkin, Oleg ; Wollaeger, Ryan T. ; Fryer, Christopher L. ; Hungerford, Aimee L. ; Rosswog, Stephan ; Fontes, Christopher J. ; Mumpower, Matthew R. ; Chase, Eve A. ; Even, Wesley P. ; Miller, Jonah ; et al ( April 2021 , The Astrophysical Journal)

   The detailed observations of GW170817 proved for the first time directly that neutron star mergers are a major production site of heavy elements. The observations could be fit by a number of simulations that qualitatively agree, but can quantitatively differ (e.g., in total r-process mass) by an order of magnitude. We categorize kilonova ejecta into several typical morphologies motivated by numerical simulations, and apply a radiative transfer Monte Carlo code to study how the geometric distribution of the ejecta shapes the emitted radiation. We find major impacts on both spectra and light curves. The peak bolometric luminosity can vary by two orders of magnitude and the timing of its peak by a factor of five. These findings provide the crucial implication that the ejecta masses inferred from observations around the peak brightness are uncertain by at least an order of magnitude. Mixed two-component models with lanthanide-rich ejecta are particularly sensitive to geometric distribution. A subset of mixed models shows very strong viewing angle dependence due to lanthanide “curtaining,” which persists even if the relative mass of lanthanide-rich component is small. The angular dependence is weak in the rest of our models, but different geometric combinations of the two components lead to a highly diverse set of light curves. We identify geometry-dependent P Cygni features in late spectra that directly map out strong lines in the simulated opacity of neodymium, which can help to constrain the ejecta geometry and to directly probe the r-process abundances.

    

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2. Observation of radiative double electron capture for

   https://doi.org/10.1002/xrs.3063  

   Kumara, Nuwan ; La Mantia, David S. ; Buglione, Stephanie L. ; McCoy, Craig P. ; Taylor, Charles J. ; White, Jacob S. ; Kayani, Asghar ; Tanis, John A. ( June 2019 , X-Ray Spectrometry)

   Radiative double electron capture (RDEC), occurring when two electrons are captured to a projectile ion with the simultaneous emission of a single photon, has been investigated. RDEC can be considered as the time inverse process of double photoionization. Strong evidence for RDEC is found in F⁹⁺+ N₂collisions and additionally for one‐electron F⁸⁺for which the probability for the process is expected to be considerably smaller. Preliminary values for the cross sections for RDEC have been determined. A significant advantage of the gas target is that multiple‐collision effects seen for a solid target are avoided due to the single‐collision conditions that prevail for gas targets.

    

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3. Significant Effective Radiative Forcing of Stratospheric Wildfire Smoke

   https://doi.org/10.1029/2022GL100175  

   Liu, Cheng‐Cheng ; Portmann, Robert W. ; Liu, Shang ; Rosenlof, Karen H. ; Peng, Yifeng ; Yu, Pengfei ( September 2022 , Geophysical Research Letters)

   The radiative forcing (RF) of volcanic sulfate is well quantified. However, the RF of pyrocumulonimbus (pyroCb) smoke with absorbing carbonaceous aerosols has not been considered in climate assessment reports. With the Community Earth System Model, we studied two record‐breaking wildfire events, the 2017 Pacific Northwest Event (PNE) and the 2019–2020 Australian New Year event (ANY), that perturbed stratospheric chemistry and the earth's radiation budget. We calculated a global annual‐mean effective RF (ERF) of −0.04 ± 0.02 and −0.17 ± 0.02 W/m²at the top of the atmosphere (TOA) for PNE and ANY, respectively. The complexity of longwave RF led to an uncertainty of about 50% in the ERF at the TOA among climate models. We found that modeled ERF from wildfire smoke was 70%–270% more negative than the ERF of mass‐equivalent sulfate aerosol, highlighting its important role in the climate radiative budget.

    

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4. Bounding Global Aerosol Radiative Forcing of Climate Change

   https://doi.org/10.1029/2019RG000660  

   Bellouin, N. ; Quaas, J. ; Gryspeerdt, E. ; Kinne, S. ; Stier, P. ; Watson‐Parris, D. ; Boucher, O. ; Carslaw, K. S. ; Christensen, M. ; Daniau, A. ‐L. ; et al ( March 2020 , Reviews of Geophysics)

   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 m⁻², or ‐2.0 to ‐0.4 W m⁻²with 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.

    

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5. Vapor condensation with daytime radiative cooling

   https://doi.org/10.1073/pnas.2019292118  

   Zhou, Ming ; Song, Haomin ; Xu, Xingyu ; Shahsafi, Alireza ; Qu, Yurui ; Xia, Zhenyang ; Ma, Zhenqiang ; Kats, Mikhail A. ; Zhu, Jia ; Ooi, Boon S. ; et al ( March 2021 , Proceedings of the National Academy of Sciences)

   A radiative vapor condenser sheds heat in the form of infrared radiation and cools itself to below the ambient air temperature to produce liquid water from vapor. This effect has been known for centuries, and is exploited by some insects to survive in dry deserts. Humans have also been using radiative condensation for dew collection. However, all existing radiative vapor condensers must operate during the nighttime. Here, we develop daytime radiative condensers that continue to operate 24 h a day. These daytime radiative condensers can produce water from vapor under direct sunlight, without active consumption of energy. Combined with traditional passive cooling via convection and conduction, radiative cooling can substantially increase the performance of passive vapor condensation, which can be used for passive water extraction and purification technologies.

    

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