Feed aggregator

The Effects of Summer Snowfall on Arctic Sea Ice Radiative Forcing

JGR–Atmospheres - Thu, 07/18/2024 - 09:32
Abstract

Snow is the most reflective natural surface on Earth. Since fresh snow on bare sea ice increases the surface albedo, the impact of summer snow accumulation can have a negative radiative forcing effect, which would inhibit sea ice surface melt and potentially slow sea-ice loss. However, it is not well known how often, where, and when summer snowfall events occur on Arctic sea ice. In this study, we used in situ and model snow depth data paired with surface albedo and atmospheric conditions from satellite retrievals to characterize summer snow accumulation on Arctic sea ice from 2003 to 2017. We found that, across the Arctic, ∼2 snow accumulation events occurred on initially snow-free conditions each year. The average snow depth and albedo increases were ∼2 cm and 0.08, respectively. 16.5% of the snow accumulation events were optically thick (>3 cm deep) and lasted 2.9 days longer than the average snow accumulation event (3.4 days). Based on a simple, multiple scattering radiative transfer model, we estimated a −0.086 ± 0.020 W m−2 change in the annual average top-of-the-atmosphere radiative forcing for summer snowfall events in 2003–2017. The following work provides new information on the frequency, distribution, and duration of observed snow accumulation events over Arctic sea ice in summer. Such results may be particularly useful in understanding the impacts of ephemeral summer weather on surface albedo and their propagating effects on the radiative forcing over Arctic sea ice, as well as assessing climate model simulations of summer atmosphere-ice processes.

Role of the Boreal Autumn Antarctic Oscillation in Controlling the Winter Frequency of Severe Pollution Events in the Beijing–Tianjin–Hebei Region, China

JGR–Atmospheres - Thu, 07/18/2024 - 08:44
Abstract

The Antarctic Oscillation (AAO), which is the main mode of extratropical circulation in the Southern Hemisphere, also has a substantial effect on the Northern Hemisphere climate. We investigated the influence of the early AAO on the frequency of late severe pollution events (SPEF) in the Beijing–Tianjin–Hebei region (SPEFBTH) of China during winter. The results show that the winter (December–January–February) SPEFBTH is negatively correlated with the AAO from the previous autumn (August–September–October). The controlling mechanism can be briefly described as follows: the autumn AAO is positively correlated with the mid-latitude sea surface temperature (SST) in the South Atlantic Ocean. The SST preserves the autumn anomaly signal into the following winter. This anomalous SST regulates changes in the tropical western Indian Ocean–Intertropical Convergence Zone (IN–ITCZ) via air–sea coupling. Subsequently, as a response to the IN–ITCZ anomalies, anomalous wave trains are excited in the upper troposphere from the tropical western Indian Ocean to East Asia. In addition, the local meridional circulation is modulated; therefore, the circulation field and other meteorological elements favorable for the SPEFBTH appear and exacerbate the SPEFBTH. This study describes a new physical mechanism for the pathway of the AAO influence on subsequent SPEFBTH and finds a predictable source in the Southern Hemisphere air–sea system.

We need better and more PopSci by scientists

Science - Thu, 07/18/2024 - 07:00
Science, Volume 385, Issue 6706, July 2024.

A Multi‐Objective Optimization‐Based Reflective Metasurface for Enhanced Multi‐Point Focusing With Diffraction Suppression

Radio Science - Thu, 07/18/2024 - 07:00
Abstract

Metasurface arrays can achieve beam control at low cost and high quality by providing different phase compensations for each unit, effectively focusing microwave energy on target locations. With the development of short-range communication technology or microwave power transmission technology, the demand for focusing has also increased. Using metasurface arrays to achieve multi-target focusing has wide application value. However, as the number of focal points increases, the superposition of electromagnetic wave propagation paths leads to significant interference phenomena, which can impact potential applications. Existing solutions are unable to solve such complex problems involving a large number of targets with conflicts between them. Multi-objective algorithms, by iteratively obtaining a set of optimal solutions, provide decision support for designers in complex multi-objective problems. This paper alters the phase of cells in a reflective array, calculates the near-field electric field model using the Fresnel diffraction formula, and employs various solutions using the Non-dominated Sorting Genetic Algorithm III (NSGA-III) combined with different constraints. Finally, we select the balanced solution to establish the array. After simulation, three adjacent focal points with normalized central values of 1, 0.86, and 0.88 were obtained, with the maximum electric field value outside the focal points being only 0.58, demonstrating the feasibility of multi-objective algorithms in solving complex multi-focal problems.

Structure-guided discovery of ancestral CRISPR-Cas13 ribonucleases

Science - Thu, 07/18/2024 - 05:59
Science, Volume 385, Issue 6708, Page 538-543, August 2024.

When civilizations collapse

Science - Thu, 07/18/2024 - 05:58
Science, Volume 385, Issue 6706, Page 263-263, July 2024.

Element of surprise

Science - Thu, 07/18/2024 - 05:58
Science, Volume 385, Issue 6706, Page 262-262, July 2024.

Ph3PCN2: A stable reagent for carbon-atom transfer

Science - Thu, 07/18/2024 - 05:58
Science, Volume 385, Issue 6706, Page 305-311, July 2024.

My weekly reset

Science - Thu, 07/18/2024 - 05:58
Science, Volume 385, Issue 6706, Page 338-338, July 2024.

In Other Journals

Science - Thu, 07/18/2024 - 05:58
Science, Volume 385, Issue 6706, Page 269-270, July 2024.

Theme by Danetsoft and Danang Probo Sayekti inspired by Maksimer