Organization metrics were originally developed to measure how densely convective clouds are arranged at mesoscales. In this work, we apply organization metrics to describe tropical synoptic scale convective activity. Such activity is identified by cloud-precipitation (hybrid) regimes defined at 1-degree and 1-hourly resolution. Existing metrics were found to perform inadequately for such convective regime aggregates because the large domain size and co-existence of sparse aggregate occurrences with noisy isolated convection often violate assumptions inherent in these metrics. In order to capture these characteristics, the existing “convective organization potential” (COP) metric was modified so as to: (1) focus on local organization and (2) provide increased weight to aggregate size. The resulting “area-based COP” (ABCOP) is found to outperform existing metrics in tropical convective events at synoptic scales. Moreover, this new organization metric can match the performance of existing metrics, or arguably be better, over a wide range of domain sizes.

Enhanced Geothermal Systems could provide a substantial contribution to the global energy demand if their implementation could overcome inherent challenges. Examples are insufficient created permeability, early thermal breakthrough, and unacceptable induced seismicity. Here we report on the seismic response of a meso-scale hydraulic fracturing experiment performed at 1.5 km depth at the Sanford Underground Research Facility. We have measured the seismic activity by utilizing a novel 100 kHz, continuous seismic monitoring system deployed in six 60 m-length monitoring boreholes surrounding the experimental domain in 3-D. The achieved location uncertainty was on the order of 1 m, and limited by the signal-to-noise ratio of detected events. These uncertainties were corroborated by detections of fracture intersections at the monitoring boreholes. Three intervals of the dedicated injection borehole were hydraulically stimulated by water injection at pressures up to 33 MPa and flow rates up to 5 L/min. We located 1933 seismic events during several injection periods. The recorded seismicity delineates a complex fracture network comprised of multi-strand hydraulic fractures and shear-reactivated, pre-existing planes of weakness that grew unilaterally from the point of initiation. We find that heterogeneity of stress dictates the outcome of hydraulic stimulations, even when relying on theoretically well-behaved hydraulic fractures. Once hydraulic fractures intersected boreholes, the boreholes acted as a pressure relief and fracture propagation ceased. In order to create an efficient sub-surface heat exchanger, production boreholes should not be drilled before the end of hydraulic stimulations.

The solar tides of the mesosphere and lower thermosphere (MLT) show great variability on timescales of days to years, with significant variability at interannual timescales. However, the nature and causes of this variability remain poorly understood. Here, we present measurements made over the interval 2005 to 2020 of the interannual variability of the 12-hour tide as measured at heights of 80 to 100 km by a meteor radar over Rothera (68S, 68W). We use a linear regression analysis to investigate correlations between the 12-hour tidal amplitudes and several climate indices, specifically the solar cycle (as measured by F10.7 solar flux), El Niño Southern Oscillation (ENSO), the Quasi-Biennial Oscillation (QBO) at 10 hPa and 30 hPa and the Southern Annular Mode (SAM). Our observations reveal that the 12-hour tide has a large amplitude and a clearly defined seasonal cycle with monthly mean values as large as 35 ms-1. We observe substantial interannual variability, with monthly mean 12-hour tidal amplitudes at 95 km exhibiting a two standard-deviation range (2σ) in spring of 13.4 ms-1, 11.2 ms-1in summer, 18.6 ms-1 in autumn and 7.0 ms-1 in winter. We find that F10.7, QBO10, QBO30 and SAM all have significant correlations to the 12-hour tidal amplitudes at the 95% level, with a linear trend also present. Whereas we detect very minimal correlation with ENSO. These results suggest that variations in F10.7, the QBO and SAM may contribute significantly to the interannual variability of 12-hour tidal amplitudes in the Antarctic MLT.

Authors and affiliationsChristopher Masafu1, Richard Williams1, Martin D. Hurst11School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, UKCorresponding Author: Christopher Masafu ([email protected])

Smoke influence in urban areas is relatively easy to detect at high concentrations, but more challenging to detect at low concentrations. For this reason, we have evaluated an approach using thermal desorption gas chromatography mass spectrometry (TD-GC-MS) to detect volatile organic compounds (VOCs) in particular oxygenated VOCs in urban areas. The goal of this work is to develop a method that can reliably quantify smoke tracers in an urban environment at relatively low cost and complexity. We present here the development and validation of a double-bedded thermal desorption tube with an auto sampler to collect continuous samples of VOCs. To evaluate the method performance, we have tested stability during storage, interferences (e.g., water and O3), and reproducibility for six VOCs, namely, acetonitrile, acetone, pentane, iso-pentane, benzene, and toluene. The results demonstrate that these can be quantified reproducibly with an error ≤ 20% between the collection and analysis with a storage time of up to 21 days. For acetone, similar results were obtained until day 14. Calibration experiments performed over a dynamic range of 10–150 ng loaded over thermal desorption tubes at different relative humidity showed excellent linearity (r2 ≥ 0.91). At this time, we are utilizing this method during the summer 2019 FIREX-AQ intensive experiment at the Boise ground site in Idaho. These results will be presented along with the quality control data.

Icy moons around the ice giant planets may contain subsurface oceans. Their oceans could be detected and characterized using measurements of magnetic fields induced by the host planet’s time-varying magnetospheric field. We explore the possibility of detecting and characterizing subsurface oceans among the five major moons of Uranus—with a particular focus on Ariel—using spacecraft magnetometry measurements. We find that the magnetic field at each moon is dominated by the synodic frequency with amplitudes ranging from ~4 nT at Oberon up to ~300 nT at Miranda. If these bodies contain oceans with sufficient thicknesses (>~6-100 km) and conductivities (>2 S m-1), the induced surface fields should have amplitudes exceeding the typical ~1 nT sensitivity of spacecraft magnetometry investigations. Furthermore, the magnetic field at the moons spans periods ranging from 1 to 103 h. This could enable long-term measurements to separately constrain ocean and ice thicknesses and ocean salinity.

Our understanding of geomagnetic field intensity prior to the era of direct instrumental measurements relies on paleointensity analysis of rocks and archaeological materials that serve as magnetic recorders. Only in rare cases absolute paleointensity datasets are continuous over millennial timescales, in sub-centennial resolution, and directly dated using radiocarbon. As a result, fundamental properties of the geomagnetic field, such as its maximal intensity and change rate have remained a subject of lively discussion. Here, we place firm constraints on these two quantities using Bayesian modeling of well-dated archaeomagnetic intensity data from the Levant and Upper Mesopotamia. We report new data from 23 groups of pottery collected from 18 consecutive radiocarbon-dated archaeological strata from Tel Megiddo, Israel. In the Near East, the period of 1700–550 BCE is represented by 84 groups of archaeological artifacts, 55 of which were dated using radiocarbon or a direct link to clear historically-dated events, providing unprecedented sub-century resolution. Moreover, stratigraphic relationships between samples collected from multi-layered sites enable further refinement of the data ages. The Bayesian curve shows four geomagnetic spikes between 1050 and 600 BCE, with virtual axial dipole moment (VADM) reaching values of 155–162 ZAm2 – much higher than any prediction from geomagnetic field models. Rates of change associated with the four spikes are ~0.35–0.55 μT/year (~0.7–1.1 ZAm2/year), at least twice the maximum rate inferred from direct observations spanning the past 190 years. The increase from 1750 BCE to 1030 BCE (73 to 161 ZAm2) depicts the Holocene’s largest change in field intensity.

The Transantarctic Mountains (TAM) separate the warmer lithosphere of the West Antarctic rift system and the colder East Antarctic craton. Low velocity zones beneath the TAM imaged in recent seismological studies have been interpreted as warm low-density mantle material, suggesting a strong contribution of thermal support to the uplift of the TAM. We present new Curie Depth Point (CDP) and geothermal heat flow (GHF) maps of the northern TAM and adjacent Wilkes Subglacial Basin (WSB) based on high resolution magnetic airborne measurements. We find shallow CDP and high GHF, beneath the northern TAM reinforcing the idea of thermal support of the topography of the mountain range. Additionally, locally high GHF is observed in the Central Basin of the WSB and the Rennick Graben, which has not been resolved previously, while the broader WSB show lower GHF. Across the study area the GHF values range from 30 to 110 mW/m2. Lastly, we compare our CDP estimates to recent Moho depth estimates and our GHF estimates to sparse in situ GHF measurements as well as to existing continent-wide GHF estimates, which shows closed agreement to previous seismic estimates.

The withdrawal of fluid from a reservoir results in a decline of the fluid pressure followed by a consequent change in stress state in porous rocks. Stress change may cause irreversible deformation and compaction. Such compaction is generally the result of pore collapse and shear-enhanced compaction caused by changes at a microscopic level in the porous rocks. Pore collapse and shear-enhanced compaction are considered as potential problems during reservoir production and drilling operations. The purpose of this paper is to analyze the pore collapse and shear-enhanced compaction in hydrocarbon reservoirs using coupled poro-elastoplasticity and permeability. This coupling is implemented using a sequentially coupled scheme with a fixed stress split. In this coupling, the poro-elastoplasticity analysis includes the linear component based on Biot’s theory and the nonlinear component based on a cap plasticity model. The fluid flow formulation is defined by Darcy’s law, including nonlinear permeability model. The numerical approximation is implemented using continuous finite element approximations for rock deformation and mixed finite element approximation for pore pressure and flux. Several numerical simulations are performed to indicate the onset of pore collapse and shear-enhanced compaction and evaluate their effects on reservoir performance.

A version of This Work has been submitted to _J. Physical Oceanography_ This Work has not yet been peer-reviewed and is provided by the contributing Author(s) as a means to ensure timely dissemination of scholarly and technical Work on a noncommercial basis. Copyright and all rights therein are maintained by the Author(s) or by other copyright owners. It is understood that all persons copying this information will adhere to the terms and constraints invoked by each Author’s copyright. This Work may not be reposted without explicit permission of the copyright owner. Copyright in this Work may be transferred without further notice. ABSTRACT Deep estuaries are often separated from the open ocean by sills and constrictions. These constrictions are areas of intense mixing often dominating the total estuarine mixing. The amount and depth of the estuarine exchange depends sensitively on the mixing and the densities of the waters on the two sides of the mixing region. Thus, the density, nutrient concentration, oxygen saturation, and dissolved inorganic carbon content of the incoming estuarine flow depend on local tidal mixing processes and large scale buoyancy dynamics. We have investigated this process using a numerical model (SalishSeaCast) of the Salish Sea on the West Coast of North America, straddling the Canada/USA border. The region receives considerable freshwater dominated by the outflow of the Fraser River. The Fraser River first flows into the deep Strait of Georgia but the freshwater must traverse the strongly tidally mixed shallower passages through the Gulf/San Juan Islands before it reaches the Pacific Ocean. The model correctly reproduces the deep water flow into the Strait of Georgia as evaluated against Ocean Networks Canada (ONC) four bottom-mounted, continuously recording, conductivity-temperature instruments which capture this incoming flow. Using a four-year hindcast from the model we determine the amount, depth and position of the outflow and inflow. We show that 95% of the variance of the 4-day average baroclinic flux through the tidal mixing region can be explained by the density difference across the region and a Richardson Number based on the tidal velocities. The outgoing flux includes both surface and intermediate waters and the incoming flux includes both intermediate and deep waters. Laterally, fluxes into and out of the Strait of Georgia and across Victoria Sill show the impact of the Coriolis force and local bathymetry. INTRODUCTION A classic lock exchange experiment in a laboratory separates two different densities by a lock that is removed (_e.g._ ). As the lock is removed, the lighter water flows over the heavier and the heavier water flows under the lighter. These two gravity current flows travel quickly, on the order of the internal wave speed, quickly redistributing the density. Performing the experiment on a rotating table reduces the lateral width of the gravity currents but does not significantly change their speed . On the other hand, introducing turbulence, say in the form of a bubble region, breaks up the gravity currents and significantly increases the time for density exchange . These basic dynamics, a contrast in densities driving exchange, and turbulence reducing the rate of exchange, are expected to explain real oceanographic situations. Here we look at their application to an estuarine system with a highly constricted, very turbulent tidal mixing “hotspot”. Using the results from a well-resolved three-dimensional ocean model, we ask if the laboratory dynamics apply and what they tell us about the exchange flow for this estuary. In the oceanographic literature, the estuarine exchange problem has a long, and mostly separate history from these laboratory studies. In a real estuary, the problem is greatly complicated by the presence of tides. We cannot remove them (even from our model) as they are determining the mixing in the system. However, at any given time, the instantaneous velocity is largely determined by the tides, advecting water in and out. A traditional way to determine the net estuarine transport from observations is to assume two layers and to use Knudsen’s Relations, that is, conservation of water and salt. However, adding symmetrical mixing, as opposed to just entrainment into the upper layer, makes the system under-determined. One can use temperature and heating versus salinity to remove this ambiguity and then invert temperature and salinity profiles to determine the transport assuming a layer structure . The water advected in and the water advected out by the tides may be largely the same, and what we want to extract is the difference. From model results, one can analyze time averages, giving the tidally averaged velocities and tidally averaged salinity. However, this process neglects the strong correlations in the fluctuations. A more complete way to do this is to bin the water and salt fluxes by salinity bin and calculate TEF or total exchange flow . This method captures both the estuarine exchange flow and the transport due to the tides, and thus is a total or maximal exchange . The estuary we will consider is the large, semi-enclosed Strait of Georgia (SoG), which is connected to the Pacific Ocean through a western and a northern entrance (Figure [fig:map]). The primary flow is through the western entrance; the northern entrance is small and flux and exchange there are significantly smaller than at the west. The major source of fresh water is the Fraser River, about 60% of the total to the SoG which enters the SoG near its south end. At the south end of the SoG are the Gulf/San Juan Islands that form lateral constrictions. The water through this region is also shallower (Figure [fig:transects]). Thus, tidal flows are high, up to 4.5 m s−1, and turbulent mixing is strong (Figure [fig:transects]). Water exiting the SoG flows through this region and then into the relatively straight Juan de Fuca Strait (Figure [fig:map]), although there is a significant sill, Victoria Sill, at the eastern end of Juan de Fuca Strait (Figure [fig:transects]). Exchange through this region has been studied through observations and models . Exchange is seasonally variable with pulses of freshwater exiting Juan de Fuca Strait during the Fraser River Freshet, weak neap tides, and winds to the south in SoG . Deep water renewals similarly occur during neap tides during spring through fall . The observed dense water cascading from Boundary Pass Sill into the deep SoG has been successfully explained as a gravity current . Net fluxes have been estimated at 46 mSv out from Boundary Pass or 114 mSv in from Victoria Sill . These estimates are based on mass, salt and heat balances and are necessarily coarse in their vertical resolution and do not include lateral resolution. Using the TEF method the flux into the SoG is estimated as 83 mSv , updated to 70 mSv . These two estimates include both the estuarine component and the net tidal impact. Estimates not including the tidal impact are lower (28 mSv, ). However, all these estimates include both the flux that transitions the turbulent region and flux that is recycled within it. In particular, the flux into and out of Haro Strait is different in because much of the deep flow into Haro Strait is entrained into the surface flow and exits back out in the surface outflow to Juan de Fuca Strait. Indeed, although the exchange is maximum during neap tides, the maximum residual flow actually occurs at spring tides due to this entrained flux . This short-circuited flow is referred to as the reflux ( _e.g.,_ , ). Here we will use a Lagrangian tracking method that allows us to separate the reflux and focus on the flux that travels through the mixing region. This method does include the effect of the tides. Typically the SoG is divided into three layers: a surface layer above 50 m, an intermediate layer, and a deep layer below 200 m (e.g. , ; , ). Looking at the monthly climatology in the central SoG these depths would correspond to salinities of 30 g kg−1 (range 29.9 g kg−1 (July) to 30.4 g kg−1 (November)), for 50 m and 31.2 g kg−1 (range 31.0 g kg−1 (May) to 31.4 g kg−1 (October)) for 200 m.

Field reversals are some of the most prominent and commonly known temporal variations of the geomagnetic field. Polarity changes have been observed in seafloor magnetisation patterns, volcanic records, sediment sequences, speleothem records, and have been reported in geodynamo simulations. However, open questions remain concerning the phenomenology and underlying causes of this process. In particular, there is currently no consensus about the temporal scales over which geomagnetic reversals occur. Numerical simulations aimed at understanding Earth’s million-year evolution have predicted a time scale on the order of thousands of years. On the other hand, analysis of a lacustrine sequence in the central Italian Apennines suggests that the most recent geomagnetic reversal (the Matuyama-Brunhes) took place in as short as 13 years, requiring VGP latitudinal changes of the order of 10 degrees/yr [Sagnotti, L. et al. (2015). GJI, 204(2), 798-812]. This extremely short decadal time scale challenges our current understanding of the geodynamo and present-day numerical models. Here we derive fluid flows at the top of Earth’s outer core that optimise either the rate of dipole decay or directional changes local to the Italian Apennines, subject to a minimal number of physical ingredients. Specifically, we neglect the internal dynamics and prescribe a total flow kinetic energy that is consistent with observational bounds. Our optimal flows can drive an instantaneous VGP latitudinal change of at most 5 degrees/yr during the Matuyama-Brunhes transition. Extending the methodology to account for the spatio-temporal evolution of the magnetic field, we find that this solution does not drive a global reversal, but only changes that are highly localised around the Mediterranean and West-African regions. Solutions that optimise the rate of dipole decay suggest that full reversal would take at least 380 years.

Precise understanding of complex physical mechanisms of mesoscale process require high resolution observations of temperature, moisture, wind, precipitation, clouds. Using all collocated observations of microwave radiometer, wind profilers, electric field mill, weather radars over South-East India an observational analysis is conducted for the first time. Analysis suggests that these systems developed in warm, moist environment associated with large-scale low-level convergence. Passage of system is accompanied by convective regions with intense upward motion and towers extending up to higher levels indicating developing phase and presence of upward/downward motion comprising of heavy precipitation representing mature phase of the system followed by stratiform regions with prominent downdraft motion and less precipitation related to decay phase. Large (small) values of reflectivity and cloud liquid water values represent presence of deep (shallow)convective (stratiform) regions. Cloud to Ground (CG) lightning activity associated with storm electrification processes showed the existence of both +CG and –CG flashes in convective and dominant –CG in stratiform regions. Presence of different sized cloud liquid hydrometers in convective regions resulted in bipolar nature due to their collisions however in stratiform regions their distribution is mostly uniform and resulted in single polarity. Combination of different observations has provided the unique opportunity to examine interrelations of different physical mechanisms in storm environment. Inspection of reflectivity, CG lightning and cloud liquid water measurements have demonstrated the relationship of lightning mechanism with storm dynamics and cloud microphysics. Combined investigation of temperature, moisture and wind measurements have given considerable insight of thetae ridge formations resulting from thermal and moisture advections. Isentropic upgliding and downgliding facilitated the unique way to visualize the vertical transport of temperature and moisture through ascent and descent of air parcel. Blend of observations presented considerable insight of synoptic and complex mesoscale processes and their mutual interactions in the storm environment and provided encouraging results in explaining MCS structure.

We analyzed the scale features of satellite infrared (IR) water vapor (WV) brightness temperature observations of tropical cyclones (TCs). This is to characterize the storm information at dominate scales in all-sky radiance assimilation for TC numerical weather prediction. This paper presents the results from the study of Hurricane Patricia (2015). Our study shows that IR WV brightness temperatures have the ability to observe multiscale structures of TCs, ranging from a size of above 1,000 km that covers the entire storm and its surrounding areas to a scale resolving individual convective clouds embedded in the TC. The atmospheric moisture for TC development is mainly represented by large scales covering the storm and surrounding areas while the storm structures are characterized basically by all scales. The large-scale moisture and small-scale convection demonstrate strong correlation and are closely related to the TC development, suggesting the need for all-sky radiance assimilation at multiple scales.

Global river models are crucial for simulating and forecasting floods, especially in regions lacking dedicated flood forecasting systems. Reservoir operations significantly affect flow simulations, impacting forecast accuracy. In this study, we improved a storage-outflow-type global reservoir operation scheme of the global river hydrodynamics model CaMa-Flood, which calculates reservoir outflow based on reservoir storage. First, a non-linear storage-outflow function using convex and concave curves was implemented to enhance flood control and reduce the number of required parameters. Second, a gradual transition in the storage-outflow function was proposed to avoid simulated outflow instability. Third, the outflow during the water-use phase was recalibrated to reflect water availability in dry periods, rather than using annual mean discharge. A case study involving 85 dams in Mainland Southeast Asia was conducted to evaluate the efficacy of the three key modifications by comparing the proposed reservoir operation scheme against three degraded schemes. Using a linear storage-outflow function caused 43% of the 61 reservoirs with a flood control capacity greater than 100 million cubic meters (MCM) to overutilize their flood control capacity during the non-flood water-excess phase. The proposed non-linear function reduced the number of such reservoirs to 27%. In addition, the gradual transition of the storage-outflow function eliminated unrealistic outflow oscillation. Furthermore, parameter estimation for water-use outflow based on reservoir water-use capacity and dry period river discharge enabled better utilization of reservoir capacity during dry seasons. Overall, the proposed reservoir operation scheme holds promise for enhancing the accuracy of global flood simulation within global river models.

Preparedness is important for reducing potential losses from various disasters. There are limited studies that investigated the concrete reasons for not adopting a specific preparedness action. This paper fills such a gap using representative national survey data from China. Seven disaster preparedness actions, namely “preparing food and water at home,” “pay attention to disaster-related information,” “making emergency plans,” “being aware of nearest shelters,” “being aware of building code,” “participating in exercise or drills” and “being a volunteer for emergencies” are used as the measure of preparedness behaviors. Overall, the public has adopted more material-related preparedness actions, equipped with fewer awareness activities, and had the least community participation-related preparedness behaviors. The primary reasons for not adopting these actions are “not aware,” “don’t know where to buy or where to reach,” and “the action is not useful, there is no necessary,” while “costly,” “need special knowledge,” “don’t have time,” “need collaboration with others,” “energy-consuming” and “not my responsibility” are the less chose reasons. Besides, trust in government, relocation due to disasters, living in urban areas, and a higher degree of socioeconomic status are positively correlated with higher probabilities of adopting all the seven preparedness activities. These findings highlight the importance of community outreach from emergency management professionals to increase the public’s awareness of preparing for potential disasters. It is necessary to let the general public know the existence of these preparedness actions, and these actions can reduce losses.

NOAA/National Ocean Service’s (NOS) Center for Operational Oceanographic Products and Services (CO-OPS) provides users with real-time currents at more than sixty stations, currents predictions at thousands of historic and active stations, and operational currents nowcast and near-term forecast information in navigable estuaries, harbors, rivers, and coastal regions of the United States as an integral part of its safe navigation mission. CO-OPS performs at least one current survey each year to update currents predictions in regions of particular interest to stakeholders. NOS’ Operational Forecast Systems (OFS) operate and maintain fully 3-D hydrodynamic models that provide regional nowcast and forecast (48-60 hours) guidance for water levels, currents, salinity, and temperature. By combining the information available from real-time observations, current surveys, historic current predictions, and OFS output, both the tidal current predictions and the OFS forecast products can be improved. Tidal current predictions are traditionally generated based on analysis of at least one month of six-minute observation data obtained from a physically deployed current meter using harmonic least squares techniques to resolve tidal constituents. By using longer time series and traditional techniques combined with additional statistical methods, a more accurate representation of the tidal flow and a more exact match to the shape of the tidal current curve is obtained. By applying these methods to long-term OFS output at locations where long-term physical observations also exist, tidal current predictions based on model data within the model domain can be verified. Once verified, the number of available “virtual stations” exponentially increases the repository of tidal current predictions. Users can choose any location of interest and receive tidal current predictions that can be incorporated into integrated, user-friendly navigation products and tools. We will evaluate this technique in the lower Chesapeake Bay using output from the Chesapeake Bay Operational Forecast System (CBOFS) and real-time currents data.

Recent, record-breaking discharge in the Yenisei River, Siberia, is part of a larger trend of increasing river flow in the Arctic driven by Arctic Amplification (AA). These changes in magnitude and timing of discharge can lead to increased risk of extreme flood events, with implications for infrastructure, ecosystems, and climate. To better understand the changes taking place, it is useful to have records that help place recent hydrological changes in context. In addition to an existing network of river gauges, wood anatomical features in riparian trees have been shown to record extreme flooding. Along the lower reaches of the Yenisei River we collected white willow (Salix alba) samples from a fluvial fill flat terrace that occasionally floods when water levels are extremely high. At the end of certain annual growth rings these samples displayed terminal white bands, a type of intra-annual density fluctuation (IADF). To identify the characteristics and causes of these features we use an approach known as quantitative wood anatomy (QWA) to measure variation in fiber cell dimensions across tree rings, particularly fiber lumen area (LA) and cell wall thickness (CWT). We investigate (1) which cell parameters and method to extract intra-annual data from annual tree rings best capture terminal white bands identified in Salix, and (2) if these patterns are related to flood magnitude and/or duration. We find that fiber CWT best captures the IADFs found in Salix rings. For some trees, time series of normalized CWT correlate with July flood durations, which have changed since the 1980s. Understanding how riparian vegetation responds to extreme flood events can help us better manage riparian ecosystems and understand changes to the Arctic hydrological regime.

We examine and contrast the simulation of Sahel rainfall in phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). On average, both ensembles grossly underestimate the magnitude of low-frequency variability in Sahel rainfall. But while CMIP5 partially matches the timing and pattern of observed multi-decadal rainfall swings in its historical simulations, CMIP6 does not. To classify model deficiency, we use the previously-established link between changes in Sahelian precipitation and the North Atlantic Relative Index (NARI) for sea surface temperature (SST) to partition all influences on Sahelian precipitation into five components: (1) teleconnections to SST variations; the effects of (2) atmospheric and (3) SST variability internal to the climate system; (4) the SST response to external radiative forcing; and (5) the “fast” response to forcing, which is not mediated by SST. CMIP6 atmosphere-only simulations indicate that the fast response to forcing plays only a small role relative to the predominant effect of observed SST variability on low-frequency Sahel precipitation variability, and that the strength of the NARI teleconnection is consistent with observations. Applying the lessons of atmosphere-only models to coupled settings, we imply that the failure of coupled models in simulating 20th century Sahel rainfall derives from their failure to simulate the observed combination of forced and internal variability in SST. Yet differences between CMIP5 and CMIP6 Sahel precipitation do not mainly derive from differences in NARI, but from either their fast response to forcing or the role of other SST patterns.