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In this study, we obtained the first leading mode and principal component 1 (PC1) of North Pacific sea surface temperature (SST). The PC1‐related SST anomalies, located relatively north/south, are referred to as North/South PC1 events. Model outputs, observations, reanalysis datasets and sensitivity experiments show that during the North PC1 events, an enhanced Aleutian low occurs and is located relatively north, favoring anomalous southerlies over western North America. The anomalous southerlies induce a strong warming anomaly over North America via warm advection of the anomalous southerlies and temperature advection of the climatological westerlies over North America. However, the Aleutian low anomaly and corresponding southerly anomaly associated with South PC1 events shift southward, favoring weakened effects of South PC1 events on atmospheric circulations and surface temperatures over North America. The meridional position of PC1 events deserves to be considered in the studies of the PC1 and its related climate changes. Plain Language Summary: Understanding of surface temperature variations is important since it largely affects human and society. This paper categorizes the North Pacific sea surface temperature anomaly events, which are associated with the first leading mode of North Pacific sea surface temperature, into North and South events according to their meridional positions. Using model outputs, observations, reanalysis datasets and sensitivity experiments, we found that the surface temperature anomalies over North America during the North events are quite different from those during the South events. During the North events, an enhanced Aleutian low occurs over high‐latitude North Pacific. The enhanced Aleutian low tends to induce anomalous southerlies over western North America. The anomalous southerlies favor warming anomalies over North America via the warm advection of anomalous southerlies and temperature advection of climatological westerly. However, the Aleutian low anomaly and meridional wind anomaly during the South events shift southward, leading to weakened effects of the South events on atmospheric circulations and surface temperatures over North America. Key Points: North American warming anomaly occurs during North Pacific sea surface temperature anomaly events located northThe warming anomaly is related to an enhanced Aleutian low anomaly located north and climatological westerlyDuring the events located south, North American surface temperature responses are weak due to a southward‐shift Aleutian low anomaly [ABSTRACT FROM AUTHOR]

The lack of evidence for large‐scale glacial landscapes on Mars has led to the belief that ancient glaciations had to be frozen to the ground. Here we propose that the fingerprints of Martian wet‐based glaciation should be the remnants of the ice sheet drainage system instead of landforms generally associated with terrestrial ice sheets. We use the terrestrial glacial hydrology framework to interrogate how the Martian surface gravity affects glacial hydrology, ice sliding, and glacial erosion. Taking as reference the ancient southern circumpolar ice sheet that deposited the Dorsa Argentea formation, we compare the theoretical behavior of identical ice sheets on Mars and Earth and show that, whereas on Earth glacial drainage is predominantly inefficient, enhancing ice sliding and erosion, on Mars the lower gravity favors the formation of efficient subglacial drainage. The apparent lack of large‐scale glacial fingerprints on Mars, such as drumlins or lineations, is to be expected. Plain Language Summary: Water accumulates under ice masses, including glaciers and ice sheets, lubricating the base of the ice and accelerating ice motion. On Earth, this glacial motion has produced scoured landscapes in northern Europe and North America. Mars lacks such large‐scale glacial erosion even in areas with other signs of widespread glaciation. This paper uses the existing framework describing the physical interactions of water and ice, and how they affect ice motion, to show that a lack of landforms recording glacial erosion is expected even if glaciation were widespread on Mars. Key Points: Glacial hydrology feedback dynamics can explain the lack of glacial sliding on the Martian geological recordSubglacial water drainage develops faster, and is more resilient under lower Martian gravityThe fingerprints of Martian wet‐based glaciation are predicted to be channels and eskers [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]

Precipitation changes in full response to CO2 increase are widely studied but confidence in future projections remains low. Mechanistic understanding of the direct radiative effect of CO2 on precipitation changes, independent from CO2‐induced SST changes, is therefore necessary. Utilizing global atmospheric models, we identify robust summer precipitation decreases across North America in response to direct CO2 forcing. We find that spatial distribution of CO2 forcing at land surface is likely shaped by climatological distribution of water vapor and clouds. This, coupled with local feedback processes, changes in convection, and moisture supply resulting from CO2‐induced circulation changes, could determine North American hydroclimate changes. In central North America, increasing CO2 may decrease summertime precipitation by warming the surface and inducing dry advection into the region to reduce moisture supply. Meanwhile, for the southwest and the east, CO2‐induced shift of subtropical highs generates wet advection, which might mitigate the drying effect from warming. Plain Language Summary: How precipitation changes in full response to increased CO2 remains unclear. Mechanistic understanding of how increasing CO2 alone changes precipitation can help us better predict future precipitation in full response to CO2 increase. We find that the precipitation responses are much stronger during summer than winter in North America. During summer, precipitation significantly decreases in central North America in response to the direct CO2 radiative effect, while in the southwest and the east, precipitation changes are small. There might be stronger longwave radiation forcing near the surface induced by CO2 increase in arid regions due to weaker masking effect of water vapor and clouds. This, along with local feedbacks, significantly warms the central region. Meanwhile, the direct forcing of CO2 induces northward shifts in subtropical highs, consequently generating anticyclonic anomalies. These wind anomalies result in drier air advected into central North America, leading to moisture divergence and hence reducing moisture supply. The reduced water supply, coupled with the warming, may decrease precipitation in the region. For the southwest and the east, the anticyclonic anomalies cause wetter air advected into the regions and generate moisture convergence, which increases moisture supply and might mitigate the drying effect caused by CO2‐induced warming. Key Points: Robust precipitation decreases during summer in response to CO2 direct radiative effect are identified in central North AmericaClimatology and changes of hydrological environment may collectively modulate the regional CO2 radiative effect on summer precipitationCO2‐induced circulation changes could alter the moisture supply to reshape the regional hydrological cycle [ABSTRACT FROM AUTHOR]

The crustal evolution of the southernmost ∼2000–1800 Ma Trans‐Hudson orogen (THO) is enigmatic due to burial by Phanerozoic sediments. We provide new insights through petrochronologic analysis of a paragneiss drill core sample. Detrital zircon age peaks at 2625, 2340, and 1880 Ma and Hf isotopes suggest Paleoproterozoic arc development proximal to Archean source(s). Phase equilibria modeling and ternary feldspar thermometry suggest peak conditions of ≥1 GPa, ≥900°C, the first recognition of extreme, ultra‐high temperature metamorphism in the THO. The largely isobaric P‐T path, rapid heating rate, and ∼20 Myr duration (1872–1850 Ma) of peak conditions suggest that this metamorphism occurred in a back‐arc tectonic setting. The sample records post‐peak (1850–1815 Ma) mid‐crustal residence, slow cooling, and exhumation. Further retrogression occurred during Proterozoic regional exhumation (1630–1470 Ma) and Phanerozoic (360–220 Ma) reheating and/or fluid influx. Evidence for Paleoproterozoic arc(s) supports geophysical data for Archean cratonic and Paleoproterozoic arc crust in this region. Plain Language Summary: The Trans‐Hudson orogeny was a Himalayan‐scale collisional mountain building event approximately 1.8 billion years ago that formed the core of North America. The southern portion of the Trans‐Hudson orogen (THO) is poorly understood because it is almost entirely buried by younger rocks. It is unknown whether the southern THO is underlain by Archean or Proterozoic crust. The timing, conditions, and setting of high‐grade metamorphism in this region are also poorly known. We carried out petrologic, geochemical, and geochronologic analyses on a metasedimentary rock sample recovered from drill core. Detrital zircon and tracer isotopic data show derivation from both Paleoproterozoic and Archean sources. This suggests that Paleoproterozoic magmatic arc(s) developed on or near Archean crust. The rock sample experienced extreme temperatures (≥900°C, ≥1 GPa) and partial melting between approximately 1870 and 1850 million years ago perhaps in a back‐arc tectonic setting. This marks the first recognition of extreme, ultra‐high temperature metamorphism in the THO. Later retrograde metamorphism occurred in the Mesoproterozoic and Phanerozoic. These constraints provide new understanding of the enigmatic southern THO and highlight the ability of a combined petrologic, geochemical, and geochronologic study to extract a comprehensive record of crustal evolution from a single sample. Key Points: Paleoproterozoic arc(s) buried beneath North Dakota developed proximal to, or on, Archean craton(s)Metamorphic temperatures of >900°C are the first recognition of ultra‐high temperature (UHT) metamorphism in the Trans‐Hudson orogenBack‐arc setting for UHT metamorphism indicated by isobaric P‐T path and short timescales of heating and peak conditions [ABSTRACT FROM AUTHOR]

ENSO's atmospheric teleconnections drive anomalous North Pacific sea surface temperatures through changes in surface heat fluxes ("the atmospheric bridge"). Previous research focusing on the bridge as a seasonal phenomenon did not consider how ENSO‐related changes in synoptic variability might also impact surface turbulent heat fluxes (STHF). In this study, we find that while well over half of ENSO's impact on STHF occurs on low‐frequency (>8 days) time scales, up to 20% of its impact arises on high‐frequency (<8 days) time scales, through changes in the covariance between surface wind speed and air‐sea enthalpy difference that typically warms the ocean south of the storm track. During El Niño, the North Pacific storm track and its attendant sea surface warming shift southward, reducing warming of the central North Pacific ocean and thereby enhancing the bridge signal there. Additionally, changes in the bulk formula coefficients between ENSO phases drive STHF differences (5%–10%). Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) has global impacts through teleconnections, which can influence the underlying ocean via the "atmospheric bridge." The atmospheric bridge results in upward surface heat flux and colder sea surface temperature (SST) over the central North Pacific and downward surface heat flux and warmer SST along the coast of North America during El Niño winters. While previous research has studied the influence of longer timescale features on this bridge‐related surface heat flux pattern, the corresponding impact of shorter timescale variability remains unexplored. We find that while longer timescales (>8 days) dominate, shorter timescale influence on the fluxes is non‐negligible. Shorter timescale variability warms the ocean south of the track of North Pacific storms. This warming contribution shifts with the storm location between the two ENSO phases. While the resulting difference between ENSO phases is small, it is mostly aligned with the total surface turbulent heat flux (STHF) difference between El Niño and La Niña. Also, the bulk formula coefficients used to compute the fluxes vary, leading to 5%–10% of the STHF difference between ENSO phases. In summary, the contribution of shorter timescale variability and coefficient changes to the North Pacific bridge‐related STHF is small but non‐negligible. Key Points: While seasonal variability dominates ENSO‐related surface turbulent heat fluxes over the North Pacific, synoptic effects are non‐negligibleENSO‐related storm track shift affects the high‐frequency contribution to the turbulent heat fluxesDifferences in the bulk formula coefficient between two ENSO phases have a small but non‐negligible influence on the surface heat fluxes [ABSTRACT FROM AUTHOR]

In boreal winter, the El Niño/Southern Oscillation (ENSO)‐induced Pacific‐North American (PNA) teleconnection pattern is farther westward during La Niña relative to that in El Niño, causing discernible distinct climate implications. However, there has been a lack of consensus regarding the underlying mechanism driving this asymmetric structure. This study highlights the contribution of nonlinear kinetic energy advection (nKA) to this asymmetry. The zonally symmetric responses to ENSO, specifically the anomalies in zonal mean zonal flow, generate opposing nKA patterns by advecting anomalous eddy kinetic energy in the North Pacific, which leads to the shift of the PNA teleconnection pattern. In addition to nKA, transient eddy activities responded to changes of baroclinicity help maintain the asymmetry through a feedback effect. These findings underscore the importance of considering extratropical factors, such as nonlinear energy processes and synoptic‐scale transient eddies, in understanding the mechanism responsible for the asymmetric structure of the PNA teleconnection pattern. Plain Language Summary: The El Niño/Southern Oscillation (ENSO)‐induced atmospheric anomalies over the North Pacific and North America (PNA region) are more westward during La Niña relative to that during El Niño in boreal winter. The disparity of atmospheric responses causes discernible distinct climate implications, and limits the seasonal prediction. The mechanism underlying this asymmetry, however, remains in disagreement. Some believe that it is due to variations in the location of tropical convective anomalies. Whereas others show that the climatological zonal flow could anchor the disturbance. Utilizing a more comprehensive energy diagnostic framework, we find that the nonlinear component, in particular, the nonlinear kinetic energy advection and the feedback effect of synoptic‐scale disturbances contribute to the asymmetric atmospheric responses. The study emphasizes the importance of nonlinear processes and multi‐scale interactions in the asymmetric structure of ENSO‐induced atmospheric anomalies in the PNA region, which are essential for understanding ENSO teleconnections, comprehending model biases, and improving seasonal predictions. Key Points: The El Niño/Southern Oscillation‐induced Pacific‐North American (PNA) teleconnection pattern is farther westward during La Niña relative to that in El NiñoThe nonlinear energy advection redistributes the kinetic energy, hence contributing to the asymmetric PNA teleconnectionsDifferent synoptic‐scale transient eddy activities help to maintain and amplify the asymmetry through a feedback effect [ABSTRACT FROM AUTHOR]

SNOwpack TELemetry observations and model simulations both demonstrate that the fractional contribution of October through December (early season) snowfall to peak snow accumulation in North America increases with latitude due to both colder temperatures and Pacific storm tracks focusing further north earlier in the season. Early season snowfall also makes up greater than 60 percent of peak accumulation in interior low‐precipitation locations leeward of mountains, particularly those that are subject to strong, warm winds and midwinter snow loss. Early season snow observations show promise in predicting peak snow water equivalent in locations where large‐scale ocean‐atmosphere patterns similarly influence fall and winter conditions, and in northern maritime locations where winter temperatures are warm enough that rain on snow and midwinter melt occur. Because climate change is likely to increase the extent of midwinter melt, the latter relationship is expected to become important over more locations in the future. Plain Language Summary: Across North America, snow accumulates from October until the following spring. Early season snow, defined as the snow that accumulates by the end of December, is a greater fraction of total snow accumulation at higher latitudes and at colder locations. Early season snow accumulation can be used to predict peak snow accumulation. Predictions are more skillful at locations where fall precipitation is correlated with winter precipitation because more snow at the end of December indicates that weather patterns are favorable for greater than average snowfall to continue. Predictions also have skill at warmer northern locations where more snow on the ground early season increases the likelihood that mixed rain‐snow events add water to the snowpack rather than melting the snow. Predictions at warm southern locations do not have skill because winter and spring snowfall is highly variable, and frequently little to no snow has accumulated by the end of December. Key Points: Fall snow contributes more to peak snow at colder and more northerly locationsFall snow can be used to predict peak snow where large scale ocean and atmosphere patterns influence annual snowfall variationsFall snow regulates cold content, which in warm regions may tip a snowpack between lasting or ablating midwinter, influencing peak snow [ABSTRACT FROM AUTHOR]

In recent decades, severe cold winters and springs have frequently occurred over mid‐latitude North America, despite the anthropogenic global warming trend. In this study, we reveal a possible mechanism by investigating the teleconnection between tropical oceans and North America. Through observational analysis and numerical experiments, we reveal that an anomalous tropical Atlantic warming can trigger a cold spring over central‐western mid‐latitude North America. The tropical Atlantic warming intensifies regional deep atmospheric convection and generates a stationary Rossby wave train propagating poleward, forming an anomalous low pressure center over the mid‐latitude North Atlantic. This low‐level circulation adjustment further intensifies the cold advection and increases the cloud cover over central‐western North America, cooling the surface through cloud radiative feedback. The mechanisms revealed in this study may contribute to the improvement of predictability of cold springs over North America, and have broad implications for agriculture production, power supply, and public health. Plain Language Summary: North America has experienced a series of cold springs in recent decades, even under the background of global warming. These cold springs have large impacts on transportation, agriculture, power supply, and public health. In this study, we find that anomalous cold springs over mid‐latitude North America are tightly associated with the tropical Atlantic variability. In particular, an increase in the tropical Atlantic temperature of 1°C may induce up to 4°C decrease over central‐western North America. Further investigation based on observational analysis and numerical model experiments reveals the pathway of this linkage. The tropical Atlantic warming triggers planetary waves, forming an anticlockwise circulation anomaly over the mid‐latitude North Atlantic. This circulation adjustment transports cold air from the higher‐latitudes to central North America. It meanwhile transports more moisture from the North Atlantic to central‐western North America and increases cloud cover, which reflects the solar radiation and further cools the land surface. While previous studies focus on the impacts of Arctic amplification and tropical Pacific variabilities on cold winters/springs over North America, this work highlights the importance of the tropical Atlantic in triggering North American cold springs. Key Points: Sea surface temperature warming over the tropical Atlantic can induce a cold spring over mid‐latitude North AmericaTropical Atlantic warming can trigger a cyclonic circulation anomaly over the mid‐latitude North Atlantic through Rossby wave dynamicsAtmospheric circulation adjustment further drives North American cooling through cold advection and cloud radiative feedback [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]

Subsidence after a subduction zone earthquake can cause major changes in estuarine bathymetry. Here, we quantify the impacts of earthquake‐induced subsidence on hydrodynamics and habitat distributions in a major system, the lower Columbia River Estuary, using a hydrodynamic and habitat model. Model results indicate that coseismic subsidence increases tidal range, with the smallest changes at the coast and a maximum increase of ∼10% in a region of topographic convergence. All modeled scenarios reduce intertidal habitat by 24%–25% and shifts ∼93% of estuarine wetlands to lower‐elevation habitat bands. Incorporating dynamic effects of tidal change from subsidence yields higher estimates of remaining habitat by multiples of 0–3.7, dependent on the habitat type. The persistent tidal change and chronic habitat disturbance after an earthquake poses strong challenges for estuarine management and wetland restoration planning, particularly when coupled with future sea‐level rise effects. Plain Language Summary: The land in many estuaries along the Pacific Rim has been repeatedly changed by major earthquakes. Previous earthquakes, such as the CE 1700 rupture along the 1,000‐km Cascadia Subduction Zone of western North America, produced as much as 2 m of land‐surface lowering. This study employs a hydrodynamic model to show that the relative sea‐level rise resulting from such lowering would increase tidal range and affect nearly all existing wetland habitat in the lower Columbia River Estuary. In our primary scenario, approximately ∼93% of current wetland habitat converts to lower‐elevation types, with changes largely due to land‐surface lowering but also influenced by tidal changes. Thus, the chronic, long‐term disturbance to habitat conditions after an earthquake poses a similar long‐term risk to estuarine ecology as extreme global sea‐level rise scenarios. Understanding such earthquake effects may assist the development of more resilient habitat restoration strategies. Key Points: Earthquake‐induced subsidence results in the movement of ∼93% of intertidal habitat to lower habitat zonesPost earthquake, tidal range increases by up to 0.25 m in channels; capturing such changes requires a dynamic modelBoth subsidence and changes in tidal range alter habitats, especially sandflats and low marshes [ABSTRACT FROM AUTHOR]

Our understanding of Earth's paleogeography relies heavily on paleomagnetic apparent polar wander paths (APWPs), which represent the time‐dependent position of Earth's spin axis relative to a given block of lithosphere. However, conventional approaches to APWP construction have significant limitations. First, the paleomagnetic record contains substantial noise that is not integrated into APWPs. Second, parametric assumptions are adopted to represent spatial and temporal uncertainties even where the underlying data do not conform to the assumed distributions. The consequences of these limitations remain largely unknown. Here, we address these challenges with a bottom‐up Monte Carlo uncertainty propagation scheme that operates on site‐level paleomagnetic data. To demonstrate our methodology, we present an extensive compilation of site‐level Cenozoic paleomagnetic data from North America, which we use to generate a high‐resolution APWP. Our results demonstrate that even in the presence of substantial noise, polar wandering can be assessed with unprecedented temporal and spatial resolution. Plain Language Summary: Records of Earth's ancient magnetic field preserved in rocks provide valuable information for understanding past tectonic plate motions. These "paleomagnetic" records are collected from individual rock samples and subsequently grouped to develop global‐scale paths called apparent polar wander (APW) paths. However, the standard methods for analyzing and grouping paleomagnetic data are limited in the way they propagate and quantify uncertainties, and the consequences of these limitations are not known. In this study, we address these limitations through the introduction of a new methodological approach, which we use to study a large data set of paleomagnetic data from North America for the past 60 million years. We demonstrate that through our new methodology it is possible to generate APW paths with unprecedented spatial and temporal resolution, which may offer new insights into Earth's deep time evolution. Key Points: We present an extensive compilation of Cenozoic paleomagnetic and geochronologic data from North America at the site levelA bottom‐up Monte Carlo uncertainty propagation scheme enables the propagation of errors from site level data into apparent polar wander pathsThese advances allowed us to describe Cenozoic North American polar wander at the unprecedented temporal resolution of 1 Myr [ABSTRACT FROM AUTHOR]

Winter cold spells over North America have been correlated with European wind extremes, but the physical mechanisms behind such "pan‐Atlantic" compound extremes have not been clarified yet. In this study, we propose that pan–Atlantic cold and windy extremes occur following two possible dynamical pathways. The first one involves the propagation of a Rossby wave train from the Pacific Ocean, associated with windstorms over north‐western Europe in the 5–10 days after the cold spell peak. The second is associated with a high‐latitude anticyclone over the North Atlantic and an equatorward‐shifted jet, leading to windstorms over south‐western Europe already in the days preceding the cold spell peak. European windstorms are thus systematically tied to North American cold spells according to the different flow configuration. The analysis underscores that apparently similar surface extremes might be driven by different processes, and conflating them together could lead to misleading conclusions. Plain Language Summary: Previous research noticed that cold spells over North America and windstorms over Europe tend to occur within a few days of each other. This connection is supported by the fact that winds usually blow from west to east over the North Atlantic, so that cyclones forming off the coast of North America move toward western Europe. However, the chain of processes behind this connection remained not fully clarified. Here we explain the complex relationship between the occurrence of North American cold spells and European windstorms. While previous work tried to identify a single physical mechanism, we suggest that two separate pathways can connect the two types of extremes. The first pathway involves the propagation of a train of cyclones and anticyclones from the North Pacific to the North Atlantic, leading to a cold spell over central North America and, a few days later, to windstorms over north‐western Europe. The second pathway, on the other hand, involves an anomalous anticyclone over the North Atlantic, which acts to induce cold spells over North America and windstorms over south‐western Europe roughly at the same time: this still leads to a correlation between the two extremes, but without a clear causality direction. Key Points: North American cold extremes and European windy extremes can be connected physically by two distinct dynamical pathwaysThe first pathway involves Rossby wave propagation from the North Pacific and the cold spell preceding the European windstormThe second pathway features both extremes occurring roughly at the same time thanks to an upper‐level anticyclone west of Greenland [ABSTRACT FROM AUTHOR]

The El Niño‐Southern Oscillation (ENSO) influences climate variability across the globe. ENSO is highly predictable on seasonal timescales and therefore its teleconnections are a source of extratropical forecast skill. To fully harness this predictability, teleconnections must be represented accurately in seasonal forecasts. We find that a multimodel ensemble from five seasonal forecast systems can successfully capture the spatial structure of the late winter (JFM) El Niño teleconnection to the North Atlantic via North America, but the simulated amplitude is half of that observed. We find that weak amplitude teleconnections exist in all five models throughout the troposphere, and that the La Niña teleconnection is also weak. We find evidence that tropical forcing of the El Niño teleconnection is not underestimated and instead, deficiencies are likely to emerge in the extratropics. We investigate the impact of underestimated teleconnection strength on North Atlantic winter predictability, including its relevance to the signal‐to‐noise paradox. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) describes the cycle of warmer and cooler sea surface temperatures in the tropical Pacific Ocean, which influences climate around the globe. The high heat capacity of the ocean means that ENSO changes relatively slowly and so the ENSO phase—known as El Niño or La Niña—can be predicted with high accuracy several months ahead. Far‐flung influences—known as teleconnections—of ENSO can provide predictability away from the tropics in seasonal forecasts if they are accurately modeled. In this work, the late winter (January–March) ENSO teleconnection to the North Atlantic, traveling via the North Pacific and North America, is investigated in five forecast models. We find that in each model, the pattern of the teleconnection is accurately captured, but the strength of the modeled teleconnection is half of that in the real world. We find that the strength of processes in the tropics which cause the El Niño teleconnection—including changes in sea surface temperatures and rainfall—are not underestimated by models, meaning that the problem arises further along the pathway to the extratropics. This error likely contributes to the currently unresolved "signal to noise paradox" in climate forecasts. Key Points: Seasonal forecasts severely underestimate the response to El Niño‐Southern Oscillation (ENSO) in the extratropical North PacificThe underestimated model response exists throughout the troposphere and is present for both El Niño and La NiñaTropical processes which generate the El Niño teleconnection are well predicted and so the error does not appear to originate in the tropics [ABSTRACT FROM AUTHOR]

Separating the climate response to external forcing from internal climate variability is a key challenge. While most previous studies have focused on surface responses, here we examine zonal‐mean patterns of North Pacific subsurface temperature responses. In particular, the changes since 1950 driven by anthropogenic aerosol emissions are found by using a pattern recognition method. Based on the single‐forcing large‐ensemble simulations from two models, we show that aerosol forcing caused a nonmonotonic temporal response and a characteristic zonal‐mean pattern within North Pacific, which is distinct from the pattern associated with internal variability. The aerosol‐forced pattern with the nonmonotonic temporal feature shows a substantial temperature change in subpolar regions and a reversed change on the southern flank of the subtropical gyre. A similar characteristic pattern and nonmonotonic time evolution are extracted from the subsurface observations, which likely reflect the subsurface responses to the aerosol forcing, although differences exist with the simulated responses. Plain Language Summary: Pacific climate has long been of interest as considerable evidence has emerged of a decades‐long change. As the background noise, such as Interdecadal Pacific Oscillation and El Niño‐Southern Oscillation, is very strong in the Pacific, it remains a major challenge to detect and understand the changes due to human activities. In this study, we take advantage of a pattern recognition method to investigate the North Pacific subsurface temperature response to aerosol emissions, a suspension of fine particles in air, due to industrial development. The results are primarily based on two sets of model simulations with different phases of background noise and identical external forcing, which stems from anthropogenic aerosol emissions only. We find that the aerosol emissions from North America and Europe cause a clear nonmonotonic time evolution (increased during 1950–1985 and then decreased afterward) and a characteristic zonal mean pattern of the subsurface ocean temperature within the North Pacific. The extracted temporal and spatial features from ocean observations are broadly consistent with those from models, although there are some differences. Key Points: A pattern recognition method is applied to extract aerosol‐induced subsurface temperature pattern from internal variability in North PacificBased on two large‐ensemble simulations, aerosols govern a nonmonotonic feature in temperature change with a characteristic patternThis spatiotemporal feature can be obtained from observations since 1950, although there are some differences with the modeled results [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]

Climate model hindcasts are analyzed to reveal the impacts of the North Atlantic Oscillation (NAO) on the North Atlantic subpolar ocean, which exhibits variability on seasonal to decadal timescales. The ocean response to a single winter NAO event is separated into fast and slow responses. The fast response persists over winter–spring seasons, during which wind stress and heat flux anomalies associated with the NAO rapidly modify ocean temperatures via changes in Ekman transport and ocean‐atmosphere heat exchanges. The slow response persists for 3–4 years, during which overturning and gyre circulations redistribute opposing‐signed surface temperature anomalies created by the NAO. This redistribution modifies east‐west temperature contrasts altering the meridional heat transport associated with gyres and changing the strength of the overturning circulation. Hence, the fast and slow responses lead to opposing‐signed subpolar temperature anomalies in time from the competing effects of local forcing and horizontal heat convergence. Plain Language Summary: The North Atlantic Oscillation (NAO) index is one of the most common metrics to characterize atmospheric regimes in the northern hemisphere, revealing how different patterns of atmospheric winds and air‐sea fluxes over Europe and North America affect the ocean state. In the present research, coupled climate model simulations are utilized to study the impacts of particular atmospheric events on the subpolar North Atlantic Ocean. Using NAO indices during the winter season, sets of multiple simulations having similar types of atmospheric events are created to carry out a composite analysis. The analyses reveal that the impact of atmospheric events on the oceans can last up to 4–5 years (or even longer in some cases). The fast response is controlled by the effect of the local winds and air‐sea heat fluxes, while the slow response is related to the role of the meridional overturning circulation and ocean gyres in transporting heat anomalies from the subtropics to the subpolar ocean. The combination of these fast and slow responses leads to the sign reversal of the subpolar surface temperature anomalies in time. Key Points: Subpolar ocean changes due to the North Atlantic Oscillation (NAO) are separated into competing fast, seasonal and slow, inter‐annual responsesFast response is related to the anomalous Ekman transport and air‐sea heat exchange associated with the NAOSlow response is due to the redistribution of subtropical temperature anomalies via overturning and gyre circulations [ABSTRACT FROM AUTHOR]

Observations from the RAPID array at 26.5°N suggest a weakening in the Atlantic meridional overturning circulation between 2004 and 2020. The shortness of this time series raises the question of whether this weakening should be thought of as natural variability or as related to climate change. To estimate natural variability, preindustrial control runs of the Coupled Model Intercomparison Project Phase 6 are used and the observed weakening is found to fall within the distribution of naturally occurring trends. These trends result from model variability on periods longer than the observational window, and variation between models at these frequencies is especially pronounced. Finally, adding noise to inflate model variability also inflates model trends; however, the effect on trends is sensitive only to the low frequency portion of the noise spectrum. Plain Language Summary: The Atlantic meridional overturning circulation (AMOC) is a major ocean circulation system that transports heat northward in the Atlantic basin thus contributing to the regulation of the climate system. Fluctuations in the AMOC have been linked with changes in Arctic sea ice and to variations in the climate of Europe and North America. The longest direct observational record of the AMOC spans only 15.8 years and has shown a weakening of the circulation. Whether this weakening is due to natural oscillations in the climate system or is a response to anthropogenic greenhouse gases in the atmosphere is unclear. To assess whether the ocean circulation produces spontaneously weakening signals of such intensity, long simulations of climate models run under a preindustrial scenario are used to estimate the natural variability of the AMOC. These models suggest that the current weakening of the AMOC is consistent with natural variability. An accurate representation of slow timescale fluctuations in the AMOC is what matters most to the detection of an anthropogenically driven AMOC trend. This variability, however, differs markedly across models. Key Points: The 2004–2020 observed Atlantic meridional overturning circulation (AMOC) trend is not significantly relative to Coupled Model Intercomparison Project Phase 6 (CMIP6) model natural variabilityCMIP6 models largely disagree on AMOC variability, including at decadal and longer periodsIt is periods longer than the observational window that set AMOC trend detectability thresholds [ABSTRACT FROM AUTHOR]

The consecutive occurrence of meteorological dry and wet extremes has been receiving increasing attention due to potentially larger social and environmental impacts than single extremes. However, the changing characteristics of transitions between dry and wet periods remain poorly understood. Here we investigate the dynamic evolution of dry‐to‐wet transitions in response to climate warming, using the Standardized Precipitation Evapotranspiration Index as well as observations and general circulation models for the periods of 1954–2014 and 2040–2100. We find that approximately three‐fifths of global land area are projected to experience an accelerated dry‐to‐wet transition. Southern Asia has been experiencing the most severe dry‐to‐wet transitions and is projected to suffer more frequent, more intense, and accelerated dry‐to‐wet transitions. The increasing potential evapotranspiration (PET) variability plays an important role in accelerating the dry‐to‐wet transition in Southern Asia, while precipitation and PET variabilities contribute to the intensification of dry‐to‐wet transitions in Southern North America. Plain Language Summary: The consecutive occurrence of droughts and floods has widespread impacts on agriculture, the ecosystem, and the environment. Here we examine the changes in frequency, intensity, and elapsed time of transitions between dry and wet periods under a warming climate, based on observations and an ensemble of 10 Coupled Model Intercomparison Project Phase 6 climate simulations. We find that approximately 59% of global land area are expected to experience a shorter transition time between dry and wet periods. Southern Asia suffers the most severe dry‐to‐wet transition. Furthermore, our findings reveal that enhanced potential evapotranspiration (PET) variability contributes to the accelerated transition between dry and wet periods over Southern Asia, and the acceleration of dry‐to‐wet transitions in Southern North America is associated with an increase in precipitation and PET variabilities as climate warms. Key Points: Approximately three‐fifths (59%) of global land area are projected to experience accelerated transition between dry and wet periodsSouthern Asia suffers the most from severe transition between dry and wet periodsEnhanced precipitation and potential evapotranspiration variabilities contribute to the accelerated dry‐to‐wet transitions [ABSTRACT FROM AUTHOR]

This study investigates the seasonality of near‐surface wind speeds associated with extratropical cyclones (ETCs) over northeastern North America using a global reanalysis data set during 1979–2020. As opposed to most studies that emphasize winter storms, ETCs during the fall exhibit significantly stronger 10‐m winds over this region due to the slightly stronger continental cyclones and significantly weaker low‐level stability during that time of the year. Also, ETCs favor inland lakes and Hudson Bay during the low‐ice‐content fall season, leading to lower surface roughness. Combining these results, we derive simple linear regressions to predict the 10‐m wind speed given three variables: 850‐hPa wind speed, low‐level Richardson number, and surface roughness length. This formula captures the observed seasonality and serves as a valuable tool for cyclone near‐surface wind risk assessment. Plain Language Summary: Extratropical cyclones can bring powerful winds that can cause severe damage to infrastructure. We find that cyclones with severe winds are the most frequent in the fall season over continental northeastern North America. Three reasons are found responsible: stronger continental cyclones, weaker low‐level atmospheric stability, and the lower surface roughness over lakes and Hudson Bay, where cyclones frequently occur in fall. A simple formula that can effectively assess the near‐surface wind speeds associated with cyclones is derived based on these results. Key Points: Extratropical‐cyclone‐associated 10‐m wind speeds are the strongest in the fall season over northeastern North AmericaBesides stronger continental cyclones and 850‐hPa winds, weaker low‐level stability in fall favors stronger 10‐m wind speeds in this regionLinear regression using 850‐hPa wind, Richardson number, and surface roughness well predicts cyclones' 10‐m wind speeds and seasonality [ABSTRACT FROM AUTHOR]

A warmer climate impacts streamflows and these changes need to be quantified to assess future risk, vulnerability, and to implement efficient adaptation measures. The climate simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5), which have been the basis of most such assessments over the past decade, are being gradually superseded by the more recent Coupled Model Intercomparison Project Phase 6 (CMIP6). Our study portrays the added value of the CMIP6 ensemble over CMIP5 in a first North America wide comparison using 3,107 catchments. Results show a reduced spread of the CMIP6 ensemble compared to the CMIP5 ensemble for temperature and precipitation projections. In terms of flow indicators, the CMIP6 driven hydrological projections result in a smaller spread of future mean and high flow values, except for mountainous areas. Overall, we assess that the CMIP6 ensemble provides a narrower band of uncertainty of future climate projections, bringing more confidence for hydrological impact studies. Plain Language Summary: Greenhouse gas emissions are causing the climate to warm significantly, which in turn impacts flows in rivers worldwide. To adapt to these changes, it is essential to quantify them and assess future risk and vulnerability. Climate models are the primary tools used to achieve this. The main data set that provides scientists with state‐of‐the‐art climate model simulations is known as the Coupled Model Intercomparison Project (CMIP). The fifth phase of that project (CMIP5) has been used over the past decade in multiple hydrological studies to assess the impacts of climate change on streamflow. The more recent sixth phase (CMIP6) has started to generate projections, which brings the following question: is it necessary to update the hydrological impact studies performed using CMIP5 with the new CMIP6 models? To answer this question, a comparison between CMIP5 and CMIP6 using 3,107 catchments over North America was conducted. Results show that there is less spread in temperature and precipitation projections for CMIP6. This translates into a smaller spread of future mean, high and low flow values, except for mountainous areas. Overall, we assess that using the CMIP6 data set would provide a more concerted range of future climate projections, leading to more confident hydrological impact studies. Key Points: A comparison of hydrological impacts using Coupled Model Intercomparison Project version 5 (CMIP5) and Coupled Model Intercomparison Project Phase 6 (CMIP6) ensembles is performed over 3,107 catchments in North AmericaThe CMIP6 ensembles provide a narrower band of uncertainty for hydrological indicators in the futureIt is recommended to update hydrological impact studies performed using CMIP5 with the CMIP6 ensemble [ABSTRACT FROM AUTHOR]

We report 20 10Be exposure ages from glacial erratics and bedrock on the west coast of British Columbia, Canada, which add to existing chronologies of Cordilleran Ice Sheet retreat along ∼600 km of coastal North America. Collectively, these data show the western ice limit reached the present coast by 18–16 ka then retreat slowed for ∼4,000 years until 14–13 ka. We attribute initial retreat to destabilization and grounding line retreat resulting from rising sea level and/or ocean warming in the northern Pacific. Subsequent stability of the ice sheet at the present coastal margin was likely due to the transition from marine to terrestrial margins despite increasing temperatures that may have driven ice sheet thinning. Our findings demonstrate the importance of understanding both climatic and nonclimatic drivers of ice sheet change through time. Plain Language Summary: The Cordilleran Ice Sheet once covered western North America and was similar in size and characteristics to the modern Greenland Ice Sheet. It is therefore a good analog for how the Greenland Ice Sheet may respond to changing climate and underlying topography in the future. We show the western margin of the Cordilleran Ice Sheet retreated rapidly from around 18,000 years ago but then stabilized for several thousand years close to the present coastline. Ice may still have been lost during this period of relative stability, but through vertical thinning rather than lateral retreat, demonstrating the importance of understanding ice sheets in three‐dimensions. Our reconstruction shows that atmospheric and oceanic temperatures and underlying topography can all control ice sheet stability. We also show that hundreds of kilometers of coastline were free of ice prior to an important period of early human migration into the Americas. Key Points: Consistent, western ice sheet margin retreat at ∼18–16 ka driven by destabilization due to sea level rise and/or ocean warmingRetreat stabilized during ∼17–13 ka after reaching present coastIce sheet margin may have thinned before ∼13 ka, consistent with interior but without substantial marginal retreat [ABSTRACT FROM AUTHOR]

In the early summer (late June–early July) of 2021, a prolonged and extremely high temperature event was observed in the Northwest United States and Southwest Canada. In this study, a connection was found between the subseasonal variations of the East Asian monsoon system and the anomalous heat dome over western North America (WNA). Around 2–3 pentads prior to the period of maximum heat, a northward‐propagating rain belt and abnormally intensified jet stream in East Asia excited a Rossby wave train, causing the high‐pressure anomaly over WNA that was responsible for the occurrence of this heat wave in 2021. Multivariate singular value decomposition analysis results using historical data and a series of numerical experiments further supported the finding of this East Asia–western North America teleconnection. The results provide precursor signals for better monitoring and predicting heat waves over WNA. Plain Language Summary: A persistent and extremely high temperature event was observed in several states in the Northwest United States and Southwest Canada in summer 2021. This severe heat wave resulted in the hottest early‐summer season in western North America (WNA) since 1979 and huge social and economic losses. Although the heat dome (high‐pressure anomaly) over WNA was the factor responsible for this mega heat wave, the cause of this high‐pressure anomaly was unclear. The present study reveals the importance of an atmospheric wave train emanating from East Asia toward North America in inducing the heat dome over WNA. The generation of the wave train is attributable to a northward‐propagating rain belt and abnormally enhanced jet stream over East Asia from 10 to 15 days before the peak of this heat wave. Thus, monitoring the East Asian summer monsoon and associated wave train activity may help in predicting heat waves in WNA, and therefore in knowing when to put measures in place to mitigate against their effects. Key Points: An extreme heat wave occurred in western North America (WNA) in the early summer of 2021, causing huge socioeconomic losses in several big citiesThe subseasonal activity of East Asian summer monsoon contributed to the occurrence of the heat wave via excitation of a Rossby wave trainThe East Asia‐North America teleconnection can provide precursor signals for forecasting heat waves in WNA [ABSTRACT FROM AUTHOR]

Previous studies have reported that enhanced eddy moisture convergence causes future increase of winter precipitation in the eastern North America in a warmer climate. This study investigates the mechanisms of the change in moisture convergence. Using ensemble simulations from climate models and composite analysis of moisture budget, we show that in the southeast United States, two thirds of the enhanced moisture convergence is caused by local thermodynamics due to increase of moisture, while one third is caused by stronger eddy wind convergence. In the north, it is primarily caused by the increase of moisture gradient associated with the spatial distribution of both the climatological temperature and the large amplitudes of the eddy temperature in the region of the storm tracks. Results help to better understand the physical mechanism of more winter precipitation in the eastern North America in a warmer climate. Plain Language Summary: It has been reported that winter precipitation will increase in the eastern North America under global warming, which is caused by the enhanced eddy moisture convergence. We perform composite analysis of moisture budget using large ensemble simulations of climate models, and find out that the enhanced eddy moisture convergence in the southeast United States can be explained by the combination of climatological eddy wind convergence and increase of moisture content. The intensity of eddy wind convergence will enhance and contribute about one third of the eddy moisture convergence increase in the southeast United States. In the north of eastern North America, the climatological eddy wind brings more moisture into the region due to enhanced moisture gradient. The contrast of different mechanisms in the south and north can be explained by the climatology and future change of the spatial pattern of water vapor and temperature. These results help us to better understand the physical mechanisms that are responsible for the future precipitation increase during winter in the eastern North America under global warming. Key Points: Winter precipitation increases with warming due to enhanced eddy moisture convergence in the eastern North AmericaLocal thermodynamics associated with increased moisture and stronger eddies induce more moisture convergence in the southeast United StatesEnhanced moisture gradient in regions of large eddy magnitudes causes more moisture convergence in the north of eastern North America [ABSTRACT FROM AUTHOR]

We present the first application of a fast super resolution convolutional neural network (FSRCNN) based approach for downscaling earth system model (ESM) simulations. Unlike other SR approaches, FSRCNN uses the same input feature dimensions as the low resolution input. This allows it to have smaller convolution layers, avoiding over‐smoothing, and reducing computational costs. We adapt the FSRCNN to improve reconstruction on ESM data, we term the FSRCNN‐ESM. We use high‐resolution (∼0.25°) monthly averaged model output of five surface variables over North America from the US Department of Energy's Energy Exascale Earth System Model's control simulation. These high‐resolution and corresponding coarsened low‐resolution (∼1°) pairs of images are used to train the FSRCNN‐ESM and evaluate its use as a downscaling approach. We find that FSRCNN‐ESM outperforms FSRCNN and other super‐resolution methods in reconstructing high resolution images producing finer spatial scale features with better accuracy for surface temperature, surface radiative fluxes, and precipitation. Plain Language Summary: High resolution global climate data is computationally expensive to run but crucial for assessing climate change effects at local and regional scales. Here, we adapt a new deep learning technique, called fast super‐resolution convolutional neural network, to remap climate data from low resolution to high resolution grids. This approach is faster and more accurate for statistical downscaling climate data compared to other prevalent methods. Key Points: We present a fast super resolution convolutional neural network (FSRCNN) based approach for downscaling gridded earth system model (ESM) dataFSRCNN‐ESM's reconstruction of high resolution spatial patterns improves upon both traditional and machine learning downscaling methodsThe FSRCNN is computationally less expensive to train than other machine learning downscaling methods [ABSTRACT FROM AUTHOR]

Unaweep Canyon (Uncompahgre Plateau, Colorado) represents an enigmatic landscape with a complex evolution. Interpretations for its origin have ranged from ancestral fluvial erosion in the late Cenozoic to glacial erosion in the Paleozoic, or some combination thereof, with significant implications for global climatic and large‐scale tectonic reconstructions. To address the conflicting interpretations, we acquired a high‐resolution seismic reflection profile to investigate the depth, structure, and sedimentary infill in the canyon. The data set is further complemented with an electrical resistivity survey. Integrated with other geophysical and geological data, the results show an overdeepened Precambrian basement with transverse U shape and support the hypothesis of a pre‐Quaternary glacial origin. Our data constitute the first detailed image of a buried pre‐Quaternary glacial valley in North America; if substantiated with core studies, these results have far‐reaching implications for our understanding of global ice houses as well as the tectonic conditions, enabling preservation of such systems. Plain Language Summary: The shape of valleys depends on the processes that created them. Broad valleys with the transverse shape of a "U" are distinct signs of glaciers, which carved the valley in the bedrock. Since old valleys are filled up with sediments, we need geophysical tools to image their structure in the buried subsurface. Using such tools, we have found a buried U‐shaped valley in western Colorado. Since we know from other observations that there were no glaciers in this specific location in the last ice age, the valley must have been created in a previous ice age. The most likely time period is the late Paleozoic, ca. 300 million years ago. Due to plate tectonics, the landmass of Colorado was located at the equator during that time. This implies that there was ice at the equator at this time, which further means there were globally much lower temperatures than we think. Our result is the first example in North America of a glacial mountain valley carved by an ancient glacier. Key Points: We present the first high‐resolution seismic image of a buried paleovalley shaped by alpine glaciation in Earth's pre‐Quaternary recordOur data support the hypothesis of late Paleozoic glaciation at latitudes and elevations lower than suggested by current paleoclimate models [ABSTRACT FROM AUTHOR]

Plate motion changes provide powerful constrains on plate tectonic forces. North America is ideal to explore these forces. We use recently published high‐temporal resolution plate reconstructions of North America, which reveal a velocity slow‐down at ∼17 Ma, roughly coeval with the eruption of the Yellowstone plume, together with a stratigraphic analysis of hiatus surfaces across the continent, which provides proxy information for paleotopography. Using a simple Couette/Poiseuille flow models we estimate asthenosphere flow beneath North America and its impact on Neogene plate motion. We find that North America's Neogene plate motion change can be explained by Poiseuille flow in the asthenosphere generated upon the arrival of the Yellowstone plume and that the flow length‐scale matches the extent of hiatus surfaces. While plume driven upper mantle flow constitutes a geodynamically viable model to explain North America's Neogene plate motion change it provides an intrinsic link between vertical and horizontal plate motions. Plain Language Summary: Plate motion changes are increasingly well documented in the geologic record. However, the underlying forces that initiate these plate motion changes remain poorly understood. Over the past years a pressure driven, so‐called Poiseuille flow, model for upper mantle flux in the asthenosphere has gained increasing geodynamic attention–for a number of fluid dynamic arguments. This elegantly simple model makes a powerful testable prediction: Plate motion changes should coincide with regional scale mantle convection induced elevation changes. The latter are best inferred for continents from stratigraphic evidence. In this study we analyse newly available constrains on the Neogene kinematic plate history of North America together with a novel stratigraphic frame‐work based on the principle of hiatus analysis. The stratigraphic frame work provides proxy information for paleo elevation. Combining these newly available constrains we show for the first time that: (a) Poiseuille flow induced by the arrival of the Yellowstone hotspot provides a compelling explanation for the observed coeval velocity and topographic change of North America, and (b) the Yellowstone plume push force is sufficient to initiate a plate motion change of North America under considerations of a quantitative geodynamic force balance analysis. Key Points: We analyse the Neogene kinematic plate history of North America together with a stratigraphic frame‐work base on the principle of hiatusPoiseuille flow model links changes in dynamic topography and plate motion changes via a geodynamically plausible modelYellowstone plume provides a dynamically viable mechanism to drive Neogene North America platemotions [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) exert significant socioeconomic impacts in western North America, where 30% of the annual precipitation is determined by ARs that occur in less than 15% of wintertime. ARs are thus beneficial to water supply but can produce extreme precipitation hazards when making landfall. While most prevailing research has focused on the subseasonal (≤5 weeks) prediction of ARs, only limited efforts have been made for AR forecasts on multiseasonal timescales (≥3 months) that are crucial for water resource management and disaster preparedness. Through the analysis of reanalysis data and retrospective predictions from a new seasonal‐to‐decadal forecast system, this research shows the existing potential of multiseasonal AR frequency forecasts with predictive skills 9 months in advance. Additional analysis explores the dominant predictability sources and challenges for multiseasonal AR prediction. Plain Language Summary: Atmospheric rivers (ARs), narrow corridors of intense moisture transport and heavy precipitation, are an important water resource but also a cause of flooding‐related disasters for western North America. Consequently, predictions of AR frequency several seasons in advance potentially would be of great value, but such operational forecasts are currently lacking due to the challenges in simulating such intense, small‐scale weather phenomena and their predictability sources on seasonal timescales. In this study, we examine the forecast skill of AR frequency on seasonal‐to‐multiseasonal timescales (≥3 months) in a new generation seasonal‐to‐decadal prediction system developed at the Geophysical Fluid Dynamics Laboratory. We find that AR frequency can be skillfully forecast at least 9 months in advance over certain regions of the west coast of North America, such as California and Alaska, while the forecasts are only reliable for the first season in other regions. This regional variability can be further explained by the large‐scale climate variability pattern that is responsible for much of the skill, which is strongly modulated by slowly varying sea surface temperature (SST) variations. A prototype probabilistic seasonal AR forecast product is proposed. Key Points: Atmospheric river frequency can be skillfully forecast at least 9 months in advanceThe skills are significant over certain regions of western North America such as Alaska and CaliforniaEl Nino‐Southern Oscillation and Interdecadal Pacific Oscillation are important predictability sources [ABSTRACT FROM AUTHOR]