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• Synoptic wind durations can range from one-hour to about 10 h. • Time durations for synoptic wind speed about the ultimate return period are close to but slightly longer than one hour in most regions across North America. • Time durations for synoptic wind speed at lower return periods can be much longer than one hour in most regions across North America. • The effect of synoptic wind duration has limited impact on elastic strength design but a non-negligible impact on serviceability and the Cladding and Component (C&C) design. • The engineering implication of climate change impact on synoptic wind durations across North America is limited. In modern wind engineering practice, wind load effects are often defined as a function of a basic design wind speed, an aerodynamic force coefficient, several multipliers to consider surrounding terrain, topographic effect, and the directionality of the wind climate. Among these variables, the basic design wind speed is associated with an averaging time (also known as gust duration), e.g., 0.02-second, 3-second, 10-minute, or one hour. The design level aerodynamic force coefficients are defined as a specific percentile within a reference period, representing the generic time duration of wind events, i.e., wind duration, which is assumed to be one hour. A recent study showed that the hurricane wind duration could differ from this assumption. There has not been any study that investigated synoptic wind duration and its engineering implementations comprehensively. It is also unclear whether climate change impacts the synoptic wind duration. Historical records, often less than 50 years, are insufficient to calculate the wind duration for threshold wind speeds at a higher return period. Therefore, this study employed 15 long-term hourly wind speed simulations covering most of North America, each of which has 70 years in the past (1050 years in total) and 80 years into a future changing climate (1200 years in total), to investigate the wind durations in the current and future changing climate. It was found that the durations for winds of about 700-year return period are close to the traditionally assumed one hour and have limited effects on the wind loads for the strength design. However, wind durations can be much longer than one hour for the lower return period level wind speeds, which can impact the wind responses for serviceability limit state design and cladding and component (C&C) design. [ABSTRACT FROM AUTHOR]

Wind energy is one of the renewable energies considered by many nations as a strategy to mitigate the impact of climate change. There are also impacts of climate change on wind energy. Previous studies investigated the effect of climate change on wind energy in North America by using future projections with spatial resolutions of about 100 km (i.e., around 1° × 1° simulation grid) and monthly to yearly average wind speeds or a high spatial resolution (< 50 km) but a few simulations (< 5). A coarse resolution can create biases and is insufficient to appreciate extremes. A smaller number of simulations (e.g., < 5) are inadequate for understanding the modeling uncertainties. To better appreciate the impact of climate change on wind energies in a future changing climate, 15 simulations from high-resolution Reginal Climate Models (RCMs) considering the Representative Concentration Pathway (RCP) 8.5 emission scenario were used in the present study. These datasets have a spatial resolution of about 0.4° and a temporal resolution of one hour from 1950 to 2100. The impact of climate change on wind energy was studied on a seasonal and yearly basis. The impact of climate change on design-level wind speeds and structural reliability across North America was also investigated. • The impact of climate change on the annual and seasonal wind energies exhibits large geographical variations across North America. • Seasonal wind energy changes contribute to the annual wind energy changes differently across North America. • Climate change has geographically different impacts on extreme wind climates across North America. • Climate change has a compound impact on wind energy by affecting both wind energy availability and structural safety. [ABSTRACT FROM AUTHOR]

• The conventional return period climatic design values can lead to an increased probability of failure in a strength-increasing future climate. • Periods when the total probability of failure is less than or close to the target vary from half of the design life to the end of the design life. • Nonstationary methods result in the annual probability of failure close to the target at the end of the design life. • The impact of climate change on structural reliability is limited when the principal climatic load effects are not dominant. Extreme wind speeds and ground snow loads for many regions across North America exhibit non-stationarity in projected future climates. The adequacy of conventional return period design values estimated in the past for the future design life needs to be investigated. Nonstationary extreme value analysis methods were used in several previous studies to evaluate the nonstationarity of extreme wind and snow loads based on the latest future projections for Canada in the RCP8.5 (where RCP denotes the representative concentration pathway) emission scenario. These methods have not been considered in nonstationary reliability analyses. This study will examine the effect of including these nonstationary extreme value analysis methods in the reliability analysis. Investigations were conducted by applying the design value estimated in past stationary climate to the reliability analysis considering nonstationary climatic load effects in the future design life. Two non-stationary extreme value analysis methods were then used to determine the design level value in the nonstationary future climates for mitigating the climate change impact. These two approaches target different risk levels. Both nonstationary methods provide design level values greater than the conventional return period values and can maintain the probability of failure close to the target value at the end of the design life. Analyses were also conducted to examine the climate change impact on the structural reliability for considering principal wind load effects or snow load effects with the companion live load effects. [ABSTRACT FROM AUTHOR]

After the recent release of the historical runs by community Earth system model version 2–the whole atmosphere community climate model (CESM2-WACCM), the major sudden stratospheric warming (SSW) events in this model and in its previous version (CESM1-WACCM) are compared based on a modern reanalysis (JRA55). Using the World Meteorological Organization (WMO) definition of SSWs and a threshold-based classification method that can describe the polar vortex morphology, SSWs in models and the reanalysis are further classified into two types, vortex displacement SSWs and vortex split SSWs. The general statistical characteristics of the two types of SSW events in the two model versions are evaluated. Both CESM1-WACCM and CESM2-WACCM models are shown to reproduce the SSW frequency successfully, although the circulations differences between vortex displacement SSWs and vortex split SSWs in CESM2-WACCM are smaller than in CESM1-WACCM. Composite polar temperature, geopotential height, wind, and eddy heat flux anomalies in both the two models and the reanalysis show similar evolutions. In addition, positive Pacific–North America and negative Western Pacific patterns in the troposphere preceding vortex displacement and split SSWs are observed in both observations and the models. The strong negative North Atlantic oscillation-like pattern, especially after vortex split SSW onset, is also identified in models. The near-surface cold Eurasia–warm North America pattern before both types of SSW onset, the warm Eurasia–cold North America pattern after displacement SSW onset, and the cold Eurasia–cold North America pattern after split SSW onset are consistently identified in JRA55, CESM1-WACCM, and CESM2-WACCM, although the temperature anomalies after the split SSW onset in CESM2-WACCM are somewhat underestimated. [ABSTRACT FROM AUTHOR]

Using the historical simulation from the CESM1-WACCM coupled model and based on the JRA55 and NCEP/NCAR reanalyses, the general statistical characteristics of the major sudden stratospheric warmings (SSWs) in this stratosphere-resolving model are assessed. The statistical and diagnostic results show that CESM1-WACCM can successfully reproduce the frequency of SSW events. As in the JRA55 and NCEP/NCAR reanalyses, five or six SSW events, on average, occur in a model decade. The seasonal distribution of SSWs is also well simulated with the highest frequency in January (35%). The unprecedented low SSW frequency observed in 1990s from the two reanalyses is also identified in a model decade (1930s). In addition, the overestimated duration of SSW events in the earlier WACCM version is not identified in CESM1-WACCM when compared with the two reanalyses. The model can well reproduce the downward propagation of the stratospheric anomaly signals (i.e., zonal wind, height, temperature) following SSWs. Both the modelling and observational evidences indicate that SSWs are proceeded by the positive Pacific–North America (PNA) and negative Western Pacific (WP) pattern. The negative North Atlantic Oscillation (NAO) develops throughout the SSW life cycle, which is successfully modeled. A cold Eurasian continent–warm North American continent pattern is observed before SSWs at 850 h Pa, while the two continents are anomalously cold after SSWs in both the reanalyses and the model. [ABSTRACT FROM AUTHOR]

Dictyostelium discoideum is a eukaryotic microbial model system for multicellular development, cell-cell signaling, and social behavior. Key models of social evolution require an understanding of genetic relationships between individuals across the genome or possibly at specific genes, but the nature of variation within D. discoideum is largely unknown. We re-sequenced 137 gene fragments in wild North American strains of D. discoideum and examined the levels and patterns of nucleotide variation in this social microbial species. We observe surprisingly low levels of nucleotide variation in D. discoideum across these strains, with a mean nucleotide diversity (pi) of 0.08%, and no strong population stratification among North American strains. We also do not find any clear relationship between nucleotide divergence between strains and levels of social dominance and kin discrimination. Kin discrimination experiments, however, show that strains collected from the same location show greater ability to distinguish self from non-self than do strains from different geographic areas. This suggests that a greater ability to recognize self versus non-self may arise among strains that are more likely to encounter each other in nature, which would lead to preferential formation of fruiting bodies with clonemates and may prevent the evolution of cheating behaviors within D. discoideum populations. Finally, despite the fact that sex has rarely been observed in this species, we document a rapid decay of linkage disequilibrium between SNPs, the presence of recombinant genotypes among natural strains, and high estimates of the population recombination parameter rho. The SNP data indicate that recombination is widespread within D. discoideum and that sex as a form of social interaction is likely to be an important aspect of the life cycle., Competing Interests: The authors have declared that no competing interests exist.