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SUMMARY: Scots pine (Pinus sylvestris L.) is one of the most widespread and economically important conifer species in the world. Applications like genomic selection and association studies, which could help accelerate breeding cycles, are challenging in Scots pine because of its large and repetitive genome. For this reason, genotyping tools for conifer species, and in particular for Scots pine, are commonly based on transcribed regions of the genome. In this article, we present the Axiom Psyl50K array, the first single nucleotide polymorphism (SNP) genotyping array for Scots pine based on whole‐genome resequencing, that represents both genic and intergenic regions. This array was designed following a two‐step procedure: first, 192 trees were sequenced, and a 430K SNP screening array was constructed. Then, 480 samples, including haploid megagametophytes, full‐sib family trios, breeding population, and range‐wide individuals from across Eurasia were genotyped with the screening array. The best 50K SNPs were selected based on quality, replicability, distribution across the draft genome assembly, balance between genic and intergenic regions, and genotype–environment and genotype–phenotype associations. Of the final 49 877 probes tiled in the array, 20 372 (40.84%) occur inside gene models, while the rest lie in intergenic regions. We also show that the Psyl50K array can yield enough high‐confidence SNPs for genetic studies in pine species from North America and Eurasia. This new genotyping tool will be a valuable resource for high‐throughput fundamental and applied research of Scots pine and other pine species. Significance Statement: In this paper, we present the first high‐throughput single nucleotide polymorphism genotyping array for a pine species developed from whole‐genome resequencing, and thus spanning genic as well as intergenic regions. This array was developed for Scots pine and successfully tested in six other pine species from North America and Eurasia, being useful for fundamental and applied studies in the fields of population genetics, evolution, genomic selection, and breeding. [ABSTRACT FROM AUTHOR]

This paper compares surface signatures of the zonally symmetric and asymmetric modes of stratospheric variability, which describe the strength of the polar vortex and a planetary wave‐1 pattern, respectively. Unlike a weak polar vortex followed by negative Arctic Oscillation–like anomalies, strong stratospheric wave activity features a polar vortex displacement with a deep planetary wave‐1 structure, resulting in positive North Atlantic Oscillation–like North American cooling in about 10 days. Moreover, the linkage between the stratosphere and surface is examined in two reanalyzes and four models of different configurations, which show more robust North American cooling following the displacement of the polar vortex due to strong stratospheric wave activity than the zonally symmetric weakening of the polar vortex. This suggests strong stratospheric wave activity acts as a better predictor for cold spells in the northern U.S. and Canada compared with a weak polar vortex. Plain Language Summary: A weak polar vortex in the winter stratosphere is likely associated with cold spells at the surface, yet there are large uncertainties in predicting surface cold events based on stratospheric signals. This study introduces a new method to separate stratospheric variability into the leading modes of zonally symmetric and asymmetric circulations. The zonally symmetric mode describes the strength of the polar vortex. A weak polar vortex is followed by cooling over northern Eurasia and midlatitude North America. In contrast, the zonally asymmetric mode characterizes a displacement of the polar vortex or a planetary wave‐1 pattern, with the positive phase featuring a high anomaly over North America and a low anomaly over Eurasia. This stratospheric wave pattern extends down to the surface, resulting in North American cooling and Eurasian warming in about 10 days. While both stratospheric modes are associated with surface cooling over North America, the linkage is more robust for the displacement than the zonally symmetric weakening of the polar vortex, based on analyses of several reanalyzes and models. This indicates that strong stratospheric wave activity serves as a better predictor for cold air outbreaks in the northern U.S. and Canada than the commonly used weak polar vortex events. Key Points: Distinct North American cooling signatures follow zonally symmetric and asymmetric modes of the stratosphereStrong stratospheric wave activity precedes positive North Atlantic Oscillation like North American coolingThe linkage between the stratospheric wave activity and the surface is robust in reanalyzes and models [ABSTRACT FROM AUTHOR]

Tropical atmospheric convection generated by the El Niño–Southern Oscillation (ENSO) plays a crucial role in affecting the western Pacific pattern (WP) in the boreal winter by triggering an atmospheric teleconnection. Here we show from analysis of observations and model simulations that the Atlantic Multidecadal Oscillation (AMO) asymmetrically modulates the relationship between ENSO and WP. We find a significant modulatory effect of AMO on the relationship between wintertime El Niño and WP. A robust El Niño−WP relation can be attributed to the negative AMO phase (−AMO), yet a weak relationship during the positive AMO phase (+AMO). In contrast, the relationship between La Niña and WP is independent of AMO modulation. Furthermore, during the −AMO period, stronger El Niño amplitudes lead to stronger atmospheric convection anomalies over the tropical western North Pacific, which excites stronger atmospheric teleconnection and thus has a more significant effect on WP than during the +AMO period. Plain Language Summary: The western Pacific pattern (WP) is one of the most crucial teleconnection patterns in boreal winter over the Northern Hemisphere, which exerts substantial impacts on weather and climate in Eurasia and North America. El Niño–Southern Oscillation (ENSO) is the most prominent air‐sea coupling system in the tropics, considered to exert great impacts on the WP via triggering atmospheric teleconnection. In this study, we revealed that the Atlantic Multidecadal Oscillation (AMO) has a significant asymmetrical modulation on the relation between the ENSO and WP. In particular, a significant El Niño‒WP connection only occurs in the negative AMO phase (‒AMO). Physical mechanisms of the modulation effects of AMO on the ENSO–WP relationship are further analyzed. The results suggest that stronger El Niño amplitude during the −AMO phase leads to larger atmospheric convection anomalies in the equatorial central Pacific and tropical western North Pacific compared to those during the +AMO phase. As such, stronger atmospheric convection anomalies during El Niño events have a greater impact on WP events during the −AMO phase; however, for La Niña events, there is no significant impact on WP events during the −AMO phase. Results obtained in this study may help to improve our understanding of the WP variability. Key Points: The connection between El Niño–Southern Oscillation (ENSO) and the western Pacific pattern (WP) varies markedly in different Atlantic Multidecadal Oscillation (AMO) phasesA robust connection between ENSO and the WP in the boreal winter can only be observed during the negative AMO phaseThe AMO influences the ENSO‐WP relationship via modulating the ENSO amplitude and the associated change in atmospheric convection [ABSTRACT FROM AUTHOR]

Summary: Previous paleobotanical work concluded that Paleogene elements of the sclerophyllous subhumid vegetation of western Eurasia and western North America were endemic to these disjunct regions, suggesting that the southern areas of the Holarctic flora were isolated at that time. Consequently, molecular studies invoked either parallel adaptation to dry climates from related ancestors, or long‐distance dispersal in explaining disjunctions between the two regions, dismissing the contemporaneous migration of dry‐adapted lineages via land bridges as unlikely.We report Vauquelinia (Rosaceae), currently endemic to western North America, in Cenozoic strata of western Eurasia. Revision of North American fossils previously assigned to Vauquelinia confirmed a single fossil‐species of Vauquelinia and one of its close relative Kageneckia.We established taxonomic relationships of fossil‐taxa using diagnostic character combinations shared with modern species and constructed a time‐calibrated phylogeny.The fossil record suggests that Vauquelinia, currently endemic to arid and subdesert environments, originated under seasonally arid climates in the Eocene of western North America and subsequently crossed the Paleogene North Atlantic land bridge (NALB) to Europe. This pattern is replicated by other sclerophyllous, dry‐adapted and warmth‐loving plants, suggesting that several of these taxa potentially crossed the North Atlantic via the NALB during Eocene times. See also the Commentary on this article by Hill & Kahn, 238: 2261–2263. [ABSTRACT FROM AUTHOR]

The regional amplitude and phase characteristics of surface (2 m) air temperature (SAT) annual cycle (AC) over the Northern Hemisphere land area are analysed by the clustering method for the period 1953–2018. The five clusters are found in the nonlinear changes of AC amplitude and the six clusters are found in the AC phase. The spatial distributions of clusters are not the same for amplitude and phase, but the similarity is that both the amplitude and phase have remarkably different trends in the mainland of Eurasia and North America, even though these two regions locate over the similar latitudinal zone. Descending trends of AC amplitude are found for the whole period 1953–2018 in most areas, except in and around Greenland. However, when checking the nonlinear variation and making a piece‐wise linear fit, the abnormal increasing trend (stronger seasonality) appears in the major part of Eurasia after the year 1990. The comparisons of surface radiation fluxes in Eurasia and North America indicate that the long‐term reduction of the reflection and absorption of clouds and aerosols with the declined surface albedo after 1980–1985 may lead to the amplitude amplification after 1990 in Eurasia. In contrast, the variation of surface radiation in North America remains unchanged, where the decreasing trend of amplitude may result from other causes. The overall phase trend is increasing (toward earlier season), but in North America after 1990, the phase shift becomes delayed. The phase variations are correlated to North Atlantic Oscillation (NAO) cold season index over almost all regions, especially in Europe. [ABSTRACT FROM AUTHOR]

This work uses reanalysis and NOAA Geophysical Fluid Dynamics Laboratory's Coupled Model Intercomparison Project 6 model, CM4, to investigate the colocation of heat extremes and atmospheric blocking in the current climate and an end of 21st century, extreme‐emissions projection. In the present day, the colocation of heat events and blocking is greatest for the strongest heat events. Block‐heat extreme colocation is found to be less prevalent over ocean than land, exhibiting regional variation throughout the Northern Hemisphere. Over North America, colocation is greatest near the northwestern and northeastern coasts, minimizing near the center; over Eurasia, colocation is most prevalent in northern regions. In an RCP 8.5 projection, the historical 90th percentile temperature decreases to 0–70th percentile, depending on the region. This is primarily driven by mean state warming. Blocking is found to decrease along with the colocation of blocking and heat extremes, suggesting that in some regions, the mechanisms driving heat extremes will change in future climates. Plain Language Summary: This work investigates extreme heat events and atmospheric blocks (persistent high‐pressure systems), which are known to be strongly linked. The analysis herein shows that the strongest extreme heat events coincide with atmospheric blocks, however, the likelihood of the events being colocated varies from region to region. In a high emissions warming scenario, temperatures exceeding the warmest 10% in the current climate, occur 30%–100% of the time depending on the region. This is mostly driven by an increase in average temperature everywhere—rather than an increase in the variability of the temperature. At the same time, the model predicts that blocking, and the colocation of extremes heat events with blocking, decreases, suggesting the physical drivers of heat extremes will change in a warmer climate. Key Points: Blocking is more colocated with heat extremes over land than ocean. Stronger heat extremes are more colocated with blockingEnd of 20th century 90th percentile temperatures become 0–70th percentile by the end of the 21st century in a high emissions scenarioLand heat extreme duration is unchanged in RCP 8.5, but colocated blocking decreases, suggesting changes in dynamics driving heat extremes [ABSTRACT FROM AUTHOR]

The Arctic stratospheric polar vortex is an important driver of winter weather and climate variability and predictability in North America and Eurasia, with a downward influence that on average projects onto the North Atlantic Oscillation (NAO). While tropospheric circulation anomalies accompanying anomalous vortex states display substantial case‐by‐case variability, understanding the full diversity of the surface signatures requires larger sample sizes than those available from reanalyses. Here, we first show that a large ensemble of seasonal hindcasts realistically reproduces the observed average surface signatures for weak and strong vortex winters and produces sufficient spread for single ensemble members to be considered as alternative realizations. We then use the ensemble to analyze the diversity of surface signatures during weak and strong vortex winters. Over Eurasia, relatively few weak vortex winters are associated with large‐scale cold conditions, suggesting that the strength of the observed cold signature could be inflated due to insufficient sampling. For both weak and strong vortex winters, the canonical temperature pattern in Eurasia only clearly arises when North Atlantic sea surface temperatures are in phase with the NAO. Over North America, while the main driver of interannual winter temperature variability is the El Niño–Southern Oscillation (ENSO), the stratosphere can modulate ENSO teleconnections, affecting temperature and circulation anomalies over North America and downstream. These findings confirm that anomalous vortex states are associated with a broad spectrum of surface climate anomalies on the seasonal scale, which may not be fully captured by the small observational sample size. Plain Language Summary: The strength of the winds in the stratosphere over the Arctic provides useful information for seasonal forecasts of wintertime weather over Europe and North America. When we study these linkages, it is a challenge that we have few winters—only about 40—with reliable observations from the stratosphere. Here, we use data from a seasonal forecast model to generate a large collection of 3,000 possible winters, and we use these to examine different patterns of surface temperature and sea level pressure for winters with the strongest and weakest winds in the polar stratosphere. Some real‐world episodes have attracted wide attention, including recent cold winters linked to weak stratospheric winds, and there seems to be an anticipation that weak winds in the stratosphere are synonymous with extremely cold weather in many regions. However, our results indicate that these expected surface signatures are in fact not particularly common. There are also scenarios when instead the opposite surface signature emerges. We find that it is not sufficient to know the state of the stratosphere; regional sea surface temperatures can either support or counteract the stratospheric influence on winter weather in any given year. Key Points: The broad spectrum of surface signatures of stratospheric polar vortex anomalies is obscured by the small observational sample sizeA large ensemble indicates the observed magnitude of negative North Atlantic Oscillation and related surface anomalies during weak vortex winters may be inflatedOver North America the main driver of winter temperature variability is El Niño–Southern Oscillation (ENSO), but the stratosphere can modulate ENSO teleconnections [ABSTRACT FROM AUTHOR]

The lower incisor enamel microstructure of the fossil rodent family Eomyidae was believed to be three‐layered and highly derived but rather uniform throughout the clade. Here, we describe a new four‐layered schmelzmuster in Eomyidae consisting of a three‐fold portio interna with longitudinal oriented, uniserial Hunter‐Schreger bands and a one‐fold portio externa, accounting for a unique enamel microstructure character combination in Rodentia. This new schmelzmuster type has developed early in eomyid evolution and is detectable already in the late Eocene (Chadronian) of North America. In European eomyids, it first occurs in the early Miocene (MN 3), implying that this four‐layered schmelzmuster was not present in all members of the family but restricted to species included in Eomyini and some genera currently considered Eomyidae incertae sedis within Eomyidae. Additionally, our analysis recognizes three taxa with schmelzmuster divergent from all other eomyids. Incisor enamel microstructure does not advocate a close phylogenetic relationship of Eomyidae to either fossil or extant Heteromyidae and Geomyidae, nor to fossil Heliscomyidae and Florentiamyidae. Our results rather support the view that Eomyidae are placed outside Geomorpha. [ABSTRACT FROM AUTHOR]

Temporal evolution of relationships between surface temperature and modes of low‐frequency circulation variability is compared between five reanalyses (20CRv3, 20CRv2c, ERA‐20C, JRA‐55, and NCEP‐1) in winter from 1958 to 2010 over the northern Extratropics. The relationships are evaluated using 15‐year running correlations between temperature anomalies (from the CRU TS v. 4.03 data set) and the intensity of circulation modes (detected in 500 hPa heights by rotated principal component analysis). The analysis, utilizing mean absolute differences between time series of running correlations, points to the large agreement between ERA‐20C, JRA‐55, and NCEP‐1. Circulation modes in those reanalyses are highly similar, which in turn lead to the agreement in temporal development of correlations. In contrast, relationships of some circulation modes with temperature in 20CRv3 and 20CRv2c differ due to differences in the position, strength, and shape of the action centres. This concerns circulation modes located over Eurasia and the Atlantic, mainly North Atlantic Oscillation and Eurasian mode type 1 (EU1). Composite maps, calculated for all running periods, indicate dissimilar temporal evolution of action centres in both 20CR reanalyses. Increased differences in correlations occur mainly during periods when the position and strength of action centres diverge the most. Relationships of circulation modes located over North America and the Pacific with temperature share large resemblance between all reanalyses, including those from the 20CR family. Differences appear to be smaller in 20CRv3 compared to the preceding version, 20CRv2(c), suggesting that the development of the 20CR reanalysis has succeeded in correcting and diminishing biases. [ABSTRACT FROM AUTHOR]

To investigate the evolutionary relationships and biogeographical history among the species of Calamagrostis and other members of subtribes Agrostidinae, Calothecinae, Echinopogoninae, and Paramochloinae, we generated a phylogeny based on DNA sequences from one nuclear ribosomal (ITS) and three plastid regions (rpl32‐trnL spacer, rps16‐trnK spacer, and rps16 intron). Based on our phylogeny, we identified seven species groups (clades) within Calamagrostis: the Meridionalis group comprises two species from Central and South America, the Americana group comprises species from North America, the Deyeuxia and Epigeios groups comprise species from Eurasia, the Orientalis group comprises species from East Asia, the Purpurea group comprises species from Eurasia and North America, and the Calamagrostis group comprises species from Eurasia and North America. We hypothesize that Calamagrostis originated in North America with the primary split of the Meridionalis group, followed by split between the autochthonous Americana group and two future Eurasian branches encompassing all the remaining groups, which possibly dispersed into Eurasia independently. The molecular data suggest that hybridization and genomic introgression played a prominent role in the evolutionary history of Calamagrostis. We propose a new genus, Condilorachia, segregated from Trisetum s.l., with three species from South America for which we propose new combinations: Condilorachia bulbosa, Condilorachia brasiliensis, and Condilorachia juergensii; a new combination in Greeneochloa, Greeneochloa expansa; and the subsumption of Dichelachne into Pentapogon with 20 new combinations: Pentapogon avenoides, Pentapogon brassii, Pentapogon chaseianus, Pentapogon crinita, Pentapogon densus, Pentapogon frigidus, Pentapogon gunnianus, Pentapogon hirtella, Pentapogon inaequiglumis, Pentapogon lautumia, Pentapogon micrantha, Pentapogon parva, Pentapogon quadrisetus, Pentapogon rara, Pentapogon robusta, Pentapogon scaberulus, Pentapogon sclerophyllus, Pentapogon suizanensis, Pentapogon sieberiana, and Pentapogon validus. We provide a diagnosis, description, and a key to the species of Condilorachia. [ABSTRACT FROM AUTHOR]