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"Nielsen, John"
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Evaluation of Three Planetary Boundary Layer Schemes in the WRF Model
Accurate depiction of meteorological conditions, especially within the planetary boundary layer (PBL), is important for air pollution modeling, and PBL parameterization schemes play a critical role in simulating the boundary layer. This study examines the sensitivity of the performance of the Weather Research and Forecast (WRF) model to the use of three different PBL schemes [Mellor–Yamada–Janjic (MYJ), Yonsei University (YSU), and the asymmetric convective model, version 2 (ACM2)]. Comparison of surface and boundary layer observations with 92 sets of daily, 36-h high-resolution WRFsimulations with different schemes over Texas in July–September 2005 shows that the simulations with the YSU and ACM2 schemes give much less bias than with the MYJ scheme. Simulations with the MYJ scheme, the only local closure scheme of the three, produced the coldest and moistest biases in the PBL. The differences among the schemes are found to be due predominantly to differences in vertical mixing strength and entrainment of air from above the PBL. A sensitivity experiment with the ACM2 scheme confirms this diagnosis.
Journal Article
U.S. winter wheat yield loss attributed to compound hot-dry-windy events
Climate extremes cause significant winter wheat yield loss and can cause much greater impacts than single extremes in isolation when multiple extremes occur simultaneously. Here we show that compound hot-dry-windy events (HDW) significantly increased in the U.S. Great Plains from 1982 to 2020. These HDW events were the most impactful drivers for wheat yield loss, accounting for a 4% yield reduction per 10 h of HDW during heading to maturity. Current HDW trends are associated with yield reduction rates of up to 0.09 t ha
−1
per decade and HDW variations are atmospheric-bridged with the Pacific Decadal Oscillation. We quantify the “yield shock”, which is spatially distributed, with the losses in severely HDW-affected areas, presumably the same areas affected by the Dust Bowl of the 1930s. Our findings indicate that compound HDW, which traditional risk assessments overlooked, have significant implications for the U.S. winter wheat production and beyond.
The authors show that in recent decades compound climate extremes (i.e., hot, dry, and windy events) have increased and have reduced winter wheat yields in the U.S. Great Plains. The area most affected is the same area as that in 1930s Dust Bowl.
Journal Article
American national security
\"As it enters its seventh edition, American National Security remains one of the most comprehensive texts on US national security, foreign policy, and defense. With critical reviews of the changing security environment in key regions of the world--Russia, East Asia, the Middle East, Sub-Saharan Africa, Latin America, and Europe--American National Security identifies the issues that the United States must face in the next century: peace operations, conflict and arms control, and the widening array of missions undertaken by US armed forces. Building on previous editions, the seventh edition fully details the policies and developments following President Barack Obama's election, investigating their significant implications for the broader trajectory of US national security strategy and policy. Highlights of the seventh edition include: - Greater perspectives on US vulnerability after September 11th - Greater discussion of globalization and human security - Further emphasis on diplomacy as an instrument of power - A reframing of the chapters on military power - The Edward Snowden revelations and their implications for the National Security Agency and the US intelligence community\"--Provided by publisher.
Book
Anatomy of an Extreme Event
The record-setting 2011 Texas drought/heat wave is examined to identify physical processes, underlying causes, and predictability. October 2010–September 2011 was Texas’s driest 12-month period on record. While the summer 2011 heat wave magnitude (2.9°C above the 1981–2010 mean) was larger than the previous record, events of similar or larger magnitude appear in preindustrial control runs of climate models. The principal factor contributing to the heat wave magnitude was a severe rainfall deficit during antecedent and concurrent seasons related to anomalous sea surface temperatures (SSTs) that included a La Niña event. Virtually all the precipitation deficits appear to be due to natural variability. About 0.6°C warming relative to the 1981–2010 mean is estimated to be attributable to human-induced climate change, with warming observed mainly in the past decade. Quantitative attribution of the overall human-induced contribution since preindustrial times is complicated by the lack of a detected century-scale temperature trend over Texas. Multiple factors altered the probability of climate extremes over Texas in 2011. Observed SST conditions increased the frequency of severe rainfall deficit events from 9% to 34% relative to 1981–2010, while anthropogenic forcing did not appreciably alter their frequency. Human-induced climate change increased the probability of a new temperature record from 3% during the 1981–2010 reference period to 6% in 2011, while the 2011 SSTs increased the probability from 4% to 23%. Forecasts initialized in May 2011 demonstrate predictive skill in anticipating much of the SST-enhanced risk for an extreme summer drought/heat wave over Texas.
Journal Article
Dinosaur rap
\"Travel back in time to dance and sing with a prehistoric posse of dinosaurs and kids. Then learn more about the creatures you've met in the notes at the end\"--Back cover.
Book
Semantic Segmentation and 3D Reconstruction of Concrete Cracks
Damage assessment of concrete structures is necessary to prevent disasters and ensure the safety of infrastructure such as buildings, sidewalks, dams, and bridges. Cracks are among the most prominent damage types in such structures. In this paper, a solution is proposed for identifying and modeling cracks in concrete structures using a stereo camera. First, crack pixels are identified using deep learning-based semantic segmentation networks trained on a custom dataset. Various techniques for improving the accuracy of these networks are implemented and evaluated. Second, modifications are applied to the stereo camera’s calibration model to ensure accurate estimation of the systematic errors and the orientations of the cameras. Finally, two 3D reconstruction methods are proposed, one of which is based on detecting the dominant structural plane surrounding the crack, while the second method focuses on stereo inference. The experiments performed on close-range images of complex and challenging scenes show that structural cracks can be identified with a precision of 96% and recall of 85%. In addition, an accurate 3D replica of cracks can be produced with an accuracy higher than 1 mm, from which the cracks’ size and other geometric features can be deduced.
Journal Article
Variant PNLDC1, Defective piRNA Processing, and Azoospermia
A particular class of small noncoding RNAs are transcribed from DNA and then processed by enzymes to generate short oligonucleotides that then control gene expression. This study underscores their relevance to human health and fitness.
Journal Article
Climate simulations: recognize the ‘hot model’ problem
The sixth and latest IPCC assessment weights climate models according to how well they reproduce other evidence. Now the rest of the community should do the same.
The sixth and latest IPCC assessment weights climate models according to how well they reproduce other evidence. Now the rest of the community should do the same.
Journal Article